Memory & Cognition1983,11 (6), 631-640

Imagery effects and semantic similarityin sentence recognition memory

JON M. SLACKOpen University, Milton Keynes, England

The idea that subjects often use imagery to discriminate semantically similar sentences wastested in three experiments. In the first experiment, subjects heard subject-verb-object sen­tences in the context of either a comprehension task or an image-generation task. Their memoryfor the sentences was tested using a two-alternative forced-choice recognition test in which dif­ferent types of distractor sentence were used. A sentence semantically similar to the target sen­tence was one type; a sentence with the same subject and object nouns as the target sentence,but dissimilar in meaning, was another type; and a sentence similar in meaning to one of thestimulus sentences, but not to the target sentence, was a third type. The results showed thatthe image-generation instructions enhanced later recognition performance, but only for seman­tically similar test items. A second experiment showed that this finding only holds for high­imagery sentences containing concrete noun concepts. A third experiment demonstrated thatthe enhanced recognition performance could not be accounted for in terms of a semantic modelof test-item discrimination. Collectively, the results were interpreted as providing evidence forthe notion that subjects discriminate the semantically similar test items by elaborating the sen­tence encodings through image processing.

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The functional role of imagery within cognition re­mains unclear even though a large corpus of evidenceimplicating it as a factor in a range of cognitive tasks hasaccumulated (Kosslyn, 1980; Paivio, 1971). Part of thisevidence suggests that imagery is used in understandingcertain types of sentences (Begg & Paivio, 1969; Glass,Eddy, & Schwanenflugel, 1980). The present studyattempted to show that imagery may play a role in thediscrimination of semantically similar sentences, anddemonstrated the influence of this process on recogni­tion memory.

If subjects are asked to describe the differences inmeaning between a pair of semantically close sentences,such as (Sl) "The man strolled through the park," and(S2) "The man sauntered through the park," they oftenreport using imagery to achieve the task. Their intro­spections suggest that they derive their responses fromsome form of image-comparison process. That is, imageryis used to elaborate the internal representations of thetwo sentences in order to maximize the semantic differ­ences between them. Anderson and Bower (1973) arguedthat when a subject forms an image of a sentence, he "un­packs" its conceptual components into more primitiveterms. This semantic elaboration is transformed, throughvarious processes, into additional propositions that areconnected to human associative memory's (HAM's)conceptual-propositional representation for the sentence.

If this notion of semantic elaboration through imageryis valid, then it has implications for a range of cognitive

The author's mailing address is: Department of Psychology,Open University, Walton Hall, Milton Keynes MK7 6AA, England.

tasks that have been shown to be influenced by thevariable of semantic similarity. In particular, on aforced-choice recognition memory task using semanti­cally similar test sentences, subjects will use imagery tocreate discriminable representations for the test items,and match these against the memory traces of thestudied sentences. However, Anderson (Note 1) showedthat such test items are likely to be confused, implyingthat subjects are unable to utilize the differentiated test­trial encodings to improve their recognition accuracy.But recognition performance is also influenced by theencoding instructions. According to the encodingspecificity principle (e.g., Tulving & Thompson, 1973),recognition performance is a function of the overlapbetween the encoding and retrieval environments. Thus,if subjects use imagery to produce differentiated test­item representations, these codes will be effective inaugmenting recognition performance only if they pro­duce a more sensitive match with the study-trial encod­ings. To maximize the overlap between the encodingand retrieval environments, it is necessary for subjectsto generate images for the sentences on the study trials(Fisher & Craik, 1980). Since Anderson's (Note 1)subjects were not instructed to produce images for thestudy sentences, the overlap in content between thestudy- and test-trial encodings was insufficient for thetarget and distractor sentences to be accurately dis­criminated.

A number of studies have shown that recognition per·formance is inversely related to the similarity betweenthe old and new test items (Bower & Glass, 1976;Nagae, 1980; Weaver& Stanny, 1978). However, Tulving

Copyright 1984 Psychonornic Society, Inc.

632 SLACK

(1981) recently showed that the effects of similarity onrecognition memory are more complex than these studiessuggested. On a forced-choice recognition memory taskemploying pictures as stimulus items, he found that,under certain conditions, subjects are more accurate atdiscriminating between similar than between dissimilartest items. To explain this result, he distinguished be­tween two types of similarity relations, perceptual andecphoric, which independently affect recognition mem­ory performance. Perceptual similarity exists betweenitems that are physically present at the same time, suchas between alternative recognition test items on aforced-choice task, whereas ecphoric similarity is thesimilarity existing between a test item and informationstored in memory, such as the traces of the study­trial items. Tulving's results showed that subjects weremore accurate at discriminating between perceptuallysimilar test items than between items with a low degreeof perceptual similarity but with the distract or itemhaving a high degree of ecphoric similarity. This lattersimilarity relation was varied by making the distractorperceptually similar to one of the study-trial pictures,but not to the target with which it was paired on the testtrial. He concluded that it is necessary to isolate theeffects of both types of similarity relation in discussingthe results of experiments in which similarity is thevariable of interest. In the context of recognition mem­ory for sentences, the notion of perceptual similaritycorresponds to the relation of semantic similarityexisting between two sentences.

These arguments underlie the rationale for Experi­ment 1: A subject is presented with a sentence on astudy-trial and asked either to form an image for it orjust to comprehend it. The different encoding instruc­tions should produce sentence representations differingin content. The imagery instructions should produceencodings that emphasize perceptual aspects of the sen­tence meanings, whereas the comprehension instructionsshould produce less elaborate, and more abstract, repre­sentations. However, whether these differences lead todifferences in recognition performance depends on thenature of the distractor sentences. On a two-alternativeforced-choice recognition memory test, using semanti­cally related target and distractor sentences, the theoryclaims that subjects use imagery to discriminate betweenthe sentences. This establishes the appropriate retrievalconditions for the image-derived study-trial encodingsto augment recognition performance. The subjects inthe comprehension condition also use imagery to dis­criminate the test sentences, but their recognition per­formance should not be enhanced, because the stimulussentence encodings do not overlap sufficiently with theenriched test-trial encodings for the latter to be accuratelydistinguished. On the other hand, if the test sentenceshave a low degree of semantic similarity, it is not neces­sary for subjects to use imagery to discriminate betweenthem. In this test condition, recognition accuracyshould be higher than in the semantically related condi-

tion, but should be relatively unaffected by the encodinginstructions. This is because there is no predicted differ­ence in the degree of overlap between the differentstudy-trial encodings and the test-item representations.In a third test condition, corresponding to Tulving's(1981) ecphoric similarity condition, the distractorsentence is semantically similar to one of the study­trial sentences, but not to the target sentence with whichit is paired. As in the dissimilarity condition, subjectsdo not need to use imagery to discriminate the testsentences, and thus the different encoding instructionsshould not produce differential performance. However,if Tulving's results can be extended to recognitionmemory for sentences, the overall level of recognitionaccuracy on this condition should be lower than on thesemantically similar condition. In summary, recognitionaccuracy should be highest in the dissimilarity conditionand lowest in the ecphoric similarity condition, and theencoding instructions should only produce differentialperformance on the semantic similarity condition. Thesepredictions were tested in Experiment 1.

EXPERIMENT 1

MethodSubjects. The subjects, all volunteers, were 48 adult educa­

tion students. They were run individually, and each experi­mental session lasted about 1 h.

Materials. One hundred and fifty pairs of subject-verb­object (S-V-Q) sentences were generated such that the sentenceswithin a pair had the same subject and object noun phrases,but different verbs. The verbs within each sentence pair wereselected to be close synonyms and were matched for length(±2 letters) and frequency of occurrence in written English(Kucera & Francis, 1967). The set of sentence pairs was splitto form two lists, Lists 1 and 2, such that each list containedonly one member of each pair. Fifteen subjects rated the sen­tences in List 1 for image-evoking value, and a different 15 sub­jects rated the sentences in List 2. The subjects were drawn fromthe same pool as the experimental subjects. All the subjectswere instructed to rate the sentences for ease of image formationon a scale ranging from 1 (extremely low imagery) to 7 (ex­tremely high imagery). Each subject received a different randomordering of the sentences within a list. The correlation betweenthe imagery values for the sentences within a pair was r = .88,showing that the sentences were close in image-evoking value aswell as in meaning.

The stimulus materials consisted of 64 sentence pairs: the32 pairs with the highest mean imagery-evoking values and the32 pairs with the lowest mean values. The mean imagery valuesfor the high- and low-imagery groups were 5.47 and 2.87,respectively. A sample of the stimulus materials, along with thecorresponding distractor sentences used in the recognition tests,is given in Table 1. Forty-eight unique stimulus lists were gen­erated; each list contained one of the sentences from each ofthe 64 sentence pairs. The sentences were allocated randomlyto the lists, with each sentence appearing on half the lists. Theorder of the sentences was randomized across lists. For eachsentence pair, a recognition test distractor sentence using thesame subject and object noun phrases was generated. The verbsof the sentences were chosen from the same class of verbs usedto generate the stimulus sentences, but did not overlap withthem in meaning. In addition, they were matched for tense,length, and frequency.

IMAGERY EFFECTS IN SENTENCE RECOGNITION 633

Table 1A Sample of the Materials Used in Experiment I, Showing Both High(H)- and Low(L)-Imagery-Value Sentences

-----Verbs

ImagerySubject Noun Phrase Value Synonyms Distractor Object Noun Phrase

The man H strolled sauntered cycled through the parkThe prisoner H scribbled scrawled sealed his final letterThe attendant H drenched watered planted the flower bedsThe schoolboy L invented concocted recited the heroic storiesThe politicians L governed managed exploited the poor coloniesThe creatures L depleted exhausted covered their food supply

Three types of test item were constructed to be used in atwo-alternative forced-choice recognition memory test. Thethree types corresponded to the three experimental test condi­tions, as follows: Using a notation based on Tulving (1981), letSl, S2, S3, ... designate the stimulus sentences presented in thestudy phase, Sl ', S2', S3', '" the sentences that are closelyrelated to them in meaning, and D'l ', D2', D3', ... the corre­sponding distractor sentences. The three experimental testconditions and associated test items can now be defined as:(1) synonym condition (Sl-Sl '), in which the two alternativesin a test item are closely related in meaning; (2) distract or condi­tion (Sl-D1'), in which the alternative sentences only share thesame subject and object noun phrases; and (3) ecphoric simil­arity condition (Sl-S2'), in which the two sentences are notsynonymous with each other but the nontarget sentence issynonymous with another previously studied sentence (S2).This last condition was included to test Tulving's (1981) pro­posal concerning different types of similarity and their effectson recognition performance. In the two-alternative, forced­choice recognition test, each subject was tested on 48 items,16 items in each of the three test conditions. Each test itempresented the subject with one of the stimulus sentences and a"lure." Since the stimulus sentences associated with the lures inthe Sl-S2' condition did not appear in the recognition test, the64 stimulus sentences were tested using only 48 pairs of alterna­tives. For each stimulus list, a unique recognition memory testlist was constructed such that the target sentences appeared inthe same ordinal position on both lists. This procedure attemptedto balance the item lag between study and test on any targetsentence. On each test, half the items in each condition pre­sented pairs of high-imagery sentences, and the other halfof the items consisted of low-imagery sentences. Each stimulussentence served equally often in the three test conditions and asone of the sentences used to derive the lures in the SI-S2'condition. Furthermore, in this latter condition, the targetsentences and lures were matched for imagery; that is, the 8high-imagery stimulus sentences were paired with the 8 high­imagery sentence lures, and similarly for the low-imagery sen­tences.

Design. The 48 subjects were assigned randomly to receiveone of the stimulus lists in one of the two study conditions, thecomprehension condition or the imagery condition. Equalnumbers of subjects were assigned to the two conditions. Fol­lowing this, all the subjects were asked to complete the two­alternative forced-choice recognition memory test correspondingto the stimulus list that they had received. This was a 2 (studycondition: comprehension vs. imagery) x 3 (test condition:SI-Sl ' vs. Sl-Dj ' vs. Sl-S2') x 2 (imagery-evoking value: high vs.low) design, with the first variable being between subjects andthe last two being within subjects.

Procedure. The two study conditions were identical exceptfor the instructions given to the subjects. All the stimulussentences were presented in the auditory modality over head­phones connected to a tape recorder controlled by a computer.The stimulus lists were presented in the auditory mode in anattempt to minimize any modality interference effects between

the two study conditions (Eddy & Glass, 1981). Each trialbegan with a l-sec auditory signal that served as a "ready"signal. This was followed by a stimulus sentence. A digital timerwas started by a 1000-Hz pulse on a separate channel of thetape recorder. The pulse was set such that the timer was startedat the onset of the last syllable of each sentence. The subjectsresponded by pressing a button placed under the first finger oftheir dominant hand. To facilitate rapid responding, the subjectsrested their fingers on the button between responses. Theresponse times were recorded. There was a 5-sec interval betweenthe subjects' responses and the start of the next trial.

In the comprehension condition, the subjects were instructedto listen to the stimulus sentence and to press the responsebutton as soon as they felt they had fully comprehended thesentence. They were informed that their memory for the sen­tences would be tested afterwards.

In the imagery condition, the subjects were asked to generatea mental image that depicted the meaning of the stimulus sen­tence and to press the response button as soon as they hadformed a complete image. These subjects were also informedthat their memory for the sentences would be tested afterwards.

Each subject received 10 practice trials on sentences similarin nature to the stimulus sentences. After the experimenteranswered questions clarifying any uncertainties regarding theinstructions, the stimulus sentences were presented.

Following presentation of the stimulus sentences, the sub­jects were given an interpolated task for 2 min. The subjectswere required to write down the names of as many Englishcities as they could think of. The subjects were then asked tocomplete the two-alternative forced-choice recognition testappropriate to the stimulus list they had received. The test listswere presented with a projection tachistoscope; 10 sec wereallowed for each test item. The subjects were asked to turn to apage of the response booklet on which were listed the numbers1 through 48. The letters "a.b" were printed next to each num­ber; these identified the alternative sentences in each item. Onthe same line were printed the digits "1," "2," and "3," whichwere to be used for the confidence-rating judgments. The sub­jects were told that on each test item they would see two sen­tences, labeled "a" and "b," and that one, and only one, of thesentences had been presented as a stimulus sentence. They wereasked to indicate by a check mark against the appropriate letterwhich sentence of the two they had heard during the first partof the experiment. It was emphasized that the subjects shouldmark one sentence for each test item, and should guess if theywere unsure. The subjects also gave a confidence judgmentto accompany their decisions by circling one of the digits on the3-point scale, with 3 designating high confidence and 1 repre­senting guessing.

ResultsA preliminary analysis of the subject's recognition

performance showed that the data could be pooled overthe entire set of stimulus sentences; that is, performancewas symmetrical for the synonymous sentences within

634 SLACK

Table 2Hit Ratesand Mean Confidence Ratings for Hitsin the ThreeConditions on the Forced-Choice

Recognition Test, for the Two Study Conditions and Sentence TypesUsed in Experiment 1

Test Conditions

Hit Rates Mean Confidence RatingsImagery

Study Condition Value SI-S1' SI-Dl' SI-S2' SI-S1' SI-D1' SI-S2'

ComprehensionHigh .67 .82 .64 2.11 2.27 2.07Low .69 .81 .65 2.04 2.23 1.91

Image GenerationHigh .81 .81 .63 2.25 2.32 2.09Low .77 .79 .66 2.19 2.28 2.01

a pair. Table 2 shows the hit rates and the mean confi­dence ratings for hits in the three conditions on theforced-choice recogntion test, for each study conditionand sentence type.

A 2 (study condition) x 3 (test condition) x 2 (imageryvalue) mixed analysis of variance was performed on thehit rates. The results of the analysis showed that twomain effects were significant: Image generation leads tobetter recognition performance than does compre­hension [F(l,46) = 5.14, P < .05] , and performance isaffected by the nature of the lures [F(2,92) = 7.28,p < .01]. In addition, there was a reliable interactionbetween study condition and recognition test condition[F(2,92) = 6.83, p < .01]. The results of a Newman­Keuls test of pairwise comparisons indicated that recog­nition performance was significantly better in Condi­tion 81-Dl' than in the other two test conditions;the differences in performance on these latter twoconditions were nonsignificant. However, this result istrue only for performance in the comprehension studycondition. The data show that image-generation instruc­tions led to improved recognition performance inCondition 81-S1' than in Condition SI-82'. Further­more, these results seem to be consistent for both high­and low-imagery sentences. The means show no syste­matic differences in recognition performance as a func­tion of imagery-evoking value of the stimulus sentences(F < 2.50).

The means of the confidence judgments for hits areshown in Table 2 as a function of study and test condi­tions and sentence type. These means reflect the samegeneral effects reported for correct responses. An anal­ysis of variance carried out on the confidence judgmentdata showed that the study- and test-eondition main ef­fects were again significant [F(l,46) = 4.25, p < .05,and F(2,92) =4.76, P < .025, respectively] , as was thestudy x test condition interaction [F(2,92) = 4.02,p < .05]. A number of studies have reported strongpositive correlations between recognition accuracy onforced-choice tests and subjects' confidence in theirjudgments (Bower & Glass, 1976; Tulving, 1981).

DiscussionThe findings confirm the prediction that imagery­

encoding instructions produce more sensitive recognition

memory for sentences than do comprehension instruc­tions, but only in the semantic similarity (S 1-SI') testcondition. In the other two test conditions, encodinginstructions did not differentially affect recognitionaccuracy. However, the fact that there were no reliableeffects associated with image-evoking value is ratherdisturbing, given the theoretical rationale of the experi­ment. Accounting for the data in terms of overlappingmemory traces produced through image processing atencoding and retrieval would lead one to predict that thequality of that processing for different sentences, pre­sumably reflected in the image-evoking values, shouldinfluence recognition performance. One plausible ex­planation for the noneffect relates to the content of theexperimental sentences. On inspection of the sentences,it is apparent that, whereas the verbs range from high tolow in terms of image-evoking value, the subject andobject noun phrases represent a more restricted set,tending to be of high imagery. Thus, it is possible thatthe materials span a relatively restricted range of image­evoking values. Subjects may use imagery to discriminatethe test sentences providing that the subject and objectconcepts are relatively easy to image, irrespective of theimage-evoking value of the verbs. By using a wider rangeof sentences, including those with abstract subject andobject concepts, it should be possible to test whether thenoneffect due to image-evoking value is a product ofthe sentence sample used or a general finding that wouldbe detrimental to the theory being proposed. Experi­ment 2 repeated Experiment 1, using such sentences.

EXPERIMENT 2

MethodMaterials. Fifty additional pairsof S-Q-V sentences similar to

those used in Experiment 1 were generated. The sentenceswithin each pair shared the same subject and object nounphrases, but contained different verbs that had been selected asclose synonyms. However, unlike the pairs of sentences used inExperiment 1, the shared subject nouns were chosen from a setof low-imagery words (imagery value less than 3.5 on a scalerange of 1-7 in the Toglia & Battig, 1978, norms). These newsentence pairs were added to the set of stimulus sentence pairsused in Experiment 1 to form a total set of 114 sentence pairsthat were rated for imagery-evoking value and comprehensi­bility. Two lists of sentences were produced,Lists 1 and 2, suchthat each list contained only one member of eachsentence pair.

IMAGERY EFFECTS IN SENTENCE RECOGNITION 635

In all, 56 subjects rated the sentence pairs, using the proceduredescribed previously. For each list, half the subjects were in­structed to rate the sentences for ease of image formation, andhalf for ease of comprehension.

As had been found in generating the materials for Fxperi­ment I, the imagery-evoking values of the sentences within apair correlated highly (r = .85), as did the comprehensibilityratings (r = .88). Furthermore, the imagery and comprehensi­bility ratings correlated quite highly with each other (r = .48),showing that high-imagery sentences tended to be rated as easierto understand than low-imagery sentences. More importantly,the original 64 stimulus sentences were rated higher in image­evoking value (mean =5.12) than were the new sentences con­taining low-imagery subject nouns (mean = 3.05) [t(27) = 3.88,p < .00I). The new rating data also validated the ordinal prop­erties of the original imagery ratings; the rank order correlationbetween the two sets of imagery ratings for the original stimulussentences was r =.86.

Sixty-four sentence pairs were chosen to be used as thestimuli in Experiment 2. The 32 sentences with the lowest meanimagery-evoking values were used, all of which had low-imagerysubject nouns. The 32 high-imagery sentence pairs were chosenfrom the set of 60 sentence pairs with the highest mean imageryratings. Although high- and low-imagery sentences appeared todiffer systematically in terms of mean comprehensibility rating,there was sufficient variance in the set of 60 sentence pairs tomatch the high- and low-imagery sentences for comprehensi­bility. Each high-imagery sentence pair was matched with a low­imagery sentence pair for sentence length (tolerance, ±I syllable)and comprehensibility (tolerance, ±.3 rating points). The meanimagery-evoking values for the high- and low-imagery sentencepairs were 4.88 and 2.85, respectively, and the equivalent meancomprehensibility ratings were 3.61 and 3.47, respectively.

A recognition test distractor sentence was generated for eachsentence pair, using the same subject and object noun phrasesbut semantically different verbs. A sample of the stimulus andtest sentences is given in Table 3. Forty-eight stimulus lists andassociated recognition test lists were constructed in the sameway as were those in Experiment I.

Subjects. Forty-eight new subjects were drawn from the samepopulation used for Experiment I. All the subjects were testedindividually; each experimental session lasted about 1.25 h.

Design and Procedure. The general procedures and designof Experiment 2 were the same as those employed in Experi­ment 1. The subjects were assigned randomly to receive one ofthe stimulus lists in one of two study conditions, comprehensionor image generation, and then completed the appropriate two­alternative recognition test comprising items in three test condi­tions, SI-SI', SI-Dl', and SI-S2'.

ResultsLooking first at the analysis of the response times

for the two study conditions and sentence types, we findthat both main effects were reliable, as was the study

condition x sentence type interaction [F(1,46) = 13.72,p < .001]. In general, it takes longer to construct animage for a sentence (mean response time =1,654 msec)than it does to comprehend it (mean response time =1,228 msec) [F(1,46) = 22.61, P < .001]. Furthermore,the response times for high-imagery sentences (meanresponse time = 1,322 msec) are shorter than the re­sponse times for low-imagery sentences (mean responsetime = 1,561 msec) [F(I,46) =8.11, p < .01]. A pair­wise comparison of the mean response times showedthat the high- and low-imagery sentences were com­prehended equally quickly (difference in mean responsetimes was 22 msec), but it took much longer to formimages for low-imagery sentences (mean response time =1,882 msec) than for high-imagery sentences (meanresponse time = 1,426 msec). This fmding validates thedesign in showing that the stimulus sentences are dis­tinguishable in terms of imagery properties but not interms of ease of understanding.

The analysis of the subjects' recognition performanceconfirmed the fmdings of the previous experiment; boththe study and test conditions produced significanteffects [F(1,46) = 4.68, P < .05, and F(2,92) = 8.47,p < .001, respectively] , and the study x test conditioninteraction was also reliable [F(2,92) =7.64, P < .001].However, in this experiment, there was also a reliablemain effect due to imagery-evoking value [F( 1,46) =5.07, P < .05], and the triple interaction was significant[F(2,92) = 6.82, p < .01]. The hit rates in the threetest conditions, for each study condition and sentencetype, are shown in Table 4. Individual paired compari­sons contrasting test conditions within study conditionswere performed. The analysis showed that, for high­imagery sentences, recognition performance was betterin the SI-D l ' condition than in the other two test con­ditions, irrespective of the encoding instructions, withthe exception that performance in the S1-8l ' conditionfor subjects receiving imagery instructions was as good asin Condition SI-Dl'. However, the pattern of resultsdiffered for low-imagery sentences in that the latterexception did not hold; performance in Condition 81-Dl 'was always better than in the other test conditions,regardless of study condition. Furthermore, Test Condi­tions 81-S1' and 81-82' could not be differentiated onthe basis of recognition performance.

Table 3A Sample of the Materials Used in Experiment 2, Showing Both High(H)- and l.ow(L)-lmagery-Value Sentences

VerbsImagery

Subject Noun Phrase Value Synonyms Distractor Object Noun Phrase

The builders H twisted warped erected the support frameThe detective H searched scoured tidied his dingy officeThe gangster H disliked resented ignored the biased questionsThe statistics L enhanced enriched supported the report's findingsThe scheme L required demanded received total cooperationThe rumors L ridiculed derided reinforced the man's reputation

636 SLACK

Table 4Hit Rates in the Three Conditions on the Forced-Choice

Recognition Test, for the Two Study Conditionsand Sentence Types Used in Experiment 2

Test ConditionsImagery

Study Condition Value si-sr Sl-Dl' Sl-S2'

ComprehensionHigh .70 .84 .66Low .67 .82 .65

Image GenerationHigh .82 .83 .69Low .71 .80 .64

The analysis of the subjects' confidence ratingstotally supported the pattern of the recognition ac­curacy data.

DiscussionThe fmdings of Experiment 2 indicate that the lack

of effects due to image-evoking value in Experiment 1were related to the restricted range of stimulus sentencesused. The rating data clearly demonstrate that theoriginal sentences were drawn from a more restrictedset, on the basis of image-evoking value, than were thepresent materials. However, the original findings stillstand, but with an additional constraint. Recognitionaccuracy is enhanced in the sisr test condition forsubjects performing the image-generation task, but asExperiment 2 showed, this result only holds for high­imagery sentences. For low-imagery sentences containingabstract noun concepts, recognition accuracy is at thesame low level on both the si.sr and Sl-S2' conditions,regardless of the encoding task. Thus, it seems that thequality of a mental image, or the ease with which onecan be derived for a given sentence, influences eitherthe choice or the effectiveness of the retrieval strategyin discriminating between semantically similar sentences.Furthermore, the results of the two experimentsseem to imply that the image-evoking quality of thenoun concepts, rather than the verb concept, is themajor determining factor in the subjects' use ofimagery.

An alternative explanation of the data is that subjectselaborate the test sentences in the Sl-S l ' condition byusing purely semantic processing rather than imagery(Kieras, 1978). The rationale of the experiments remainsessentially unchanged, except that it is unnecessary touse imagery to discriminate the test alternatives; se­mantic elaboration of the sentence representations issufficient. Moreover, the image-evoking-value effects canbe explained in terms of the argument that high-imagerysentences produce richer semantic encodings than dolow-imagery sentences, leading to increased study­and test-trial encoding overlap. Experiment 3 was de­signed to counter this explanation.

In the study phase of Experiment 3, all the subjectsengaged in a sentence classification task in which theywere required to make a binary response on the basisof one of three criteria. The criteria differed in terms

of both the type and depth of processing required tomake a judgment. In one condition, the subjects wereasked to classify the sentences according to how EASYor HARD they were to understand. In a second condi­tion, the classification criterion was the ease with whicha sentence evoked a mental image. Finally, in a thirdcondition, referred to as the "implied actors" condition,the subjects had to classify the sentences on the basisof whether they thought a sentence directly implied theinvolvement of actors not explicitly mentioned. Forexample, the sentence "The scheme required totalcooperation" is likely to produce a positive responsebecause the concept "cooperation" alludes to implicitactors who are required to cooperate for the scheme tobe successful. On the other hand, additional actors can­not be inferred from the sentence "The detective searchedhis dingy office," because none of the componentconcepts requires the involvement of actors in additionto the detective. In all other respects, Experiment 3 wasidentical to Experiment 2.

The rationale underlying the use of the three encod­ing tasks hinges on the assumption that the "impliedactors" classification task involves deeper semanticprocessing than does the comprehension classificationtask. In the former task, a subject is required to drawspecific inferences based on the conceptual content ofa sentence, in addition to constructing a representationfor it. Most current theories of sentence comprehension(Norman & Rumelhart, 1975; Schank, 1975) proposethat such inferences require the representation of theverb to be expanded through decomposition into moreprimitive semantic elements, producing a semanticallyelaborated trace. There is considerable evidence thatsentence classification tasks of this type produce moreelaborate encodings for sentences than do simple com­prehension tasks (Jacoby & Craik, 1979; Kolers, 1975).Thus, the study-trial encodings resulting from the "im­plied actors" task should incorporate expanded verb rep­resentations, in comparison with those produced by thecomprehension task. The SI-Sl' test sentences differonly in terms of their verb components, so if they arediscriminated through purely semantic processing, thenincreased recognition accuracy for subjects performingthe "implied actors" task should result. This is becauseboth the study- and test-trial encodings will containexpanded representations for the verbs, which increasesthe degree of overlap between the encodings for a targetitem. However, if subjects use imagery to elaborate theS1-Sl' test-trial encodings, the additional perceptualinformation they incorporate will be less compatiblewith the sentence representations produced by the"implied actors" task, but will match up with the per­ceptually enriched encodings produced by the imageryclassification task. This should result in a higher degreeof overlap between target sentence encodings associatedwith the latter task, which should produce more sensi­tive discrimination between the test alternatives. Thus,S l-S l ' recognition accuracy should be highest for sub-

IMAGERY EFFECTS IN SENTENCE RECOGNITION 637

jects performing the imagery classification task, but onlyfor high-imagery sentences. There may also be signifi­cant differences in performance between the other twostudy conditions, but such differences should not belimited to the data for high-imagery sentences in theS1-Si' test condition.

EXPERIMENT 3

MethodSubjects. Seventy-two subjects were drawn from the same

population used for Experiment 1.Materials. The experimental materials comprised 72 stimulus

sentence lists and corresponding forced-choice recognition testlists, generated using the 64 stimulus sentence pairs and dis­tractor sentences that had been used in Experiment 2. Of the 32low-imagery sentences, the experimenter classified 18 as positiveand 14 as negative examples of sentences that imply the involve­ment of actors not explicitly mentioned. For the high-imagerysentences, however, the corresponding figures were 21 and 1LTo balance the ratio of responses for the two types of stimulussentence, three new triples were substituted in the high-imageryset, so that the ratio of probable responses was 18:14 for bothsets. The new sentence triples were chosen from the original poolof stimulus sentences generated for Experiment 2, and matchedthe substituted sentences on image-evoking value and compre­hension rating.

Design. The experimental design was similar to that used inExperiment 2, except that it was extended to include a thirdstudy condition. The subjects were assigned randomly to receiveone of the stimulus lists in one of the three study conditions,the "comprehension" condition, the "imagery" condition, or the"implied actors" condition.

Procedure. All three study conditions involved a binaryclassification task, but differed in terms of the basis on whichthe judgment had to be made. Again, all the sentences werepresented in the auditory modality. The response keyboard hadtwo microswitches on which the subject rested one finger fromeach of his or her right and left hands. The response keys wereused to terminate the timer. The subject's responses and re­sponse times were recorded on the computer.

In the "comprehension" condition, the subjects were askedto listen to each stimulus sentence, to decide whether theywould rate it as EASY or HARD to understand, and to makethe appropriate response as quickly as possible. The subjectswere given lengthy instructions concerning how they shouldinterpret the response categories.

The subjects in the "imagery" condition were given similarinstructions, except that they were asked to rate the sentencesas either EASY or HARD on the basis of the ease with which asentence evoked a mental image.

The "implied actors" condition was slightly different in thatthe subjects were asked to make a YES/NO response for eachsentence on the basis of whether it implied the involvement ofactors other than those explicitly mentioned. The subjects weregiven extensive instructions about what constituted a directimplication of additional actors. As in the other two studyconditions, emphasis was placed on both speed and accuracy ofresponse.

All the subjects were told that their memory for the sen­tences would be tested at the end of the experiment. Each sub­ject received 20 practice trials on sentences similar to those usedin the actual experiment. The mapping of response categoriesonto response keys was alternated between subjects. At the endof the experiment, each subject was given the appropriateforced-choice recognition memory test to complete, the pro­cedure being identical to that used in Experiment I.

ResultsThe concordance between the experimenter and sub­

ject classifications in the "implied actors" condition was.76, showing that the subjects were completing the taskas specified. In the analysis of the response times, allthe responses were included. Again, both main effectswere reliable. In general, high-imagery sentences (meanresponse time = 1,662 msec) produced faster responsesthan did low-imagery sentences (mean response time =1,771 msec) [F(l,69) = 5.87, P < .05], and responsetime was influenced by the nature of the classificationtask [F(2,69) = 6.85, P < .01]. The interaction was alsosignificant [F(2,69) = 6.32, P < .01] . A comparison-of­means test showed that response times were faster onthe comprehension classification task (l,542 msec)than on the other two tasks (imagery task, 1,773 msec;"implied actors" task, 1,835 msec). These last twoconditions could not be separated. Moreover, only onthe imagery condition did the two types of stimulussentence produce reliable differences in response time(difference in means =192 msec).

A mixed analysis of variance of the subjects' recogni­tion performance showed that all three main effectswere significant. That is, performance was influencedby the study task [F(2,69) = 3.87, P < .05], test condi­tion [F(2,69) = 7.86, P < .001], and sentence type[F(I,69) = 4.26, P < .05]. The study x test conditioninteraction was significant [F(4,138) = 3.16, p < .05],as was the three-way interaction [F(4,138) = 4.87,P < .01]. A comparison-of-means test showed thatrecognition accuracy was equally high in the "imagery"and "implied actors" conditions in comparison with thelevel of performance on the "comprehension" condition.The differences in performance on the test conditionswere in the same direction as had been found in theprevious two experiments, as shown in Table 5. Indi­vidual paired comparisons contrasting test conditionswithin study conditions revealed additional structure.Performance on the SI-Dl ' test condition was not af­fected by study condition or sentence type. Performanceon the other two test conditions was at an equally lowlevel, independent of study condition and sentence type,but there were two important exceptions to this. First,as had been found in Experiment 2, recognition ac-

Table 5Hit Rates on the Three Test Conditions in Experiment 3

as a Function of Encoding Task and Sentence Type

Encoding Classifi- ImageryTest Condition

cation Task Mean Value SI-Si' SI-Dl' SI-S2'

Comprehension .73High .70 .84 .68Low .69 .80 .65

Implied Actor .77High .69 .85 .75Low .75 .82 .73

Imagery .76High .85 .84 .68Low .71 .82 .66

Mean .73 .83 .69-----

638 SLACK

curacy on the SI-SI' condition was enhanced to thelevel of S1-Dl ' performance for high-imagery sentencesin the imagery study condition. Second, on the SI-S2'test condition, recognition accuracy was higher in the"implied actors" condition, irrespective of sentencetype, than in the other two study conditions, but didnot reach the level of S1-Dl ' performance. The patternof the recognition accuracy data was, as in the other twoexperiments, reflected in the subjects' confidence judg­ments.

DiscussionThe pattern of the data in the comprehension and

imagery conditions was unchanged from that in Experi­ment 2. The only difference between the two sets ofdata relates to the response times on the imagery­related study tasks. The convergence of response timesfor high- and low-imagery sentences in the classificationtask is to be expected, given the nature of the task. Thevery high- and very low-imagery sentences are relativelyeasy to classify and produce low response times, bring­ing the means for the two types of sentences together.

Inclusion of the data for the "implied actors" condi­tion brings out more interesting comparisons. The highlevel of recognition performance in this condition,relative to that in the comprehension condition, is in linewith the majority of findings in the levels-of-processingliterature (Cermak & Craik, 1979). Also, the responsetime data show that the task is relatively unaffected bythe imagery variable, implying that it involves purelysemantic processing. Moreover, the differences in per­formance in the sisr test condition for subjects in the"implied actors" and "imagery" conditions lead one tothe conclusion that the semantically elaborated encod­ings produced by the former task have a relatively lowdegree of overlap with the test sentence encodings.Only imagery-related encoding tasks seem to producerepresentations that overlap sufficiently with the differ­entiated SI-SI' test-trial encodings to augment retrieval.This result strongly suggests that these latter encodingsare the product of image-related processing, therebyconfirming the original idea that imagery is used todiscriminate semantically similar sentences, albeit onlywhen the concreteness of the content nouns makes it afeasible strategy.

Two interesting aspects of the data relate to thedifferences in recognition performance in the "impliedactors" condition. First, there is an enhancement in theaccuracy in the SI-S2' condition. Second, performancein the S1-Sl ' condition is better for low-imagery sen­tences than for high-imagery sentences, although thisdifference did not quite reach significance. Both findingsmight be explained by the notion that the subjects takeadvantage of the semantically elaborated study-trialencodings to improve their recognition accuracy. In theSI-S2' test condition, subjects may adopt the strategyof producing semantically rich representations for testsentences, leading to an increased overlap in the study­and test-trial encodings for target items. This strategy is

ineffective for subjects in the other study conditionsbecause the study-trial encodings either are too impover­ished or are incompatible, depending on the encodingtask. The "implied actors" subjects may also use thisstrategy in discriminating the low-imagery test sentencesin the SI-Sl' condition as an alternative to using imagerythat is inhibited by the abstract content of the sentences.Again, the resulting increase in the overlap of the targetitem encodings produces more sensitive performance.However, the same subjects use imagery to discriminatethe high-imagery sentences in the Sl-S I' condition,producing encodings that are less compatible with thetraces laid down during the study phase, which leadsto poorer performance.

GENERAL DISCUSSION

The three experiments showed that on a two­alternative forced-choice recognition memory task usingsemantically similar distractors, recognition accuracy forhigh-imagery target sentences is enhanced if subjectsperform imagery-related tasks on the study trials. Underthe same test conditions, comprehension and other re­lated semantic encoding tasks do not produce equivalentimprovements in performance. Furthermore, the firsttwo experiments show that the high-imagery constraintexcludes only those sentences that contain abstractsubject and object nouns; the effect seems to be inde­pendent of the image-evoking qualities of the verbcomponent.

It could be argued that the differences in recognitionperformance are an artifact of the differences in thestudy trial durations; on average, the subjects processedthe sentences considerably longer on the image-relatedtasks than on the semantic tasks. However, this explana­tion does not account for the within-condition differ­ences in recognition accuracy. For example, it wouldpredict an imagery effect on performance that is in theopposite direction from the one found. The image­generation times for high-imagery sentences are signifi­cantly shorter than those for low-imagery sentences,but recognition accuracy is lower for the latter than forthe former, particularly on the semantic similaritycondition. The general findings seem to be consistentacross the three experiments, regardless of the encodingtasks employed.

The present results strongly suggest that the improvedperformance in the si.sr test condition for subjects inthe imagery-encoding conditions can be attributed to thegeneration of images as part of the processing requiredto differentiate the test sentences. This conclusion isconcordant with the results of Fisher and Craik (1977,1980), who showed that elaborate encodings producedby study tasks are effective in enhancing later recogni­tion only if the encoding environment is reinstated atthe time of retrieval. That is, the encodings produced bythe imagery tasks are effective in augmenting perfor­mance because imagery is also used in differentiating theSI-SI' test sentences. Moreover, using different encoding

IMAGERY EFFECTS IN SENTENCE RECOGNITION 639

and testing environments in a recognition memory task,Groninger and Groninger (1982) showed that similarimages of the same stimulus-item referent have to begenerated at encoding and retrieval for image congru­ence to enhance accuracy.

Kieras (1978) argued, rightly, that some form ofsemantic interpretation, however minimal, needs to beestablished before image processing can begin. Giventhat this is true, why should subjects evoke imagery todiscriminate the test sentences rather than continueprocessing them semantically? One simple reason mightbe that the high-imagery sentences evoke it. That is,imagery is the most readily available processing medium.However, this explanation is not supported by thepresent data. The first two experiments showed thatsubjects used imagery to differentiate test sentencescontaining verbs spanning a range of image-evokingvalues. The SI-SI' alternatives differ only in terms oftheir verb components, so it seems that subjects useimage processing regardless of the imageability of themajor elements to be discriminated. Only when the nounconcepts are difficult to image does the strategy breakdown. An alternative reason for using imagery mightbe that it provides the most direct access to informationthat can be used to differentiate the sentences. It may beeasier to elaborate the verb components through theuse of imagery than to expand their representationsthrough purely semantic processing. Taking this argu­ment further, it is possible that the semantic system doesnot contain the information necessary for maximizingthe discrimination of the sentences. This informationmay be represented only in perceptual codes accessedthrough imagery. This possibility is partially supportedby the work of Walter and Fox (1981). They arguedthat, in sentence memory, one of the primary objec­tives of semantic processing is to construct encodingconfigurations that provide easy access to perceptualinformation. Thus, it is possible that subjects useimagery to make available the perceptual informationthat maximizes the differentiation of the test sentenceencodings.

Finally, it seems, on first inspection, that the presentdata support Tulving's (1981) findings in that overallrecognition performance is highest in the S1-0 I' testcondition, next highest in Condition SI-S1', and worstin Condition SI-S2'. Thus, Tulving's results, which werebased on forced-choice tasks involving perceptualsimilarity, seem to generalize to tasks involving semanticsimilarity, and in particular to recognition memory forsentences. Unfortunately, the picture becomes cloudyonce you isolate the data for the different study-trialtasks. From the data in Table 5, for example, it is ap­parent that performance is equally poor on Condi­tions SI·S I' and SI·S2' for all study conditions andsentence types, except for high-imagery sentences in theimagery study condition. In this latter case, Condi­tions SI-S}' and SI-D l ' are indistinguishable in terms oflevel of accuracy. However, this parity in performanceis not particularly significant, because Sl-D l ' perfor-

mance is highly dependent on the nature of the dis­tractor sentences employed and their precise relation­ship to the target sentences. Tulving's results, then,hold only for the specific case of high-imagery sentencesunder imagery-encoding instructions. On the basis ofthe assumption that imagery involves perception-likeprocesses, a supposition for which there is considerableevidence (Finke, 1980), it might be concluded that thedifferences in recognition accuracy shown in the presentdata reflect the same set of processes that underlieTulving's original findings. This idea is consistent withTulving's conjecture that his reversal of the classicaltest-item similarity effect is possibly due to subjects'adopting the strategy of elaborative processing of theretrieval information in the S}·S}' condition. Thisspeculation leads one to conclude either that Tulving'sfindings hold only for perceptually related test itemsor that the degree of semantic similarity used in theSI-S I' condition is not comparable to the degree ofperceptual similarity used by Tulving. However, theboundary limits of these results require greater empiricalspecification before such speculations can be takenfurther.

REFERENCE NOTE

I. Anderson, J. R. Recognition confusionsin sentence memory.Unpublished manuscript, Stanford University, 1972.

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(Manuscript received December 10, 1982;revision accepted for publication July 29, 1983.)