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Auditorymemoryandtheirrelevantsoundeffect:Furtherevidenceforchanging-statedisruption

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DOI:10.1080/09658210143000335·Source:PubMed

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Auditory memory and the irrelevant sound effect: Further

evidence for changing-state disruption

Tom Campbell, C. Philip Beaman, and Dianne C. Berry

University of Reading, UK

Four experiments investigate the hypothesis that irrelevant sound interferes with serial recall of auditory

items in the same fashion as with visually presented items. In Experiment 1 an acoustically changing

sequence of 30 irrelevant utterances was more disruptive than 30 repetitions of the same utterance (thechanging-state effect; Jones, Madden, & Miles, 1992) whether the to-be-remembered items were visually

or auditorily presented. Experiment 2 showed that two different utterances spoken once (a heterogeneous

compound suffix; LeCompte & Watkins, 1995) produced less disruption to serial recall than 15 repetitionsof the same sequence. Disruption thus depends on the number of sounds in the irrelevant sequence. In

Experiments 3a and 3b the number of different sounds, the ‘‘token-set’’ size (Tremblay & Jones, 1998), in

an irrelevant sequence also influenced the magnitude of disruption in both irrelevant sound and com-pound suffix conditions. The results support the view that the disruption of memory for auditory items,

like memory for visually presented items, is dependent on the number of different irrelevant sounds

presented and the size of the set from which these sounds are taken. Theoretical implications are dis-cussed.

Irrelevant sounds played either during visualpresentation of to-be-recalled material or during apost-presentation retention interval disrupt sub-sequent serial recall of the to-be-recalled list.Irrelevant speech sounds have been shown todisrupt recall of lists of visually presented itemsacross the entire list, even when instructions stressthat the speech is to be ignored (e.g., Banbury &Berry, 1998; Beaman & Jones, 1998; Colle &Welsh, 1976; Jones & Macken, 1993; Neath, Sur-prenant, & LeCompte, 1998; Salame & Baddeley,1982, 1989). In addition to its practical relevanceto human factors research (Banbury & Berry,1997, 1998; Banbury & Jones, 1998), the ‘‘irrele-vant sound effect’’ (Beaman & Jones, 1997) hasalso provided a probe into how pre-attentiveperceptual, attentional, and memory mechanismsinteract to support cognitive performance.

An influential account of the irrelevant soundeffect has been advanced within Baddeley’s (1986)working memory (WM) model. This accountstates that only speech-like irrelevant sound dis-rupts phonological storage in immediate memory(Salame & Baddeley, 1989). A problem for thisview, however, is the finding that a changingsequence of non-speech tones, which arguablysounded nothing like speech, significantly dis-rupted serial recall (Jones & Macken, 1993).However, a single, repeated speech item does notnecessarily produce a significant disruptive effect(Jones & Macken, 1993; Jones et al., 1992; but seealso LeCompte, 1995). Speech is thus neithernecessary nor sufficient to disrupt recall, a pointemphasised by Beaman and Jones (1997).According to the changing-state hypothesis (Joneset al., 1992) the critical factor is whether or not the

MEMORY, 2002, 10 (3), 199–214

# 2002 Psychology Press Ltdhttp://www.tandf.co.uk/journals/pp/09658211.html DOI:10.1080/09658210143000335

Requests for reprints should be sent to Philip Beaman, Department of Psychology, University of Reading, Earley Gate,

Whiteknights, Reading RG6 6AL, UK. Email: c.p.beaman@reading.ac.uk

Tom Campbell is now at the School of Psychology, University of Leeds. Thanks are due to Dylan Jones, Alastair Nicholls, and

Sebastien Tremblay for productive discussions. Nigel Holt deserves particular gratitude for his assistance with headphone calibration.

Tom Campbell received support for his work from the UK’s Engineering and Physical Science Research Council.

sound contains changing-state information. Fordisruption to occur, there must be segmentationbetween each physical unit within the soundstream, and each unit must be different from theone that preceded it. The sound must ‘‘change instate’’.1 The assumption is that changing soundscontain serial order cues that interfere withmemory processes which would otherwise main-tain to-be-recalled material in sequence. Studiesof the effects of irrelevant speech sound haveshown that disruption of serial recall of visualitems by changing-state speech is readily obser-vable (Jones, 1994; Jones et al., 1992). Unchan-ging, ‘‘steady-state’’ speech in which a single wordor utterance is repeated produced only a small andnon-significant disruptive effect in these studies.When this small steady-state disruption hasreached significance then changing speech soundaccrues additional disruption over steady-statematerial (LeCompte, 1995; Tremblay & Jones,1998).

The changing-state hypothesis constitutes acore assumption of the Object-Oriented EpisodicRecord (O-OER) model of short-term memory(Jones, 1993; Jones, Beaman, & Macken, 1996).Two seriation processes are assumed to operate inimmediate memory: The first, deliberate, serialrehearsal process retains attended items in thecorrect order. The second, pre-attentive, seriationprocess retains the order of the auditory itemswhen there is a mismatch between successiveitems. A separate assumption of the O-OERmodel is termed ‘‘the unitary hypothesis’’. Simplyput, this states that these two processes of seria-tion operate on a common unitary resource—an‘‘episodic surface’’—that stores the order of pre-sentation of both irrelevant and attended itemsregardless of the modality of presentation. Accessto this resource for visual material is dependent ondeliberate rehearsal. Auditory material is regis-tered on this surface automatically. This unitaryhypothesis is shared with Baddeley’s WM model(Baddeley, 1986) which also assumes a common(phonological) level of representation for visual-verbal and auditory-verbal stimuli with automaticrepresentation of auditory-verbal stimuli and

subvocal recoding of visual-verbal stimuli. Thelocus of irrelevant sound disruption differsbetween the two models, however. In the WMmodel there is assumed to be confusion betweentwo sets of phonological representations regis-tered in a common phonological store. In the O-OER model conflict of the two seriation processeson the episodic surface permits irrelevant auditorymaterial to disrupt the order in which the attendedvisual items are rehearsed and, eventually,recalled.

One further model that addresses irrelevantsound effects is the feature model (FM) of Neath(2000). Currently, although a large number ofmathematical/computational models of immedi-ate memory exist, only the FM directly addressesthe irrelevant sound effect (although others claimto be capable of simulating the effect in princi-ple—see Burgess & Hitch, 1999; Norris, Page, &Baddeley, 1995). Neath’s (2000) FM is an exten-sion of Nairne’s original (1990) feature model (seealso Neath & Nairne, 1995). Within this modelirrelevant sound reduces levels of attention whenencoding items and this reduction is greater withchanging-state irrelevant sound than with steady-state irrelevant sound. If the irrelevant sound isspeech then there is an additional effect. Speech isincorporated into the modality-independent(presumably phonological) features of the verbalto-be-recalled material at encoding, rendering allthe list items more similar to one another and thusincreasing the risk of recalling the items in thewrong serial order (Neath, 2000; for commentariessee Baddeley, 2000; Jones & Tremblay, 2000).

These models are based on data from numer-ous studies examining the effects of changing-stateirrelevant sound on visually presented to-be-recalled material, whether orthographic (Jones &Macken, 1993; LeCompte, 1995), lip-read (Jones,1994), or visuo-spatial (Jones, Farrand, Stuart, &Morris, 1995). Fewer studies have examined theeffects of irrelevant sounds when the to-be-recal-led and irrelevant material are both presented inthe same modality, presumably because extanttheories are concerned with interference at anamodal level. This scarcity of studies is surprisingas one would expect a same-modality interferenceeffect to be well-documented, as for example withthe stimulus suffix effect. Same-modality inter-ference is often assumed in dual-task situations(e.g., Wickens, 1992) so one might actually expectto see a larger irrelevant sound effect with audi-tory presentation of to-be-recalled material thanwith visual presentation. In fact, those few studies

1 As pointed out by an anonymous reviewer, no indepen-

dent index of changing-state exists and with speech stimuli

there are rapid spectral and intensity changes within each unit.

However, following Jones, Macken, and Murray (1993) we

suppose that for our stimuli to qualify as changing-state the

units within a sequence must be physically segmented by

pauses in presentation.

200 CAMPBELL, BEAMAN, BERRY

that have examined the irrelevant sound effectwithin the auditory modality have presented theto-be-recalled and irrelevant material con-currently (Hanley & Broadbent, 1987; Surpre-nant, LeCompte, & Neath, 2000; Surprenant,Neath, & LeCompte, 1999). Concurrent pre-sentation unfortunately leaves upon the possibi-lity that the effects observed were eitherperceptual/discrimination or encoding difficultiesrather than memory effects per se. For example,Martin-Loeches, Schweinberger, and Sommer(1997) found that with acoustic materials recordedat a sampling rate of 20 KHz, dichotic presenta-tion of the to-be-recalled and irrelevant materialrendered the to-be-recalled information un-identifiable when presentation was synchronous.

Hanley and Broadbent (1987, Exp. 2) wentsome way to addressing this concern by ensuringthat perceptual identification of the to-be-recalleditems under conditions of irrelevant sound wasnear perfect before administering the memorytest. However it is at least plausible that underconditions of existing memory-load, whereinattention is directed at maintaining those itemsalready encoded, the attentional capacity foraccurate registration of new items will be reduced(e.g., Lavie, 2000). Thus, the existence of an irre-levant sound effect within the auditory modalitytaking the same form as in the visual modality isopen to some doubt. It remains questionablewhether the effect is of the same magnitude andobeys the same laws as the more familiar irrele-vant sound effect within the visual modality.

Two studies have looked directly at whether achanging-state effect occurs with concurrent pre-sentation of to-be-recalled and irrelevant auditorymaterial. Experiment 3 of LeCompte (1996)directly examined irrelevant sound effects in thevisual and auditory modalities and found no dif-ferences between the two in the appearance of theeffect. However, LeCompte also reportedequivalent disruptive effects of steady-state andchanging-state material with auditory presenta-tion (overall proportion correct in both cases was.54 compared with the control level performanceof .60 correct). With visual presentation, however,the standard changing-state effect occurred andchanging-state irrelevant material proved moredisruptive than steady-state irrelevant material. Incontrast, a study by Hamilton and Hockey (1974,Exp. 2) provides some support for a changing-state disruption of memory for auditory items.When auditory to-be-recalled digits were inter-leaved with a changing-state sequence of irrele-

vant letters, a larger disruption was found thanwhen the interleaved irrelevant material was arepeated irrelevant letter. However, in Hamiltonand Hockey’s interleaved presentation procedurethe closer temporal proximity of the to-be-recal-led items to the irrelevant items also resulted instronger disruption of performance (Hamilton &Hockey, 1974, Exp. 3) and use of interleaved digitsproduced greater disruption of recall of to-be-recalled digits (Hamilton & Hockey, 1974, Exp.2). Both of these findings are contrary to resultsobtained from related investigations of the irre-levant sound effect (Buchner, Irmen, & Erdfelder,1996; Macken, Mosdell, & Jones, 1999). Arguably,the findings of Hamilton and Hockey’s study, orthat of LeCompte (1996), which also used inter-leaved presentation of irrelevant and to-be-recal-led material, could have arisen from a perceptualmasking phenomenon or a disruption of encoding,rather than of memory. Similar criticisms of otherstudies hold, as the precautions taken by Hanleyand Broadbent (1987) in their study (outlinedearlier) were not carried out. For example, per-ceptual disruption might also have occurred in thestudies of Surprenant et al. (1999, 2000) becauseirrelevant and to-be-recalled items were pre-sented to the same ear with no overt control oversynchrony of presentation.

Thus, although an irrelevant sound effect withauditory presentation of to-be-recalled items iswell established (Hamilton & Hockey, 1974;Hanley & Broadbent, 1987; LeCompte, 1996;Surprenant et al., 1999, 2000) there is little evi-dence that the effect is a memory phenomenon.There is even less evidence to decide whether theeffect is of the same type as that viewed with visualpresentation. If the two effects are indeed thesame, one might expect the predictions of thechanging-state hypothesis to hold, suggestinggreater disruption will be observed with changing-than steady-state irrelevant sound. Arguably, theWM model might predict the same result, as(presumably) the greater the number of differentitems entering the phonological store, the greaterthe potential for disruption. The FM, however,contains no obvious mechanism whereby post-listirrelevant material might interfere with repre-sentations in memory in this way. In the modeleither interference occurs at an amodal level ofrepresentation during encoding (Neath, 2000) or itoccurs through overwriting of the immediatelypreceding item at both modality-specific andamodal levels of representation (Nairne, 1990).Thus, the FM can account for effects of irrelevant

AUDITORY CHANGING-STATE EFFECTS 201

sound at encoding (concurrent effects) but cannotaccount for effects of irrelevant sound in memory(retrospective effects; Miles, Jones, & Madden,1991; Norris, Page, & Baddeley, 2001) beyond theoperation of a single item stimulus suffix.

Although the evidence so far suggests a retro-spective changing-state disruption of memory forauditory items, it is not conclusive. If no suchchanging-state effect is observed with auditorypresentation of to-be-recalled items then the uni-tary assumption of the O-OER model, and pos-sibly also the WM model, is seriously challenged.Experiment 1 provides a test of the unitary andchanging-state hypotheses in a comparison of therelative disruptive effects of changing-state andsteady-state irrelevant sound in both sensorymodalities. The remaining experiments will thenconsider whether disruption by irrelevant materialto recall of auditorily presented material is medi-ated by the number of utterances presented. Theeffects of the absolute number of irrelevantutterances presented will be tested (Experiment2) and the number of different irrelevant utter-ances presented under conditions where theabsolute number of irrelevant utterances is low(Experiment 3a) and high (Experiment 3b) willalso be examined.

EXPERIMENT 1

In Experiment 1, participants were given twodifferent serial recall tasks. On one task, partici-pants heard a list of items, and on the other theysaw a list of items presented silently on a computerscreen. The irrelevant sequence that followed waseither a steady-state sequence—a repeated sylla-ble—or a changing-sequence sequence whereeach utterance differed from that which precededit. The unitary hypothesis of both the WM and O-OER models predicts that the same pattern ofdisruption would occur, regardless of the modalityof the to-be-remembered items. The changing-style hypothesis also predicts that this pattern ofdisruption would show a greater disruption with achanging-state than with a steady-state irrelevantsequence.

Method

Participants . A total of 24 students and stafffrom Reading University participated in exchangefor course credit or a small honorarium. Allreported intact hearing and normal or corrected to

normal vision. All had English as their firstlanguage.

Materials and design. A 3 (irrelevant speech:quiet, steady-state , changing-state) 6 9 (serialpositions) 6 2 (modality: auditory, visual) repe-ated-measures design was used, with ‘‘errorprobability’’ as the dependent measure. In thequiet control condition, serial recall was per-formed under conditions of 52 dB (+ .5 SPL) ofequipment hum, measured in situ, prior toattenuation by the cup of the headphone.

Each list of to-be-recalled material comprisedthe digits 1–9 chosen randomly and withoutreplacement. Easy-to-remember sequences wereremoved. There were 30 trials in each modality,presentation of which was blocked and counter-balanced. On visual trials, digits were presentedin the centre of the screen. All visual materialswere presented in white Times New Roman 72-point font on a black background. Each digit waspresented for 800 ms with an inter-item intervalof 200 ms when the screen was black. On auditorytrials, presentation was synchronised with thepresentation of a fixation cross (+) in the centreof the screen. Each heard digit lasted 500 ms fol-lowed by an inter-item silence of 500 ms ensuringthat the total presentation time was equivalentacross the two modalities. To-be-recalled audi-tory digits were spoken in a female voice, to-be-ignored irrelevant items were spoken in a malevoice. All speech sound was recorded digitally to16-bit resolution, with a sampling rate of 44 kHz,using Goldwave 3.03 software. Use of VisualBasic 4.0 with Mabry Software Hi-Time andWave Custom Controls upon a Pentium II pro-cessor gave millisecond accuracy in timing.Auditory material was presented as a sound levelof 70 dB (+ 0.5) SPL as calibrated with a 1 KHzpure tone, measured with KEMAR (Knowleselectroacoustic mannequin for acousticalresearch) and a Bruel and Kjœr type 2425 micro-volt meter. All sound was presented via C110-headphones.

Before each list a row of five dots appeared,equidistant from one another, displaced just tothe right of the centre of a VDU screen. Thesedots disappeared one-by-one, from left to right,at a rate of one dot per second. A warningtone, 3 seconds before the list, accompaniedthe disappearance of the third dot during thisvisual ‘‘countdown’’. The screen was blank for1 second following the disappearance of thelast dot. A list of nine digits followed, pre-

202 CAMPBELL, BEAMAN, BERRY

sented one at a time. A 15-second retentioninterval followed list presentation, during whichthe word ‘‘WAIT’’ appeared in the centre ofthe screen. The first irrelevant sound coincidedwith the start of the retention interval, cued bythe appearance of the word ‘‘WAIT’’, the dis-appearance of which coincided with the offsetof the final irrelevant sound, and 500 ms ofsilence followed this retention interval, whenthe screen was blank. The word ‘‘RECALL’’appeared for 10 seconds, followed by the count-down that preceded the next list.

The order of irrelevant speech conditions wasrandomised such that there were 10 lists followedby each irrelevant speech condition in each block.For changing-state trials, the changing sequenceconsisted of 30 sounds drawn randomly from theletters ‘‘B’’(bee), ‘‘I’’(eye), ‘‘J’’(jay), ‘‘N’’(enn),and ‘‘Z’’(zed), with the constraint that each letterappeared at least once. Steady-state speech con-sisted of 30 repetitions of the same letter. Thesteady-state letter used was randomly chosen,such that each letter was used twice on each block.Each irrelevant letter lasted 300 ms followed by aninter-item silence of 50 ms.

Procedure. Participants were tested in groupsof up to five at a time. Participants were asked toattend to the digits and then silently rehearse themwhile the word ‘‘WAIT’’ was visible. They wereasked to ignore any sound they might hear whilethe word ‘‘WAIT’’ was present on the screen.When the word ‘‘RECALL’’ appeared they wereasked to write down the digits presented in astrictly left to right fashion, without correction,while attempting to preserve the correct serialorder and position of those items, leaving a ‘‘I’’when uncertain about an item. Participants initi-ated the first trial on each block with the click of amouse; subsequent lists were then presented atregular intervals.

Results

The pattern of mean errors was consistent with thechanging-style hypothesis. Whether the to-be-remembered items were either heard or visuallypresented, a changing-state pattern of disruptionoccurred, as illustrated in the right hand panels ofFigure 1. A three-way repeated-measures analysisof variance (ANOVA) revealed this irrelevantsound effect to be significant: F(2, 46) = 32.33,

MSE = 0.08, p < .001. The irrelevant sound effectdid not interact significantly with the presentationmodality of the to-be-recalled items, F(2, 46) =0.24, MSE = 0.04, p = .79 consistent with thehypothesis that there is no overall modality dif-ference in the way irrelevant speech disrupts serialrecall.

Analysis of error probabilities produced theexpected changing-state effect. Steady-state irre-levant speech was significantly disruptive relativeto quiet, F(1, 46) = 12.73, p < .05, while the chan-ging-state disruptive advantage over steady-statematerial was also significant: F(1, 46) = 4.20, p <.05. The evidence thus stands as support for thechanging-state and unitary hypotheses. Overall,changing-state irrelevant speech produced a sig-nificantly greater disruption than steady-stateirrelevant speech. Although the main effect ofpresentation modality was not significant, F(1, 23)= 23.75, MSE = 0.11, p = .07, serial positioneffects were significant, F(8, 184) = 61.32, MSE =0.09, p < .001, as was the modality by serial posi-tion interaction F(8, 184) = 16.59, MSE = 0.03, p

< .001. The irrelevant sound effect also interactedsignificantly with serial position, F(16, 272) =1.99, MSE = 0.02, p = .005, with larger irrelevantsound effects apparent towards the end of the list.Importantly, the three-way interaction betweenpresentation modality, irrelevant speech condi-tion, and serial position was unreliable, F(16, 368)= 1.45, MSE = 0.01, p = .12. It thus appears thatthe modality differences in the shape of the serialposition curve operated in relative independenceto the irrelevant sound effect. In other words, thefinal-item advantage for auditory presentationremained despite the presence of speech in aretention interval that might be expected toeliminate that advantage by acting as a post-listsuffix (Crowder & Morton, 1969). This is con-sistent with data recently reported by Surprenantet al. (2000). A separate modality by irrelevantspeech condition repeated-measures ANOVA oferror probability data from the final serial posi-tion corroborated this interpretation. There was asignificant modality-specific recency effect suchthat performance was more accurate on the finalserial position with auditory than with visualitems, F(1, 23) = 25.48, MSE = 0.09, p < .001.However, this modality effect did not interactsignificantly with irrelevant speech condition,F(2, 46) = 1.13, MSE = 0.02, p = .34. Thus,regardless of the modality of presentation of theto-be-recalled material, disruption was greatestwith changing-state irrelevant material.

AUDITORY CHANGING-STATE EFFECTS 203

Discussion

The results demonstrate a changing-state disrup-tion of memory for both visually and auditorilypresented lists. This changing-state disruptionshowed no overall modality differences betweenauditory and visual presentation, consistent withunitary and changing-state hypotheses. Arguably,common mechanisms were responsible for thechanging-state disruption of memory for visually

and auditorily presented items. Some differencebetween the current experiment and that ofLeCompte (1996, Exp. 3) must, however, havebeen pivotal to the demonstration of a changing-state disruption that did not occur in LeCompte’sstudy. The most obvious methodological differ-ence in this and later experiments is that theirrelevant material was presented after rather thanduring the presentation of the to-be-recalleditems. There may be some form of disruption that

Figure 1. Experiment 1: Error-position functions (left-hand panels) and overall mean error probabilities collapsed across serial

positions (right-hand panels) for each irrelevant speech condition when the to-be-remembered items were auditorily (upper panels)

or visually presented (lower panels). Error bars represent standard error.

204 CAMPBELL, BEAMAN, BERRY

occurred at encoding in LeCompte’s auditory taskthat obscured changing-state disruption of mem-ory. One candidate form of encoding interferenceis the effort of keeping the irrelevant separatefrom the relevant items.

Whatever the underlying reason for the pastfailure to observe a changing-state effect,Experiment 1 firmly establishes for the first timethe importance of change in the irrelevant soundstream as a primary determinant of disruptionacross both visual and auditory modalities, a pre-diction derived from theories of the irrelevantsound effect. This is contrary to the more usualassumption of within-modality interference (e.g.,Nairne, 1990; Wickens, 1992). A more commonlyemployed heuristic is that interference occursprimarily within sensory modalities. If the degreeof overlap between irrelevant and to-be-recalledmaterial were important, for example, one mightexpect a greater irrelevant sound effect withauditory than with visual presentations, as theirrelevant sound would interfere with modality-specific features of the attended material as wellas modality-independent features. However,Experiment 1 failed to show any interactionbetween irrelevant sound and modality of pre-sentation supporting the assumption latterly—andcounterintuitively—made, that irrelevant speechdisrupts only modality-independent codes (Neath,2000).

It is possible, however, that a retrospectiveeffect of irrelevant sound might occur with audi-torily presented stimuli if the irrelevant sounditems are perceptually grouped with the to-be-recalled list. When an additional irrelevant itemdisrupts serial recall of the final item with audi-torily presented to-be-recalled items, that disrup-tion is termed a stimulus suffix effect (e.g.,Morton, Crowder, & Prussin, 1971). The disrup-tion is sometimes considered to result fromgrouping the suffix as part of an auditory-sensorycode that is peculiarly sensitive to end-of-listpositional codes (Frick, 1988). If the same suffix ispresented three times at the end of a list,attenuation of the disruption has been observed(Crowder, 1978; Morton, 1976). This attenuationhas been attributed to a tendency to group arepeated suffix away from the to-be-recalled list.In contrast, when a sequence of two differentsuffix items is appended to the list, it producesmore disruption than either a repeated suffix or asingle suffix (LeCompte & Watkins, 1995, Exps.1–4). This disruption has been termed a hetero-geneous compound suffix effect and it has been

argued that the heterogeneous compound suffixeffect cannot easily be accounted for by existing,modality-specific, explanations of the more tra-ditional single-suffix effect (see LeCompte &Watkins, 1995, for details).

In fact, there are ways in which accounts of thesingle-item suffix effect could be expanded toinclude the heterogeneous compound suffixeffect. For example, in the feature model recallproceeds by comparing the representations of thememory items to a search set and finding the bestmatch between a degraded memory representa-tion and a pool of possible responses (the listitems). The size of this search set is increased bythe inclusion of the suffix (cf., Beaman & Morton,2000) producing an effect akin to an increase inlist-length. One could therefore account for theheterogeneous compound suffix effect by sup-posing that both suffixes were added to the pool ofpossible responses. However, the heterogeneouscompound suffix effect also bears a strongresemblance to the changing-state effect descri-bed in Experiment 1. The compound suffix effectmay then alternatively be viewed as an instance ofthe more general rules governing disruption byirrelevant sound.

One major difference between the changing-state effect observed in Experiment 1 with audi-torily presented to-be-recalled material and theheterogeneous compound suffix effect reportedby LeCompte and Watkins (1995) is in the numberof times each irrelevant utterance was presented.This is a condition referred to by Bridges andJones (1996) as ‘‘word-dose’’. It is, arguably, themost important difference between the two stu-dies. In LeCompte and Watkins’ study, the dosewas extremely low, comprising only two separateutterances, compared to the dosage used byBridges and Jones. If the heterogeneous com-pound suffix effect is a special case of the chan-ging-state effect comprising extremely low word-dosage, then increasing the dose should increasethe disruptive effect, mirroring the resultsobtained by Bridges and Jones using visual pre-sentation of the to-be-recalled lists. If, however,the heterogenous compound suffix effect is bestaccounted for by assuming that both suffixes areadded to the pool of possible responses, thenincreasing the dose should have no effect, as byincreasing the dose no new irrelevant items areactually added to the pool of possible responses.As the increase in dose comprises only repetitionsof earlier instances, the extra items added to thesearch set are identical to existing members of the

AUDITORY CHANGING-STATE EFFECTS 205

search set. Consequently, the likelihood of erro-neous match is not increased. In this manner theFM could account for the observation that nofurther disruption is observed with homogenous(repeated) compound suffixes beyond thatobserved using a single item suffix (LeCompte &Watkins, 1995; Morton, 1976).

EXPERIMENT 2

Experiment 2 examines whether increasing thedose of the irrelevant sound does further disruptserial recall of auditory lists in a manner analo-gous to that observed with visual lists (Bridges &Jones, 1996), or whether mere repetitions of thesame irrelevant items do not add any new infor-mation to the search set at recall and so do notfurther disrupt serial recall. In this experiment,trials designated as low-dose changing-state trialswere lists of to-be-remembered auditory items,followed by a heterogeneous compound suffix,irrelevant speech consisting of just two (different)utterances—a dose of two. On trials designated ashigh-dose changing-state trials, these same twoitems were repeated 15 times each—a dose of30—also following the presentation of the list. Theexpectation is that the compound suffix effectreported by LeCompte and Watkins (1995) will bereplicated but that increasing the dosage willincrease the size of the effect in the same manneras occurs with irrelevant sound disruption of recallfor visually presented items. However, this resultwould be contrary to the assumption that a repe-ated suffix adds no new information to a search setconsulted at recall.

Method

Participants . A total of 24 staff and studentsfrom Reading participated either for course creditor a small honorarium. All participants were agedbetween 17 and 45 and were selected by the samecriteria as in Experiment 1. None had participatedin other experiments of this series.

Materials and design. The memory task wasidentical to that used in Experiment 1, with theexception that there was just one block of 60auditory lists. There were 20 trials in each of threeconditions (quiet, low-dose changing-state, andhigh-dose changing-state) and presentation orderof these trials was randomised.

For each low-dose trial the changing sequenceof two different sounds (e.g., I, Z) followed the listwhen the word ‘‘WAIT’’ was presented on thescreen. The two sounds were drawn from the fiveletters used in Experiment 1. No irrelevant soundwas presented in the remainder of the retentioninterval. High-dose sequences consisted of 15repetitions of one ordered pairing of two differentitems (e.g., I, Z, I, Z, I, Z etc.). Onset and offset ofthe changing-state sequence coincided with that ofthe word ‘‘WAIT’’. On both high- and low-dosetrials, each of the possible ordered pairings—atotal of 20 orders of two different sounds that weredrawn from a set of five tokens—was used once.

Procedure. The procedure was identical toExperiment 1, with the exception that only anauditory block of trials was presented.

Results

The pattern of mean overall error probabilities wasconsistent with the assumption that the extent ofthe disruption produced by a changing sequencewas dose-dependent , as illustrated in the right handpanel of Figure 2 (Quiet: 0.47 < Low dose: 0.54 <High dose: 0.58). The overall disruption producedby irrelevant speech was found to be significant bya two-way repeated-measures ANOVA, F(2, 46) =26.56, MSE = 0.02, p < .001. Critical comparisonsrevealed that the disruption produced by a low-dose compound suffix relative to quiet was sig-nificant, F(1, 46) = 24.19, p < .05, and that themodest further disruption of high- over low-dosetrials was also significant, F(1, 46) = 4.84, p < .05.

Main effects of serial position were significant,F(8, 184) = 54.16, MSE = 0.05, p < .001, as was theinteraction between serial position and the com-pound suffix condition, F(16, 368) = 4.27, MSE =0.01, p < .001. These bowed error-position func-tions with marked recency characterise those ofserial recall for auditory material. The significantinteraction describes the numerically greatereffect sizes that occurred on the later serial posi-tions. This interaction is assumed to be a scalareffect whereby disruption was attenuated nearfloor on primacy positions (see Figure 2).

Discussion

The results from this experiment demonstrate thatincreasing the dose of a changing-state sequencefollowing auditory presentation of the to-be-

206 CAMPBELL, BEAMAN, BERRY

recalled items increased the level of disruptionobserved. It is thus possible that ‘‘compound suf-fix’’ effect is a misnomer. The existence of changein the suffix increases the magnitude of the dis-ruption caused by a suffix (LeCompte & Watkins,1995) but, in the same manner, change alsoincreases the disruption seen with auditory pre-sentation of the to-be-recalled list and post-listirrelevant sound (Experiment 1). Equally, thelarger the dose in the suffix, the larger the dis-ruption with both auditory presentation (Experi-ment 2) and visual presentation (Bridges & Jones,1996). Experiment 1 showed a changing-statedisruption that occurred in recall of both audito-rily and visually presented items. Experiment 2showed that this changing-state effect was dose-dependent. It was not simply the number of dif-ferent irrelevant items that determined the extentof disruption, the number of repetitions of theirrelevant speech also contributed to the effect.Consequently, any explanation of the retro-spective effect of irrelevant speech based on theaddition of the post-list irrelevant item to the poolsampled at recall (Nairne, 1990; see alsoLeCompte, 1996) seems untenable.

The results of the first two experiments seem toconfirm the notion that irrelevant sound actsequally on representations derived from auditoryor visual presentation, a finding consistent withthe unitary assumption of the O-OER and WMmodels. These findings are, however, inconsistentwith the idea that modality-dependent featuresnecessarily interfere with each other (e.g., Nairne,

1990) and further suggest that no specialmechanism is necessary to account for the com-pound suffix effect beyond those already postu-lated to account for the effects of irrelevant sound.Furthermore, the idea that retrospective irrele-vant sound disruption could occur within theauditory modality by adding the irrelevant itemsto the pool sampled at recall (Nairne, 1990) wastested. It is argued that the increase in disruptionas dose increases is predicted from past studies ofirrelevant sound effects with visual presentation(Bridges & Jones, 1996). If increasing the doseadds no new items to a pool sampled at recall butsimply repeats existing (irrelevant) items, onewould not expect to see an increase in disruption.A counter-argument is that even repetitions of thesame item might be added to the pool sampled atrecall. The probability of sampling a given itemfrom the search set as the recall response for anyone to-be-recalled item could then be calculatedas a combined function of all items within thesearch set, even those that are only repetitions ofearlier instances. However, such a counter-argu-ment is difficult to sustain in the face of empiricalevidence that a single irrelevant item repeated, ahomogenous compound suffix, usually results in areduction in disruption (Morton, 1976).

A less complex situation arises when one con-siders the addition of different items to the irre-levant sound stimuli. It is non-controversial thatthese different items will add to the search set ifthe heterogeneous compound suffix effect is to beexplained in the same manner as a single suffix

Figure 2. Experiment 2: Error-position functions (left-hand panel) and mean error probabilities collapsed across serial positions

(right-hand panel) for each irrelevant speech condition. Error bars represent standard error.

AUDITORY CHANGING-STATE EFFECTS 207

effect (LeCompte & Watkins, 1995). Similarly, ifone is to explain the compound suffix effect as anirrelevant sound phenonemon, then the changing-state hypothesis contains clear predictions that theaddition of different items (new changes) to theirrelevant sound stream will not further increasedisruption unless the total word dose also increa-ses (Tremblay & Jones, 1998). It is, therefore,worth examing the possibility that adding differ-ent irrelevant items to the end of the to-be-recal-led list would affect the extent of irrelevant sounddisruption.

EXPERIMENT 3A

The explanation of the compound suffix effectgiven by the FM suggests that more disruptionshould result if more different irrelevant items arepresent in the search set (see also LeCompte,1996). Increasing the utterances in the compoundsuffix from two to five should, therefore, increasethe disruptive effect of the suffix. In contrast, thechanging-state hypothesis of the O-OER modelpredicts that irrelevant sound disruption is causedby the number of changes, not by the nature of thechanges. Thus increasing the set of utterancesfrom which the irrelevant sound is drawn from one‘‘token’’ (steady-state irrelevant sound) to twotokens (changing-state irrelevant sound) shouldproduce an irrelevant sound effect, but beyondthis there should be no further increase in dis-ruption. A brief example may be of use. If com-pound suffix disruption is a result of grouping thecompound suffix with the to-be-recalled listincreasing the utterances in the compound suffixfrom two tokens (A-B) to five tokens (A-B-C-D-E) should increase the disruptive effect of thesuffix as the number of possibilities within thesearch set will increase accordingly. From thepoint of view of the changing-state hypothesis,however, introducing new types of change to anirrelevant sound stream should have little effect:the occurrence of change is sufficient. The numberof changes in the sequence A-B-A-B-A-B-A-B-A-B is identical to the number of changes in thesequence A-B-C-D-E-A-B-C-D-E (see Tremblay& Jones, 1998, for full details).

Experiment 3a compares the effects of tokenset size on disruption of serial recall. One-tokentrials consisted of lists of auditory items, followedby a single suffix item. On two-token trials, listswere instead followed by a sequence of two dif-ferent suffix items; on five-token trials by five

different suffix items. On each trial, there were norepeats of tokens within the irrelevant sequence.The predictions are clear-cut, if change within acompound suffix operates by the principlesdescribed by the changing-state hypothesis thereshould be a changing-state effect (significant dif-ferences between token set sizes 1 and 2) but nofurther increase in disruption. If the compoundsuffix effect operates by perceptual grouping, afurther increase in disruption from two to fivetokens is anticipated as the number of irrelevantutterances grouped with the to-be-recalled list,and thus entering the search set, increases.

Method

Participants. A total of 24 students and stafffrom Reading University participated either forcourse credit or a small honorarium. All partici-pants were aged between 18 and 45 and wereselected by the same criteria as in Experiment 1.None had participated in other experiments of thisseries.

Materials and design. The memory task wasidentical to that of Experiment 2. There were 20lists in each token set-size condition. Presentationorder of the lists was randomised. The five tokensused were identical to those used in Experiments1–2. For each 1-token suffix trial, a single soundfollowed the list when the word ‘‘WAIT’’ waspresented on the screen. There were four trialsfollowed by one of the five possible tokens. On 2-token trials, one of 20 possible orderings of twotokens, chosen randomly without replacement,followed the list instead. On 5-token trials, arandom ordering of the different five consonantsfollowed the list, with no repetitions of each ran-dom order on subsequent trials. On all trials, noirrelevant sound was presented during theremainder of the retention interval. Materials andapparatus were otherwise identical to that usedfor Experiment 2.

Procedure. The procedure was identical tothat used in Experiment 2.

Results

The pattern of overall error probabilities wasconsistent with the view that the more tokens inthe irrelevant speech, the more disruption occurs(1-token < 2-tokens < 5-tokens), as depicted in

208 CAMPBELL, BEAMAN, BERRY

Figure 3. However, this pattern in the means wasnot unequivocally supported by the statisticalanalyses.

Although a 3 6 9 repeated-measure s ANOVAof error probability data revealed a significantmain effect of token set size: F(2, 46) = 9.59, MSE

= 0.03, p < .001, critical planned comparisonsrevealed that two tokens (changing-state com-pound suffix) produced reliably greater disruptionthan one token (steady-state single suffix item),F(1, 46) = 7.00, p < .01, but five tokens (changing-state 5-token suffix) did not produce a sig-nificantly greater disruption than two tokens,F(1, 46) = 2.97, p > .05. The effect of serial positionwas significant, F(8, 184) = 68.22, MSE = 0.04, p <.001, but did not interact significantly with theeffect of set size, F(16, 368) = 1.15, MSE = 0.01, p =.308.

Discussion

The results from the overall pattern in the meansand that on the final item show that despitemodest numerical increments in disruption withenlargements of set size beyond two, only theincrease from one to two tokens proved statisti-cally reliable. At first blush it appears that thepredictions of the changing-state hypothesis weresupported—the fact that the irrelevant sound waschanging determined the extent of disruptionrather than the number of tokens. Overall, only

enlargements of set size from one to two produceda significant disruption. There are several causesfor concern however. In the first place, the sta-tistically unreliable increase in disruption beyondset size 2 mirrors similar statistically unreliableincreases in disruption beyond set size 2 reportedby Tremblay and Jones (1998), suggesting that alack of statistical power might be an issue in bothstudies. It is possible that the difference betweentwo- and five-token conditions missed statisticalsignificance because of low statistical power cou-pled with a comparatively small effect size. In thesecond place, the increase in token set size fromtwo to five items in Experiment 3a also entailed anincrease in word-dose from two to five. Arguably,the impact of this increase is negligible because, inExperiment 2, a 15-fold increase in dose (from 2 to30 items) produced only a further 3% increase indisruption. However this presumes that absolute,rather than proportional, differences in dose arethe critical feature of the word-dose effect. This isobviously an empirical question, but it is worthnoting that the difference in dose proportions inBridges and Jones (1996) Experiment 1 (low:high)was approximately 2:5, the same proportion asappeared in Experiment 3a, although the absolutedifferences varied considerably between the twostudies. Experiment 3b therefore replicatedExperiment 3a using a more powerful design andhigher word-dose but holding dose constantbetween the two token-set conditions (set sizes 1,2, and 5).

Figure 3. Experiment 3a: Error-position functions (left-hand panel) and mean error probabilities collapsed across serial positions

(right-hand panel) for each irrelevant speech condition. Error bars represent standard error.

AUDITORY CHANGING-STATE EFFECTS 209

EXPERIMENT 3B

The pattern of means from Experiment 3a indi-cated that the larger the set size, the larger thedisruption. The fact that the numerical disruptiveadvantage of five over two tokens was not sig-nificant may have reflected the fact that higherdoses were a pre-condition for this disruption tobe reliable. Experiment 3b tested out this possi-bility by using high dose sequences of one-token,two-tokens, and five-tokens.

Method

Participants . A total of 24 staff and studentsfrom Reading University participated either forcourse credit or a small honorarium. All partici-pants were aged between 18 and 45. None parti-cipated in other experiments of this series and allreported intact hearing and vision with English astheir first language.

Materials and design. The memory task wasidentical to that used in Experiments 2–3a. Thetokens were identical to those used in Experi-ments 1–2. For each 1-token trial, 30 repetitions ofa token followed the list, such that, for each of thefive tokens, four trials were followed by 30 repeatsof that token. With 2-token sequences, one of 20possible orderings of two tokens, chosen randomlywithout replacement, was repeated 15 times. On5-token trials, a random ordering of the five dif-

ferent consonants followed the list. This orderingwas repeated six times on each trial with norepetitions of that random ordering on subsequenttrials. Onset and offset of the changing-statesequence coincided with those of the word‘‘WAIT’’. The materials and apparatus wereotherwise the identical to that used for Experi-ment 2.

Procedure. The procedure was identical tothat used in Experiments 2 and 3a.

Results

The pattern of overall error probabilities wasconsistent with the view that the number of tokensdetermined the extent of disruption, as depicted inFigure 4. A two-way repeated-measures ANOVAof error probability data revealed a significantmain effect of token set size, F(2, 46) = 23.23, MSE

= 0.03, p < .001. Critical planned comparisonsrevealed that two tokens (changing-state) pro-duced a greater disruption than one token (steady-state), F(1, 46) = 14.44, p < .01, and five tokensalso produced a significantly greater disruptionthan two tokens, F(1, 46) = 9.01, p < .01. There wasalso a significant main effect of serial position,F(8, 184) = 53.24, MSE = 0.06, p < .0001, althoughthere was no significant interaction of this serialposition effect with token set size, F(16, 368) =1.25, MSE = 0.01, p = .23.

Figure 4. Experiment 3b: Error-position functions (left-hand panel) and mean error probabilities collapsed across serial positions

(right-hand panel) for each irrelevant speech condition. Error bars represent standard error.

210 CAMPBELL, BEAMAN, BERRY

Discussion

The results of this experiment show that thenumber of different tokens presented during aretention interval does influence the magnitude ofthe disruptive effect. A difference between onetoken and two tokens constitutes the well-documented changing-state effect, but Experi-ment 3b further demonstrates that, with auditorypresentation, an increase in the number of tokensbeyond this two-token changing-state effectincreases the irrelevant sound effect still further.This result confirms the trend towards a token setsize effect in Experiment 3a, a trend also apparentin the results of Tremblay and Jones (1998) usingvisual presentation of the to-be-recalled material.

Methodological differences between Tremblayand Jones’s (1998) series and the current experi-ments may account for the slightly different find-ings with regard to the set-size effect. Onepossibility is that the modality of presentation ofto-be-recalled material influenced the results.However, there was no difference between thechanging-state effects shown whether the to-be-remembered items were seen or heard (Experi-ment 1). This suggests that perhaps it may not bethe presentation modality of the to-be-remem-bered items that underpins differences in set sizeeffects. As here, Tremblay and Jones (1998) usedhigh doses of phonologically distinct tokens,although their dose was spread across presenta-tion and retention intervals. That this high dosewas here confined to the retention interval seemsan unlikely candidate explanation for the differentpattern of findings. Elsewhere, equivalent levelsof disruption have occurred when irrelevantspeech was confined to the presentation orretention interval (Beaman & Jones, 1998;Macken et al., 1999; Miles et al., 1991). Whetherthe dose was presented during presentation orretention should thus have been of no functionalsignificance.

It may be that the experimental design wasmore sensitive to the effects of set size. Manip-ulation of set size within-participant, here, ratherthan between-participants (Tremblay & Jones,1998, Experiment 3), prevented individual differ-ences in the susceptibility to disruption fromobscuring the set size effect (Ellermeier & Zim-mer, 1997). Most critically, fewer conditions wereused such that, on repeated-measures designs,observations for each set-size condition camefrom 20 trials rather than the 15 used by Tremblayand Jones (Experiments 1, 2, & 5). This increase in

sensitivity was required to expose a reliable dis-ruptive advantage of five over two tokens.

GENERAL DISCUSSION

The results of the present study show that chan-ging-state effects occurred on delayed recall ofauditorily presented material (Experiment 1), in afashion that increased with both higher doses(Experiment 2) and enlargements of token set size(Experiments 3a and 3b). These set size effectswere somewhat weaker at lower doses (Experi-ment 3a). The difference between two and fiveitems observable in Experiment 3b appeared onlyas a non-significant trend at low dosage eventhough dose was higher with five items than withtwo items (Experiment 3a), suggesting that per-haps absolute rather than proportional differencesin word-dose determine the appearance of thedose effect.

The heterogeneous compound suffix effectshown with low-dose sequences (LeCompte &Watkins, 1995) thus shared many properties withthe effects of irrelevant sound on visually pre-sented lists, in that, like the irrelevant soundeffect, it was influenced by both dose and set size(Bridges & Jones, 1996; Tremblay & Jones, 1998).The current series thus questions whether there isa distinction between the compound suffix effectand the irrelevant sound effect, and raises anumber of issues for current models of irrelevantsound interference in memory.

The first issue is how models should account forthe retrospective effects of irrelevant sound foundin Experiment 1. This is not a problem for eitherthe WM model or the O-OER model, both ofwhich predict that interference occurs in memoryafter the presentation of the to-be-recalled list.The O-OER model also specifically predicts thechanging-state effect observed in Experiment 1.However, models such as the FM which assumethat irrelevant sound captures attention atencoding do face difficulties in accounting forirrelevant sound effects that occur beyond thispoint. The second issue is how to account for theseparate effects of dose and token set size. Theeffect of dose found in Experiment 2, an effect ofrepeatedly presenting the same irrelevant sounditems, again does not seem very compatible withthe FM unless it is assumed that presenting thesame items will increase the number of distractoritems in the search set. However, if this assump-tion is made, then the decrease in disruption

AUDITORY CHANGING-STATE EFFECTS 211

observed with a repeated single-item suffix(Morton, 1976) becomes problematic for themodel. The effect of token set size, an effect ofincreasing the number of novel irrelevant sounditems presented, is less problematic for the FM butcreates difficulties for the O-OER model. The O-OER model assumes that the number of changesbetween different items, rather than the nature ofthe changes, is of importance and would thereforepredict that an ABCDEABCDE irrelevant soundsequence should be no more disruptive than anABABABABAB irrelevant sound sequence,contrary to the results of Experiments 3a and 3b.Any accounts of the dose and token set-sizeeffects derived from the WM model wouldnecessarily be post-hoc, as that model is not suf-ficiently explicit in its account of irrelevant soundeffects, or of auditory processing generally, toprovide specific predictions, although there seemsno a priori reason why the model could not beexpanded to account for the effects describedhere. However, difficulties in replicating thephonological similarity effect between irrelevantsound and the to-be-recalled material which formsthe basis of the WM account of the irrelevantsound effect must be borne in mind (Bridges &Jones, 1996; Jones & Macken, 1995; Larsen,Baddeley, & Andrade, 2000; LeCompte & Shaibe,1997; Tolan & Tehan, in press).

To summarise the findings in an atheoreticalmanner, Experiment 1 demonstrated a changing-state effect with auditory presentation of the to-be-recalled material when the irrelevant materialwas presented after the to-be-recalled material.This result confirms the earlier findings of irrele-vant speech effects when speech was presentedconcurrently with the to-be-recalled material(Hamilton & Hockey, 1974; Hanley & Broadbent,1987; LeCompte, 1996; Surprenant et al., 2000),and extends the findings to establish that the effectis reliably a memory effect and subject to theprinciples of changing-state. The result also con-firms the findings of LeCompte (1996) that noextra disruption is observed with presentation ofthe to-be-recalled and irrelevant material in thesame sensory modality, consistent also with Sur-prenant et al.’s (2000) conclusion that modality-specific single suffix effects and irrelevant soundeffects are independent phenomena. We canconclude that no additional disruption of encodingoccurs when irrelevant speech is presentedalongside auditory presentation of to-be-recalledmaterial. Experiment 2 demonstrates that retro-spective effects of irrelevant sound with auditory

presentation of to-be-recalled items are influ-enced by the word-dose employed even if no newirrelevant items are actually presented. Experi-ments 3a and 3b demonstrate a further significanteffect of adding new irrelevant items when dose isheld constant (Experiment 3b), contrary to thepredictions of the changing-state hypothesis(Tremblay & Jones, 1998).

Manuscript received 28 July 2000

Manuscript accepted 5 July 2001

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