The perception of clicks in linguistic and nonlinguistic messages!

ARTHUR S. REBER2 AND JOHN R. ANDERSON3UNIVERSITY OF BRITISH COLUMBIA

Three experiments were run analyzingSs' abilities to locate clicks in auditorymessages. In Expenment 1 it was foundthat the intonation pattern of the linguisticmessage largely determined the types oferrors Ss made in click placement;syntactic factors were only marginallyeffective and semantic factors wereeffectively irrelevant. In addition to theselinguistic factors, there was evidence thatsuch nonlinguistic factors as attention,memory, and response biases werecontributing to the data. Experiment 2supplied additional evidence favoring thesenonlinguistic factors. Experiment 3 was amock-up of Experiment 2 except thatbroad-band white noise was used as theprimary message instead of Englishsentences. The patterns ofplacement errorsSs made in these several experiments(especially Experiments 2 and 3) weresufficiently similar to one another to forcethe conclusion that nonlinguistic factorsare primarily responsible for the errors Ssmake in trying to locate clicks in messages.A neo-Titchenerian attention hypothesisbased upon the law of prior entry wasproposed to account for the data.

In a widely referenced article, Fodor andBever (1965) argued that constituentstructure "plays an important role indetermining the subjective location ofnoise perceived during speech." Asevidence to support this conclusion theycited certain characteristics of thedistribution of errors Ss made inattempting to locate the position of a shortclick sound occurring in sententialmaterial. Specifically, they found that theboundaries of constituents acted asperceptual as well as linguistic boundaries.Thus, they argued that it is reasonable toregard speech perception as an "active"process where the hearer segments theinput on the basis of an abstract syntacticanalysis based upon constituent structure.

We do not quarrel with thisinterpretation of speech perception for it issupported by a great deal of data collectedwith a wide variety of experimentalparadigms (cf. Neisser, 1967; Miller &Isard, 1963; Marks & Miller, 1964; amongothers). We do, however, question theirstatement that their data clearlysubstantiate it. There were a number ofprocedural problems with their experiment

and with their data analyses that maketheir interpretation suspect.

It seems premature to regard aconstituent structure analysis of agrammatical sentence as revealing thepsychological and linguistic segments bywhich the sentence is perceived. Clearly,the analysis of any linguistic input mustinvolve a complex set of operations. As abeginning, we feel that it is essential todistinguish between the linguistic and thenonlinguistic operations. By linguistic, werefer to operations based upon such factorsas intonation, syntax, and semantics. Bynonlinguistic, we refer to operations basedupon such factors as memory andattention. We do not feel that thisdichotomization is either inclusive orexhaustive. These two operative levelsundoubtedly interact, and probably insubtle ways, but we shall not discover theways unless we perform comprehensiveexperiments.

The experiments reported below wererun in an effort to separate empirically thelinguistic and nonlinguistic operations thatSs use in the perception of a short burst ofinterfering noise (clicks) in an auditorymessage. The first two studies represent aneffort to evaluate systematically the effectsof the linguistic factors of intonation,syntax, and semantics in determining Ss'perception of the interfering stimulus. Thethird study represents an effort to isolatethe role of nonlinguistic memory andattention processes as they operate withina similar setting.

The experimental procedure in all casesinvolved the perception of extraneousnoise superimposed upon an auditorymessage. We implicitly assume (with Fodorand Bever) that the pattern of errors thatSs make in attempting to locate theposition of the noise relative to theprimary message contains informationabout the manner in which the inputs arebeing processed.

EXPERIMENT 1The paradigm for this experiment was

adapted from that of Fodor and Bever(1965). Certain aspects of their study shallbe noted since they were modified forpresent purposes. First, Fodor and Beverused sentence length ranging from 8 to 22words. Although it is impressive that such aconsistent effect was obtained despite the

wide range, this variation makes itimpossible to manipulate sentencestructure in a systematic way. In thisexperiment, stimulus length was keptconstant. Second, Fodor and Bever hadtheir Ss write down the sentences prior tomarking the click position. A number oftranscription errors resulted and a portionof the data had to be discarded. Moreover,with this procedure, it is impossible tocontrol either (1) the interval betweenhearing the sentence and marking the clickposition or (2) the interval between hearingthe click and marking its position. It is, ofcourse, impossible to control both intervalssimultaneously if click position is to vary,but it is desirable to control one of them.In the present study, Ss were not requiredto transcribe the sentences, and thus it waspossible to control the interval betweenhearing the sentence and marking theperceived click position. Finally, in theFodor and Bever study, the primarymessage was presented to one ear throughone earphone and the click to the other earthrough another earphone. When thesentence was in the left ear, Ss tended tolocate the click to the right of (i.e., laterthan) its actual position, but with theheadphones reversed, they tended to locatethe click to the left. There is no reason toassume that either condition reflected thenormal processing of language. The resultsfrom the two conditions were pooled, butthe sum of two biased sets of data cannotbe regarded as unbiased. We presented thematerials over conventional speakers.

Fodor and Bever also had no notion ofthe underlying response distribution. It isentirely possible that when Ss do not knowthe actual location of a click they havenonuniform guessing probabilities.Ladefoged (1967) reported a tendency forSs to locate imperceptible clicks nearer themajor syntactic boundaries. His experimentwas a rather informal one but the resultswere clear enough for him to conclude," ... part of the responses recorded in oursand Fodor and Bever's experiments mayhave nothing to do with a subject'sperception from the point of view of theway he scans incoming auditory data."Therefore, we ran a control group where Ssresponded to "subliminal" but actuallynonexistent clicks. The distribution ofresponses made by these Ss was used as acheck on Ss' response biases.

Perception & Psychophysics, 1970, Vol. 8 (2) Copyright 1970. Psychonomic Journals. Inc .. Austin. Texas 81

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Fig. 1. Measures of accuracy: Proportionof errors (Pe) in Experiment 1 for (a) clickpositions, all conditions pooled,(b) intonation pattern by click positions,and (c) syntax by click positions.

dis-playo +1 +2

mar-kets-2 -I

Table 1

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illustrated in Table 1. The central word Resultsspace is referred to as Position O. Each A total of 10,080 responses were madespace or syllable is counted as one unit by the Ss in the experimental group. Of

. (negatively to the left of Position 0 and these, 4,223, or .419, were errors. Of thesepositively to the right). As illustrated, one error responses, 2,158, or .511, were errorsclick was placed over Position 0 and eight I to the right of the actual click position.others symmet~cally about this position", These two measures of the Ss' responses,On.e word strmg from each. subset. ~as the probability· of an error (Pe) and theassigned randomly to each click position. probability of an error to the right of theThe clicks were produced by intro.ducin~ a actual click position (Pe,r) made up the.05-msec burst of broad-band white noise primary tools for the analyses.and were set approximately equal to the Probability ofan error,Pe. This measuremost intense speech sounds. gives an assessment of the accuracy with

The procedure for generating word which Ss were able to locate clicks.strings yielded 72 stimulus items, each Figure 1 shows how accuracy in clickrepresenting a different independent location is dependent upon (a) position ofcombination of the click position,intonation, semantic, and syntactic factorlevels in a 9 by 2 by 2 by 2 factorial design.The assignment of particular word stringsto the intonation and click position factorlevels was determined randomly. Two suchrandomizations were carried out producing ~ .4

two separate assignments. Order of wordstrings within each assignment was alsorandomized. The two assignments wereread on to one track of a tape and theclicks were appropriately placed on thesecond track. The subliminal control Ssheard the same tape as the experimental Ssexcept that the channel containing theclicks was disconnected. The experimentalSs heard both assignments incounterbalanced order; the subliminal Ssheard only one assignment.

Procedure. Ss were tested in a quiet ~ .4

room free from distraction. All Ss heardthree practice word strings before theactual experiment began. Test bookletswere constructed that contained 72unmarked word strings printed in capitalletters without punctuation. Ss under boththe click and subliminal conditions turnedto the appropriate word string in theirbooklet only after they heard it. Theymarked the position of the click with anarrow and waited to hear the next wordstring. The subliminal Ss, of course, could ,not hear the clicks. They were told thatthere was a click, but that they would not"even be aware of hearing it" and that"experiments have shown that subjectsunder these conditions locate the clickswith better than chance accuracy." Theywere asked to mark the position theythought the "click most likely occurred."

Subjects. The Ss were 82 undergraduatesat the University of British Columbia.Seventy Ss were in the experimentalcondition and 12 were run under thesubliminal control condition.

MethodMaterials. This experiment

independently altered the intonational,syntactic, and semantic integrity ofsentences. The method of manipulating thesyntactic and semantic components is thatfirst used by Miller and Isard (1963).Intonational cues were varied by usingeither normal intonation or ,a pacedmonotone. This experimental design madeit possible to determine which aspects ofthe data could be attributed to the variouslinguistic components of the structure thatexist in speech.

The term "word string" refers to any ofthe six-word sequences used in thisexperiment. One set of 18 word stringswere English sentences with similargrammatical structure (two modifiers, aplural noun subject, a present-tensetransitive verb, a modifier, and a pluralnoun object). Each word contained twosyllables. From this set of sentences, 18additional word strings were constructedby taking the first word from one sentence,the second from another, and so on. Eachword kept the same ordinal position that ithad in the original sentence, but no wordstring contained more than one word fromthe same sentence. These word strings hadgrammatical structure but weresemantically anomalous. Two more sets of18 word strings were constructed byrandomizing the order of words within theword strings of the original two sets. Thus,syntactic structure was disruptedindependently of the semantic component.This process yielded four sets of 18 wordstrings, each set representing a combinationof a syntactic factor with two levels,grammatical (G) or random (R), and asemantic factor with two levels, sentence(S) or anomalous (A). An example of eachfollows:

Naughty raucous children disruptbirthday parties-grammatical, sentence(GS)

Parties raucous disrupt childrennaughty. birthday-random, sentence(RS)

Naughty soda autos suppress flowerailments-grammatical, anomalous (GA)

Ailments soda suppress autos naughtyflower-random, anomalous (RA)Each set of 18 was divided randomly

into two equal subsets. One subset wasread with normal intonation (N) (normalfor English sentences like the GS wordstrings), while the other received a pacedmonotone intonation (M). Thus, anintonational factor was combinedindependently with the other two factors.In duration, the N word strings were about3 sec and the M word strings about 5.5 sec.

The fmal factor, click position (C), hadnine levels. These nine click placements are

82 Perception & Psychophysics, 1970, Vol. 8 (2)

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Fig. 2. Measures of directional bias:Proportion of errors to the right of actualclick position (Pe,r) in Experiment 1 for(a) click positions, all conditions pooled,(b) intonation pattern by click position,and (c) syntax by click position.

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interest since the constituent structuremodel views the major syntactic break as"attracting" clicks from both sidessymmetrically.

There was also a tendency for thedirection of the error to shift over thecourse of the experiment. In the first blockof 12 trials, average Pe,r was only .38; itincreased to .40, .50, and .53 on successiveblocks of trials. The remaining trial blockswere fairly stable, with a mean of .53. Thisshift from a left- to a right-bias has beenfound in other studies (Ladefoged &Broadbent, 1960; Fodor & Bever, 1965).

(b) Intonation. This factor was highlysignificant, F(l ,9977) =80.4, p < .001, aswas the Intonation by Click Positioninteraction, F(8,9977) = 26.6, P < .001.The interaction shown in Fig. 2b revealsquite clearly that the sharp decrease inright-bias with late click position is due

the overall decrease in Pe with late clickpositions is still found after the correctionand is not due to response biases.

(b) Intonation. Analysis of varianceshowed a highly significant effect of thepattern of intonation, F( 1,9977) =400.8,P < .001. The normal intonation pattern(N) produced considerably more errorsthan the monotone (M), a result that wasnot unexpected since N items were onlyabout 3 sec in duration while M items wereabout 5.5 sec. The value of Pe was higherfor N items in all click positions exceptPosition O. Again, we conclude thatmemory factors plus a response bias areresponsible for these results.

(c) Syntax. The syntactic factor was alsosignificant, F(I,9977) =25.9, P < .001,although the effect was somewhat lessdramatic than those of click position andintonation. Figure lc shows the values ofPe for the grammatical items (G) and therandom word strings (R) for each clickposition. Overall, the G items producedfewer errors than did the R items. Thisresult is most surprising in light ofinterpretations of previous research.According to the linguistic decodinginterpretation, the most salient factorcontrolling the errors Ss make in locatingclicks is the syntactic structure of the ~.r

items. The fact that our Ss made fewer .4

errors when the items were grammaticalcalls this interpretation into question.Perhaps G items produce fewer errorsbecause they are easier to process and thusplace less stress on the Ss' memorycapacities.

Probability of an error to the right, p"'"This measure treats only trials on which Smade an error in the location of the click.The responses were scored on the basis ofthe direction of the error and are presentedas the proportion of total errors made tothe right (toward the end of the sentence)of the actual click position. Figure 2 showsthe relationship between Pe•r and (a) clickposition, (b) intonation, and (c) syntax.

(a) Click position. Note first that therewas a slight overall bias; .511 of the totalerrors were to the right, and five of thenine click positions displayed a right-bias.There was a highly significant shift from aright-bias for clicks occurring early in anitem to a left-bias for clicks toward theend, F(8,9977) =70.6, P < .001. Thus, Ssgenerally perceived clicks occurring at thebeginning of the items as occurring laterthan they actually did and clicks occurringtoward the end of items as occurring earlierthan they actually did. Further, thetendency to locate Position -I clicks tothe right is greater than the tendency tomove Position +I clicks to the left, andfully 65% of the errors in Position 0 are tothe right. This asymmetry is of particular

the click, (b) the intonation pattern of thestimulus item, and (c) the syntacticstructure of the stimulus item.

(a) Click position. There was a highlysignificant effect of click position on Pe,F(8,9977) =94.22, P < .001. The effectwas contained in an overall decrease in Pewith successive click positions and in theoverall low Pe found in Position O. Thelinear decrease in Pe with progress throughstimulus items was significant (p < .001)and is presumably due to a short-termmemory process. Those clicks occurring atthe end of an item have a small intervalbetween the S's hearing of the click and hismarking of his response and they have lessstimulus material intervening that could actas interference. Kaplan'[ has run a similarstudy but where the Ss made theirresponses as soon as they heard the clickrather than waiting until the end of theitem. This condition produced lower Pethan a control condition that wascomparable to our procedure.

The extremely low Pe found inPosition 0 may be due partly to thepresence of a pause in the acoustic stimulusat this point. A spectrographic analysis ofeach item used in the experiment revealeda number of drops in acoustic energy atPosition 0, particularly in normallyintonated items. Although such pauseswere found in other parts of items, theyoccurred with more regularity here. Theeffect of a pause, however, is notunambiguous. A pause could allow Ss tolocate clicks that actually occurredthere more accurately. but it could alsoproduce a disproportionately high guessingrate. That is, Ss would have more time tothink they heard the click there. Adisproportionately high number ofresponses in anyone position will producean artificially low Pe there.

The data from the subliminal controlgroup discussed below (see Fig. 3), do, infact, reveal a strong response bias favoringcentral positions, particularly Position O.To partially correct for the effect of thisresponse bias, we calculated a weighted Pe,denoted P'e.P'e is an average based uponthe number of errors per response ratherthan the number of errors per clickoccurrence. Thus, P'e is given by 1 minusthe ratio of the number of correctresponses in a particular position to thetotal number of responses made in thatposition. The average P'eS"for the positionleft-of-O, 0, and those right-of-Owere .509,.418, and 0405, respectively. Although thiscorrection is only an approximation,because we do not have a theoreticalunderlying response distribution, it doesseem fairly clear that Position 0 clicks arenot necessarily easier to detect than thoseoutside of Position O. Note, however, that

Perception & Psychophysics, 1970, Vol. 8 (2) 83

Table 2Proportion of Errors "Supporting" the Linguis­tic Decoding Hypothesis of Fodor and Bever

(1965). - indicates data averagedover that condition.

primarily to the intonation pattern. Linearregression analysis showed that normallyintonated items (N) produced a dramaticshift in directional bias (p < .001), whilethe monotone (M) items had comparativelylittle effect (p < .10). However, bothconditions show the right-bias atPosition O. Clearly one of the primaryfactors causing Ss to perceive early clicksdifferently than later ones is the intonationpattern of the item.

(c) Syntax. Analysis of variance failed toshow any overall effect of syntacticstructure on direction of error, F < 1.0.There was, however, a significant Syntaxby Click Position interaction,F(8,9977) =9.79, p<.OOl, which isshown in Fig. 2c. Grammatical (G) itemstended to contribute more to the shiftfrom a right- to a left-bias than random (R)ones. Again, Position 0 produced aright-bias in both cases.

In support of their linguistic decodinghypothesis, Fodor and Bever (1965)reported that 66% of the errors were eithertoward or into the major syntactic break.The last line of Table 2 shows that the datafrom this experiment, analyzed in thisfashion, reveal a similar proportion of .59.However, as the other cells in Table 2show, this "support" is quite complex.Note that the intonation factor was themost powerful in producing agreementwith the Fodor and Bever position. Withnormal intonation, 64.1% of the errors aretoward the major syntactic break, but withthe monotone intonation only 50.7%, or

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extremely important in interpreting thedata since estimates of accuracy anddirectional bias must always be made interms of the underlying responsedistribution.P

DiscussionIt seems fairly clear that constituent

structure is not playing the critical role inthe perception of clicks that has beenhypothesized for it. Of the linguisticfactors manipulated in this study,intonation is the most powerful in thecontrol it exerts over the pattems of errorsSs make. Syntax is important but itseffects are weak compared with intonation,and the semantic factor is of noconsequence. Further, the location of theclick in the word string produces large

• effects. At a later point, we shall presentwhat we feel is an acceptable compromiseinterpretation of these results.

Intially, however, there are certainprocedural issues that need to be clarified.One objection that may be made to thisstudy is that the experimental task was sooverwhelming that the Ss never were able

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roughly chance, were toward the majorbreak. In fact, the MGSitems that are bothmeaningful and grammatical produced only49.4% supportive errors. Further, thesyntax factor, which should be critical incontrolling the direction of errors, was lesseffective than intonation, with 63.5% forgrammatical items and 54.9% for randomitems. Note that this 54.9% occurs eventhough the major syntactic break does notexist in the nongrammatical R items.

The "subliminal" condition. Thesignifcant effects were those produced byclick position, x2 (16) =126.8, p < .001,and by the Click Position by Intonationinteraction, x2 (16) =45.6, P < .OOLFigure 3 gives the total number ofplacements in each position in the Nand Mintonation conditions. There is a strongcentral tendency in both conditions,although it is much more pronouncedunder N. The data are quite clear inshowing that the underlying distribution ofSs' responses is nonuniform with the centerof an item attracting a dominantproportion of the responses. As we arguelater, this nonuniform distribution is

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-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 5 7 8

POSITION OF PLACEMENT

84 Perception & Psychophysics, 1970, Vol. S (2)

Table 3

particular sentences used or to thefamiliarity factor. Thus, in all the analysesto follow, the Ss were treated as one groupof 40 Ss.

-7 -6 -5 -4 -3 -2 -1 0 _1 +2 -3 -4 -5 -6 -7

-7 -6 -5 --4 -3 -2 -1 0 _1 -2 -3 -4 -5 -6 _7Click Position

DiscussionTwo broad aspects of the data from

these two experiments are important. First,the fact that we consistently obtainedagreement with Fodor and Bever when weperformed data analyses similar to theirsargues that we have not distorted theparadigm by introducing our stringentexperimental controls. Second, the factthat deeper analyses of the data revealedunexpected results seriously challengestheir interpretation. The clear implicationis that the data from their study and others(Garrett, 1965; Garrett, Bever, & Fodor,1965; Bever, Lackner, & Stolz, 1969;Bever, Lackner, & Kirk, 1969) are in largepart determined by factors that have not

Fig. 4. (a] Pe and (b) Pe,r by clickposition for the sentences in Experiment 2.

The effect of click position on 'Pe,r isshown in Fig. 4b. The curve is similar inmost respects to the average curve fromExperiment 1 (Fig. 2a). The decrease inPe,r across click positions is evident andreliable (p < .001), and clicks in Positions-1, 0, and +1 show the same generalpattern. The tendency to move Position -1clicks to the right is greater than thetendency to move Position +1 clicks to theleft, and the majority of Position 0 errorsare to the right.

As before, an analysis of the error datasimply in terms of constituent structureshows agreement with the Fodor and Beverhypothesis, with .654 of the errors eithertoward or into the major syntactic break.This value agrees nicely with that for theNGS items in Experiment 1 and with thevalue Fodor and Bever report.

tas-ty pro-ducts+3 +4 +5 +6 +7

ResultsThe data again were analyzed according

to the two basic measures, probability ofan error (Pe) and probability of an error tothe right (Pe ,r)'

Probability of an error, Pe. The averagePe was .609, as compared with .419 fromthe previous experiment. This difference isprobably due to a number of factors: thelack of monotone intonation thatproduced a much lower error rate, theincreased number of click positions, andthe rather boring nature of the task, tomention but a few. In any event, theaspects of the data of most concern are thepattern and direction of the errors, not thenumber.

An analysis of variance showed twomajor effects, click position,F( 14,504) =8.35, p < .001, and trialblocks, F(Il,396) =2.12, p< .02. Thetrial-block effect is largely one of a slightbut significant increase (p < .01) in theaccuracy with which Ss can locate theclick. The click position factor (Fig. 4a)has, as before, a strong effect on Ss'accuracy. The drop in Pe with later clicks isnot so marked as it was in the previousstudy, although average Pe for the firstseven click positions is significantly higher(p < .01) than for the last seven (.661 and.593, respectively). Again, when Pe isweighted by the number of responses (P'e),the low error rate in Position 0 disappears.P'e for the positions left-of-O, 0, and thoseright-of-O were .482, .475, and .421,respectively. Thus, in general, these resultsare quite comparable with those obtainedin Experiment 1.

Probability of an error to the right, Pe.r.Analysis of variance showed the same twofactors to be significant with Pe,r as withPe: click position, F(14,504) =8.29,P < .001, and trial blocks,F(Il,396) =2.48, p < .01. The trial blockeffect, as in Experiment 1, is essentially ashift from an initial left-bias on early trialsto a right-bias on later trials. The overallbias in the experiment was to the left, withmean Pe.r of .482. This average bias is dueto a strong initial left-bias (Pe.r = .38, .39on the first two trial blocks) and anasymptotic Pe,r of approximately .5, avalue somewhat below that found inExperiment 1.

dis-playo +1 +2

O-pen road-side mar-kets-7 -6 -5 -4 -3 -2 -1

to concentrate upon the linguistic aspectsof the items. Since on at least one-half ofthe trials the items were not evengrammatical, it may be argued that Ssmerely "gave up" listening to them asEnglish sentences and, instead,concentrated on a more salient variablesuch as the intonation pattern. To try totake into account this objection, we ranthe following experiment.

EXPERIMENT 2In this study we tried to get a better

understanding of the patterns of responsesthat occur under the most normal ofconditions, NGS.

MethodTwo sets of normally intonated,

grammatical, semantically coherent,six-word sentences were made up. One setwas composed of the same four sentencesused repeatedly, in fixed order; the otherset used a total of 30 different sentences.We were also interested here in whether ornot the pattern of responses that Ss makewould be different when they were highlyfamiliar with and could predict the exactsentence they would hear on any giventrial.

Clicks were introduced in a much morecomprehensive manner in this experiment.All 15 positions from -7 to +7, includingword gaps, were used. See, for example,Table 3.

All 15 click positions were representedin four blocks of 15 trials each, with orderrandomized within each block. These fullsets of 60 sentences were rerun three times,yielding a total of 180 judgments for eachS, 12 judgments on each of the 15 clickpositions. As before, the stimuli werepresented over stereo speakers in a quietroom, with the sentences presented overone speaker and the click over the other.Click intensity was adjusted to equalapproximately that of the loudest part ofthe linguistic message.

There were 40 Ss; all were University ofBritish Columbia undergraduate volunteers.They were originally divided into twogroups of 20 Ss each. One group heard thesame four sentences repeated as a cycle atotal of 45 times, the other group heard acycle of 30 different sentences repeated 6times. Two master tapes were made, usingdifferent sentences in each case to protectagainst any possible effects of theparticular sentences used. No reliabledifferences were found either due to the

Perception & Psychophysics, 1970, Vol. 8 (2) 8S

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about half-way between that observed inthe two previous experiments. An analysisof variance revealed only one significantfactor, click position, F(I4,252) =1.82,P < .05. Figure Sa shows that Pe decreasessystematically with late click positions,with Position 0 showing the lowest errorrate. Since this study contains no sententialmaterial, it is now clear that Ss' responsebiases are the major factor contributing tothe low Pe at Position 0 and memory is themajor factor contributing to the reliablelinear decrease (p < .05) in Pe forlate-occurring clicks. When Pe is correctedfor total number of responses (P'e)' thevalues for clicks left-of-O, 0, and right-of-Oare .507, .527, and .472, respectively.

Probability of an error to the right, Pe,T'The average probability of an error to theright was .527. An analysis of varianceshowed that only click position had asignificant effect on the direction of anerror, F(14,252) =1.88, P < .05. As in theprevious studies, clicks occurring to the leftof center produced errors to the right andthose to the right generally produced errorsto the left. The cross-over point where theright-bias shifts to a left-bias is even a bitfurther to the right here than inExperiments I and 2.

The failure to find a trial block effect inthis study, F(1l,198) = .93, is intriguing.In both of our previous studies, as well asin the experiments reported by others(Ladefoged & Broadbent, 1960; Fodor &Bever, 1965), an initial left-bias was foundthat gradually gave way to a right-bias.Here, however, the very first block of trialsproduced a Pe,r of .501. This experiment

Results ~ 5 ------------------------------There was a total of 3,600 responses;

they were analyzed according to the sametwo measures, P, and Pe r:

Probability of an err~r, Pe. The averageprobability of an error was .521, a value

square-wave noise with a physical durationof .05 msec. Its intensity was set equal tothat of the noise bursts. A total of 15 clickpositions was used; they corresponded tothose used in Experiment 2, e.g., seeTable 4.

The clicks corresponding to those in theword gaps (-6, -3, 0, +3, +6) were placedin the center of the silent interval, clickscorresponding to those over the rustsyllable (-5, -2, +1, +4, +7) were placed90 msec from the beginning of the rise ofthe noise burst, those over the second (-7,-4, -1, +2, +5) were placed 90 msec fromthe end of the fall of the noise burst.

The placement of clicks was randomizedwithin blocks of 15 trials so that eachblock contained one representation ofeach. Two separate master tapes consistingof four of these randomized blocks weremade up. For each experimental session,one of the tapes was rerun three times sothat each 5 judged a total of 180 clickplacements. There was no differencebetween the two randomizations, andanalyses were carried out on a pooledsample.

As in the previous experiments, responsebooklets were prepared for Ss. Afterhearing a complete stimulus, S turned theblank divider page and indicated hisresponse by placing an arrow over theposition that he perceived the click. As inExperiment 2, Ss were instructed that allresponse alternatives, including thoseoutside the noise burst train, werepermissible. To eliminate any possibleambiguity about the placement of aparticular click, the response sheets werearranged as in Table 5. All stimulusmaterials were placed directly on the tapeelectronically. The experimental sessionswere conducted in a quiet room free fromdistraction. The tapes were played on astereo tape recorder with the noise bursttrain on one channel and the clicks on theother. The Ss were 20 undergraduates atthe University of British Columbia.

Table 4

MethodThe stimulus items were sequences of six

bursts of white noise (0- I 0,000 Hz, uniformdistribution). Each burst had a duration of370 rnsec, with a rise and fall time of10 msec. The interval between noise burstswas I 10 msec, Thus, a full stimulus itemhad a duration of 2.77 sec, a value thatapproximated the average duration of thenormally intonated, grammatical sentencesused in the previous studies.

The click again was a spot of broad-band

EXPERIMENT 3This final experiment was designed to be

a replication of Experiment 2 except thatin place of the six-word grammaticalsentence the stimulus items consisted ofwhite noise. This technique allows us todetermine the extent to which the datafrom the previous studies are independentof linguistic factors.

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been systematically analyzed.s-? Thefollowing effects from the two experimentswere all highly reliable and present aconsiderable interpretive challenge:(1) Certain click positions produced ahigher error rate than others, withlater-occurring clicks being easier to locate;(2) there was no evidence that clicksoccurring at the major syntactic break wereeasier to locate than clicks occurringelsewhere; (3) early trials revealed anoverall left-bias in click placement whichdisappeared on later trials; (4) clicksoccurring early in an item produced aright-bias in location, clicks occurringtoward the end of an item produced aleft-bias; and finally, (5) normal intonationproduced a different pattern of errors thandid monotone intonation.

We feel that the following tentativeconclusions are justified at this point:( 1) Of the various linguistic factorsevaluated, intonation is clearly the mostsignificant in terms of the control it exertsover Ss' response patterns, while syntax isrelatively unimportant and semantics isirrelevant. (2) Much of the data is probablydue to other nonlinguistic factors, such asattention, memory, and response biases.

The following study was designed to tryto evaluate the role of these nonlinguisticfactors.

Table S

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86 Perception & Psychophysics, 1970, Vol. 8 (2)

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Fig. 6. Full confusion matrices showing the distribution of responses made by all Ss to each click position in (a) Experiment I,all conditions pooled, (b) Experiment 3, and (c) Experiment 2 (solid lines) and the NGS items from Experiment I (dotted lines).

differs from the others primarily in thatthe stimuli were nonlinguistic. If, as weshall argue below, the directional bias is aresult of Ss' attentional processes, thenclearly the noise bursts are attended to, atleast initially, in a different manner thansentential material.

Once more, there is superficial evidencethat Ssare misperceiving clicks so that theyappear to be "attracted" by Position O.Ofall the errors in the experiment, 56.7% ofthem were toward Position O. However, inthis experiment there is no syntacticboundary that can be attracting the clicks.

GENERAL DISCUSSIONThe data from these three studies are

more striking for the similarities amongthem than for the differences betweenthem. The same general pattern of errorswas found regardless of whether thestimulus items were English sentences orbursts of white noise. These similarities aremost easily seen by looking at the fullconfusion matrices in Figs. 6 and 7, whereall the data from each experiment ispresented in its most compact form. These

Perception & Psychophysics, 1970, Vol. 8 (2)

figures show the frequency distributions ofall responses made by all Ss to each of theclick positions. Figure 6 shows (1) thepooled confusion matrices from allconditions in Experiment 1, (2) thematrices from the noise burst study, and(3) the matrices from the six-wordsentences from Experiment 2 (solid lines)and the matrices from the NGS conditionfrom Experiment 1 (dotted lines). Notethat Click Positions -6, -5, -3, +3, +5, +6are not included in (2) and (3) so thatdirect comparisons with the data in (1) canbe carried out. Figure 7 shows the fullconfusion matrices from Experiments 2and 3, including the click positions omittedfrom Fig. 6.

Kolmogorov-Smirnov tests were run onall interexperiment comparisons withineach click position. There were nosignificant differences. Clearly, then, aninterpretation of the click migrationphenomenon must be based, in the finalanalysis, upon nonlinguistic factors.

Most of the data from these studies cannow be distilled down to threegeneralizations: (1) Clicks located early in

an item are perceived as occurring laterthan their actual placement; (2) clicksoccurring late in an item are perceived asoccurring earlier than their actualplacement; and (3) these two directionalbiases are not necessarily symmetricaround the central position.

We suggested briefly that nonlinguisticmechanisms, particularly those of attentionand memory, were important in theseexperiments. The following hypothesisrepresents a preliminary effort to formalizesome of these suggestions.

A Neo-Titchenerian HypothesisThree assumptions are needed: (1) The

perceptual process is fundamentally asingle-channel operation with only onechannel attended to at anyone time; (2) Sswill initially attend to the channelcontaining the most novel auditory input;and (3) inputs in the attended channel areperceived as occurring earlier in time than

'are contiguous inputs on the nonattendedchannel.

None of these assumptions is original.The first is merely a simplification of the

87

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primary axiom of Broadbent's (1958)theory of perception. The second issupported by the research of Berlyne(1950, 1957), Poulton (1965), and Cantorand Cantor (1966), among others, whohave shown that with rats, adults, andchildren the more novel stimulus isattended to sooner. The third is merely arestatement of Titchener's (1909) law ofprior entry.

The behavior of our Ss can thus becharacterized as follows:

(I) During the initial phases of theexperiments with sentential material, theclick constitutes a more unusual and novelacoustic stimulus than the linguistic input,and Ss will attend to the channelcontaining the click rather than to the onecontaining the human voice. Thus, initialtrials will display an overall left-bias. Onthe later, asymptotic trials, after Ss havefamiliarized themselves with the clicks,attention is distributed equally betweenthe two inputs, and the average bias iseffectively at a chance level. The failure to

Fig. 7. Full confusion matrices showingthe distribution of responses made by all Ssto each click position in the grammaticalsentences of Experiment 2 (dotted lines)and the noise bursts of Experiment 3 (solidlines).

for it. Second, as the item progresses itbecomes more and more determined andredundant and Ss can safely redirect theirattention. The fact that normal intonationproduced a very large shift in Pe,r withclick positions in Experiment I, ascompared with monotone intonation, isinteresting since normal intonationproduces very marked cues to the S,indicating progress through the item. Itmay be argued, then, that the primary roleof the linguistic factors is one ofcontrolling the manner in which Ss partialout their single perceptual channel. Note,for example, that the decrease in Pe,f inExperiment 2 was considerably moremarked than it was in Experiment 3. Whennoise bursts are the primary message thelinguistic redundancy is missing, andsomewhat more progress must be madethrough the item before Ss switch theirattention. Hence the cross-over from right­to left-bias in Experiment 3 doesn't occuruntil roughly Position +2.

From the foregoing, it appears that thisattentional interpretation can account for aconsiderable portion of the data withrelative ease. There are some problems andthey have implications for future research.First, all the verbal stimulus items used inthe experiments were symmetric with themajor syntactic boundary located in thecentral position. This fact is not criticalsince the data were asymmetrical, but it ispossible that varying the position of themajor boundary might affect Ss'attentional priorities.

Second, there is no provision in theneo-Titchenerian hypothesis for thedifferential error rates found at thedifferent click positions. It is probably thecase that low Peat Position 0 is due to aresponse bias and that low Peat late clickposition is due to memory factors.Nevertheless, it would be desirable todevelop a technique for eliminating Ss'response biases so that error rates can beexplored unambiguously.

Third, the monotone intonation patternin Experiment I produced data that wouldagree only weakly with this interpretation.An M intonation pattern, however, yieldsitems that are approximately 5~ sec induration while all others averaged onlyabout 3 sec. We do not know what theeffects on attention might be of differentitem durations.

Fourth, it is quite possible that a varietyof basic psychophysical mechanisms are

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find an initial left-bias in Experiment 3when noise bursts were used as the primarymessage is therefore to be expected, sinceboth inputs were initially novel acousticstimuli for the Ss.

(2) At asymptote, during the initialportion of an individual item, Ss attend tothe primary message. Clicks occurring herewill be in the nonattended channel andthey will be perceived as occurring later intime-a right-bias. It seems reasonable toassume that the channel containing theverbal material has higher attentionalpriority with experienced Ss simplybecause it is the first sound they hear whena trial begins.

(3) Toward the end of an item Ss shifttheir attention to the click channel, andclicks occurring here are perceived as beingplaced earlier relative to the primarymessage-a left-bias.

There are at least two reasons for Ss toshift their attention toward the end ofitems. First, since the click has notoccurred yet they "expect" it and listen

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88 Perception & Psychophysics, 1970, Vol. 8 (2)

operating in these experiments. Forexample, Ss may be locating click positionsby estimating the time between theoccurrence of the click and one of theanchor points-the beginning and end of anitem. There is evidence that under suchconditions (M. Humphreys'[) Ss tend todisplay asymmetrical estimates.

In summary, it seems safe to concludethat the interpretations of the clickmigration phenomena based upon linguisticdecoding operations are anoversimplification. We do not wish toimply that such factors as constituentstructure are not relevant in speechperception, merely that the patterns oferrors that Ss make in attempting to locateclicks in linguistic messages should not beregarded as unambiguous support for theuse of these units.

REFERENCESBERLYNE, D. E. Novelty and curiosity as

determinants of exploratory behavior. BritishJournal of Psychology, 1950,41,68-80.

BERL YNE, D. E. Attention to change. BritishJournal of Psychology, 1951,42,269-278.

BEVER, T. G., LACKNER, J. R., & KIRK, R.The underlying structures of sentences are theprimary units of immediate speech processing.Perception & Psychophysics, 1969, 5,225·233.

BEVER, T. G., LACKNER, J. R., & STOLZ, W.Transitional probability is not a generalmechanism for the segmentation of speech.Journal of Experimental Psychology, 1969,79, 387-394.

BROADBENT, D. E. Perception andcommunication. London: Pergamon Press.1958.

CANTOR, G. N., & CANTOR, J. H.Discrimination reaction time in children asrelated to amount of stimulus familiarization.Journal of Experimental Child Psychology,1966,4, 150-157.

Perception & Psychophysics, 1970, Vol. 8 (2)

FELOMAR, A. The perception of clicksembedded in sentences: Encoding ordecoding? Unpublished Master's thesis,University of Western Ontario, 1969.

FODOR, J. A., & BEVER, T. G. Thepsychological reality of linguistic segments.Journal of Verbal Learning & Verbal Behavior,1965,4,414-420.

GAR R ETT , M. Syntactic structures andjudgements of auditory events. Unpublisheddoctoral dissertation, University of Illinois,1965.

GARRETT, M., BEVER, T. G., & FODOR, J. A.The active use of grammar in speechperception. Perception & Psychophysics, 1966,1,30-32.

LAOEFOGED, P. Three areas of experimentalphonetics. London: Oxford University Press,1967. Chap. 3.

LADEFOGED, P., & BROADBENT, D. E.Perception of sequence in auditory events.Qu arterly Journal of ExperimentalPsychology, 1960, 12, 162-170.

MARKS, L. E., & ~ILLER, G. A. The role ofsemantic and syntactic constraints in thememorization of English sentences. Journal ofVerbal Learning & Verbal Behavior, 1964. 3,1-5.

MILLER, G. A., & ISARD, S. Some perceptualconsequences of linguistic rules. Journal ofVerbal Learning & Verbal Behavior, 1963, 2,217-228.

NEISSER, U. Cognitive psychology. New York:Appleton-Cc-ttury-Crof'ts, 1967.

POULTON, E. C. Listening to overlapping calls,Journal of Experimental Psychology, 1956,52, 334-339.

TITCHENER, E. B. Lectures on the psychologyof the thought processes. New York:Macmillan, 1909. NOTES

1. Supported in part by a grant from theUniversity of British Columbia Committee onResearch. Experiment 1 is based upon theHonours Thesis of 1. R. Anderson.

2. Address: Department of Psychology,University of British Columbia, Vancouver, B.C.,Canada.

3. Now at Stanford University.4. X. X. Kaplan, personal communication.5. This notion of the Ss' response bias, while

critical for interpreting click location data, isitself a particularly difficult one to understand.The subliminal control showed clearly that Sstended to think they heard clicks in the centerposition more frequently than in any otherposition. This tendency could be "perceptual" orit could be due simply to a nonuniformconfidence component. That is, for some reason,Ss may be reluctant to select a position outsideof Position 0 unless they are quite confident thatthey are correct, Thus the Position 0 data may bedistorted by a high false-alarm rate.Unfortunately, we did not collect confidenceratings from our Ss and cannot test thisinterpretation directly.

6. It should be pointed out here that there areat least two methodological problems in theBever, Lackner, and Stolz study. First, there wasno control of the syllabic structure of the wordsover which the clicks were placed. It is not clearthat errors in locating a click over the words"musician" and "eat" represent the same process.If clicks were centrally placed, the former is anerror of three positions and the latter an error ofonly one position. Second, there was no controlof the placement of clicks relative to the centerof sentences. The average click, in fact, was .33words to the left of center, a position that weargue should produce a marked right-bias.However, all the experimental effects that Beveret al report involved a tendency to locate clicksto the right of the actual position. In view of ourresults it is not clear that this effect can beunambiguously interpreted. A controlexperiment involving a replication with clickpositions balanced around the center is called for.

7. It is not clear from the results of the Bever,Lackner, and Kirk study whether the differentdistributions of errors in the various linguisticconditions are due to a perceptual process underthe control of underlying structural factors ormerely due to different response biases. A recentstudy by Feldmar (1969) showed that the Ss'response biases shift with shifts in syntacticstru cture. The subliminal control is absolu telycritical in studies of this nature and without itmeaningful conclusions cannot be drawn.

8. M. Humphreys, personal communication.

(Accepted for publication October 27, 1969.)

89