Auditory Distraction

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Keywords:Auditory distractionSemantic interference

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2008; Oberauer, Lange, & Engle, 2004; Salam & Baddeley,1982). However, an alternative, more functional, view isthat forgetting (or the impairment of retrieval) reectsthe legacy of dynamic and adaptive selective attention

ters or digits) is to be recalled in strict serial order (theirrelevant sound effecthereafter ISEe.g., Colle & Welsh,1976; Jones, Madden, & Miles, 1992; Jones & Tremblay,2000; Salam & Baddeley, 1982). The mere presence ofbackground sound depresses serial recall appreciably, theweight of evidence favoring the view that the effect resultsfrom interference-by-process, and is not a passive side-effect of having similar items to remember and to ignore

0010-0277/$ - see front matter 2008 Elsevier B.V. All rights reserved.

* Corresponding author. Tel.: +44 29 20 876788; fax: +44 029 20874858.

E-mail address: [email protected] (J.E. Marsh).

Cognition 110 (2009) 2338

Contents lists available at ScienceDirect

Cognit

elsedoi:10.1016/j.cognition.2008.08.003stimuli or events that are similar in some way to the target(see, e.g., Anderson, 2003; Baddeley, 1986; McGeoch,1942; Nairne, 1990; Nairne, 2002; Neath, 2000). Theclassical, structuralist, view has been that such interfer-ence-by-similarity-of-content directly causes forgetting,that is, forgetting is a passive side-effect of structuralchanges that result from the storing of new, similar, eventsin memory (Anderson, 1983; Cowan, 1999; McGeoch,1942; Mensink & Raaijmakers, 1988; Oberauer & Lange,

phenomena relating to impaired retrieval from memorydue to distraction from irrelevant auditory events usingthe structuralist, interference-by-similarity-of-content,approach as a theoretical counterpoint.

One line of research in which a dynamic selective atten-tion framework has been used to reconstrue putativelymnemonic phenomena is that concerned with the disrup-tive effects of to-be-ignored sound on visual-verbal serialrecall whereby a list of around 68 verbal items (e.g., let-Selective attentionInterference-by-processSemantic-category clustering

1. Introduction

One of the most inuential conssearch is interference: the ease withtrieved from memory is dictated, atwere shown to arise only when instructions emphasized recall by category rather than byserial order (Experiments 3 and 4). The results favor a process-oriented, rather than a struc-tural, approach to the breakdown of attentional selectivity and forgetting: performance isimpaired by the similarity of process brought to bear on the relevant and irrelevant mate-rial, not the similarity in item content.

2008 Elsevier B.V. All rights reserved.

s in memory re-ch items are re-in part, by other

processes (such as inhibition; e.g., Houghton & Tipper,1994) that are designed to resolve conict during theselection of candidates at retrieval (e.g., Anderson, 2003).Set within this quintessentially attentional approach toforgetting, the present article explores the nature ofmore than meaningless irrelevant sound (Experiment 1). This effect was exacerbated whenthe irrelevant speech was semantically related to the to-be-remembered material (Exper-Interference by process, not contentauditory distraction

John E. Marsh *, Robert W. Hughes, Dylan M. JSchool of Psychology, Cardiff University, Cardiff, Wales CF10 3AT, UK

a r t i c l e i n f o

Article history:Received 27 April 2007Revised 19 August 2008Accepted 20 August 2008

a b s t r a c t

Distraction by irrelevulnerability of attauditory distractionMeaningful irreleva

journal homepage: www.termines semantic

s

background sound of visually-based cognitive tasks illustrates thenal selectivity across modalities. Four experiments centred onng tests of memory for visually-presented semantic information.eech disrupted the free recall of semantic category-exemplars

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vier .com/locate /COGNIT

24 J.E. Marsh et al. / Cognition 110 (2009) 2338(Hughes & Jones, 2005; Jones & Tremblay, 2000). Speci-cally, this classical ISE is thought to result from the oblig-atory, preattentive, seriation (or ordering) of soundsequences producing competition for the deliberate pro-cess of seriating the to-be-remembered items. Here weexamine whether the principle of interference-by-processcan be extended to a setting in which the focal memorytask involves not serial processing but semantic retrievalstrategies: Does the concurrence of similar semantic pro-cessing (rather than serial processing) applied to relevantand irrelevant material now dictate the form and degreeof distraction? What little evidence there is seems to sug-gest that the structural accounts seem perfectly adequatein this context, that is, disruption from irrelevant soundin semantic memory seems amenable to a classical, andarguably simpler, interference-by-content, explanation(Beaman, 2004; Neely & LeCompte, 1999) rendering theinterference-by-process account rather paradigm-boundto serial short-term memory. The goals of the present ser-ies were to revisit the empirical signature of auditory dis-traction in the context of episodic short-term memorytasks that tap semantic memory processes (particularly gi-ven the paucity of studies on the issue) to establish the de-gree to which it is distinct from that found in serial recall,and to examine thereafter how such distinct phenomenamight be reconciled with a dynamic process-oriented ap-proach to interference.

1.1. Irrelevant sound effect in serial recall

The debate between the structuralist and process-basedstandpoints can be observed in microcosm in a body of re-search showing that the presence of irrelevant, to-be-ig-nored, sound markedly increases forgetting in a (usuallyvisually-presented) serial recall task (e.g., Colle & Welsh,1976; Jones et al., 1992; Salam & Baddeley, 1982). Theconventional viewpoint, that forgetting can occur as a di-rect and passive consequence of the structural similaritybetween to-be-remembered and irrelevant episodes orstimuli (e.g., McGeoch, 1942), is evident in several theoret-ical accounts of the ISE that view it as a mere consequenceof auditory stimuli gaining access to the same representa-tional space as the to-be-remembered items (e.g., phono-logical store, Burgess & Hitch, 1992; Gathercole &Baddeley, 1993; Salam & Baddeley, 1982; primary mem-ory, Neath, 2000). Although these accounts differ in theirdetail of how interference arises, the important point forpresent purposes is that they are all examples of an inter-ference-by-content approach: recall is impaired as a resultof the similarity in identity (i.e., content) between to-be-remembered and to-be-ignored items.

Several strands of evidence converge to weaken theinterference-by-content approach. First, non-speechsounds such as toneswhich bear little or no resemblanceto the to-be-remembered itemsproduce disruption simi-lar in degree and kind to that from irrelevant speech (e.g.,Jones & Macken, 1993; Neath & Surprenant, 2001). Second,the magnitude of disruption is unrelated to the degree ofphonological similarity between to-be-remembered andto-be-ignored items (Jones & Macken, 1995; LeCompte &Shaibe, 1997; but see Hughes & Jones, 2005) thereby dis-conrming the predictions of an early account based onthe concept of a phonological store (Gathercole & Badde-ley, 1993; Salam & Baddeley, 1982). As a result of thesendings, the phonological store account of the ISE has beenmodied and expressed computationally such that irrele-vant speech disrupts a representation of order within thepassive store rather than interfering with item representa-tions (Norris, Baddeley, & Page, 2004; Page & Norris, 2003).However, problematic for any account that views irrele-vant speech as disrupting the phonological store is recentevidence showing that rehearsal is a precondition for itsexpression (Jones, Macken, & Nicholls, 2004).

Third, the interference-by-content approach fails toacknowledge adequately the critical importance of the nat-ure of focal task processing, the impairment of recall beingchiey determined by the co-existence of similar to-be-re-called and to-be-ignored items within a store. That is, theycannot account for why the ISE is only found if the focaltask necessitates or tends to encourage a seriation process(e.g., serial rehearsal) and why the mere presence of simi-lar content between the memory material and the sound isnot sufcient (or necessary) for the effect (Beaman & Jones,1997; Farley, Neath, Allbritton, & Surprenant, 2007;Henson, Hartley, Burgess, Hitch, & Flude, 2003; Hughes,Vachon, & Jones, 2007; Perham, Banbury, & Jones, 2007).

Whilst the preoccupation of the interference-by-con-tent approach is with item identity, on the interference-by-process account, the key determinant of the disruptionin serial recall is the extent to which both the irrelevantsound and the focal memory task share similar seriation(or ordering) processes (Jones, 1993; Jones & Tremblay,2000). A key observation underpinning this account isthe changing-state effect (e.g., Jones et al., 1992) wherebya sound sequenceregardless of whether it comprisesspeech or non-speechthat exhibits abrupt changes inacoustic properties (e.g., k v h q. . ., or a sequence of toneschanging in frequency) is invariably more disruptive than acontinuous or repeating stimulus (e.g., k k k k. . ., or a re-peated tone). On the interference-by-process account it isassumed that the preattentive perception of acousticchanges between segmentable elements in the soundyields cues as to the order of those elements as a by-prod-uct of primitive, acoustic-based, perceptual organizationprocesses (cf. Bregman, 1990). These irrelevant order cuescompete forand hence impairthe deliberate seriationprocess (serial rehearsal) supporting ordered recall of theto-be-remembered items (Hughes & Jones, 2005; Jones,1993). In support of this view, the ability to encode the or-der of stimuli in an attended changing-state auditory se-quence predicts the degree to which that sequence isdisruptive when presented as irrelevant sound during seri-al recall (Macken, Phelps, & Jones, in press).

In sum, results based on research using the serial recallparadigm favor a dynamic process-based approach (Jones& Tremblay, 2000). However, the phenomenon of interfer-ence-by-process seems highly specic to a particular pro-cess (seriation) and little evidence is available withrespect to whether such conict occurs between othertypes of processes. In the present study, therefore, we ad-dressed whether the phenomenon extends to auditory dis-traction in the context of a focal task that is likely to be

J.E. Marsh et al. / Cognition 110 (2009) 2338 25dominated by semantic-based, rather than seriation, pro-cesses. This is a particularly pertinent issue in light of thefact that the little evidence there is on semantic auditorydistraction effects suggests that the interference-by-con-tent approach offers a perfectly adequate explanation.

1.2. Semantic auditory distraction: interference-by-content?

On the interference-by-process account of auditory dis-traction in serial recall, it is the processing of the precate-gorical, acoustic, attributes of the sound that is key to thedisruption (e.g., Jones & Macken, 1993). Consistent withthis view, neither the lexical-semantic content of the irrel-evant sound (when speech is used) nor the similarity interms of semantic content between the speech and theto-be-remembered list has any bearing on the magnitudeof disruption (Buchner, Irmen, & Erdfelder, 1996; Jones,Miles, & Page, 1990; LeCompte, Neely, & Wilson, 1997;Surprenant, Neath, & Bireta, 2007; but see Buchner, Roth-ermund, Wentura, & Mehl, 2004). Such ndings are easilyexplicable on the intereference-by-process account: Thekey process supporting serial recall is an articulatory-based seriation process, not a semantically-based one(e.g., Jones et al., 2004). Thus, the lexical-semantic attri-butes of irrelevant speech would not be expected to con-ict with the focal seriation process. However, theabsence of such lexical-semantic effects in the context ofserial recall can also be accommodated within the interfer-ence-by-content approach. In the typical serial recall task,the to-be-recalled items (e.g., digits, letters) are relativelyimpoverished in terms of semantic content. Thus, the rep-resentations of to-be-recalled itemsdevoid of rich seman-tic contentmay not be susceptible to degradation orretrieval-confusion as a result of activated semantic repre-sentations of the irrelevant speech items.

In line with the interference-by-content approach, theresults of a small number of studies suggest that whenthe items are semantically rich, recall is indeed impairedby the semantic attributes of the irrelevant sound(Beaman, 2004; Jones et al., 1990; Martin, Wogalter, & For-lano, 1988; Neely & LeCompte, 1999; Oswald, Tremblay, &Jones, 2000). For example, in a category-exemplar recalltask, in which a list of, say, 16 semantically-rich items(nouns) taken from a single semantic category arepresented for free recall, the semantic similarity betweenthe relevant and irrelevant items impairs performance(Beaman, 2004; Neely & LeCompte, 1999). The free recallof relatively low-dominance category-exemplars (e.g.,avocado) is disrupted (as reected in omission errors)more by related, high-dominance, irrelevant category-items (that are not included in the to-be-remembered list;e.g., apple) than by high-dominance, categorically-unre-lated, irrelevant items (e.g., hammer). Such results seemto be readily explained within an interference-by-contentapproach: The semantic representations of the to-be-re-called items may be degraded or otherwise made lessaccessible as a function of their semantic similarity to theirrelevant items (e.g., Anderson, 1983; Oberauer & Lange,2008; Oberauer et al., 2004; Rundus, 1973).

However, our central contention in this paper is thatthese semantic auditory distraction effects may also beamenable to, and indeed be better explained by, an inter-ference-by-process analysis (cf. Marsh, Hughes, & Jones,submitted for publication, 2008). The starting point for thisanalysis is that, compared to serial recall, the semanticrichness of the items in category-exemplar recall, as wellas the longer list-length, demotes the likelihood of a seria-tion strategy and instead promotes the use of semantic-based organization processes. It is this shift in the natureof the dominant process/strategy used to support perfor-mance in the focal task, not simply the semantic richnessof the to-be-recalled items, that renders such tasks vulner-able to competition from the processing of the semanticcontent of the irrelevant sound. Thus, in contrast to theinterference-by-content approach, it is not the mere co-activation or co-registration of relevant and irrelevantsemantic representations that impairs performance.Rather, it is the integrity of dynamic, semantic-based, orga-nizational processes engaged in support of retrieval that iscompromised by the semantic processing of the irrelevantsound. In this way, semantic auditory distraction may beregarded as an extension of the general case of interfer-ence-by-process: It may reect a difculty in selectingamongst two sets of semantic representations both ofwhich represent plausible candidates for populating thesemantic-organizational skill used in the focal task, justas with two sets of serial representations in the classicalirrelevant sound effect.

In the studies that follow, we scrutinize further the nat-ure of semantic auditory distraction and attempt to clarifythe extent to which semantic-organizational processing inthe focal taskas opposed to the mere semantic richness ofthe to-be-recalled itemsis responsible for disruption bythe lexical-semantic attributes of irrelevant speech. Weuse a setting in which a relatively long list of 32 exemplars(e.g., strawberry, pigeon, etc.) drawn from a smaller setof 4 semantic categories (e.g., Fruit, Birds, etc.) are pre-sented for recall. It is well established that under such con-ditions participants tend at test to cluster the randomlypresented exemplars according to their category at a great-er-than-chance level even without instruction to do so(Bouseld, 1953; Smith, Jones, & Broadbent, 1981). Thissemantic category-clustering (henceforth termed seman-tic-categorization) implies secondary organization where-by participants bring to bear pre-existing conceptualrelationships or semantic associations to guide encodingand retrieval of episodic information which is distinct fromprimary organization whereby the organization corre-sponds to the serial order of the list (Tulving, 1968).

In another study (Marsh et al., submitted for publica-tion, 2008), we have used lists of words drawn from a sin-gle semantic category to investigate the role that source-monitoring processes play in governing the false recall ofitems presented as irrelevant sound. Single category listsbeing blocked by semantic category were ideally suitedto this purpose because this method of list presentation in-creases false recall (Brainerd, Payne, Wright, & Reyna,2003). The research reported here, though conceptuallysimilar, follows a distinct empirical line. In the followingexperiments, we are not interested in false recall (indeedrandom presentation of exemplars drawn from severalsemantic categories attenuates false recall), but rather in

form of the semantic organization of responses and the

26 J.E. Marsh et al. / Cognition 110 (2009) 2338probability of producing each category at test (Burns &Brown, 2000). The purpose of the present study was thusto examine whether the meaningfulness of irrelevantspeech interferes with semantic organization during freerecall of categorizable word-lists.

Assuming quite distinct, semantic-based, processing inthe category-exemplar recall task as compared with theseriation-based processing in serial recall, what predic-tions does the interference-by-process approach make?The rst is that the empirical signature of auditory distrac-tion in semantic task settings will be qualitatively distinctfrom that found in serial recall: the semantic properties ofthe sound should be endowed with disruptive power butthe acoustic, changing-state, properties of the soundshould prove relatively impotent. Whilst this rst predic-tion also ows from the interference-by-content approach,the second is unique to the interference-by-process ap-proach: the impairment should be a product not only ofthe processing of the lexical-semantic attributes of thesound but also of the deployment of semantic-based pro-cesses as a means of supporting retrieval in the focal task.That is, the mere presence of semantic content within theto-be-recalled and irrelevant material should not be suf-cient to produce disruption. Thus, if the task does notnecessitate or encourage the use of semantic processesbut instead seriation processes, the semantic attributes ofthe sound should not have disruptive potency even whenthe to-be-recalled items are rich in semantic content. Thesame prediction holds for between-sequence semanticsimilarity effects: the greater disruption found with great-er semantic similarity between to-be-recalled and irrele-vant items is not a passive by-product of their greateroverlap within some semantic-psychological space (e.g.,Oberauer et al., 2004). Rather, such similarity exacerbatesthe difculty of coupling the correct (i.e., task-relevant)set of semantic representations to the semantic-organiza-tion processes being engaged to support retrieval.

The present series of experiments begins by seeking toestablish whether or not the action of irrelevant sound inthe context of semantically-driven episodic tasksusing acategory-exemplar taskis indeed distinct from that inthe standard serial recall setting. Later experiments inthe series investigate the nature of between-sequencesemantic similarity effects in this setting and explore thekey hypothesisbased on the interference-by-processframeworkthat when the same type of lists are subjectto primary organization (seriation) their recall should be-come immune to semantic auditory distraction.

2. Experiment 1

The rst experiment examined whether category-exemplar recall is disrupted more by meaningful than bymeaningless speech: we contrasted the effect of an Englishhow meaningful irrelevant sound may impair the recruit-ment of semantic category knowledge as an organizingprinciple. Recall of semantically categorizable lists, as com-pared with lists of words drawn from single semantic cat-egories, yields measures of semantic processing in thenarrative with that of the same narrative read in a lan-guage that the participants neither spoke nor compre-hended (Welsh). Given that the meaningfulness of speechdoes not inuence the ISE in the context of serial recall(e.g., Jones et al., 1990), an effect of meaningfulness inthe present setting would imply that semantic-based tasksare peculiarly susceptible to impairment by the lexical-semantic attributes of irrelevant speech. We also examinedwhether any such impairment could be identied with areduction in the efcacy of a semantic-organization strat-egy, as indexed by a diminution in the propensity to clusterby category (Smith et al., 1981). Furthermore, in order toassess whether meaningless irrelevant speech was capableof producing disruption that is attributable to its changing-state propertiesas is the case in the context of serial re-callwe also included a pink noise condition which con-veys no changing-state information: Aperiodic broadbandnoise such as pink noise fails to disrupt serial recall perfor-mance (Ellermeier & Zimmer, 1997) but sometimes dis-rupts tasks that involve semantic processing (see Smith &Jones, 1992).

2.1. Method

2.1.1. ParticipantsThirty-six Cardiff University students took part in re-

turn for course credit. Each participant reported normalor corrected-to-normal vision and normal hearing andwas a monolingual native English speaker.

2.1.2. Apparatus and materials2.1.2.1. To-be-remembered material. Eight instances werechosen from each of 64 categories in the Yoon et al.(2004) norms in order to construct 16 lists of 32 words,each list drawn from 4 semantic categories. Categorieschosen had minimal category-exemplar overlap, andexemplars and categories were not repeated between orwithin lists in order to reduce the inuence of proactiveinterference (e.g., Shuell, 1968). The exemplars chosenwere sampled outside of the 10 most frequently producedinstances so as diminish the likelihood that items could berecalled by simple free association or guessing (e.g., Shuell,1969).

Categories were randomly assigned to each list but withthe constraint that associated categories (e.g., MusicalInstruments and Type of Music) did not appear to-gether. Category-exemplars within each list were arrangedpseudo-randomly, so that no two members of the samecategory were presented adjacently and that each categorywas represented equally in each quarter of the list.

2.1.2.2. Irrelevant sound. The meaningful speech was Eng-lish narrative taken from a horticultural essay, recordedin a female voice and sampled with a 16-bit resolution,at a sampling rate of 44.1 kHz using Sound Forge 5 soft-ware (Sonic Inc., Madison, WI; 2000). The meaninglessspeech was a Welsh translation of this narrative. Thespeech in each of the irrelevant sound conditions wasplayed to participants at 6570 dB(A) via stereo head-phones that were worn throughout the experiment.Third-octave pink noise was generated using a C program

variance (ANOVA) with Sound Condition as the within-par-ticipant variable. Other types of response (e.g., intrusions)were so low as to defy statistical analysis.

Table 1 shows the results of the various recall measuresin the four sound conditions. Section A shows the meanscores for the overall probability of correctly recallingexemplars in each condition. These indicate generally thatperformance was numerically better in quiet than in boththe pink noise and Welsh speech conditions (performancein these latter two conditions appeared comparable),which, in turn, produced better performance than the Eng-lish speech condition. An ANOVA conrmed a main effectof Sound Condition on the overall probability of recallingcategory-exemplars, F(3, 105) = 15.50, MSE = .006,p < .001, with post hoc tests (Fishers PLSD) revealing sig-nicant differences between quiet and pink noise(p < .01), quiet and Welsh speech (p < .005), quiet and Eng-lish speech (p < .001), pink noise and English speech(p < .001), and between Welsh and English speech(p < .001). The same pattern of means was also evidentwhen considering the probability of recalling exemplarswithin each category recalled (Section B of Table 1): Perfor-mance in quiet was better than in all the sound conditionsand performance was better in the pink noise and Welsh

J.E. Marsh et al. / Cognition 110 (2009) 2338 27that generates digital waveforms (the program is availablefrom: http://www.moshier.net/pink.html). The irrelevantsounds were presented throughout the study and testphases of the task.

2.1.3. DesignThe experiment had a within-participants design with

one factor: Sound Condition which had four levels: Eng-lish speech, Welsh speech, pink noise, and quiet. The 16to-be-remembered lists were randomized but presentedin a xed order for each participant. The sound conditionswere randomized as follows: The 16 lists were divided intofour blocks. In each block the four lists were randomly as-signed to one of the four speech conditions. To control forpotential order effects, the order of the sound conditionswithin each block was counterbalanced acrossparticipants.

2.1.4. ProcedureParticipants were seated at a viewing distance of

approximately 60 cm from a PC monitor on which cate-gory-exemplars were displayed in a central position. Listsof category-exemplars appeared in lower case black 72-point Times New Roman font one word at a time against awhite background. Each word appeared for 2 s with an in-ter-stimulus interval of 1 s. Retrieval was immediate withthe end of the list being notied by the appearance of ared RECALL cue.

Participants were tested in small groups of six partici-pants in a sound-attenuated room. Participants wereseated in individual cubicles each equipped with a Sam-sung Syncmaster 171S PC and display. Participants were in-formed that they would be presented with sixteen 32-word lists, and that each list would be presented one wordat a time on the computer monitor from which they wereasked to recall as many words as possible and write thewords they remembered down in the order which they re-called them on recall sheets when a RECALL cue appearedon the screen. Recall sheets contained 17 columns of 32rows each. One practice trial was presented before theexperimental trials. Participants were not explicitly toldthat the lists were categorizable. Participants were in-formed that they would have 2 min to retrieve as muchas they could of the list and that after this time a tonewould sound to signal the beginning of the next list (some5 s later). Participants were instructed to ignore any soundthat they heard through the headphones and were toldthat they would not be tested on its content at any pointin the experiment. The experiment lasted approximately50 min.

2.2. Results and discussion

2.2.1. Recall measuresRecall measures came in three forms: the overall mean

probability of correctly recalling category-exemplarsacross all categories, the mean probability of recallingexemplars from within each category recalled, and theprobability of recalling each category (based on recallingat least one word from a category). The data from each re-call measure were analyzed using a one-way analysis ofspeech conditions than in the English speech condition.An ANOVA revealed a main effect of Sound Condition onthe probability of recalling exemplars within each categoryrecalled, F(3, 105) = 18.31, MSE = .004, p < .001, with posthoc tests (Fishers PLSD) revealing the same signicant dif-ferences as for the analysis of the overall probability of cor-rectly recalled items. However, the pattern of results wasdifferent for the probability of recalling each category (Sec-tion C of Table 1). Here, the means for performance in Eng-lish speech were lower than those for the quiet, pink noiseand Welsh speech conditions. An ANOVA revealed a maineffect of Sound Condition on the probability of recalling

Table 1Mean recall and clustering measures as a function of irrelevant soundcondition in Experiment 1. Standard errors of the means are presented inparenthesis.

(A) Overall probability of recalling category-exemplarsQuiet .51 (0.019)Pink noise .46 (0.016)Welsh speech .45 (0.021)English speech .39 (0.022)

(B) Probability of recalling exemplars from within each category recalledQuiet .53 (0.016)Pink noise .48 (0.014)Welsh speech .48 (0.019)English speech .42 (0.018)

(C) Probability of recalling each categoryQuiet .96 (0.011)Pink noise .96 (0.009)Welsh speech .94 (0.012)English speech .90 (0.019)

(D) Mean Z scoresQuiet 3.17 (0.25)Pink noise 3.04 (0.25)Welsh speech 2.88 (0.25)English speech 2.45 (0.24)

28 J.E. Marsh et al. / Cognition 110 (2009) 2338each category, F(3, 105) = 5.18, MSE = .006, p < .005. How-ever, in contrast to the other recall measures, post hoc test-ing (Fishers PLSD) revealed signicant differences onlybetween the English speech condition and all other condi-tions (p < .05, all comparisons).

2.2.2. Clustering measureWhilst there are several potential ways of measuring

semantic-categorization (for a review, see Murphy, 1979),we restricted our analyses to the Z score (Frankel & Cole,1971). Z scores range from negative to positive values themaximum of which is determined by the number of cate-gories and category-exemplars represented by the to-be-remembered list. The Z score is higher for outputted se-quences that demonstrate use of the semantic structureinherent in the to-be-remembered list. For example, theoutputted sequence: brass, lead, giraffe, pig, cherry, lem-on, pliers, chisel, that demonstrates strong use of seman-tic organization (as is evident from the number of adjacentrepetitions of same-category items) will receive a higherscore than a more randomly organized sequence: brass,lead, cherry, pliers, lemon, chisel, giraffe, pig, in which ex-actly the same number of categories and category-exem-plars are recalled but in which fewer same-categoryadjacent repetitions are produced. Severely fragmented re-call patterns such as brass, pig, cherry, pliers, giraffe, lem-on, chisel, lead will receive negative Z scores because theyrepresent below-chance clustering (in fact none of the re-sponses in this example are clustered by semantic-cate-gory as indicated by the absence of any same-categoryadjacent repetitions).

Z scores were calculated with all repeat and intrusionerrors removed. Section D of Table 1 shows the mean clus-tering measure for each sound condition. The Z scoremeans are lower in all the sound conditions than in thequiet condition, and lower in the English speech conditioncompared to the three other conditions. An ANOVA con-rmed a main effect of sound on Z scores, F(3,105) = 4.22, MSE = .84, p < .001. Follow-up post hoc tests(Fishers PLSD) revealed that the only signicant differ-ences were between the English speech condition and eachof the other sound conditions (p < .05). Thus, Englishspeech reduced the level of semantic-categorization asmeasured by the Z score.

The results of the recall measures, and the Z score clus-tering measure, suggest that there is an impairment tosemantic free recall tasks that is attributable to the mean-ingfulness of irrelevant speech, given that semantic con-tent would, arguably, have been the most salientdifference between the Welsh and English speech condi-tions. There was, however, some degree of disruption pro-duced by pink noise and Welsh speech. This is not easilyexplained if the free recall task engaged a purely seman-tic-based retrieval strategy. The pink noise and Welshspeech, being devoid of semantic content, should not haveproduced disruption. However, because there were no sta-tistically signicant differences between the pink noiseand Welsh speech conditions it is reasonable to concludethat they both exerted the same general effect of soundthat is quite often reported in the context of tasks involvingsemantic memory (Martin et al., 1988; Smith et al., 1981)rather than one attributable to acoustic variability whichproduces the classical irrelevant sound effect in serial re-call. Further evidence to buttress this conclusion was foundin a supplementary experimentone not reported in fullhere for economy of expositionwhich involved a stan-dard visually-presented serial recall task (for a typical pro-cedure, see Hughes & Jones, 2005) with the irrelevantsound stimuli used in Experiment 1. In this experimentin which the participants were 40 non-Welsh speakerssampled from the same population as in Experiment 1awithin-participant design was used. This supplementaryexperiment revealed an irrelevant sound effect, F(3,117) = 17.76, MSE = .033, p < .001that is, an effect ofsound compared to quietbut no effect of meaning thusreplicating Jones et al. (1990) with the particular materialsused in Experiment 1. The experiment also revealed no ef-fect of pink noise thus replicating Ellermeier and Zimmer(1997). The mean probability of correct recall, marked withthe strict serial recall criterion and collapsed across serialposition, did not differ between the Welsh speech condi-tion, M = .60; SE = .03, and English speech condition,M = .61; SE = .03 (p > .7), but both these means were signif-icantly lower than those in the quiet condition, M = .73,SE = .02, and the pink noise condition, M = .74, SE = .02(p < .001 for both comparisons). This result replicates priorresearch showing that the meaningfulness of irrelevantspeech does not have a disruptive effect in the serial recallsetting but also shows that the Welsh speech used inExperiment 1 was indeed capable of producing an ISE inthe serial recall context. Its failure to produce any moredisruption than pink noise in Experiment 1 suggests thatit was impotent in terms of producing a classical ISE inthe context of category-exemplar recall.

The effect of meaningfulness in Experiment 1 ap-pears to be explicable as a conict of semantic process-ing that emerges when the primary task promotes adegree of such processing. The best indication of animpairment of semantic processing produced by themeaningful irrelevant speech is that meaningful speechreduces the use of secondary organization, that is, thesemantic-categorization of the to-be-recalled material,and also reduces the probability with which a categoryis recalled. Both these recall measures are thought toreect semantic or relational processing (Burns &Brown, 2000; Hunt & McDaniel, 1993). The reductionin category recall reects, possibly, a failure to establishadequately at encoding, or use at retrieval, higher-ordersemantic encodings that can be used as a retrieval planfor enabling inter-category transitions (e.g., Bower,Clark, Lesgold, & Winzenz, 1969). One of these seman-tic encoding strategies might involve forging some kindof semantic association between category-exemplars(e.g., pigeon, chisel) or categories (e.g., Birds,Tools) where pre-experimentally there is none (cf.Wingeld, Lindeld, & Kahana, 1998). There is alsothe possibility that the meaningful speech impairs gen-eration of category-names or exemplars (e.g., for use asretrieval cues) during encoding or retrieval: It is wellaccepted that tasks that involve semantic memory areunderpinned by generation processes (Gronlund & Shif-frin, 1986).

J.E. Marsh et al. / Cognition 110 (2009) 2338 293. Experiment 2

In Experiment 2, the process-based account of semanticauditory distraction is once again scrutinized, this time notby manipulating the mere meaningfulness of the speechbut rather its semantic similarity to the to-be-recalledexemplars (see also Marsh et al., submitted for publication,2008). The interference-by-process and interference-by-content accounts both assume that greater disruption willbe found when irrelevant and to-be-remembered cate-gory-exemplars are drawn from the same semantic cate-gory but the two approaches differ with regard to thecausal mechanism underlying such a between-sequencesemantic similarity effect.

The interference-by-process approach supposes thatbetween-sequence semantic similarity will impair recallperformance not because of the mere similarity in contentbetween the to-be-recalled and irrelevant category-exem-plars but because it disrupts the strategy or processunderpinning the semantic focal task. In this way the inter-ference-by-process approach is similar to the strategy-dis-ruption interpretation which holds currency in otherdomains of forgetting research (e.g., Basden & Basden,1995; Basden, Basden, & Stephens, 2002). In the contextof semantic auditory distraction the interference-by-pro-cess account holds that the irrelevant information pro-duces disruption because it suggests an organization ofsemantic information that is incongruent with the partici-pants encoding or retrieval strategy (cf. Greitzer, 1976).For example, suppose that a given participants initial re-trieval plan involves recall of category A rst, then D, thenC, then B. If irrelevant sound related to category B coincideswith the point in the participants plan when A exemplarsare to be retrieved, the sound will specify information thatcues a category (category B) that, if responded to, wouldimpair the orderly execution of the plan. Irrelevant exem-plars that are drawn from a category represented on thelist (e.g., sparrow and robin for the category Birds)are particularly likely to provide a misleading cue in thisway than irrelevant exemplars not represented on the listbecause they convey information that is congruent-yet-incongruent with the task demand; robin is a Birdand hence context-appropriate but was not presented onthe to-be-recalled list and thus is response-inappropriate.

A unique prediction of this process-based view that be-tween-sequence semantic similarity disrupts the partici-pants capacity to adhere to their original retrieval plan isthat the irrelevant exemplars need only be semantically re-lated to a subset (e.g., one out of four) of the categories rep-resented on the to-be-remembered list. For example, itwould matter not whether there are irrelevant items thatare semantically related to category A to disrupt recall ofcategory A exemplars: so long as there are irrelevant itemson that trial that are semantically similar to at least one ofthe other subsets of exemplars (say, those comprising cat-egory B) this may still corrupt the overall integrity of theretrieval plan. In contrast, whilst the interference-by-con-tent approach predicts that greater disruption will be pro-duced with a greater similarity between to-be-recalled andirrelevant exemplars this effect should be conned solely,or largely to the set of to-be-recalled category-itemsmatching the irrelevant category-items (e.g., Anderson,1983; Oberauer et al., 2004; Rundus, 1973). Thus, in orderto adjudicate between the interference-by-process andinterference-by-content accounts we adopted the ap-proach of presenting just eight irrelevant items randomlythroughout the presentation and recall periods that, insome conditions, were semantically related to the to-be-recalled items belonging to just one of the four categoriesrepresented on the to-be-remembered list.

3.1. Method

3.1.1. ParticipantsThirty participants from Cardiff University took part in

return for course credit. Each participant reported normalor corrected-to-normal vision and normal hearing andwas a native English speaker.

3.1.2. Apparatus and materialsSixty categories were chosen from the Van Overschelde,

Rawson, and Dunlosky (2004) norms. From each of thesecategories sixteen exemplars were chosen. The 8 highest-dominant exemplars were used for the irrelevant exem-plars, whilst the to-be-remembered exemplars were cho-sen from the 11th to 18th ranked positions. The 60categories were sorted into 12 pools of 5 categories be-tween which there was no obvious semantic relation. Forthe related trials, the category presented as sound matchedone of the 4 categories represented in the to-be-remem-bered list. For the unrelated trials, the sound consisted ofthe category in each pool that was not represented onthe to-be-remembered list. The 8 irrelevant items for theunrelated and related conditions were randomly presentedthroughout the study and test phases of each trial at a rateof two per second, thus each irrelevant item was presented54 times throughout a given trial. The presence of any gi-ven category as part of the to-be-remembered list and re-lated and unrelated sound was counterbalanced betweenparticipants. This procedure resulted in the constructionof 12 categorized lists comprising 32 exemplars, 4 to beused for each of the related, unrelated and quietconditions.

3.1.3. DesignA repeated-measures design was used with a single fac-

torSound Conditionwhich had three levels: (1) Speechcategorically-unrelated to the to-be-remembered material;(2) categorically-related speech; and (3) quiet. The proce-dure was the same as in Experiment 1.


3.2.1. Recall measuresTable 2 provides the results of the various recall mea-

sures in the three sound conditions (again, intrusion andrepetition rates were too low for statistical analysis). Sec-tion A of Table 2 shows the mean scores for the overallprobability of correctly recalling category-exemplars ineach condition. The means show generally that perfor-mance was better in quiet than unrelated speech, whichin turn was better than related speech. An ANOVA con-

30 J.E. Marsh et al. / Cognition 110 (2009) 2338rmed a main effect of Sound Condition on the overallprobability of recalling category-exemplars, F(2,58) = 65.06, MSE = .002, p < .001, with post hoc tests (Fish-ers PLSD) revealing signicant differences between quietand unrelated speech (p < .001) and between unrelatedand related speech (p < .001). The same pattern of meanswas also evident for probability of recalling exemplarswithin each category recalled (Section B of Table 2): Perfor-mance in quiet was better than for unrelated speech andperformance in unrelated speech condition was betterthan for related speech. An ANOVA revealed a main effectof Sound Condition on the probability of recalling exem-plar within each category recalled, F(2, 58) = 22.61,MSE = .002, p < .001, with post hoc tests (Fishers PLSD)revealing the same signicant differences as for the analy-sis of the overall probability of correctly recalling category-exemplars (ps < .05). However, the pattern of results wasdifferent for the probability of recalling each category (Sec-tion C of Table 2). Here, the means for performance in thesound conditions were lower than in the quiet conditionbut there appeared to be no difference between the unre-

Table 2Mean recall and clustering measures as a function of irrelevant soundcondition in Experiment 2. Standard errors of the means are presented inparenthesis.

(A) Overall probability of recalling category-exemplarsQuiet .53 (0.016)Unrelated speech .44 (0.019)Related speech .40 (0.019)

(B) Probability of recalling exemplars from within each category recalledQuiet .54 (0.015)Unrelated speech .50 (0.019)Related speech .45 (0.016)

(C) Probability of recalling each categoryQuiet .99 (0.005)Unrelated speech .89 (0.018)Related speech .88 (0.017)

(D) Mean Z scoresQuiet 3.74 (0.27)Unrelated speech 2.70 (0.27)Related speech 2.48 (0.26)lated and related sound conditions. An ANOVA revealed amain effect of Sound Condition on the probability of recall-ing each category, F(2, 58) = 19.12, MSE = .006, p < .001.However, in contrast to the two other measures, post hoctesting (Fishers PLSD) revealed signicant differences onlybetween the quiet and unrelated speech and relatedspeech conditions (both p < .001). Thus, despite having aneffect on the other two recall measures, semantic related-ness had no effect on the probability of producing eachcategory.

To examine the prediction of the interference-by-pro-cess accountthat the additional disruption produced byrelated speech will not be specic to the category thatmatches the irrelevant exemplars but will be generalizedto all categories on the to-be-recalled listwe averagedthe probability of recalling category-exemplars withineach category recalled across the three categories thatdid not match the irrelevant exemplars and comparedthese with the mean probability of correctly recallingexemplars from the category that did. The resulting meanswere .45 (SE = 0.016) for the non-matching categories and.48 (SE = 0.023) for the matching category which was nota signicant difference, t(29) = 1.72, p > .05. Thus, the dis-ruption was not conned to the retrieval of to-be-remem-bered category-exemplars that matched the categoryrepresented by the irrelevant exemplars.

3.2.2. Clustering measureSection D of Table 2 shows the results of the mean clus-

tering measure for each sound condition. The Z scoremeans are lower in all the sound conditions than in thequiet condition, and lower in the related-speech conditioncompared to the unrelated speech condition. An ANOVAconrmed a main effect of Sound Condition on Z scores,F(2, 58) = 13.64, MSE = .996, p < .001. Follow-up post hoctests (Fishers PLSD) revealed signicant differences be-tween quiet and unrelated speech (p < .001), and betweenunrelated and related speech (p < .001). Thus the semanticrelationship between the to-be-recalled and irrelevantitems impairs semantic-categorization above and beyondthe effect of mere meaningfulness.

Whilst replicating the key features of Experiment 1,Experiment 2 adds to the few studies that have demon-strated between-sequence semantic similarity effects insemantic free recall tasks (Beaman, 2004; Marsh et al., sub-mitted for publication, 2008; Neely & LeCompte, 1999).Moreover, the between-sequence semantic similarity ef-fect obtained in Experiment 2 appears to t better withina process-oriented rather than an interference-by-contentapproach. The nding that appears particularly supportiveof the interference-by-process account but at the sametime problematic for the interference-by-content view isthe lack of category-specic impairment within the be-tween-sequence semantic similarity effect. That is, the dis-ruption produced by irrelevant exemplars that matchedone of the to-be-remembered categories was not connedto that matching category (for category-specic impair-ment in a different context, see Mueller & Watkins,1977). If disruption is produced as a passive side-effect ofthe structural similarity of irrelevant and to-be-remem-bered items within a representational space (e.g.,Gathercole & Baddeley, 1993; Oberauer & Lange, 2008;Oberauer et al., 2004) or changes in the nature of the hypo-thetical associative strengths between to-be-recalled itemsand retrieval cues within memory (Anderson, 1983; Run-dus, 1973), then category-specic impairment would beexpected. This nding appears consistent, however, withthe notion of process or strategy-based disruption. The dis-ruption, for example, could be attributed to the impair-ment of a retrieval strategy rather than a clash betweenthe content of the to-be-recalled and irrelevant items(Basden & Basden, 1995; Basden et al., 2002). It seems rea-sonable to suggest that the related irrelevant items can im-pair the construction, or use of, a retrieval plan (e.g., Boweret al., 1969) as sometimes the category the sound itemsactivate will be in conict with the desired (unrelated)list-category being encoded or retrieved. Impairment inrecalling exemplars from the categories that do not matchthe irrelevant speech could be a result of the related irrel-evant information suggesting an output order that isincongruent with the participants original retrieval plan

rial recall strategy.

J.E. Marsh et al. / Cognition 110 (2009) 2338 31In this experiment meaningfulness was manipulated bycontrasting forward with reversed speech. Reversingspeech removes phonetic properties that allow lexicalaccess, and thus semantic processing (Sheffert, Pisoni,Fellowes, & Remez, 2002) but preserves the overall spectralfeatures of forward speech. Given that the meaningfulnessof speech (as indicated by the comparison between for-ward and reversed speech) does not inuence the classicalISE in the context of serial recall (e.g., Jones et al., 1990), aneffect of meaningfulness in the current experiment wouldfurther support the prediction that focal semanticprocessing is peculiarly susceptible to meaningful irrele-(or perhaps reect the overhead of inhibitory processes de-signed to minimize the ensuing conict; see Section 6).

We turn now to assess the interference-by-process ac-count further by testing more directly its tenet that thesemantic effects of irrelevant sound are jointly determinedby the nature of the focal task processes and the nature ofthe sound. Thus, the hypothesis tested in Experiments 3and 4 is that the semantic effects of irrelevant soundshould only arise when (a) the irrelevant sound conveyssemantic information and (b) the focal task involvessemantic processing.

4. Experiment 3

Experiments 1 and 2 demonstrated that semantic audi-tory distraction disrupts the semantic-categorization pro-cess. This represents an entirely distinct effect from thatfound in the serial recall setting in which the acoustic,not semantic, properties of the sound disrupts the strategyof serial rehearsal (or seriation; Beaman & Jones, 1998).Experiment 3 sought further, arguably more direct, evi-dence that the two ndings are distinct by making use ofa task instruction manipulation (Marsh et al., submittedfor publication, 2008; Weist & Crawford, 1973): Byinstructing one group of participants to recall in serial or-der, and another to recall the same kind of list by category,we can assess the degree to which the dominant focalprocess modulates which attributes of the sound dictatedisruption. If the effects of the meaningfulness of irrele-vant speech in Experiments 1 and 2 are indeed due tosemantic processing of the to-be-remembered material,then we would expect semantic effects of irrelevant speechto be found when participants are instructed to retrievethe to-be-remembered material according to semanticcategory but not when encouraged to use, instead, a seria-tion process to recall the very same content by instructingrecall in serial order. In contrast, the interference-by-con-tent accounts might be taken to predict an effect of themeaningfulness of irrelevant speech regardless of taskinstruction. There is good evidence that semantic activa-tion of to-be-remembered items occurs regardless of taskinstruction (e.g., Rouibah, Tiberghien, & Lupker, 1999), thusthe propensity for passive interference between semanti-cally similar representations should not differ accordingto the particular focal task strategy employed. InExperiment 3, we use shorter lists (16-exemplars) than inExperiments 1 and 2 to facilitate the instructed use of a se-vant speech, and thus lend support to the interference-by-process account. Moreover, the interference-by-processaccount would receive further support should the mean-ingfulness of the irrelevant speech be endowed with dis-ruptive potency only when the to-be-recalled exemplarsare recalled by their meaning (e.g., by semantic-category)rather than serial order.

4.1. Method

4.1.1. ParticipantsForty students from Cardiff University (none of whom

took part in Experiments 1 and 2) participated for coursecredit. Each reported normal hearing and normal or cor-rected-to-normal vision and was a native English speaker.Participants were randomly assigned to one of two groups:semantic-categorization or seriation instructions.

4.1.2. Apparatus and materialsThese were similar to Experiment 1 with the following

exception: Four exemplars were chosen, namely, the 11thto 14th most frequently produced responses for each ofthe 72 categories chosen from the Yoon et al. (2004)norms. These were combined as in Experiment 1 to create18 lists of 16 words each, each list having 4 categories.

4.1.3. DesignA mixed design was used with one between- and one

within-participant factor. The between-participants factorwas Task Instruction of which there were two levels:semantic-categorization and seriation. The within-partici-pant factor was Sound Condition as in Experiments 1and 2.

4.1.4. ProcedureThe procedure was similar to Experiments 1 and 2 apart

from the following: Participants were informed that theywould be presented with a total of 18 lists of words thateach contained 16 exemplars, 4 from each of 4 differentsemantic categories. The category-exemplars were drawnfrom positions 1114 of each of 72 categories chosen fromthe Yoon et al. (2004) category norms. The irrelevantspeech was English narrative. Meaningless speech wasthe same narrative reversed using Sound Forge 5 software(Sonic Inc., Madison, WI; 2000). Participants given seman-tic-categorization instructions were asked to try toremember as many words as possible by semantically-cat-egorizing them and writing them down according to theircategories when the RECALL cue appeared: Participantswere told to write down the exemplars as they came tomind, and to attempt to recall all the exemplars they couldremember from one category, exhausting that category,before moving on, and doing the same with the next cate-gory and so on. They were also told that if they couldremember any individual words after the semantic-cate-gory clusters they should write them at the end of theclusters.

Participants given seriation instructions were in-structed to try and remember the words in their originalorder of presentation and to recall each exemplar byassigning it to its original serial position when the RECALL

plars in their original presentation positions (as is requiredunder seriation instructions) would guarantee category re-call for all categories represented on the to-be-recalledlists. Despite this complication, the pattern of results forthe semantic-categorization group appears to be consis-tent with Experiment 1: Meaningful speech, as comparedwith meaningless speech, disrupted the probability of cor-rectly recalling each category. Conrming this, an ANOVArestricted to the semantic-categorization group revealeda main effect of sound on the probability of recalling eachcategory, F(2, 38) = 75.38, MSE = .003, p < .001, with posthoc tests (Fishers PLSD) revealing signicant differencesbetween quiet and forward speech and between reversedand forward speech (ps < .001).

4.2.2. Clustering measureZ scores were negative for the seriation group consis-

tent with the assumption that participants in this groupwould not have clustered the to-be-recalled exemplars

32 J.E. Marsh et al. / Cognition 110 (2009) 2338cue appeared. To maximise the level of exemplar recall,participants in the seriation group were instructed thatthey could leave gaps if necessary but were also told thatif they had a list-exemplar available to them for recall,but could not remember the position, that they shouldguess the original position.

Recall sheets contained 18 columns of 16 rows each.Participants given seriation instructions were given spe-cially-prepared recall sheets with serial positions markedon them, whilst the group instructed to categorize hadthe same recall sheets but without the serial positionsmarked. Participants were explicitly instructed to ignoreany sound that they might hear during the task. Soundswere presented throughout the presentation and testphases. Because the list length was halved for this experi-ment the retrieval time allotted for each list was reducedto 1 min.


4.2.1. Recall measuresThe recall measures are distinguished as in Experiments

1 and 2. For the seriation group, items were scored as cor-rect regardless of whether they occupied their correct posi-tions in the output protocols. Section A of Table 3 showsthe overall probability of correctly recalling category-exemplars for both Task Instruction groups. Performancein quiet is clearly superior to performance in the speechconditions for both groups. Of greater interest, and consis-tent with the interference-by-process approach, perfor-mance with forward speech was poorer than that withreversed speech for the semantic-categorization groupbut not the seriation group. A 3 (Sound Condition) 2(Task Instructions) ANOVA conrmed a main effect ofSound Condition on the overall probability of correctlyrecalling category-exemplars, F(2, 76) = 58.06, MSE = .004,p < .001. There was no main effect of Task Instruction,F(1, 38) = 3.8, MSE = .032, p = .059). However, there was asignicant interaction between Sound Condition and TaskInstruction, F(2, 76) = 16.03, MSE = .004, p < .001, wherebythe disruptive effects of meaningfulness arose when the re-trieval strategy was semantic-categorization but not whenit was seriation. Simple effects analyses (LSD) revealed sig-nicant differences between quiet and the reversed andforward speech conditions for semantic-categorizationand seriation instructions (ps < .05). Additionally, therewas a signicant difference between reversed and forwardspeech for the semantic-categorization group only(p < .001). The simple effects analyses also revealed that re-call performance for the semantic-categorization group ex-ceeded that of the seriation group in the quiet conditionand the reversed speech condition (both p < .05).

The mean probability of recalling exemplars withineach category recalled can be seen in Section B of Table3. In general, this was greater for the semantic-categoriza-tion than seriation instructed group, and smaller in thespeech conditions than the quiet condition. The meanswere also higher in the reversed compared to forwardspeech condition. An ANOVA on these means revealed amain effect of Sound Condition, F(2, 76) = 23.25,MSE = .004, p < .001, and a main effect of Task Instruction,F(1, 38) = 25.04, MSE = .02, p < .001, but no interaction be-tween these variables, F(2, 76) = 1.06, MSE = .004, p > .05.Simple effects (LSD) revealed signicant differences be-tween quiet and reversed speech (p < .05), and quiet andforward speech (p < .001), and the difference between re-versed and forward speech was signicant (p < .005) forthe semantic-categorization group. In contrast, for the seri-ation group the only signicant differences were those be-tween the quiet and reversed conditions and between thequiet and forward speech conditions (p < .005). The simpleeffects analyses also revealed that recall performance forthe semantic-categorization group exceeded that of theseriation group in all three conditions (all p < .05).

Section C of Table 3 shows the mean probability of cor-rectly recalling each category. In general, category recallwas better in the seriation than semantic-categorizationgroup. For the semantic-categorization group, the proba-bility of recalling each category was lower in the forwardspeech compared to reversed speech and quiet conditions.Interpretation of this particular subset of the results iscomplicated by the fact that the probability of recallingeach category was at ceiling in the seriation group. The rea-son for this is that recalling the rst four presented exem-

Table 3Mean recall measures as a function of irrelevant sound condition and taskinstruction in Experiment 3. Standard errors of the means are presented inparenthesis.

Sound condition Categorization Seriation

Mean (SE) Mean (SE)

(A) Overall probability of recalling category-exemplarsQuiet .65 (0.027) .56 (0.027)Reversed speech .60 (0.027) .48 (0.024)Forward speech .45 (0.024) .48 (0.025)

(B) Probability of recalling exemplars from within each categoryQuiet .70 (0.020) .57 (0.027)Reversed speech .64 (0.017) .48 (0.024)Forward speech .61 (0.023) .48 (0.025)

(C) Probability of recalling each categoryQuiet .94 (0.024) 1.0 (0.002)Reversed speech .93 (0.030) .99 (0.006)Forward speech .75 (0.025) .99 (0.006)

evident in the recall protocols. These results, therefore,

speaker. Participants were randomly assigned to one ofthe between-participants groups: semantic-categorizationor seriation instructions.

5.1.2. Apparatus and materialsThese aspects of the method were similar to Experiment

2 with the following differences: The 4 highest-dominantexemplars from each category were used for the irrelevantexemplars, whilst the to-be-remembered exemplars werechosen from the 11th to 14th positions.

5.1.3. DesignA mixed design was used with one between- and one

within-participant factor. The between-participants factorwas Task instruction as in Experiment 3. The within-partic-ipants factor was, like Experiment 2, Sound Condition ofwhich there were three levels: (1) Speech categorically-unrelated to the to-be-remembered material; (2) categori-cally-related speech; and (3) quiet.

J.E. Marsh et al. / Cognition 110 (2009) 2338 33provide further support for the interpretation of auditorydistraction as process-based (e.g., Jones & Tremblay,2000) as opposed to structural or content-based (e.g.,Gathercole & Baddeley, 1993; Neath, 2000).

5. Experiment 4

The results of the current series are thus far consistentgenerally with the notion that the semantic processing re-quired by the primary task can be disrupted by semanticprocessing of irrelevant speech. Extending the rationaleof Experiment 3, this suggests that between-sequencesemantic similarity should also only be disruptive whenthe primary task requires semantic processing, but notwhen it relies on serial rehearsal. Experiment 4 soughtadditional support for the process-based interpretation ofsemantic auditory distraction by manipulating between-sequence semantic similarity (as in Experiment 2) and alsotask instructions (as in Experiment 3). Finding that be-tween-sequence semantic similarity impairs category-exemplar recall only under semantic-categorizationinstructions and not under seriation instructions wouldserve to bolster the interference-by-process approach andundermine further the interference-by-content approach.

5.1. Method

5.1.1. ParticipantsSixty students from Cardiff University took part in

Experiment 4. None had taken part in Experiments 13.Each participant reported normal hearing and normal orcorrected-to-normal vision and was a native Englishby semantic category. As such, only the scores for the cat-egorization group were included in the following analysis.The mean Z scores were lower in the reversed speech(M = 2.86, SE = 0.19) and forward speech (M = 1.79,SE = 0.16) conditions compared to the quiet condition(M = 3.14, SE = 0.17) and were lower in the forward com-pared to reversed speech conditions. An ANOVA revealeda main effect of sound on Z scores, F(2, 38) = 47.15,MSE = .213, p < .001. Post hoc testing (Fishers PLSD) re-vealed signicant differences between quiet and forwardspeech, and between reversed and forward speech (bothp < .001). Thus, like Experiments 1 and 2, the degree ofsemantic-organization was impaired bymeaningful speechas compared with meaningless speech.

Experiment 3 revealed that semantic effects of irrele-vant speechin terms of its meaningfulnessappear tobe process rather than content-driven: The mere pres-ence of similar semantic content within the relevant andirrelevant material is insufcient for disruption; thesemantic processing of irrelevant speech disrupts onlywhen dynamic semantic-organisation based processes aredeployed as a recall strategy. Consistent with Experiments1 and 2, meaningful speech, as compared with meaninglessspeech, disrupted the overall probability of recalling cate-gory-exemplars and it also produced semantic interferencethat was specic to the probability of correctly recallingeach category and the degree of semantic-categorization5.1.4. ProcedureThe procedure was the same as Experiment 3 with the

exception of the following: Participants were informedthat they would be presented with a total of 12 lists ofwords that each contained a total of 16 exemplars, 4 fromeach of 4 different semantic categories, and responsesheets contained 12 columns of 16 rows each. Like theforegoing experiments, sounds were presented throughoutthe presentation and test phases of the tasks.


5.2.1. Recall measuresThe recall measures were the same as in Experiments

13. Section A of Table 4 shows the overall probability ofcorrectly recalling category-exemplars. It is evident thatperformance in both speech conditions was poorer thanquiet regardless of task instruction. Moreover, perfor-mance in related speech was poorer than performance inunrelated speech for the semantic-categorization, but notthe seriation, group. A 3 (Sound Condition) 2 (Task

Table 4Mean recall measures as a function of irrelevant sound condition and taskinstruction in Experiment 4. Standard errors of the means are presented inparenthesis.

Sound condition Categorization Seriation

Mean (SE) Mean (SE)

(A) Overall probability of recalling category-exemplarsQuiet .62 (0.013) .53 (0.014)Unrelated speech .54 (0.019) .48 (0.018)Related speech .51 (0.022) .48 (0.015)

(B) Probability of recalling exemplars from within each category recalledQuiet .63 (0.013) .54 (0.017)Unrelated speech .63 (0.014) .48 (0.018)Related speech .58 (0.018) .48 (0.015)

(C) Probability of recalling each categoryQuiet .98 (0.006) .99 (0.006)Unrelated speech .87 (0.016) .99 (0.004)Related speech .86 (0.021) .99 (0.003)

with the notion that such effects are better explained in

34 J.E. Marsh et al. / Cognition 110 (2009) 2338Instruction) ANOVA conrmed a main effect of IrrelevantSound Condition, F(2, 116) = 37.74, MSE = .003, p < .001,and Task Instruction, F(1, 58) = 7.66, MSE = .02, p < .01,and an interaction between these variables, F(2,116) = 3.94, MSE = .003, p < .05. Simple effects analyses(LSD) revealed that, regardless of task instruction condi-tion, there were signicant differences between quiet andunrelated speech (p < .001) and between quiet and relatedspeech (p < .001). Additionally, there was a signicant dif-ference between the unrelated and related speech condi-tions but only for the semantic-categorization group(p < .01). This analysis also revealed that recall perfor-mance for the semantic-categorization group exceededthat of the seriation group in the quiet condition(p < .001), and the unrelated speech condition (p < .05).

To summarize the results for the overall probability ofrecalling category-exemplars, generally category-exem-plars were better retrieved with semantic-categorizationcompared with seriation instructions, and disruptive ef-fects of semantic similarity arose only when the retrievalstrategy required semantic-categorization.

The mean probability of correctly recalling exemplarswithin each category recalled is shown in Section B of Ta-ble 4. In general, this was greater for the semantic-catego-rization than seriation instructed group, and was smaller inthe speech conditions than in the quiet condition. More-over, the means in the related speech condition were lowerthan those in the unrelated speech condition only for thesemantic-categorization group. An ANOVA on these datarevealed a main effect of Sound Condition, F(2, 116) =15.37, MSE = .003, p < .001, and also a main effect of TaskInstruction, F(1, 58) = 33.11, MSE = .016, p < .001, and aninteraction between these variables, F(2, 116) = 3.6,MSE = .003, p < .05. Simple effects analyses (LSD) revealedsignicant differences between quiet and unrelated speech(p < .001), and quiet and related speech (p < .001) but notbetween unrelated and related speech (p > .05) for the seri-ation group. For the semantic-categorization group, therewere signicant differences between quiet and relatedspeech (p = .001), and between unrelated and relatedspeech conditions (p < .005).

Section C of Table 4 shows the mean probability ofrecalling each category. In general, category recall was bet-ter for seriation than semantic-categorization. For thesemantic-categorization groups there was a loss of catego-ries in the speech conditions which was evident for boththe unrelated and related speech conditions. For the samereason as in Experiment 3, we again restricted our analysisto the semantic-categorization group. An ANOVA revealeda main effect of Sound Condition on the probability ofrecalling each category, F(2, 58) = 25.81, MSE = .005,p < .001, with post hoc tests (Fishers PLSD) revealing sig-nicant differences between quiet and unrelated speech,and quiet and related speech (p < .001) but not betweenunrelated and related speech conditions (p > .05).

As for Experiment 2, we addressed the question ofwhether the additional disruption produced by relatedspeech in the categorization group was attributable to animpairment specic to the recall of the category thatmatches the irrelevant exemplars in that condition. Theresulting means for the probability of successfully recallingterms of a process-oriented approach than by a content-based approach to auditory distraction.

6. General discussion

The results of the current series can be summarized asfollows: Experiment 1 demonstrated that the meaningful-ness of irrelevant speech produces greater disruption tothe free recall of categorizable word lists than meaninglessspeech or pink noise. This experiment also revealed thatthe pattern of semantic interference as compared withthe disruption produced by noise (pink noise and meaning-less speech) shows a unique characteristic: it affects therecall of categories as well as the degree of semantic-cate-gorization demonstrated at test. Experiment 2 revealed aneffect of between-sequence semantic similarity wherebythe semantic relatedness between the to-be-recalled andirrelevant items produces additional disruption to theoverall probability of recalling exemplars, the probabilityof recalling exemplars within each category and the degreeof semantic-categorization observed although it has no ef-fect on the probability of recalling each category. Experi-ments 3 and 4 revealed that effects of meaningfulnessand between-sequence semantic similarity are found onlywhen semantic-categorization is adopted by the partici-pant and not when serial order is used as an organizingstrategy.

The results of all the experiments appear to be well ac-counted for within a process-oriented approach to disrup-tion from task-extraneous material (Hughes & Jones, 2005;Jones & Tremblay, 2000; Neumann, 1996). The interfer-the category-exemplars within each category recalledwere .58 (SE = 0.021) for the non-matching categories and.57 (SE = 0.024) for the matching category. A paired t-testrevealed the impairment was not specic to the recall ofthat category, t(29) = 0.44, p > .05. Thus, like Experiment2, the disruption was not conned to the retrieval of to-be-remembered category-exemplars that matched the cat-egory from which the irrelevant exemplars were drawn.

5.2.2. Clustering measureThe mean Z scores for the semantic-categorization

group were lower in the unrelated speech (M = 2.61,SE = 0.14) and related speech (M = 2.33, SE = 0.17) condi-tions than in the quiet condition (M = 3.15, SE = 0.12) andalso appeared to be lower in the related compared to unre-lated speech condition. An ANOVA revealed a main effectof Sound Condition on Z scores, F(2, 58) = 19.15,MSE = .274, p < .001. Post hoc testing (Fishers PLSD) re-vealed signicant differences between quiet and unrelatedspeech (p < .001), quiet and related speech (p < .001), andbetween unrelated and related speech (p < .05). Thus thedegree of semantic-categorization was impaired by bothunrelated and related speech but the impairment wasgreater in the related condition.

The results thus conrm that between-sequencesemantic similarity effects occur only when semantic pro-cessing is part of the retrieval strategy (see also Marsh,Hughes, & Jones, 2006, 2008). Such a nding harmonizes

J.E. Marsh et al. / Cognition 110 (2009) 2338 35ence-by-process view holds that in the case of the classicalISE, the processing of serial order in the sound is in conictwith the processing of serial order in the primary task; theinterference may be construed as the residual cost ofmechanisms (perhaps inhibition; see Hughes & Jones,2003) designed to resolve a competition-for-action con-ferred by the order cues generated from irrelevant and rel-evant sources of information. This approach explains whyneither the meaningfulness of irrelevant speech nor be-tween-sequence semantic similarity plays a role in the dis-ruption when serial recall is instructed (Experiments 3 and4; see also Buchner et al., 1996 and Jones et al., 1990): Inthis case it is the information that the irrelevant soundyields about serial order, not its meaning, that is broadlycompatible with the action (or process) of serial rehearsal.The interference-by-process approach also explains whythe meaning of speech becomes disruptive to the perfor-mance of free recall tasks only when semantic-categoriza-tion is an obvious or instructed strategy (Experiments 1-4).When the primary task involves dynamic semantic encod-ing and retrieval processesunlike the case with serial re-callthe irrelevant semantic information extracted fromthe speech produces competition for these processes.Impairment can thus be understood in terms of a relativedifculty in selecting the correct source of semantic infor-mation as they both compete for the category of actionbeing called for in the semantic recall task. That be-tween-sequence semantic similarity produces more inter-ference than mere meaningfulness (Experiment 2 and 4)is particularly supportive of a process-oriented account:The irrelevant speech in this case species highly con-text-compatible, but ultimately response-inappropriate,information in the context of the semantic recall task.

One potentially problematic nding for the process-ori-ented approach is that meaningless irrelevant speechdisrupted recall of categorizable lists when semantic-cate-gorization was either spontaneously adopted (Experiments1 and 2) or instructed (Experiments 3 and 4). However,that pink noise (which does not convey acoustic variation)in Experiment 1 produced comparable disruption to mean-ingless (Welsh) speech suggests that the effect of meaning-less irrelevant speech in this paradigm is not the typicaleffectattributable to acoustic variabilitythat disruptsserial recall. It seems, therefore, that this effect is ageneral effect of noise that often impairs performance ontasks that call upon semantic processing (see Smith &Jones, 1992).

That the disruption observed in the context of semantictasks is determined by organizational processes that arebrought to bear to meet the demands of the instructed re-trieval strategy (Experiments 3 and 4) suggests it is theprocess, rather than content, that dictates the degree andtype of disruption from irrelevant speech. This view ofthe impairment produced by irrelevant auditory stimuliis consistent with a functionalist approach to memory gen-erally which advocates that the goals of the individual andthe retrieval environment (instructions, cues, task de-mands) play a critical role in remembering and forgetting(Toth & Hunt, 1999), and according to which attempts todelineate the structure(s) of memory is an ill-rewardedendeavour.The process-oriented approach also seems to provide abetter interpretation of the results reported here thanattentional resource-based accounts of disruption fromirrelevant sound (Cowan, 1995; Neath, 2000; see alsoLange, 2005). For example, the data seem particularly atodds with an attentional capture approach (Cowan, 1995;Elliott, 2002; see also Lange, 2005). On this account, theclassical ISE is the result of acoustic changes-in-state fromone irrelevant item to the next causing an orienting re-sponse away (or capturing attention) from the focal task.At rst glance, the account might be readily extended todeal with the kind of semantic auditory distraction effectsobserved here by appeal to the notion that between-se-quence semantic similarity would also give rise to orient-ing responses via the priming of semantic features of thesound based on the semanticity of the to-be-recalled items(cf. Cowan, 1995). However, as acknowledged by Saultsand Cowan (2007), recent evidence indicates that thechanging-state effect and attentional capture effects arefunctionally distinct (Hughes, Vachon, & Jones, 2005;Hughes et al., 2007). For example, attentional capture ef-fects are evident in short-term memory tasks that are as-sumed not to engage a seriation process (missing-itemtask, cf. Beaman & Jones, 1997; Buschke, 1963) whereasthe changing-state effect is contingent on seriation in thefocal task (Hughes et al., 2007). In relation to the presentdata, there is no reason to suppose that semantic featuresof irrelevant sound should be primedand hence endowedwith attentional capturing powerany less by the to-be-recalled items under seriation instructions than undersemantic-categorization instructions. Based on the notionthat the priming of semantic features is underpinned byautomatic semantic priming (e.g., Neely, 1976), attentionalcapture due to the meaningfulness of the sound or due tobetween-sequence semantic similarity would be expectedeven when serial recall is emphasized because automaticsemantic priming occurs full blown regardless of the focaltask (see Neely & Kahan, 2001). Thus, that semantic audi-tory distraction was only produced under semantic-cate-gorization instructions (Experiments 3 and 4) providesfurther evidence against this approach. The key difcultyfor attentional resource-based accounts therefore is thatthey are too general; they cannot readily explain why thenature of auditory distraction is dictated by the prevailingmental activity, whilst this is an axiomatic tenet of theinterference-by-process approach.

One challenge that ows from the view that the disrup-tion reported in the present experiments is produced by aconict between the semantic processing of the sound andsemantic processing in the focal task is to identify moreprecisely the nature of that focal semantic processing. Thisis because it is likely that a number of diverse semanticprocesses contribute to performance on the semantic-cat-egorization task, any of which could be potentially dis-rupted by the meaning of irrelevant speech. For example,semantic processing is required in the task for at leastthe following: (a) identifying the categorical structure ofthe list (Murphy, 1979); (b) reorganizing list exemplarsto encode and rehearse same-category-exemplars together(Weist, 1972); (c) coupling semantic retrieval andrehearsal processes; same-category-exemplars (e.g., dog,

Cambridge, MA: MIT Press.Anderson, J. R. (1983). The architecture of cognition. Cambridge, MA:

517529.

36 J.E. Marsh et al. / Cognition 110 (2009) 2338horse) may be automatically (e.g., by spreading activa-tion; Collins & Loftus, 1975), or deliberately, retrievedand rehearsed together upon presentation of a related cat-egory-exemplar (bear) after intervening unrelated cate-gory-exemplars (Weist & Crawford, 1973); and (d) cuedsearch of long-term memory (Raaijmakers & Shiffrin,1981; Rundus, 1973), which involves generating list, orcandidate list, category names and exemplars for searchof, and retrieval from, long-term lexical-semantic memory(Gronlund & Shiffrin, 1986). Although there is alreadysome evidence that the latter generative process is suscep-tible to semantic-based disruption (Marsh, Hughes, &Jones, 2006, 2008), a more ne-grained analysis of whichother semantic processes are impaired is needed.

The disruption produced by irrelevant auditory stimuliseems much better captured by a process-oriented ap-proach (e.g., Hughes & Jones, 2005; Jones & Tremblay,2000) than either a structural (or content-based) approach(e.g., Gathercole & Baddeley, 1993; Neath, 2000) or anattentional resource-based approach (e.g., Cowan, 1995;Lange, 2005; Neath, 2000). Latterly the interference-by-process view has been considered in terms of the selec-tion-for-action approach to attentional selectivity (cf.Allport, 1993; Hughes & Jones, 2005; Neumann, 1996). Thisapproach holds that the planning and execution of a con-textually-appropriate actthat demanded by the primarytaskis compromised to the extent that irrelevant infor-mation is compatible with the act at a general level butincompatible with it at the level of the particular responserequired.

On the selection-for-action account, interference fromthe irrelevant information reects an overhead of the ac-tion of mechanisms that prevent it from actually assum-ing the control of action. Thus, the nature and extent ofinterference is a joint product of the character of the pri-mary task and the nature of the potentially-distractinginformation: When both irrelevant and relevant eventsconstitute plausible candidates for the skill deployed toperform the focal task a selection-for-action problem isgenerated. For example, the classical ISE with serial recallmay be conceived as a residual cost of preventing thecompeting irrelevant source of order information fromassuming control of the skill of serial rehearsal deployedto retain the to-be-remembered sequence (Hughes &Jones, 2005).

We would argue that the strength of the process-ori-ented approach, embedded in the selection-for-actionview, derives from its questioning of the more generally re-ceived wisdom that attentional selectivity is imposed bysome shortfall of the cognitive system as is traditionallyheld by structuralist approaches (e.g., a limitation on pro-cessing or a limited attentional resource or set of re-sources; Cowan, 1995; Neath, 2000). Instead, theselection-for-action view is that selection (for action) isthe problem to be solved (not the solution) and limitationsin performance (including susceptibility to disruption fromirrelevant information) are the consequence of adaptivemechanisms designed to resolve that selection problem(for extensive discussions, see Allport, 1993; Neumann,1996; see also Anderson, 2003). Thus, on the selection-for-action approach, the relationship between selectivityBeaman, C. P. (2004). The irrelevant sound effect revisited: What role forworking memory capacity? Journal of Experimental Psychology:Learning, Memory and Cognition, 30, 11061118.

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Basden, D. R., Basden, B. H., & Stephens, J. P. (2002). Part-set cuing of orderinformation in recall tests. Journal of Memory and Language, 47,and limited capacity is turned on its head: A human per-formers limited capacity (in an empirical sense) reectsthe achievement of selective attention mechanisms de-signed to ensure that only task-relevant information as-sumes the control of goal-directed action, anachievement that gives the illusion of a limited capacityin the sense of a hypothetical property of the mind. Thequalitatively different impairments that are produced bydifferent aspects of irrelevant auditory stimuli (e.g., acous-tic or semantic) in different settings (e.g., serial recall ver-sus category-exemplar recall) are the manifestation ofselective attention mechanisms operating to avoid crosstalk from information appropriate to actions or skills in-volved in, but inappropriate to the specic demands of,performing a given task. Two streams of information donot come into conict for what they contain but for howthey are processed.

Acknowledgement

The research reported in this article received nancialsupport from an Economic and Social Research Council(UK) grant awarded to Dylan Jones, William Macken andRobert Hughes (RES-000-22-1526). We thank SteveMoshier for allowing us to use his C program to generatepink noise for Experiment 1.

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Auditory Distraction