Both sides get the point: Hemispheric sensitivities to

Memory amp Cognition2005 33 (5) 871-886

Since Paul Brocarsquos discovery (1861) of an associationbetween fluent articulate speech and the left frontal op-erculum research into the neural bases of language hasuncovered a complex brain network substrate for thephonological lexical semantic and syntactic functions ofnormal language comprehension and production (for a re-view see Martin 2003) A particularly salient feature ofthis brain network is its apparent strong left-lateralityWhereas damage to certain left hemisphere (LH) areascan cause profound and permanent deficits in many lan-guage functions damage to the right hemisphere (RH) ho-mologues of these areas generally leaves basic word andsentence processing relatively intact This dissociation isone of the most striking and oft-cited examples of hemi-spheric specialization in humans

Recently however behavioral neuropsychologicaland imaging data have converged to suggest that the RHmay play a larger and more important role in languagethan has been previously assumed Data from noninva-

sive spatial neuroimaging techniques such as positronemission tomography and functional magnetic resonanceimaging have revealed language-related activation inbrain areas outside the regions classically associated withaphasia including a number of RH areas (see eg Ni et al 2000) In fact some imaging studies particularlythose focusing on the comprehension of complex narra-tives (Robertson et al 2000 St George Kutas Martinezamp Sereno 1999) or nonliteral language (Bottini et al1994) have found not just bilateral activation patternsbut a predominance of RH activity One must then asknot why the RH is unable to process language but whatlanguage functions the RH supports how they differfrom LH functions and what role they play in normallanguage processing

Whereas patients with LH damage often show severedifficulties in the most basic aspects of language pa-tients with damage to the RH have also been found toshow changes in their language comprehension and pro-duction For example language production after RH dam-age is marked by socially inappropriate remarks tangen-tial speech circumlocutions and digressions of topic aswell as reduced informational complexity (JoanetteGoulet amp Hannequin 1990) Studies of language com-prehension in patients with RH damage have noted dif-ficulties extracting the main points from narratives andconversations (Gardner Brownell Wapner amp Michelow

871 Copyright 2005 Psychonomic Society Inc

The work reported here was supported by a German National Scholar-ship Foundation award to HM and by National Institute of Child Healthand Human Development Grant HD22614 and National Institute onAging Grant AG08313 to MK Correspondence relating to this articlecan be addressed to K D Federmeier Department of Psychology 603E Daniel University of Illinois Champaign IL 61820 (e-mail kfedermespsychuiucedu)

Both sides get the pointHemispheric sensitivities to sentential constraint

KARA D FEDERMEIERUniversity of Illinois at Urbana-Champaign Urbana Illinois

HEINKE MAIUniversity of Magdeburg Magdeburg Germany

and

MARTA KUTASUniversity of California San Diego La Jolla California

Behavioral studies have consistently reported striking differences in the impact of sentence-level in-formation on the processing of words presented in the right (RVF) versus the left (LVF) visual fieldwith context effects apparent only for RVF items The consistent lack of such effects in the LVF hasbeen taken to mean that right hemisphere language comprehension is largely insensitive to message-level meaning We used the functional specificity afforded by event-related potential measures to as-sess this claim Target words completing strongly and weakly constraining sentence contexts in whichconstraint arose at the sentence level rather than from lexical associations were presented laterally inthe LVF or RVF Increased constraint significantly reduced N400 amplitudes with presentation in bothVFs with no differences in the timing or amplitude of these effects These results are inconsistent withthe view that the VF asymmetries found in behavioral measures reflect differential hemispheric ca-pacities at the level of semantic analysis and integration although VF-based differences on earlier com-ponents (P2) suggest asymmetries in the impact of sentential context on perceptual aspects of wordprocessing in the two hemispheres

872 FEDERMEIER MAI AND KUTAS

1983) appreciating discourse structure (Delis WapnerGardner amp Moses 1983 Wapner Hamby amp Gardner1981) and drawing and revising inferences (Beeman1993 Brownell Potter Bihrle amp Gardner 1986) RHdamage has also been associated with problems in pro-cessing at least some types of nonliteral language suchas jokes (Brownell Michel Powelson amp Gardner 1983)and indirect requests (Weylman Brownell Roman ampGardner 1989) These findings suggest that although theRH might not be necessary to support the basic functionsessential for the processing of individual words or sim-ple sentences it may make important contributions tohigher level meaning processingmdashfor instance by link-ing words and sentences across larger language units andallowing language information to be used in a flexibleand context-sensitive manner

The RHrsquos contribution to language comprehension inneurologically intact individuals has also been examinedby means of the visual half-field (VF) technique (seeBanich 2002 for a review) This technique takes ad-vantage of the fact that stimuli presented in the left halfof visual space are initially processed exclusively by(early) visual cortical areas in the RH and vice versa Inthe intact brain transfer of at least some informationacross the corpus callosum is possible at later processingstages however that information is delayed and likely tobe incomplete because of the relative sparseness of cal-losal relative to intrahemispheric connections (Berardiamp Fiorentini 1997) andor biases and strategies thatmake it more efficient for the directly stimulated hemi-sphere to assume more of the processing load (egBanich 2003) Thus although the potential contributionof callosal transfer and other factors unrelated to hemi-spheric dominance to the observed VF patterns must al-ways be given due consideration the technique is gener-ally believed to skew processing toward the directlystimulated hemisphere This canonical view seems jus-tified given that several decades of hemifield studies withbrain-intact individuals have documented consistent per-formance differences for stimuli presented to the rightvisual field as opposed to the left and many of these re-sults have been corroborated by evidence from patientswith unilateral brain damage andor from studies ofcommissurotomized (so-called split-brain) patients

Research using the VF technique has led to the con-clusion that the two hemispheres differ in the meaningthat each derives from individual words and sentencesAssessment has largely been based on measures of prim-ing in lexical decision (wordnonword judgment) taskscompared across VFs For example with presentation ineither VF response times (RTs) are equally facilitatedfor target words (eg DOG) preceded by a closely relatedword (cat) or by an unrelated word (table) By contrastpriming for more distantly related word pairs (eg goatndashDOG) is greater with LVFRH presentation (ChiarelloBurgess Richards amp Pollock 1990) Greater facilitationfrom ldquosummation primesrdquo (three words weakly relatedto the target) also has been observed for LVFRH pre-sentation (Beeman Friedman Grafman amp Perez 1994)

as well as more priming at least in some contexts (seeTitone 1998) for the subordinate meanings of ambigu-ous words (eg bridalndash vs freightndashTRAIN Burgess ampSimpson 1988) These results have been interpreted assuggesting that a critical difference between the hemi-spheres may lie in the ldquocoarsenessrdquo of their semantic cod-ing with narrow focused meaning activation in the LHand weak diffuse activation in the RH (Beeman 1998)The broader range of meanings thus ldquoconsideredrdquo by theRH has been offered as part of the explanation for its rolein high-level (and especially nonliteral) language

However studies using sentences as primes have ledto claims that the RHrsquos language competence is limitedto word-level information and lexical associative rela-tionships between words (eg Chiarello Liu amp Faust2001 Faust 1998) For example with LVFRH presen-tation lexical decision latencies for sentence-final wordswere unaffected by scrambling the order of the contextwords (Faust Babkoff amp Kravetz 1995) or increasing theamount of context from one to three to six words (FaustKravetz amp Babkoff 1993) In some cases LVFRH wordprocessing has even proven insensitive to message-levelincongruity (eg ldquoThe patient parked the MEDICINErdquoFaust et al 1995) although some recent studies havefound effects of overt anomalies for LVF processing Forinstance Chiarello et al (2001) found RT inhibition foranomalous targets in both VFs as long as the contextcontained no lexically associated words Faust Bar-Levand Chiarello (2003) found effects of anomaly forLVFRH targets even in the presence of a lexical associ-ate however they also found that in the LVFRH (unlikethe RVFLH) RT facilitation for congruent words was in-sensitive to message-level meaning with equal facilita-tion for a lexically associated word in a meaningful or ina scrambled or nonsensical context On the basis of thesefindings it has been hypothesized that only the LH caneffectively integrate lexical syntactic and semantic in-formation to derive the message-level meaning of a mul-tiword utterance The RH instead may be able to notewhether or not a word is globally consistent with otherwords in the context (eg toothpaste does not coherewell with the words angry jury and confront as de-scribed by Chiarello et al 2001) but it is argued doesnot construct a higher level meaning representation thatis sensitive to factors such as word order or message-level constraint

Clearly there is an intriguing disparity between theconclusions drawn from neuropsychological studieswhich have tended to suggest that intact RH languagefunctions are particularly crucial for deriving message-level meaning and those drawn from studies of healthyadults which have concluded that although the RH maybe broadly sensitive to word-level meaning it is gener-ally not able to combine words effectively to construct amessage-level representation One consideration is thatthe materials and tasks used in the two cases have typi-cally been quite different In particular whereas neuro-psychological studies have often used untimed measuresdesigned to directly assess comprehension (eg true

BILATERAL SENSITIVITY TO CONSTRAINT 873

false questions or choice of story ending) studies withhealthy adults have largely used speeded lexical deci-sions Given evidence from aphasia suggesting that dif-ferent processes subserve lexical decision and semanticclassification (Bub amp Arguin 1995) as well as concernsraised from studies of split-brain patients that suggestthat lexical decision tasks may underreport the RHrsquos se-mantic abilities (Baynes amp Eliassen 1998 Zaidel 1990)questions remain about the extent to which the observedasymmetries may be task specific

To circumvent some of these difficulties and to exam-ine language processing asymmetries with a differentmeasure Federmeier and Kutas (1999a) recorded event-related brain potentials (ERPs) in a VF paradigm ERPsare small voltage fluctuations in the electroencephalogramthat are time-locked to sensory motor or cognitive eventsthey are the scalp reflections of synchronous synaptic ac-tivity associated with informational transactions in thebrain One advantage of ERPs is that they can be col-lected while individuals merely read for comprehensionthus avoiding the difficulty of disentangling asymme-tries in language processing from asymmetric compe-tencies with specific tasks and the associated decision-making and response processes Another key advantageis that a particular ERP component the N400 has beenclosely linked to semantic processing The N400 is anegative wave peaking around 400 msec after stimulusonset (for a review see Kutas amp Federmeier 2001 Kutasamp Hillyard 1980b) that is elicited in response to all po-tentially meaningful items including spoken writtenand signed words as well as pictures The amplitude ofthe N400 shows a strong inverse correlation with the pre-dictability of the eliciting item within its local context(word list sentence or discourse Bentin McCarthy ampWood 1985 Kutas amp Hillyard 1984) N400 amplitudesalso vary with factors that are related to the ease of ac-cessing information from memory such as word fre-quency (Van Petten amp Kutas 1990) repetition (Nagy ampRugg 1989) and semantic memory organization (Fed-ermeier amp Kutas 1999b) However the N400 is typicallynot modulated by grammatical violations and other stim-ulus and task manipulations that do not affect meaning(Kutas amp Hillyard 1980a 1983) It is thus a sensitiveand functionally specific measure of meaning access andintegration

In the Federmeier and Kutas (1999a) study ERPs wererecorded as participants read pairs of sentences forcomprehensionmdashfor example ldquoHe caught the pass andscored another touchdown There was nothing he en-joyed more than a good game of rdquo One of three typesof sentence-final words was presented in the LVF orRVF ldquoexpected exemplarsrdquo (eg FOOTBALL) ldquobetween-category violationsrdquo (eg CHESS) or ldquowithin-categoryviolationsrdquo (eg BASEBALL) Two key findings emergedfrom this study and a follow-up using sentence-final pic-tures (Federmeier amp Kutas 2002) First N400 responsesin the two VFs were equally affected by congruencymdashthat is reduced for expected exemplars relative to between-category violations Indeed the responses to

these two ending types were statistically indistinguish-able in the two VFs Thus there was no evidence to sug-gest that LVF processing was less affected by message-level plausibility However a striking VF-based differencewas observed in the N400 response to within-categoryviolations or unexpected words from the same semanticcategory as the expected endings When presented to theRVFLH these violations elicited N400 responses ofintermediate amplitude However in the LVFRH re-sponses to these items were no different from responsesto the between-category violations Since the contextual(im)plausibility of the within- and between-category vi-olations was matched on average LVFRH responses inthis case were seemingly even more affected than RVFLH responses by a wordrsquos fit to the message-level mean-ing of the sentence

The N400 data therefore cohere with neuropsycho-logical data to suggest that message-level information im-pacts processing in both VFs and by inference in bothhemispheres The root of language processing asymme-tries would thus seem to lie not in whether each hemisphereconstructs a message-level representation of the contextbut how each uses message-level information to guidethe processing of subsequent words Federmeier and Kutas(1999a) however compared responses to plausible andimplausible sentence pair completions Although carewas taken to exclude lexical associates from the target-containing sentences it remains possible that word-levelinformation alone might have provided sufficient cuesfor expected and unexpected completions to be distin-guished in the LVFRH As a much stronger test of theclaim that message-level information does not impactprocessing for LVFRH stimuli therefore the presentstudy uses ERPs to examine the effects of sentential con-straint on the processing of words presented to each VF

Participants were asked to read for comprehension aset of entirely congruent sentences that differed only inthe extent to which the sentence-final (target) word wasconstrained by message-level meaning informationmdashforinstance

Strongly constrained ldquoShe was suddenly called backto New York and had to take a cab to the AIRPORTrdquo

Weakly constrained ldquoShe was glad she had brought abook since there was nothing to read at the AIRPORTrdquo

Numerous behavioral and ERP studies have shown thatincreased constraint is associated with increased facili-tation for word processing in the form of faster RTs inlexical decision tasks (eg Schwanenflugel amp Shoben1985) and reduced N400 responses (Kutas Lindamoodamp Hillyard 1984) These effects of message-level con-straint on the N400 have been shown to occur indepen-dently of lexical associative effects (Van Petten 1993)In the present study the same words were used as (plau-sible) completions of strongly and weakly constrainingsentences and lexical-associative relationships withinthose sentences were minimized The conditions thusdiffer only in how strongly the target words are predicted


by the sentence message-level information With pre-sentation to the RVFLH we expect to replicate the N400constraint effects observed for these types of materialswith central presentation However if the VF-based dif-ferences observed in behavioral studies arise becauseLVFRH-initiated semantic processing is insensitive tomessage-level meaning information (Chiarello et al2001 Faust et al 2003) N400 constraint effects shouldnot be observed (or should be strikingly reduced) withinitial presentation to the LVFRH

In addition to looking at constraint and VF effects onsemantic processing as indexed by the amplitude and la-tency of the N400 response we examined earlier com-ponents of the ERP linked to perceptual analysis Whenpictures were used as sentence endings (Federmeier ampKutas 2002) and were presented initially to the RVFLHwe found congruency effects on the P2 component afrontally distributed positive-going potential that peaksaround 200 msec P2 amplitude modulations have beenlinked to the detection and analysis of visual features inselective attention tasks (Hillyard amp Muumlnte 1984 Luckamp Hillyard 1994) with increased amplitudes for stimulicontaining the target feature For stimuli in the RVF (butnot in the LVF) P2 amplitudes were larger for expectedthan for unexpected endings suggesting that context canprovide top-down information allowing for more effi-cient visual feature extraction from expected targets butonly for stimuli initially projected to the LH Here we ex-amined whether similar top-down effects can be ob-served for visual word processing as a function of con-textual constraint

METHOD

MaterialsStimulus materials consisted of 160 sentence-final target words

embedded in 160 weakly and 160 strongly constraining sentence con-texts Eight strongly constraining sentence contexts and 49 weaklyconstraining sentence contexts were taken from published sourcesthat reported cloze probabilities for sentences (Bloom amp Fischler1980 Griffin amp Bock 1998 Rayner amp Well 1996 Sanocki amp Oden1984)1 The remaining 152 strongly constraining and 111 weaklyconstraining sentence contexts were chosen from an unpublishedset Cloze probabilities for these sentences were obtained from40ndash80 UCSD undergraduate students (across different sessions)The student volunteers were asked to complete each sentence con-text with ldquothe first word that comes to mindrdquo Weakly constrainingsentences (from all sources) were defined as sentences with nomore than 40 agreement (range 16ndash40) for the most com-mon completion whereas strongly constraining sentences (from allsources) were defined as those with at least 70 agreement (range70ndash100) for the most common completion Mean sentencelength (in number of words) was matched for strongly and weaklyconstraining contexts In addition strongly constraining sentenceswere chosen such that the constraint on the sentence-final targetword arose from world knowledge at the sentence message leveland not as a function of simple lexical association Only 12 of the160 sentences (75) contained any lexical item with an associativestrength (Kiss Armstrong Milroy amp Piper 1973) of greater than20 with the sentence-final target word These associated itemswere always at least two words away from the target with a meandistance of seven words Since lexical priming effects have been

shown to dissipate quickly (Gough Alford amp Holley-Wilcox 1981Ratcliff amp McKoon 1988) any observed facilitation for the targetwords in strongly constraining sentences is very unlikely to be dri-ven by word-level priming alone

Strongly constraining sentence contexts were paired with theending obtaining the highest cloze probability for that context (al-ways 70 or above) These same 160 words were then paired withthe weakly constraining sentence contexts to yield plausible low-cloze-probability endings (cloze probability always 40 or below)Across the experiment therefore sentence-final target words in thetwo constraint conditions were perfectly matched for all lexicalvariables (mean length 5 letters SE 01 mean frequency [Fran-cis amp Kucera 1982] 118 SE 15) The strongly and weaklyconstraining sentences were then divided into halves and combinedin two lists of 160 sentences each such that the same target wordwas not repeated in a list Half of each context type within each listwas shown to the LVF and half to the RVF counterbalanced acrossparticipants Within each list sentence-final targets were matchedfor word length and frequency (Francis amp Kucera 1982) acrossboth constraint and VF conditions The Appendix gives examplesof the stimuli

ParticipantsThirty-two UCSD undergraduate volunteers (16 men and 16

women 18ndash24 years of age mean age 19) participated in the ex-periment for cash or class credit All were right-handed as assessedby the Edinburgh Inventory (Oldfield 1971) 4 reported having aleft-handed member of their immediate family All were monolin-gual English speakers with no history of reading difficulties or neurologicalpsychiatric disorders Eight participants were ran-domly assigned to each of the four stimulus lists

ProcedureThe volunteers were tested in a single experimental session con-

ducted in a soundproof electrically shielded chamber They wereseated in a comfortable chair 40 in in front of a monitor and wereinstructed to read the stimulus sentences for comprehension

The presentation of each sentence was preceded by a series ofcrosses (500-msec duration with a stimulus onset asynchrony vary-ing randomly between 1000 and 1500 msec) to orient the volun-teer toward the center of the screen Sentences were then presentedone word at a time horizontally for a duration of 200 msec with astimulus onset asynchrony of 500 msec Non-sentence-final wordswere presented in the center of the screen but sentence-final wordswere presented pseudorandomly2 in the left or right visual hemi-field with the inner edge 2ordm of visual angle from fixation A centralfixation point remained visible throughout the trial positioned ahalf degree below the bottom-most edge of the centrally presentedwords The volunteers were asked not to blink or move their eyesduring sentence presentation The final target word was followedby a blank screen for 3000 msec after which the next sentence ap-peared automatically

The volunteers were given a short break after every 20 sentencesAt the conclusion of the recording session the participants weregiven a surprise recognition memory test over the sentence-finaltarget words The 160 target words were mixed with 160 new wordsnot previously seen in any part of the experimental session Newwords were matched for length frequency and part of speech withthe target words The participants were asked to circle all of thewords they remembered seeing in the experiment

EEG Recording ParametersThe electroencephalogram (EEG) was recorded from 26 tin elec-

trodes embedded in an Electro-Cap (Electro-Cap InternationalEaton OH) referenced to the left mastoid These sites included mid-line prefrontal (MiPf) left and right medial prefrontal (LMPf andRMPf) left and right lateral prefrontal (LLPf and RLPf) left and


right medial frontal (LMFr and RMFr) left and right mediolateralfrontal (LDFr and RDFr) left and right lateral frontal (LLFr andRLFr) midline central (MiCe) left and right medial central (LMCeand RMCe) left and right mediolateral central (LDCe and RDCe)midline parietal (MiPa) left and right mediolateral parietal (LDPaand RDPa) left and right lateral temporal (LLTe and RLTe) mid-line occipital (MiOc) left and right medial occipital (LMOc andRMOc) and left and right lateral occipital (LLOc and RLOc)Blinks and eye movements were monitored via electrodes placedon the outer canthus (left electrode serving as reference) and infra-orbital ridge of each eye (referenced to the left mastoid) Electrodeimpedances were kept below 5 k The EEG was processed throughGrass amplifiers (Grass-Telefactor West Warwick RI) set at abandpass of 001ndash100 Hz was continuously digitized at 250 Hz andwas stored on hard disk for later analysis

Data AnalysisData were rereferenced offline to the algebraic average of the left

and right mastoids Trials contaminated by eye movements blinksexcessive muscle activity or amplifier blocking were rejected offlinebefore averaging approximately 15 of trials in each hemifieldwere lost because of such artifacts ERPs were computed for epochsextending from 100 msec before to 920 msec after stimulus onsetAverages of artifact-free ERP trials were calculated for target wordsin the two constraint conditions (strongly or weakly constraining)in each hemifield (RVF or LVF) after subtraction of the 100-msecprestimulus baseline ERPs were filtered with a digital bandpassfilter of 02ndash20 Hz prior to measurement and analysis All p valuesare reported after epsilon correction (HuynhndashFeldt) for repeatedmeasures with more than one degree of freedom

RESULTS

BehaviorVolunteers correctly identified as ldquooldrdquo an average of

468 of the sentence-final target words on the recogni-tion memory test with a false alarm rate of 009 (notethat there is only a single false alarm rate since testitems were not lateralized) dprime was 145 across both VFconditions (148 for stimuli presented in the RVF and

142 for those in the LVF) Participants were thus able todifferentiate words studied in both VFs from new wordsindicating that they must have generally been able toread the peripherally presented words in both the left andright visual fields

To examine the influences of VF and constraint onrecognition memory hit rates were subjected to an om-nibus 2 (visual field RVF vs LVF) 2 (sentential con-straint strongly vs weakly constraining) ANOVA Therewas a main effect of sentential constraint [F(131) 471p 05] with better recognition memory for targets thathad been viewed in weakly rather than in strongly con-straining contexts and a marginal effect of visual field[F(131) 326 p 08] with somewhat better recog-nition for targets presented in the RVF As can be seen inFigure 1 these effects were modulated by a significantinteraction between constraint and visual field [F(131) 666 p 01] Planned comparisons revealed an effectof constraint on recognition memory for target wordswhen presented to the RVF (t 367 p 001) withbetter recognition memory for words that had been seenin weakly rather than in strongly constraining sentencesbut no effect of constraint for words presented to the LVF(t 039 p 70) There was no significant differencein hit rates as a function of visual field for targets thathad been embedded in strongly constraining contexts(t 098 p 33) but in weakly constraining contextsrecognition memory was better for words presented inthe RVF (t 302 p 01) Overall then recognitionwas selectively improved for words that had been viewedin weakly constraining contexts and were presented ini-tially to the LH (RVF)

Event-Related PotentialsGrand average ERPs to sentence-final target words in

each VF are shown in Figure 2 Early components in all

Figure 1 Recognition accuracy Mean hit rates (with standard errors) are plottedfor recognition of target words as a function of VF in which they were originallyviewed and constraint provided by the context in which they originally appearedRecognition rates were highest for target words presented in weakly constraining con-texts to the RVFLH


conditions and hemifields include at posterior sites a pos-itivity (P1) peaking around 80 msec a negativity (N1)peaking between 150 and 200 msec (depending on VF andchannel) and a positivity (P2) peaking around 225 msecAs expected these effects are strongly lateralized beingmost prominent over posterior sites contralateral to thevisual half-field of presentation At frontal sites all con-ditions include a negativity (N1) peaking around 150 msecand a positivity (P2) peaking around 250 msec Earlycomponents are followed most prominently for targetsin weakly constraining sentence contexts by a broadlydistributed negativity (N400) between 300 and 500 msecand in both conditions by a posterior lateralized negative-going effect extending from about 300 msec to the endof the epoch

ERPs were measured and analyzed in four time win-dows To confirm the success of the lateralized presenta-tion visual N1 responses (100ndash200 msec) were analyzedfor lateralization over the back of the head where thiscomponent tends to be largest (channels LDCe RDCeLDPa RDPa LMOc RMOc LLTe RLTe LLOc andRLOc) The sustained posterior negativity was also mea-sured at these same channels between 300 and 900 msec

Then in order to examine the influence of the experimen-tal variables on perceptual and semantic processing frontalP2 responses (200ndash300 msec) were measured over ante-rior channels (MiPf LLPf RLPf LMPf RMPf LDFrRDFr LLFr RLFr LMFr and RMFr) and N400 responses(300ndash500 msec) were measured over all channels andboth were analyzed as functions of VF and constraint

Visual N1 and selection negativity Figure 3 showsERP responses at posterior channels to words presentedin the right and left visual fields collapsed across con-straint To confirm that lateralized presentation of the stim-uli resulted in the expected lateralization of visual pro-cessing mean amplitude N1 responses (100ndash200 msec)were measured at 10 posterior channels These measureswere subjected to an omnibus 2 (visual field RVF vsLVF) 2 (hemisphere left vs right) 5 (electrode)ANOVA There were no main effects of either visual field[F(131) 124 p 27] or hemisphere [F(131) 105 p 31] but there was a significant interaction ofthe two [F(131) 8774 p 001] As expected forRVF presentations N1s were larger over left (119 μV)than over right (058 μV) scalp sites and for LVF pre-sentations N1s were larger over right (169 μV) than

Figure 2 ERP constraint effects Grand average ERP waveforms are shown for target words in stronglyand weakly constraining contexts at all 26 electrode sites The head diagram shows the electrode arrange-ment ERPs elicited during left hemisphere (RVF) presentation are shown on the left and those elicited dur-ing right hemisphere (LVF) presentation are shown on the right Negative is plotted up here and in all sub-sequent plots Responses to visual words in both VFs are characterized by the same set of early components(P1 N1 P2) and N1 amplitudes are lateralized as expected for lateralized stimulus presentation For pre-sentation in both VFs responses in the 300- to 500-msec time window (N400) were more negative for tar-get words in weakly rather than in strongly constraining contexts In addition with RVF presentation re-sponses over frontal sites in the 200- to 300-msec time window (P2) were more positive for strongly thanfor weakly constrained targets


over left (063 μV) scalp sites N1 responses were alsodelayed over ipsilateral relative to contralateral sites byan average of 10 msec [F(131) 388 p 001] re-flecting callosal transfer

Previous studies measuring ERPs to lateralized visualstimuli have reported a sustained late negative-goingeffect over lateral and posterior scalp sites contralateralto the VF of stimulus presentation (Federmeier amp Kutas1999a 2002 Neville Kutas amp Schmidt 1982) and wealso observed a visually similar effect in this study Tocharacterize this negative-going process mean ampli-tude measures from 300ndash900 msec were taken from thesame 10 posterior electrodes and were subjected to anomnibus 2 (visual field RVF vs LVF) 2 (hemisphereleft vs right scalp sites) 5 (electrode) ANOVA Therewas a main effect of hemisphere [F(131) 1029 p 01] with greater negativity over left than over rightscalp sites as well as a nonsignificant tendency for morenegative responses with LVF presentation [F(131) 211 p 16] As expected visual field and hemisphereinteracted [F(131) 10011 p 001] with greaternegativity over scalp sites contralateral to the VF ofpresentation

In summary we observed the expected general effectsof stimulus lateralization on both early and later ERPresponses

Frontal P2 As was described in the introductionfrontal P2 responses have been associated with higherorder perceptual and attention-related processing To ex-amine the effects of VF and constraint on these pro-cesses mean amplitude measures were taken from 200ndash300 msec at the 11 anterior scalp sites Figure 4 showsthese responses (at two representative frontal channels)for each VF as a function of constraint These measureswere subjected to an omnibus 2 (visual field RVF vsLVF) 2 (sentential constraint strongly vs weakly con-straining) 11 (electrode) ANOVA There were maineffects of both visual field [F(131) 533 p 03] and

sentential constraint [F(131) 1931 p 001] withlarger overall P2 responses to items presented in the RVFand for targets in strongly constraining contexts Thesemain effects were modulated by a visual field con-straint interaction [F(131) 402 p 05] Plannedcomparisons revealed that P2 amplitudes did not differas a function of visual field for targets in weakly con-straining sentences [F(131) 025 p 62] but werelarger with RVF (567 μV) than with LVF (451 μV) pre-sentation for targets in strongly constraining sentences[F(131) 832 p 01] Overall constraint stronglymodulated P2 amplitudes for initial presentation to theLH (RVF) 567 versus 397 μV in strongly versus weaklyconstraining contexts respectively [F(131) 2107 p 001] The effect of constraint on P2 amplitudes withLVF presentation was smallermdash451 versus 379 μVmdashand was only marginally significant [F(131) 386 p 058]

In summary the presence of a strongly constraining sen-tence context affected word processing between 200 and300 msec postndashstimulus onset presumably at a percep-tual level more strongly for targets presented initially tothe LH (RVF) rather than to the RH (LVF)

N400 To examine the effects of VF and constraint onthe semantic processing of target words mean amplitudemeasures were taken from 300ndash500 msec at all 26 elec-trode sites These measures were subjected to an omnibus2 (visual field RVF vs LVF) 2 (sentential constraintstrongly vs weakly constraining) 26 (electrode) ANOVAThere was a main effect of visual field [F(131) 584p 02] with more negative responses to words pre-sented in the LVF3 There was also a main effect of sen-tential constraint [F(131) 6706 p 001] withgreater N400 amplitudes to targets in weakly (294 μV)rather than strongly (540 μV) constraining contextsThere was no interaction between visual field and sen-tential constraint [F(131) 001 p 91] and no hintof such an interaction even over a more restricted subset

LEFT OCCIPITAL SITE RIGHT OCCIPITAL SITE

Right visual field

Left visual field0 200 400 600 800 msec

5

Figure 3 Effects of stimulus lateralization on ERP To show the general ERPeffect of stimulus lateralization responses to target words (collapsed across con-straint) presented to the RVF and LVF are overplotted at left and right occipitalscalp sites (where such effects were largest) N1 responses (100ndash200 msec) arelargest contralateral to VF of presentation and are followed from about 300 msecby an extended negative-going effect that is also largest contralaterally


of electrodes [visual f ield sentential constraint electrode F(25775) 054 p 97]

Planned comparisons were conducted within each visualfield using an omnibus 2 (sentential constraint stronglyvs weakly constraining) 26 (electrode) ANOVAThese analyses revealed a significant effect of sententialconstraint in both visual fields For RVF presentationmean amplitudes were 573 μV to targets in stronglyconstraining sentences and 330 μV to targets in weaklyconstraining sentences [F(131) 4000 p 001] ForLVF presentation mean amplitudes in the same compar-ison were 507 and 258 μV respectively [F(131) 3550 p 001] In order to compare responses at eachconstraint level as a function of VF planned compar-isons were conducted using the four central channels(LMCe RMCe MiCe and MiPa) these channels werechosen because N400 effects are typically maximal atthese channels and because using a more restricted setof electrodes helps minimize overlap with the lateralizedposterior effect already described For targets in stronglyconstraining sentence contexts an omnibus 2 (visual fieldRVF vs LVF) 4 (electrode) ANOVA revealed no maineffect of visual field [F(131) 036 p 55] Thesame analysis on the targets in the weakly constrainingsentence contexts also revealed no effect of visual field[F(131) 105 p 31]

To further characterize the distribution and latency ofthe N400 constraint effect difference ERPs were createdfor each VF condition by doing a point-by-point subtrac-tion of targets in strongly constraining sentences fromtargets in weakly constraining sentences (Figure 5) Thisprocedure removes effects of stimulus lateralization that

are consistent across experimental conditions (eg N1effects and the sustained posterior difference) allowinga comparison of the N400 constraint effect across VFsMean amplitude of the constraint effect was measuredbetween 300 and 500 msec at 16 scalp electrodes4 andsubjected to an omnibus 2 (visual field RVF vs LVF) 2 (hemisphere left vs right scalp sites) 2 (lateralitylateral vs medial scalp sites) 4 (anteriority prefrontalfrontal parietal or occipital) ANOVA There was no ef-fect of visual field [F(131) 001 p 94] and no in-teractions of visual field with hemisphere [F(131) 124p 27] laterality [F(131) 004 p 84] or anterior-ity [F(393) 054 p 58] Effects in both VFs had thegeneral distributional pattern characteristic of the N400biggest over medial and posterior sites and with a right-lateralized skew There was however a significant visualfield hemisphere anteriority interaction [F(393) 468 p 01] For LVF presentation the rightward skewof the scalp distribution of the N400 increased steadilyas one moved from more frontal to more posterior sitesreaching its maximum over the back of the head For RVFpresentation the rightward skew was similar over frontalsites but was at its minimum over the most posterior sitesThus as can be seen in Figure 6 at the most posterior sitesN400 effect distributions were shifted contralateral tothe VF of presentation with greater right-lateralizationof the N400 for LVFRH presentation and reduced right-lateralization for RVFLH presentation

Peak latency of the N400 effect in each VF was mea-sured using the difference ERP between 350 and 450 msecat the middle central channel (MiCe) where N400 ef-fects are usually most pronounced and subjected to an

Figure 4 Effects of constraint on the P2 component Responses are shown to targetwords in strongly and weakly constraining contexts at right (RMPf) and left (LMPf)medial prefrontal sites (where P2 effects tend to be largest) Responses with left hemi-sphere (RVF) presentation are on the left and those with right hemisphere (LVF) pre-sentation are shown on the right For RVF presentation P2 responses (200ndash300 msec)were significantly larger (more positive) for target words in strongly rather thanweakly constraining contexts


omnibus ANOVA on two levels of visual field (RVF vsLVF) Peak latency was 384 msec for RVF presentationand 390 msec for LVF presentation these peak latenciesdid not differ [F(131) 065 p 42]5 Because of theimportance of latency differences for assessing the pos-sibility of callosal transfer as an explanation for the re-sult pattern we did an additional analysis comparing atthe 15 central and posterior sites where N400 effects aremost prominent the mean amplitude of the differenceERP across VFs in successive 25-msec time windowsfrom 200ndash400 msec There was no significant differencein any of the eight time windows (all ps 1) suggest-ing that not only the peak but also the time course of thebuildup of the N400 constraint effect was similar forboth VFs

In summary and as expected N400 responses werelarger for target words in weakly as opposed to stronglyconstraining sentences This was true for presentation inboth VFs There was no evidence in any of the compar-isons for a difference in the magnitude or latency of theN400 response to the two types of target words as a func-tion of which hemisphere initially received the stimulus

There was however a VF-based skew in the N400 effectdistribution over posterior channels

DISCUSSION

This experiment was designed to test the claim that thesemantic processing of words presented initially to theRH does not benefit from message-level context infor-mation Hypotheses derived from priming measures inlexical decision tasks have predicted a striking differencein the impact of sentential constraint on the processing ofsentence-final target words presented in the LVF versusthe RVF Such studies have consistently found thatLVFRH word processing is largely insensitive to ma-nipulations of message-level meaning such as the num-ber (Faust et al 1993) or order (Faust et al 1995) of wordsin the context or the cloze probability of the terminal word(Faust amp Kravetz 1998) By contrast these same ma-nipulations do modulate the facilitation observed withinitial presentation to the RVFLH Furthermore such datahave suggested that when word-level information andmessage-level information come into conflict LVFRH

N400 CONSTRAINT EFFECT

WEAKLY ndash STRONGLY CONSTRAINED TARGETS

PREFRONTAL

FRONTAL

PARIETAL

OCCIPITAL

Right visual field Left visual field

0 400 800

5

Left Right

Lateral Medial Medial Lateral

Figure 5 N400 constraint effects Difference waves are plotted that show theN400 constraint effect (responses to targets in weakly constraining contextsminus responses to targets in strongly constraining contexts) The waveformsat the 16 electrode sites (LLPf LLFr LLTe LLOc LMPf LDFr LMCeLMOc RMPf RDFr RMCe RMOc RLPf RLFr RLTe and RLOc) illustratethe distribution of the N400 effect which is largest over medial central sites asis typical for the N400 responses also tend to be larger over right than over leftscalp sites although this tendency is increased for presentation to the righthemisphere (LVF) Constraint effects start earlier (in the P2 time window) overfrontal sites with RVF presentation but in the N400 time window (300ndash500 msec) are statistically indistinguishable in both amplitude and latency forthe two VFs


measures are primarily driven by the word-level infor-mation (eg lexical association) whereas RVFLH mea-sures are primarily driven by the message-level informa-tion (Faust et al 1995) This pattern has been interpretedas showing that the RH can exploit lexical-level context butthat the LH is superior in ability to integrate lexical syn-tactic and semantic information to construct a message-level representation of meaning (Chiarello et al 2001Faust et al 2003)

In order to test this hypothesis the present experimentused ERP measures to examine the processing of sentence-final target words under different degrees of contextualconstraint All target words were plausible completionsof the sentences but the contexts were designed to pro-vide different amounts of message-level constraint onthem In addition care was taken to ensure that the tar-gets could not be differentially predicted on the basis ofsimple lexical-level associations Therefore divergentpatterns of facilitation here measured using N400 am-plitudes would be expected depending on whether onlylexical-level information is processed as has been hy-pothesized for LVFRH stimuli or a message-levelmeaning of the sentence is constructed and used as hasbeen assumed for RVFLH stimuli To the extent thatonly lexical-associative information is available to affectword processing little if any difference in facilitationshould be observed for target words within contextscharacterized by strong versus weak message-level con-straint In contrast to the extent that the message-level

meaning of the sentence is constructed and used duringa wordrsquos processing more facilitation (greater N400 am-plitude reductions) would be expected for words instrongly constraining contexts as compared with whenthese same lexical items are embedded in weakly con-straining contexts

As expected a significant effect of message-levelconstraint was evident in the N400 responses observedafter RVF presentation with reduced amplitudes to (lex-ically identical) target words when they were embeddedin strongly as opposed to weakly constraining sentencesStrikingly however we also observed a significant N400constraint effect after LVF presentation To our knowl-edge this is the first demonstration that message-levelconstraint modulates the semantic processing of plausi-ble sentence-final words presented to the LVFRH Asalready described prior behavioral studies using lexicaldecision response times have found no effects of con-straint or other message-level manipulations for congru-ent targets in the LVF (although effects on incongruenttargets have sometimes been observed) With a differentdependent measure however we found that message-level information can and does impact the semantic pro-cessing of stimuli initially presented to the RH Indeednot only did we find significant simple effects of con-straint for presentation in both VFs we found no evi-dence whatsoever that this N400 constraint effect dif-fered in either size or timing as a function of VF Therewas thus no indication that message-level informationwas differentially important for the semantic integrationof words presented initially to the right rather than theleft hemisphere

We interpret the significant effect of constraint withLVF presentation as indicating that the RH like the LHuses message-level information when processing wordsWithout additional information it is probably not rea-sonable to assume that in neurologically intact adultsstimuli presented in one VF will be processed solely bythe contralateral hemisphere since the two hemispheresare connected Several aspects of our results howeverindicate that hemifield presentation was likely success-ful in shifting the relative balance of processing towardthe contralateral hemisphere as is generally acceptedFirst it is worth noting that VF-based asymmetries in be-havioral measures of word processing in young adultsare commonplace (see eg reviews by Chiarello 2003and Faust 1998)6 Moreover our prior ERP studies evi-denced such asymmetries for the N400 under task con-ditions identical to those used here (Federmeier amp Kutas1999a) Thus we have every reason to believe a priorithat under such conditions visual half-field methods dosample asymmetrically from the two hemispheres whenneurally intact college undergraduates read sentences Infact in a result that replicates our prior hemifield ERPstudies (Federmeier amp Kutas 1999a 2002) we found thatposterior N1 responses were largest contralateral to pre-sentation VF demonstrating that relatively early visualprocessing was lateralized to the contralateral hemisphereThese early sensory potentials were followed by a con-

RVF

LVF

540486432378324270216162108054000ndash054ndash108ndash162ndash216ndash270ndash324ndash378ndash432ndash486ndash540

Figure 6 Topography of the N400 effect Topographic voltagemaps (as seen from the top of the head for a 20-msec windowaround 390 msec) of the N400 constraint effect are shown forRVF and LVF presentation Over the posterior part of the scalpthe distribution of the N400 effect is skewed toward electrode sitescontralateral to the presentation VF (ie more right-lateralizedafter LVF presentation and vice versa)


tralaterally skewed negative potential (the selection neg-ativity) that extended throughout the 1-sec recordingepoch further demonstrating that at least some aspectsof the time-locked neural activity continued to dependon VF during the time frame of all the ERP measures ofinterest for the present study Finally there were differencesdependent on VF of presentation even on the delayed-recognition memory task Thus at no point in time dur-ing the recording epoch was brain processing wholly un-affected by VF of initial presentation

Of course the presence of a VF-based asymmetry in andof itself does not rule out the possibility that the language-dominant LH was largely if not solely responsible for allof the semantic context effects observed Several aspectsof the behavior of the N400 response however argueagainst this view Interhemispheric transfer of informa-tion takes time Callosal relay times have been measuredto be on the order of 10ndash25 msec (see eg the review byHoptman amp Davidson 1994) and ERPs have the tem-poral resolution to detect such delays Indeed we foundsignificant delays of 10 msec on the N1 component (theipsilateral portion of which is known to arise from hemi-spheric transfer [Rugg Milner amp Lines 1985]) and hadsufficient power to be able to detect comparable delayson the N400 were they present We did not however findany reliable peak latency differences for the N400 effectas would have had to occur under the hypothesis that theLH performs the message-level integration regardless ofVF of presentation but only after transfer from the RHfollowing LVF presentation At the same time whereasN400 latencies and amplitudes did not differ as a func-tion of VF the amplitude distribution of the N400 effectacross the scalp was skewed toward electrodes over thehemisphere contralateral to presentation VF (greaterright lateralization for LVFRH presentation and reducedright lateralization for RVFLH presentation) Ratherthan finding identical constraint effects that were shiftedin time we found functionally identical effects that wereslightly shifted in space (due to nonoverlapping neuralgenerators) in a direction consistent with contralateralprocessing Overall then multiple aspects of our datastrongly support the hypothesis that LVF presentationleads to a greater degree of RH processing than doesRVF presentation and vice versa

Our finding that message-level constraint informationhas a significant impact on LVF-initiated RH word pro-cessing contrasts with predictions based on behavioraldata collected under similar conditions although it co-heres with the reported absence of any reliable VF-baseddifferences in N400 amplitude reduction for contextu-ally congruent versus wholly incongruent sentence com-pletions (Federmeier amp Kutas 1999a) The disparity be-tween the behavioral and ERP results clearly merits furtherstudy and a number of differences between the mea-sures materials and paradigms that have been used witheach could be the basis for the disparity Arguably onecritical distinction is that our N400s to lateralized targetwords were recorded as participants simply read forcomprehension without any concomitant speeded overt

response With RT measures for lateralized target wordsthere is always the potential confound of an overall RVFLH advantage for speeded responding in language taskssuch as naming and lexical decision Inferences aboutthe language abilities of the two hemispheres based onlexical decision tasks have been questioned on othergrounds as well As mentioned previously investigationsin split-brain patients have revealed that the lexical deci-sion task which studies of hemispheric differences in sen-tence processing have used almost exclusively under-represents the semantic abilities of the RH (Baynes ampEliassen 1998 Zaidel 1990) Perhaps then the RH isable to use message-level information to process wordsfor comprehension (as reflected in N400 responses ob-tained during reading as well as in the types of tasksoften used in neuropsychological studies) but not tomake speeded lexical decision responses Alternatively aswill be explored in more detail below the behavioral pat-terns may reflect asymmetries arising at a different pro-cessing level The functional specificity of the N400 mea-sure for semantic processing allows us to be reasonablyconfident that the facilitation we observe in both VFs isrelated to semantic access and integration processes

In fact we did find VF-based dissociations for otherERP components and behavioral measures of recogni-tion in the present study Specifically we observed VF-based differences between the hemispheres in the effectsof constraint on recognition memory for the target wordsTarget words were more likely to be recognized at theend of the experiment if they had been viewed in weaklyconstraining sentences but only for presentation to theRVFLH With presentation to the LVFRH there was nodifference in memory for target words as a function ofconstraint and memory for strongly constrained targetswas not different as a function of VF presentation Therewas thus a selective improvement in recognition memoryfor words presented in the RVF (but not the LVF) if theyhad originally completed weakly constraining contextsIt seems reasonable to suppose that the decreased pre-dictability of words in less constraining contexts resultedin increased attention andor elaborative encoding dur-ing processing improving subsequent recognition mem-ory for these items Indeed this hypothesis is consistentwith our finding discussed in more detail later that theearlier P2 component which has been linked to percep-tion and attentional processes was affected by constraintonly with RVF presentation Whatever the basis for thiseffect however it occurred only for words initially pro-cessed by the LH Little is known about hemispheric dif-ferences in memory function although a few studieshave reported a recognition memory advantage for ver-bal material presented initially to the RVF (Coney ampMacDonald 1988 Dee amp Fontenot 1973) To our knowl-edge this study is the first to report a VF-based differ-ence in the effect of contextual variables on recognitionmemory in brain-intact individuals More generally thedifference between our ERP and behavioral resultsmakes clear that multiple processes are affected by theVF manipulation and can be affected in different ways


In sum whereas we found constraint-based facilitationof semantic processing in both VFs constraint-based fa-cilitation of explicit recognition memory performancewas found only for RVF presentation

Although our results demonstrate that message-levelinformation is available and used to facilitate semanticprocessing for stimuli presented initially to either hemi-sphere they need not imply that this message-level in-formation will always impact semantic processing in thesame way for the two VFs Indeed unexpected sentenceendings from the same category as the expected com-pletions (within-category violations) have been shown toelicit different N400 responses in the two VFs (Feder-meier amp Kutas 1999a) When presented to the RVFLHthese violations elicited smaller N400 responses than didunexpected items from a different semantic category(between-category violations) However in the LVFRHresponses to within- and between-category violationswere of the same magnitude The LVFRH responsesmirrored the message-level plausibility of the endingtypes (which was empirically determined and controlled)but the RVFLH responses revealed a sensitivity to the fea-tural overlap between an ending that was presented andone that could be expectedmdashbut never actually appeared

On the basis of these findings we hypothesized thatthere is a fundamental difference in how the two hemi-spheres make use of context to create a message-levelrepresentation In particular we proposed that the LHbut not the RH uses context information to actively pre-pare for the processing of likely upcoming stimulimdashthatis to preactivate (predict) According to this hypothesisword processing initiated by either hemisphere is im-pacted by the message-level representation shaped by thewords in the context among other factors The RHrsquosmessage-level representation is made up of informationderived directly from the ongoing context in a bottom-upfashion This representation is compared with the fea-tures activated by the word at hand and the observablefacilitation is then primarily a function of that fit (eghow well baseball coheres with context features such aspass and touchdown) In the LH in contrast processingreflects a bidirectional interplay between bottom-up andtop-down processing of the ongoing sentence contextthe consequence of which is the preactivation of seman-tic and possibly even perceptual features of likely up-coming words and the observable facilitation is a func-tion of the overlap between the target actually presentedand that contextually derived prediction (eg how simi-lar baseball is to the predicted footballmdashon all salientfeatures not just those highlighted by the context)

We cannot assess this hypothesis with the N400 datafrom the present study since increased contextual con-straint could be expected to aid the semantic processingof target words under both ldquointegrationrdquo (RH) and ldquoex-pectancyrdquo (LH) strategies Certainly a more constrainingcontext would seem to allow for better prediction by plac-ing more constraints on the set of likely upcoming wordsandor concepts Nonetheless constraint effects couldalso emerge without predictive processing since more

constraining contexts are likely to provide more andorbetter information with which to integrate incomingstimuli In this study we found no evidence that the useof constraining contextual information differentially af-fected semantic aspects of word processing as a functionof VF of presentation However other aspects of thepresent data do relate to our hypothesis that RVF pre-sentation triggers a predictive strategy that LVF presen-tation does not Specifically we observed constraint-based VF effects on the P2 component of the ERP7

The P2 is a fronto-central positivity peaking around250 msec that often coincides with the onset of an N400effect Both the precise functional significance of the P2component and its neural source remain imperfectly un-derstood Amplitude differences in the P2 however typ-ically have been linked to the detection and analysis ofvisual features in attention paradigms with increasedamplitudes for stimuli containing target features (Hill-yard amp Muumlnte 1984 Luck amp Hillyard 1994) P2 thusseems to reflect some stage of higher order visual pro-cessing In the present experiment we observed an inter-action between constraint and VF P2s to words in weaklyconstraining contexts did not differ with VF but those towords in strongly constraining contexts were larger (morepositive) for RVFLH presentation This pattern is remi-niscent of that observed for congruency effects with sentence-final pictures larger P2s for congruent pic-tures but only with initial presentation to the LH (Fed-ermeier amp Kutas 2002) This pattern is also similar tobehavioral effect patterns in which contextual informa-tion facilitates response speed for RVF but not LVFwords If these patterns are indeed linked it would indi-cate that the behavioral asymmetries arise primarilyfrom perceptual rather than semantic processing differ-ences in contrast to what is typically assumed Our P2findings thus suggest that the message-level informationpreviously extracted from a sentence context can providetop-down information which in turn allows for more ef-ficient visual extraction from expected and especiallyfrom highly constrained target stimuli This facilitativeeffect of predictive language information on higher levelvisual processing seems however to occur only for stim-uli initially processed by the LH recall that these wordswere also generally less well remembered

In summary then we found that the semantic process-ing of a visual word stimulus is influenced by the message-level constraint of a sentence context for initial presen-tation to either the LH or RH This in turn suggests thatthe asymmetries found with behavioral measures for theimpact of sentence-level information on the processingof LVF and RVF words do not arise because RH seman-tic processing has no or less access to message-levelmeaning information as has been commonly thought Atthe same time however we found that higher order per-ceptual visual processing was more affected by senten-tial constraint with initial presentation to the LH in ac-cord with the hypothesis that the LH (but not the RH)uses context information to predict the semantic and per-ceptual features of likely upcoming words VF-based


differences were also revealed in participantsrsquo recogni-tion memory for the lateralized target words which wasaffected by constraint only for RVFLH presentationHemispheric asymmetries thus seem to arise at multipleprocessing levels and to manifest differently across taskswhich may help to explain disparities in the conclusionsthat have been drawn about RH language capacities fromneuropsychological behavioral and electrophysiologi-cal measures Thus far ERP data are consistent with thehypothesis that both hemispheres make use of higherlevel meaning information to guide semantic processingalthough they likely use such information differently

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Banich M T (2003) Interaction between the hemispheres and its im-plications for the processing capacity of the brain In R Davidsonand K Hugdahl (Eds) Brain asymmetry (2nd ed pp 261-302)Cambridge MA MIT Press

Baynes K amp Eliassen J C (1998) The visual lexicon Its accessand organization in commissurotomy patients In M Beeman amp C Chiarello (Eds) Right hemisphere language comprehension Per-spectives from cognitive neuroscience (pp 79-104) Mahwah NJErlbaum

Beeman M (1993) Semantic processing in the right hemisphere maycontribute to drawing inferences from discourse Brain amp Language44 80-120

Beeman M (1998) Coarse semantic coding and discourse compre-hension In M Beeman amp C Chiarello (Eds) Right hemisphere lan-guage comprehension Perspectives from cognitive neuroscience(pp 255-284) Mahwah NJ Erlbaum

Beeman M Friedman R B Grafman J amp Perez E (1994) Sum-mation priming and coarse semantic coding in the right hemisphereJournal of Cognitive Neuroscience 6 26-45

Bentin S McCarthy G amp Wood C C (1985) Event-related po-tentials associated with semantic priming Electroencephalographyamp Clinical Neurophysiology 60 343-355

Berardi N amp Fiorentini A (1997) Interhemispheric transfer ofspatial and temporal frequency information In S Christman (Ed)Cerebral asymmetries in sensory and perceptual processing (pp 55-79) New York Elsevier

Bloom P A amp Fischler I (1980) Completion norms for 329 sen-tence contexts Memory amp Cognition 8 631-642

Bottini G Corcoran R Sterzi R Paulesu E S Schenone PScarpa P Frackowiak R S J amp Frith C D (1994) The role ofthe right hemisphere in the interpretation of figurative aspects of lan-guage A positron emission tomography activation study Brain 1171241-1253

Brownell H H Michel D Powelson J amp Gardner H (1983)Surprise but not coherence Sensitivity to verbal humor in right-hemisphere patients Brain amp Language 18 20-27

Brownell H H Potter H H Bihrle A M amp Gardner H(1986) Inference deficits in right brain-damaged patients Brain ampLanguage 27 310-321

Bub D N amp Arguin M (1995) Visual word activation in pure alexiaBrain amp Language 49 77-103

Burgess C amp Simpson G B (1988) Cerebral hemispheric mecha-nisms in the retrieval of ambiguous word meanings Brain amp Lan-guage 33 86-103

Chiarello C (2003) Parallel systems for processing language Hemi-spheric complementarity in the normal brain In M T Banich amp M Mack (Eds) Mind brain and language Multidisciplinary per-spectives (pp 229-247) Mahwah NJ Erlbaum

Chiarello C Burgess C Richards L amp Pollock A (1990) Se-mantic and associative priming in the cerebral hemispheres Some

words do some words donrsquot sometimes some places Brain ampLanguage 38 75-104

Chiarello C Liu S amp Faust M (2001) Bihemispheric sensitivityto sentence anomaly Neuropsychologia 39 1451-1463

Coney J amp MacDonald S (1988) The effect of retention intervalupon hemispheric processes in recognition memory Neuropsycho-logia 26 287-295

Dee H L amp Fontenot D J (1973) Cerebral dominance and lateraldifferences in perception and memory Neuropsychologia 11 1167-1173

Delis D C Wapner W Gardner H amp Moses J A (1983) Thecontribution of the right hemisphere to the organization of para-graphs Cortex 19 43-50

Faust M (1998) Obtaining evidence of language comprehension fromsentence priming In M Beeman amp C Chiarello (Eds) Right hemi-sphere language comprehension Perspectives from cognitive neuro-science (pp 161-185) Mahwah NJ Erlbaum

Faust M Babkoff H amp Kravetz S (1995) Linguistic processesin the two cerebral hemispheres Implications for modularity vs in-teractionism Journal of Clinical amp Experimental Neuropsychology17 171-192

Faust M Bar-Lev A amp Chiarello C (2003) Sentence priming ef-fects in the two cerebral hemispheres Influences of lexical relatednessword order and sentence anomaly Neuropsychologia 41 480-492

Faust M amp Kravetz S (1998) Levels of sentence constraint and lex-ical decision in the two hemispheres Brain amp Language 62 149-162

Faust M Kravetz S amp Babkoff H (1993) Hemisphericity andtop-down processing of language Brain amp Language 44 1-18

Federmeier K D amp Kutas M (1999a) Right words and left wordsElectrophysiological evidence for hemispheric differences in mean-ing processing Cognitive Brain Research 8 373-392

Federmeier K D amp Kutas M (1999b) A rose by any other nameLong-term memory structure and sentence processing Journal ofMemory amp Language 41 469-495

Federmeier K D amp Kutas M (2002) Picture the difference Elec-trophysiological investigations of picture processing in the cerebralhemispheres Neuropsychologia 40 730-747

Francis W N amp Kucera H (1982) Frequency analysis of Englishusage Boston Houghton Mifflin

Gardner H Brownell H H Wapner W amp Michelow D(1983) Missing the point The role of the right hemisphere in theprocessing of complex linguistic materials In E Perecman (Ed)Cognitive processing in the right hemisphere (pp 169-191) NewYork Academic Press

Gough P B Alford J A Jr amp Holley-Wilcox P (1981) Wordsand contexts In O J L Tzeng amp H Singer (Eds) Perception ofprint Reading research in experimental psychology (pp 85-102)Hillsdale NJ Erlbaum

Griffin Z M amp Bock K (1998) Constraint word frequency and therelationship between lexical processing levels in spoken word pro-duction Journal of Memory amp Language 38 313-338

Hillyard S A amp Muumlnte T F (1984) Selective attention to colorand location An analysis with event-related brain potentials Per-ception amp Psychophysics 36 185-198

Hoptman M J amp Davidson R J (1994) How and why do the twocerebral hemispheres interact Psychological Bulletin 116 195-219

Joanette Y Goulet P amp Hannequin D (1990) Right hemisphereand verbal communication New York Springer

Kiss G R Armstrong C Milroy R amp Piper J (1973) An asso-ciative thesaurus of English and its computer analysis In A J AitkinR W Bailey amp N Hamilton-Smith (Eds) The computer and liter-ary studies (pp 153-165) Edinburgh Edinburgh University Press

Kutas M amp Federmeier K D (2001) Electrophysiology reveals se-mantic memory use in language comprehension Trends in CognitiveSciences 4 463-470

Kutas M amp Hillyard S A (1980a) Event-related brain potentialsto semantically inappropriate and surprisingly large words Biologi-cal Psychology 11 99-116

Kutas M amp Hillyard S A (1980b) Reading senseless sentencesBrain potentials reflect semantic incongruity Science 207 203-205

Kutas M amp Hillyard S A (1983) Event-related brain potentials to


grammatical errors and semantic anomalies Memory amp Cognition11 539-550

Kutas M amp Hillyard S A (1984) Brain potentials during readingreflect word expectancy and semantic association Nature 307 161-163

Kutas M Lindamood T E amp Hillyard S A (1984) Word ex-pectancy and event-related brain potentials during sentence process-ing In S Kornblum amp J Requin (Eds) Preparatory states and pro-cesses (pp 217-237) Hillsdale NJ Erlbaum

Luck S J amp Hillyard S A (1994) Electrophysiological correlates offeature analysis during visual search Psychophysiology 31 291-308

Martin R C (2003) Language processing Functional organizationand neuroanatomical basis Annual Review of Psychology 54 55-89

Nagy M E amp Rugg M D (1989) Modulation of event-related po-tentials by word repetition The effects of inter-item lag Psychophysi-ology 26 431-436

Neville H J Kutas M amp Schmidt A (1982) Event-related po-tential studies of cerebral specialization during reading I Studies ofnormal adults Brain amp Language 16 300-315

Ni W Constable R T Mencl W E Pugh K R Fulbright R KShaywitz S E Shaywitz B A Gore J C amp Shankweiler D(2000) An event-related neuroimaging study distinguishing formand content in sentence processing Journal of Cognitive Neuro-science 12 120-133

Oldfield R C (1971) The assessment and analysis of handednessThe Edinburgh inventory Neuropsychologia 9 97-113

Ratcliff R amp McKoon G (1988) A retrieval theory of priming inmemory Psychological Review 95 385-408

Rayner K amp Well A D (1996) Effects of contextual constraint oneye movements in reading A further examination Psychonomic Bul-letin amp Review 3 504-509

Robertson D A Gernsbacher M A Guidotti S J Robertson R R W Irwin W Mock B J amp Campana M E (2000) Func-tional neuroanatomy of the cognitive process of mapping during dis-course comprehension Psychological Science 11 255-260

Rugg M D Milner A D amp Lines C R (1985) Visual evoked po-tentials to lateralised stimuli in two cases of callosal agenesis Jour-nal of Neurology Neurosurgery amp Psychiatry 48 367-373

Sanocki T amp Oden G C (1984) Contextual validity and the effectsof low-constraint sentence contexts on lexical decisions QuarterlyJournal of Experimental Psychology 36A 145-156

Schwanenflugel P J amp Shoben E J (1985) The influence of sen-tence constraint on the scope of facilitation for upcoming wordsJournal of Memory amp Language 24 232-252

St George M Kutas M Martinez A amp Sereno M I (1999)Semantic integration in reading Engagement of the right hemisphereduring discourse processing Brain 122 1317-1325

Taylor W L (1953) ldquoCloze procedurerdquo A new tool for measuringreadability Journalism Quarterly 30 415-433

Titone D (1998) Hemispheric differences in context sensitivity dur-ing lexical ambiguity resolution Brain amp Language 65 361-394

Van Petten C (1993) A comparison of lexical and sentence-levelcontext effects in event-related potentials Language amp CognitiveProcesses 8 485-531

Van Petten C amp Kutas M (1990) Interactions between sentencecontext and word frequency in event-related brain potentials Mem-ory amp Cognition 18 380-393

Wapner W Hamby S amp Gardner H (1981) The role of the righthemisphere in the apprehension of complex linguistic materialsBrain amp Language 14 15-33

Weylman S T Brownell H H Roman M amp Gardner H (1989)Appreciation of indirect requests by left- and right-brain-damaged

patients The effects of verbal context and conventionality of word-ing Brain amp Language 36 580-591

Zaidel E (1990) Language functions in the two hemispheres followingcomplete cerebral commissurotomy and hemispherectomy In F Bolleramp J Grafman (Series Eds) amp R D Nebes amp S Corkin (Vol Eds) Hand-book of neuropsychology (Vol 4 pp 115-150) Amsterdam Elsevier

NOTES

1 The cloze probability for a given word in a given sentence contextis defined as the proportion of individuals choosing to complete thatparticular context with that particular word (Taylor 1953)

2 Equal numbers of each constraint condition were shown to eachhemisphere in an experimental session Order of presentation was ran-domized with the stipulation that no more than three stimuli in a row bepresented to the same hemifield

3 This is the same effect previously described for the late lateralizednegativity and it may reflect overlap of the two responses

4 In order to examine scalp distribution we used the standard proce-dure of dividing scalp electrodes into regions (left right mediallateralanteriorposterior) Not all electrode sites can be used (eg the fourmidline channels cannot be classified with respect to hemisphere) herewe used 16 Left lateral sites were (from front to back) LLPf LLFrLLTe and LLOc Left medial sites were LMPf LMFr LMCe andLMOc Right medial sites were RMPf RMFr RMCe and RMOc Rightlateral sites were RLPf RLFr RLTe and RLOc

5 There were also no peak latency differences at more posterior[MiPa F(131) 061 p 44] or more frontal [MiPf F(131) 084p 37] channels The standard deviation of N400 peak effect latencyis typically around 30 msec for measurements made at a single channelFor the test employed here (within-subjects ANOVA with two levels ofone factor) we had statistical power of 06 to see differences of 12 msec(the value typically measured for sensory components Hoptman ampDavidson 1994) and power of 10 to see differences greater than 25 msec(which is in the upper range of measured differences)

6 The task used for this study reading for comprehension is ar-guably even more likely than behavioral measures to reflect laterally bi-ased processing since lexical decision judgments seem to be more dif-ficult for the isolated RH than semantic comprehension (Baynes ampEliassen 1998 Zaidel 1990) and studies in other domains have shownthat levels of interhemispheric cooperation tend to increase with taskdifficulty (Banich 2003)

7 Because of the potential for temporal overlap between P2 andN400 effects it is important to ascertain that the earlier effect of con-straint for the LVF stimuli reflects something other than an earlier onsetof the N400 constraint effect Since P2 effects have a more frontal scalpdistribution than do N400 effects a distributional analysis can helpmake this differentiation We compared the RVF constraint effect in thetwo time windows (200ndash300 msec and 300ndash500 msec) using an om-nibus 2 (time window) 2 (anteriority 11 frontal channels as alreadydescribed for the P2 analysis and 11 posterior channels including thoseused in the N1 analysis plus MiOc) 11 (electrode) ANOVA In addi-tion to a main effect of time window [F(131) 601 p 02] with alarger effect between 300 and 500 msec we observed a significantcrossover interaction between time window and anteriority [F(131) 2357 p 001] with larger effects over frontal than over posterior sitesbetween 200 and 300 msec but larger effects over posterior than over frontalsites between 300 and 500 msec A split within the 300- to 500-msecwindow itself did not yield this distributional interaction [F(131) 064 p 43] Thus the effect between 200 and 300 msec does notseem to be simply an earlier onset of the N400 effect and in fact has ascalp distribution consistent with that typically observed for P2


APPENDIXExamples of Stimuli Used in the Experiment

One hundred sixty target words were each paired with a strongly (S) and a weakly (W) con-straining sentence context Below are 30 representative examples of these stimuli with targetwords in italics Note that individual participants saw each target word only once

S She was suddenly called back to New York and had to take a cab to the airportW She was glad she had brought a book since there was nothing to read at the airport

S The magician took out his hat and made a rabbit appearW At the end of the grand feast the queen waited patiently for the man to appear

S My grandmother keeps her wedding gown and old photos in the atticW Upon motherrsquos strict orders the catrsquos smelly litter box was kept in the attic

S No one at the reunion recognized Dan because he had grown a beardW At the childrenrsquos park next to the beach she saw a man with a beard

S He was cold most of the night and finally got up to get another blanketW They decided to declaw the feisty cat so he wouldnrsquot tear up the blanket

S Tracy and her husband werenrsquot Catholic but she was glad when the priest warmly welcomed their three children

W She bought several colorful and scenic postcards to send to her children

S Within minutes of arriving at the office the detective spilled his thermos full of coffeeW After getting out of the hot shower he sat down to have coffee

S The tenants decided to take their landlord to courtW He wanted to sit in the front of the court

S He didnrsquot worry about burglars because he kept two fierce dogsW They both have jobs but they get some extra income by raising dogs

S They stood on the bridge tossing stale bread to the ducksW He grew corn in one of his expansive fields to feed his ducks

S The janitor saw the vacuum cleaner bag explode and was afraid the room would soonbe covered in dust

W He finished washing the second load of laundry and started to dust

S The man who was carried into the emergency room had been stabbed in a fightW Sam practiced at his friendrsquos house every day in anticipation of the fight

S The white gull dove down and caught a fishW They had to drive for another hour before finding a place to fish

S He tried to put the pieces of the broken plate back together with glueW She walked across the large room to Mikersquos messy desk and returned his glue

S Most television shows last about an hourW Liz and Marie sat at the large conference table and they discussed the topic for the

next hour

S Marie would have been here but she never received the invitationW He was so busy and overwhelmed that he forgot to respond to the invitation

S When George couldnrsquot get into his car he got down on one knee and reached under thebumper for the extra key

W He smiled nervously at the young detective as he searched through his pockets for a key

S The cold drink was served with a slice of lemonW The only food left in the barren refrigerator was a moldy lemon

S At the grocery store I always wind up in the slowest moving lineW The young couplersquos three little girls enjoyed playing together in the line

S To help everyone find her house Lisa drew a mapW She helped him out with his project by putting the finishing touches on the map

S Before she arrived he opened a bottle of wine and put on some soft musicW She took the baby out when he started to cry and had to miss the rest of the music

S She picked up a wallet on the street and was honest enough to try to locate the ownerW Once he finished organizing all the binders he returned the hole punch to the owner

S The game was called because of rainW She wore heavy wool socks and her sturdiest boots to go walking in the rain


APPENDIX (Continued)

S She wished she had brought something to readW She asked her distracted son what he wanted to read

S Every morning Susan braids her little girlrsquos hair then helps her dress for schoolW He called early in the morning to arrange his monthly appointment at the school

S He never let Fluffy sleep on his couch because she shedW The cat was crouched in the tall grass down by the shed

S Peter painted the walls of the bird exhibit light blue so that it would resemble the skyW Before going out on the open seas they always checked the sky

S He canrsquot be held responsible for the killing because he was crazy at the timeW I started to put new plants in my garden but ran out of time

S She pulled her head out from under the faucet and reached for a towelW After politely standing in line at the hotel desk the boy asked for another towel

S The construction worker had developed very powerful arms from unloading bags of cement from the truck

W Nobody knew why there were a lot of old boxes stored in the truck

(Manuscript received August 20 2003revision accepted for publication September 2 2004)


1983) appreciating discourse structure (Delis WapnerGardner amp Moses 1983 Wapner Hamby amp Gardner1981) and drawing and revising inferences (Beeman1993 Brownell Potter Bihrle amp Gardner 1986) RHdamage has also been associated with problems in pro-cessing at least some types of nonliteral language suchas jokes (Brownell Michel Powelson amp Gardner 1983)and indirect requests (Weylman Brownell Roman ampGardner 1989) These findings suggest that although theRH might not be necessary to support the basic functionsessential for the processing of individual words or sim-ple sentences it may make important contributions tohigher level meaning processingmdashfor instance by link-ing words and sentences across larger language units andallowing language information to be used in a flexibleand context-sensitive manner

The RHrsquos contribution to language comprehension inneurologically intact individuals has also been examinedby means of the visual half-field (VF) technique (seeBanich 2002 for a review) This technique takes ad-vantage of the fact that stimuli presented in the left halfof visual space are initially processed exclusively by(early) visual cortical areas in the RH and vice versa Inthe intact brain transfer of at least some informationacross the corpus callosum is possible at later processingstages however that information is delayed and likely tobe incomplete because of the relative sparseness of cal-losal relative to intrahemispheric connections (Berardiamp Fiorentini 1997) andor biases and strategies thatmake it more efficient for the directly stimulated hemi-sphere to assume more of the processing load (egBanich 2003) Thus although the potential contributionof callosal transfer and other factors unrelated to hemi-spheric dominance to the observed VF patterns must al-ways be given due consideration the technique is gener-ally believed to skew processing toward the directlystimulated hemisphere This canonical view seems jus-tified given that several decades of hemifield studies withbrain-intact individuals have documented consistent per-formance differences for stimuli presented to the rightvisual field as opposed to the left and many of these re-sults have been corroborated by evidence from patientswith unilateral brain damage andor from studies ofcommissurotomized (so-called split-brain) patients

Research using the VF technique has led to the con-clusion that the two hemispheres differ in the meaningthat each derives from individual words and sentencesAssessment has largely been based on measures of prim-ing in lexical decision (wordnonword judgment) taskscompared across VFs For example with presentation ineither VF response times (RTs) are equally facilitatedfor target words (eg DOG) preceded by a closely relatedword (cat) or by an unrelated word (table) By contrastpriming for more distantly related word pairs (eg goatndashDOG) is greater with LVFRH presentation (ChiarelloBurgess Richards amp Pollock 1990) Greater facilitationfrom ldquosummation primesrdquo (three words weakly relatedto the target) also has been observed for LVFRH pre-sentation (Beeman Friedman Grafman amp Perez 1994)

as well as more priming at least in some contexts (seeTitone 1998) for the subordinate meanings of ambigu-ous words (eg bridalndash vs freightndashTRAIN Burgess ampSimpson 1988) These results have been interpreted assuggesting that a critical difference between the hemi-spheres may lie in the ldquocoarsenessrdquo of their semantic cod-ing with narrow focused meaning activation in the LHand weak diffuse activation in the RH (Beeman 1998)The broader range of meanings thus ldquoconsideredrdquo by theRH has been offered as part of the explanation for its rolein high-level (and especially nonliteral) language

However studies using sentences as primes have ledto claims that the RHrsquos language competence is limitedto word-level information and lexical associative rela-tionships between words (eg Chiarello Liu amp Faust2001 Faust 1998) For example with LVFRH presen-tation lexical decision latencies for sentence-final wordswere unaffected by scrambling the order of the contextwords (Faust Babkoff amp Kravetz 1995) or increasing theamount of context from one to three to six words (FaustKravetz amp Babkoff 1993) In some cases LVFRH wordprocessing has even proven insensitive to message-levelincongruity (eg ldquoThe patient parked the MEDICINErdquoFaust et al 1995) although some recent studies havefound effects of overt anomalies for LVF processing Forinstance Chiarello et al (2001) found RT inhibition foranomalous targets in both VFs as long as the contextcontained no lexically associated words Faust Bar-Levand Chiarello (2003) found effects of anomaly forLVFRH targets even in the presence of a lexical associ-ate however they also found that in the LVFRH (unlikethe RVFLH) RT facilitation for congruent words was in-sensitive to message-level meaning with equal facilita-tion for a lexically associated word in a meaningful or ina scrambled or nonsensical context On the basis of thesefindings it has been hypothesized that only the LH caneffectively integrate lexical syntactic and semantic in-formation to derive the message-level meaning of a mul-tiword utterance The RH instead may be able to notewhether or not a word is globally consistent with otherwords in the context (eg toothpaste does not coherewell with the words angry jury and confront as de-scribed by Chiarello et al 2001) but it is argued doesnot construct a higher level meaning representation thatis sensitive to factors such as word order or message-level constraint

Clearly there is an intriguing disparity between theconclusions drawn from neuropsychological studieswhich have tended to suggest that intact RH languagefunctions are particularly crucial for deriving message-level meaning and those drawn from studies of healthyadults which have concluded that although the RH maybe broadly sensitive to word-level meaning it is gener-ally not able to combine words effectively to construct amessage-level representation One consideration is thatthe materials and tasks used in the two cases have typi-cally been quite different In particular whereas neuro-psychological studies have often used untimed measuresdesigned to directly assess comprehension (eg true














METHOD

















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DISCUSSION




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0 400 800

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RVF

LVF



















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DISCUSSION




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RVF

LVF



















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Documents

Both sides get the point: Hemispheric sensitivities to