Contextual effects in vowel perception II evidence for two processing mechanisms

Perception & Psychophysics 1980, Vol 27 (5), 421-434 Contextual effects in vowel perception II: Evidence for two processing mechanisms JAMES R SAWUSCH, HOWARD C NUSBAUM and EILEEN C SCHWAB State University of New York, Buffalo, New York 14226 Recent experiments have indicated that contrast effects can be obtained with vowels by anchoring a test series with one of the endpoint vowels These contextual effects cannot be attributed to feature detector fatigue or to the induction of an overt response bias In the present studies, anchored ABX discrimination functions and signal detection analyses of identification data Ibefore and after anchoring} for an [i]-[I] vowel series were used to demonstrate that [i] and [I] anchoring produce contrast effects by affecting different perceptual mechanisms The effects of [i] anchoring were to increase within-[’:] category sensitivity, while [I] anchoring shifted criterion placements When vowels were placed in CVC syllables to reduce available auditory memory, there was a significant decrease in the size of the [I]-anchor contrast effects The magnitude of the Ill-anchor effect was unaffected by the reduction in vowel information available in auditory memory These results suggest that [i] and [I] anchors affect mechanisms at different levels of processing The [i] anchoring results may reflect normalization processes in speech perception that operate at an early level of perceptual processing, while the [I] anchoring results represent changes in response criterion mediated by auditory memory for vowel information Previous research in speech perception has consistently revealed differences between the perception of stop-consonants and vowels In experiments on dichotic listening, stop-consonants consistently yield a right-ear advantage (Shankweiler & StuddertKennedy, 1967; Studdert-Kennedy & Shankweiler, 1970), while a right-ear advantage is not found for steady-state vowels under similar circumstances (Darwin, 1971 ; Haggard, 1971; Studdert-Kennedy & Shankweiler, 1970) Experiments on categorical perception also yield consistent differences between stop-consonants and vowels For the stop consonants, discrimination is typically categorical That is, the ability to determine whether two stimuli are different is limited by the ability to identify the same stimuli (Liberman, Harris, Hoffman, & Griffith, 1957; Pisoni, 1971, 1973) The discrimination of vowels, however, is typically much better than would be predicted from identification data (Pisoni, 1973, 1975; Fujisaki & Kawashima, Note 1, Note 2) Finally, stop-consonants tend to show little or no influence of contextual information on their identification (Eimas, This work was supported by NINCDS Grant NS-12179 to Indiana University (which supported development of the speech synthesizer used in Experiment 3), NIMH Grant MH31468-01 to SUNY/Buffalo, NSF Grant BNS7817068 to SUNY/Buffalo, and SUNY Research Foundation and University Awards grants The authors would like to thank Dr David B Pisoni for making the facilities of the Speech Perception Laboratory at Indiana University available for stimulus preparation and Jerry C Forshee for his assistance in constructing the tapes for Experiments and Reprint requests should be sent to the first author at the Department of Psychology, 4230 Ridge Lea Road, Buffalo, New York 14226 Copyright 1980 Psychonomic Society, Inc 1963; Fry, Abramson, Eimas, & Liberman, 1962; Simon & Studdert-Kennedy, 1978; Sawusch & Pisoni, Note 3), while vowels show large changes in identification as a function of context and surrounding vowels (Fry et al., 1962; Ladefoged & Broadbent, 1957; Repp, Healy, & Crowder, 1979; Sawusch & Nusbaum, 1979) The question of contextual influences in speech perception has been addressed by a number of procedures Eimas (1963), Fry et al (1962), and more recently, Repp et al (1979) have requested subjects to identify stimuli presented in a discrimination task format One general finding for all these experiments is that identification of any individual stimulus item tends to migrate toward categories other than those of the items it is presented with This contrastive effect is especially pronounced for ambiguous syllables (those near a phonetic category boundary) Furthermore, the contrastive effects in isolated, steady-state vowel identification are substantially larger than the effects found with stop-consonants (see Eimas, 1963) Using a similar procedure in which stimuli were presented in groups of four, Diehl, Elman, and McCusker (1978; Diehl, Lang, & Parker, in press) have also reported small contrastive changes in stop-consonant identification for near boundary stimuli A different procedure was employed by Ladefoged and Broadbent (1957; Broadbent & Loadefoged, 1960) in which an ambiguous word was placed at the end of a sentence The first formant frequencies of the carrier sentence were systematically varied The 421 0031-5117/80/050421-14501.65/0 422 SAWUSCH, NUSBAU~M, AND SCHWAB effect of the various carrier sentences on the ambiguous test items (which differed in their vowel) was one of contrast That is, with a carrier sentence that was synthesized with first-formant frequencies low in their range, a word that was ambiguous between "bit" and "bet" would be heard as "bet" (higher F1) With a high first-formant carrier sentence, the same word would be heard as "bit" (lower F1) A third procedure that has been used to investigate contextual influences in speech perception is anchoring (Sawusch & Nusbaum, 1979; Simon & StuddertKennedy, 1978; Sawusch & Pisoni, Note 3; Rosen, Note 4) In this procedure, subjects are presented with a set of stimuli to be identified under two conditions The first is an equiprobable control in which each stimulus occurs equally often In the second, anchor condition, one of the stimuli occurs more often than the other stimuli This procedure has been used to investigate the perception of brightness (Helson, 1964), dots varying in numerosity (Helson & Kozaki, 1968), heaviness of lifted weights (Parducci, 1963, 1965), and tones varying in frequency or intensity (Cuddy, Pinn, & Simons, 1973; Sawusch & Pisoni, Note 3), as well as vowels and stop-consonants In general, small contrast effects or no effects at all have been found for stop-consonants as a function of anchoring (Simon & Studdert-Kennedy, 1978; Sawusch & Pisoni, Note 3) However, large, consistent effects have been found in anchoring experiments with vowels (Sawusch & Nusbaum, 1979; Simon & Studdert-Kennedy, 1978; Sawusch & Pisoni, Note 3) A number of possible processing mechanisms have been considered in connection with these contrast effects with vowels Sawusch and Nusbaum grouped these into three classes: feature detector fatigue, changes in auditory ground (adaptation level), and changes in response bias The feature detector fatigue explanation seems to be implausible because the extra occurrences of a stimulus in the anchor condition are usually widely separated in time and are interspersed with presentations of other stimuli Thus, although virtually identical patterns of results are found for vowels with adaptation (Morse, Kass, & Turkienicz, 1976) and anchoring procedures (see Sawusch & Nusbaum, 1979), both results probably reflect processes other than feature detector fatigue The response bias explanation was explored in an experiment by Sawusch and Nusbaum (1979), who found identical contrast effects for subjects who were informed of the extra occurrences of the anchoring vowel and subjects who were not This would seem to eliminate any overt response bias explanation of the vowel anchoring results in which the subjects simply tried to use the available response categories equally often (cf Parducci, 1975) The third possibility concerns changes to an auditory ground (see Sawusch & Nusbaum, 1979; Simon & Studdert-Kennedy, 1978) The auditory ground represents a standard against which incoming stimuli are compared The composition of this auditory ground could include information from long-term memory about auditory characteristics, pattern.,;, or features for various items as well as information from auditory memory concerning the immediately preceding stimuli During baseline identification test.ing, no one stimulus would dominate the auditory ground, since each stimulus is equally likely How.ever, when in an anchoring procedure, one stimulus occurs more often than any of the other stimuli, it is more likely that auditory memory information about this stimulus will be available for comparison with subsequent stimuli Thus, the auditory ground is more likely to contain information about the anchoring stimulus than any other stimulus This will cause ambiguous stimuli to be mapped on to categories other than that of the anchoring stimulus The influence of the more frequently occurring stimulus could come about in one of two ways One possibility is that the presentation of any particular stimulus now has a higher probability of being preceded by the anchor stimulus If the subject retains some trace of the quality of the preceding stimulus and uses this in evaluating the current stimulus, the effect of anchoring would be to give the anchored stimulus the largest weight in this comparison The second possibility is that a cumulative adaptation level, as suggested by adaptation level theory (Helson, 1964), is the basis of vowel anchoring results Since the anchored vowel occurs more often than any other vowel, it would have a disproportionate weight in determining this adaptation level Recent results reported by Nusbaum and Sawusch (Note 5) support the adaptation level description In their experiment, a target vowel from the middle of an [i]-[II vowel series was preceded by either an [i] or an [I] endpoint vowel and the interval between the two vowels was varied At very short ISis, both endpoint vowels caused contrast effects in the identification of ambiguous test vowels However, this influence decreased substantially as ISI was increased to 500 msec Given that the ISI in previous anchoring studies was sec, the contrast effects found in vowel anchoring can not be adequately explained simply on the basis of auditory memory for the immediately preceding stimulus Rather, vowel anchoring seems to involve the buildup of information about the anchoring vowel, possibly in the form of an adaptation level If this adaptation level is, indeed, auditory in nature, it may be in a form similar to Massaro’s (1972) synthesized auditory memory The auditory ground explanation is consistent with the vowel anchoring results previously reported It is also consistent with the anchoring data for stop.consonants Since stops show less evidence of auditory memory than vowels (Pisoni, 1971, 1973; Fujisaki CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II 423 & Kawashima, Note 2), they should have a smaller at Buffalo All subjects were right-handed, native speakers of auditory memory component in determining their English with no reported histories of any speech or hearing disThe subjects were paid $3/h for their participation auditory ground This should lead to little or no orders Stimuli The stimuli consisted of a set of seven isolated, effect of anchoring upon stop-consonant identifica- steady-state vowels which ranged perceptually from [i] as in tion, which has, in general, been the case (see Simon beet to [I] as in bit These vowels were originally generated by & Studdert-Kennedy, 1978; Sawusch & Pisoni, Note 3, Pisoni (1971) using the vocal tract analogue synthesizer at the for review) The experiments described below were Research Laboratory of Electronics, Massachusetts Institute of All of the stimuli were 300 msec in duration and conconducted as a further test of the auditory ground Technology tained five formants These stimuli varied in their formant freand response bias explanations of anchoring effects quencies for their first three formants from 270 Hz (F1), 2,300 Hz with vowels (F2), and 3,019 Hz (F3) for the [i] end of the series to 374 Hz EXPERIMENT The first experiment was designed to test the effects of anchoring upon ABX discrimination of vowels Previous experiments that have investigated the relationship between isolated steady-state vowel identification and ABX discrimination have found that listener’s discrimination is not categorical (Pisoni, 1971, 1973, 1975; Fujisaki & Kawashima, Note 1, Note 2) Rather, the discrimination of vowels from within a phonetic category is typically well above chance Thus, listeners can discriminate vowels that are identified as belonging to the same category Pisoni (1973, 1975) and Fujisaki & Kawashima (Note 2) have attributed this within-category discrimination to the use of information in auditory memory about the three stimuli in an ABX triad Thus, to the extent that changes in auditory memory or other early perceptual processes underlie the contrast effects found with the anchoring procedure, we would expect systematic changes in ABX discrimination within a phonetic category as a function of anchoring That is, discrimination should change systematically at the anchored end of the vowel series On the other hand, if the contrast effects due to anchoring are a result of a criterion shift in the labeling (identification) process, then only betweencategory changes in discriminability would be expected as a function of anchoring The change in the phonetic category boundary caused by anchoring would lead to a shift in the peak of the ABX discrimination function (since discrimination across the category boundary seems to rely on identification labels in STM; see Pisoni, 1973, 1975; Repp et al., 1979; Fujisaki & Kawashima, Note 2) However, unless changes were found in identification within a phonetic category as a function of anchoring, no change in within-category discriminability would be expected That is, no changes in discriminability would be expected for the anchored end of the series Thus, the nature of changes in ABX discrimination as a function of anchoring will provide evidence of the relative involvement of early perceptual processes vs later criterion shifts in vowel contrast effects Method Subjects The subjects in this experiment were 12 undergraduate and graduate students at the State University of New York (F1), 2,070 Hz (F2), and 2,666 Hz (F3) for the [I] end of the series in six logarithmic steps A more complete description of these stimuli can be found in Pisoni (1971) These seven vowels were recorded on audiotape and then digitized using the PDP-11 computer in the Speech Perception Laboratory at Indiana University These stimuli were then reconverted to analogue form to make six test tapes Three of these tapes were identification tapes In the baseline identification tape, each of the seven stimuli occurred 10 times in random order In the [i]-anchor tape, Stimulus occurred 40 time and each of the other six stimuli occurred 10 times In the [l]-anchor tape, Stimuli through each occurred 10 times and Stimulus occurred 40 times In each of the anchor tapes, the order of stimuli was randomized, with the restriction that no single stimulus could occur more than three times in succession All three tapes were recorded with sec between stimuli The other three tapes were ABX discrimination tapes All discrimination tapes were composed of the six one-step ABX triads In any given triad, the first two stimuli (A and B) were adjacent stimuli from the series The third stimulus (X) was identical to either the first or the second stimulus For any given pair of stimuli, this allowed four distinct triads: ABA, ABB, BAA, and BAB Each of these four compositions for each of the six adjacent pairs occurred four times (96 total triads) in the baseline ABX tape In the [i]-anchor ABX tape, the Stimulus 1,2 triads (121, 122, 211, 212) each occurred 16 times and the other triads occurred times each In the [l]-anchor ABX tape, the Stimulus 6,7 triads occurred 16 times each and the other triads occurred four times In all three ABX tapes, the order of triads was random, with the restriction that no more than three triads from one particular stimulus pair could occur in succession In all tapes, there was sec between items within a triad and sec between triads Procedure The subjects were divided into two groups of six subjects each They were run in small groups of from two to four subjects each Each subject participated in two 1-h sessions on successive days The stimulus tapes were reproduced on a Revox A-700 tape deck and presented binaurally to subjects via Telephonics TDH-39 matched and calibrated headphones The intensity of the stimuli was set to 80 dB SPL for a steady-state calibration vowel ([i]) for all tapes Each group listened to the baseline identification and ABX tapes at the beginning of each session The subjects were informed that they would be listening to synthetic syllables that would sound like the vowels [i] and [I] They were asked to make two responses to each item on the identification tape First, they were requested to identify each vowel as either [i] or [I] Their second response was to be a rating indicating how sure they were that they had identified the stimulus correctly A 4-point scale was used, with a indicating that the subject was positive her (his) identification was correct, a indicating a probable correct, a indicating a possible correct, and a indicating a guess For the ABX tapes, the subjects were informed that they would be hearing groups of three stimuli In these groups, the first two stimuli would always be different while the third would be identical to either the first or the second They were to indicate whether the third item sounded most like the first stimulus or most like the second Following the control tapes, each of the two groups listened to a different set of anchor tapes The [i] group heard [i] identifi- 424 SAWUSCH, NUSBAUM, AND SCHWAB [i] Anchor [I] Anchor 7¸ STIMULUS VALUE Figure Rating functions for the control (solid circles) and anchor (open circles) conditions with data for the [i]-anchor group on the left and the [i]-anchor group on the right cation and [i] ABX anchor tapes, while the other group heard the corresponding [I]-anchor tapes The subjects were not given any new instructions regarding these tapes They used the same response procedures for the two types of anchor tapes that they had used for the baseline tapes By the end of the experiment, each subject had provided at least 20 identification responses to each stimulus under both baseline and anchoring conditions They had also provided at "least 32 discrimination responses to each pair of stimuli under each condition Results The identification and rating responses for the identification tapes were converted to an 8-point scale A rating of indicated an extremely confident [i] response, ratings of and indicated [i] and [I] guesses, while a rating of indicated a positive [I] response The results for the two groups are shown in Figure Both groups showed significant shifts in their category boundaries toward the category of the anchoring stimulus [t(5) = 3.80, p < 02, for the [i]anchor group and t(5) = 4.90, p < 01, for the [I]anchor group].’ These contrast effects are essentially identical to those previously reported by Sawusch and Nusbaum (1979) and Sawusch and Pisoni (Note 3) The ABX discrimination results are shown in Figure The category boundaries for the corresponding identification functions are shown by the arrows The peak in the [i]-anchor group discrimination function is shifted toward the [i] end of the series, relative to the baseline condition (Figure 2, left side) A corresponding shift in the [I]-anchor ABX peak was found for the [I] group (right side, Figure 2) Of the 12 subjects, 11 show this pattern of a shift in the discrimination function peak toward the anchored category (which is significant, p = 012, using a twotailed sign test) The one subject who did not show the expected shift was in the [I]-anchor group This subject showed no evidence of a discrimination peak shift In addition to a shift in peak discriminability, the [i]-anchor group showed a marked increase in the discriminability of the Stimulus 1,2 pair (the anchoring pair) Each of the six [i]-anchor-group subjects showed this increase in discriminability, which was significant [t(5) = 5.72, p < 01, for the 16.8°70 mean increase in discriminability] No comparable increase, in discriminability for the Stimulus 6,7 pair was found for the [I]-anchor group (Three subjects showed increases in discrimination and three showed decreases following the [I] anchor.) Discussion For the [I]-anchor group, no changes in within- category discriminability were found as a function of anchoring The discriminability of the Stimulus 6,7 pair showed no change due to anchoring Thus, for the [I] anchor, the contrast effects found could be due to criterion shifts Criterion shifts in the identification of stimuli would lead to a shift in the ABX discrimination peak if, as is usually assumed, implicit identification (categorization) underlies the between- category discrimination of subjects (see Pisoni, 1973; Repp et al., 1979; Fujisaki & Kawashima, Note 2) The criterion shift explanation of anchoring predicts no change in within-category ABX discrimination because no change in identification performance within either category was found The criterion shift explanation does not, however,, appear to be an adequate explanation of the [i] anchor results In the [i]-anchor group, a large increase in discriminability was found within the [i] category, for the anchored, Stimulus 1,2 pair This increase can not be accounted for by the small and inconsistent change in identification (rating) for Stimulus fol.lowing [i] anchoring (see Figure l, left side)? The [ill anchoring results seem to be due, in part, to a change ABX DISCRIMINATION [i] Anchor [I] Anchor 100 50 z w ~ Control o -0 Anchor w ~ 456 STIMULUS VALUE Figure Percent correct discrimination for the [i]-anchor group (left) and the [D-anchor group (right) Rating category boundaries (see text) are marked by arrows CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II in perceptual processing prior to identification of the stimulus Thus, these results indicate that two distinct types of processing changes may be involved in the contrast effects found with vowels The next experiment was conducted as a further test of whether [i] and [I] anchoring effects reflect the involvement of distinct perceptual processing mechanisms EXPERIMENT If two distinct processes are involved in anchoring effects with vowels, and one of these represents an early perceptual change while the other represents a higher level change, then we might expect them to show up as sensitivity changes and criterion shifts, respectively, in a signal detection analysis However, our previous experiments have collected far too few judgments per stimulus to allow the use of this type of data analysis The present experiment was designed to collect a sufficient number of subject responses to each stimulus for a signal detection analysis of individual subject data The variation of signal detection theory proposed by Durlach and Braida (1969; Braida & Durlach, 1972) will be used to evaluate the data If the within-category discriminability increase for [i] vowels that was found in Experiment reflects an early perceptual change, we would expect an increase in sensitivity for the Stimulus 1,2 pair as a result of [i] anchoring However, to the extent that anchoring induces changes at a later stage in perceptual processing, we would expect to find criterion shifts as a result of both [i] and [I] anchoring Method Subjects The subjects in this experiment were 14 undergraduates at the State University of New York at Buffalo who participated for course credit These subjects met the same requirements as those in Experiment Stimuli The same seven vowel series used in Experiment was also used here These stimuli were recorded to make two additional baseline, two [i]-anchor and two[l]-anchor tapes (yielding three tapes of each type) As before, all stimuli were recorded in random order, with no more than three occurrences of any stimulus in succession Procedure The experimental tapes were reproduced and presented to subjects in a manner similar to that of Experiment The subjects were divided into two groups of seven All seven subjects in a group were run simultaneously Each subject participated for a total of h spread over days In each session, the subjects listened to three presentations of baseline tapes (all using different stimulus orders on any given day) and then, after a short break, listened to three presentations of an anchoring tape (again, all different on any given day) One group listened to [i]-anchor tapes and the other listened to [I]-anchor tapes In addition, on Day 1, the subjects listened to the seven vowel stimuli in order and one extra presentation of a baseline tape for practice purposes The subjects were informed that the tapes contained random orders of seven different vowels varying from [i] to [11 The 425 subjects then listened to the seven stimuli, in order, from the [i] endpoint to the [I] endpoint They were asked to use a 7-point response scale and to attempt to uniquely identify each of the seven vowels A response of was to denote the [i] endpoint vowel, while a was to denote the [I] vowel The values in between were to identify the intermediate vowels Subjects then listened to the vowels in order a second time Following this, they used the seven responses to identify the stimuli from a baseline tape for practice The results of the practice tape were not included in the data analysis By the end of the experiment, each subject had provided at least 120 responses (4 sessions × tapes × 10 occurrences) to each of the seven stimuli in both baseline and one of the anchoring conditions, exclusive of the practice tape Results The data for of the 14 subjects were dropped from the experiment because these subjects did not use all seven responses One subject in the [i] group did not use Responses and and one subject in the [I] group did not use Response The average rating functions for the remaining six subjects in each group are shown in Figure In both groups, a significant shift in the category boundary toward the category of the anchor was found [t(5) = 4.71, p < 01, and t(5) = 5.21, p < 01, for the [i]and [I]-anchor groups, respectively) Each of the 12 subjects showed the expected shift in their category boundary The confusion matrices (seven stimuli by seven responses) for both baseline and anchored conditions for each subject were submitted to a signal detection analysis The version of signal detection analysis proposed by Durlach and Braida (1969; Braida & Durlach, 1972) was used The individual confusion matrices were converted to cumulative probability matrices with entries accumulated over responses for each stimulus These cumulative probabilities were converted to z scores, with the restriction that only probabilities between 008 and 992 were converted Cells with probabilities outside this range were considered indefinite and were not used [i] Anchor [I] Anchor Z6 4 67 12 STIMULUS VALUE 67 Figure Rating functions for the [i]-anchor (left) and [l]-anchor groups of Experiment in both control (solid circles) and anchored (open circles) conditions 426 SAWUSCH, NUSBAUM, AND SCHWAB tests showed that only the increase in d’ for the Stimulus 4,5 pair was significant (p < 05) Thus, 2,0’ the d’ results from the present experiment are generally consistent with the discriminability changes in Experiment Consistent d’ changes were found both within the [i] category, for the Stimulus 1,2 pair and across the category boundary for [i] anchoring, but little consistent change in d’ was found for I the [I]-anchor condition I Criterion cut points were determined for each II I response pair, based on the previously computed values for d’ Cumulative criterion placements were 0.0 calculated by determining the z score that corresponded to each criterion based on a cumulative 1,2 2,3 3,4 4,5 5,6 6,7 1,2 2,3 3.4 4,5 5,6 6,7 d’ scale The six cumulative criterion placements for STIMULUS PAIR the seven response categories for both baseline and Figure Paired d’ values for the [i]-anchor (left) and Ill[i] anchoring are shown on the left side of Figure anchor (right) groups in both control (solid circles) and anchored Although there does appear to be an overall shift (open circles) conditions in the criteria toward the [i] end of the series, this was not consistent across subjects Rather, four of subjects showed a shift in all of their criteria in determining either sensitivities (d’) or criterions the The d’ for each adjacent pair of stimuli was computedtoward the [i] end of the series, while two showed by taking the mean difference between z scores fora shift in all criteria toward the [I] end of the series the two stimuli over the seven response alternatives.Thus, the direction of criterion shift for two of the The paired d’ values for baseline and [i]-anchoredsubjects is opposite the shift in the category boundconditions are shown in Figure on the left Aary However, these two subjects also showed the number of aspects of the data should be noted smallest category boundary shifts due to [i] anchoring First, every subject showed an increase in d’ for theThus, the criterion shifts may account for part of Stimulus 1,2 pair and every subject showed a the category boundary shifts for the [i] anchor How.decrease in d’ for the Stimulus 4,5 pair Second,ever, all of the [i]-anchor shift for two of the subfor three of the subjects, the category boundary felljects was due to sensitivity changes, while at least between Stimuli and 5, while for the other threepart of the [i]-anchor effect for the other four subsubjects, the boundary fell between Stimuli and 4.jects was due to sensitivity changes The cumulative Each of the six subjects showed a decrease in d’ criteria for the baseline and [I]-anchored functions are shown on the right side of Figure Every one for the stimulus pair which spanned (one stimulus on either side of) the baseline category boundary The paired d’ values for the baseline and [I]-anchor [i] Anchor [I] Anchor conditions are shown in the right-hand side of Figure In contrast to the [i]-anchor results, there was no significant change in d’ for the stimulus pair spanning the baseline category boundary [t(5) = 1.64, p > 1] Separate two-way ANOVAs were used to evaluate the d’ results for [i] and [I] anchoring For the [i] anchoring condition, the main effect of stimuli was significant [F(5,25) = 7.50, p < 001], but the main effect of anchoring was not [F(1,5) = 32, p > 25] The interaction between anchoring and stimuli was significant [F(5,25) = 2.71, p < 05] Post hoc Newman-Keuls tests revealed that for the Stimulus 1,2 pair, anchoring caused a significant increase in d’, while for the Stimulus 4,5 pair, anchoring led to a significant decrease (both p < 05) 1,2 2,3 3,4 4,5 56 1,2 23 3,4 45 5,6 67 For the comparable [I]-anchor analysis, the main RESPONSE PAIR effect of stimuli was significant [F(5,25) = 6.01, p < 001], but the effect of anchoring was not [F(I,5) Figure Cumulative criterion cutpoints (in z units) for the [i]= 1.04, p > 25] The interaction was marginallyanchor (left) and [I]-anchor (fight) groups in both control (solid significant [F(5,25) = 2.42, 05 < p < 1] Post hoc circles) and anchored (open circles) conditions {i] Anchor [I] Anchor CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II [i] Anchor 1.0¸ 75 [I] Anchor 427 Anchor interaction was marginally significant [F(5,25) = 2.23, 05 < p < 1], and none of the stimulus pairs showed a significant change using post hoc tests No consistent differences were found in P(A) as a function of [I] anchoring Thus, the results for P(A) and d’ for the [I]-anchor subjects are virtually identical and show little or no influence of the [I] anchor on sensitivity measures Discussion The increases in sensitivity found with both P(A) 5O (area under the ROC curve) and d’ for stimuli within 1,2 2,3 3,4 4,5 5,6 6,7 1,2 2,3 :3,4 4,5 5,6 6,7 the [i] category following [i] anchoring mirror the STIMULUS PAIR increase in ABX discriminability for the [i] category Figure Paired values of the sensitivity index P(A) for the found in Experiment I The Stimulus 1,2 pair showed [i]-anchor (left) and [l]-anchor (right) groups in both control increases in discriminability in both experiments In (solid circles) and anchored (open circles) conditions addition, decreases in sensitivity were found for both measures at the category boundary after [i] anchoring of the six subjects exhibited a shift in all six of their When coupled with the inconsistent changes in criteria toward the [I] end of series as a result ofcriterion placement across subjects for the [i| anchor, [I1 anchoring these results indicate that the contrast effects found As a check on the validity of the d’ results, awith [i] anchoring on an [i]-[I] series are predomnonparametric measure of sensitivity was also com-inantly due to changes in sensitivity By comparison, puted for each pair of stimuli from the cumulative consistent changes in sensitivity were not found as probability matrix for each subject The area undera consequence of [I] anchoring Rather, systematic the ROC curve [P(A); see Green & Swets, 1974] shifts in criteria toward the [I] category would seem was computed as our alternative measure of paired to be responsible for the contrast effects found for sensitivity since it does not depend upon the equalan [I] anchor variance, normal distribution assumptions of the Although both Experiments and demonstrate Durlach and Braida (1969) model.3 The mean values that different processing changes underlie [i] and of P(A) (across subjects) for the baseline and [i]- [I] vowel anchoring, these experiments not isolate anchor conditions are shown in Figure (left side).the processing changes themselves However, since As with the d’ results, a significant decrease in sensi-one of the major differences between these vowel tivity was found for the stimulus pair spanning the stimuli (which show anchoring effects) and stop conbaseline category boundary for each subject It(5) = sonants (which not consistently show anchoring 4.92, p < 01] A similar P(A) analysis was done for effects) is the degree of available auditory memory the [I]-anchor subjects, and the mean results are (Pisoni, 1973; Fujisaki & Kawashima, Note 2), some shown in Figure on the right As with the para-form of auditory memory, as outlined earlier, may metric analysis, no significant change in sensitivity underlie part of the anchoring effects found with was found for the stimulus pair spanning the base-vowels Experiment was designed to investigate the line category boundary [t(5) = 1.23, p > 2] As role of auditory memory in anchoring with the d’ data, separate two-way ANOVAs were run on the P(A) data for the [i]- and [I]-anchor EXPERIMENT conditions For the [i]-anchor group, the main effect of stimuli was significant, while the effect of anchor- As noted earlier, Nusbaum and Sawusch (Note 5) ing was not [F(5,25) = 5.62, p < 01, and F(1,5) have provided evidence that if some form of audi= 33, p > 25, respectively] The Stimulus bytory memory is involved in vowel-anchoring effects, Anchoring interaction was significant [F(5,25) =it is not the auditory memory trace of only the 6.62, p < 001] and post hoc tests revealed that immediately preceding vowel This would seem to both the Stimulus 1,2 and Stimulus 2,3 pairs showedindicate that the auditory memory explored by significant increases in sensitivity as a result of Crowder (1971, 1973; Crowder & Morton, 1969), anchoring, while both the Stimulus 3,4 and Stimu-termed precategorical acoustic storage, or PAS, is lus 4,5 pairs showed significant decreases (all p 25, respectively] The Stimulus by in our vowel-anchoring results, it is probably not the 428 SAWUSCH, NUSBAUqVl, AND SCHWAB short-lived PAS However, there is evidence that A third possibility is that reducing the informasome form of precategorical information does persisttion available in auditory memory will have no at durations of sec or more Repp et al (1979) effect on the contrast effects caused by either (SiC found that even with a 2-sec interval filled with or CIC anchors This results is predicted by a model repetitions of an extraneous semivowel, AX vowelrecently proposed by Fujisaki and Shigeno (1979), discrimination was well above chance Thus, somein which auditory memory underlies assimilation vowel information does seem to persist in a formeffects (not contrast) in identification According to where it could influence the identification of a folthis model, contrast effects in identification are lowing vowel ’This vowel information may be mediated by categorical (phonetic) short-term memory, involved in our anchoring results The discriminwhile auditory memory underlies assimilation ability of vowels, using either an AX procedureeffects Thus, reducing the available auditory mem(Repp et al., 1979) or an ABX procedure (Pisoni, ory information should either increase the size of 1973, 1975) can thus serve as an index of the strength the contrast effects found as a function of vowel anchoring (due to a larger reliance on categor~cal of this memory trace in determining the role of auditory memory in vowel anchoring results STM) or leave these contrast effects unchanged The The vowel stimuli used in Experiments and arefollowing experiment, in which vowels were placed perceived more nearly continuously than categori-in CVC syllables to reduce the available auditory cally (see Pisoni, 1973) In the present experiment, memory for vowels, should allow us to discern the we embedded vowels in CVC contexts in an effort role of auditory memory in vowel anchoring to reduce the influence of auditory memory upon identification (see Stevens, 1968; Sachs, Note 6) To Method Subjects The subjects were 20 undergraduates at the State the extent that this is successful, ABX discrimination University of New York at Buffalo, who participated to fulfill results for the CVCs should be less continuous thana course requirement They met the same requirements as subjects the isolated vowel results of Pisoni (1973) and morein the previous experiments categorical The results of Experiments and Stimuli The stimuli consisted of two sets of seven CVC sylshowed that two distinct processes are involved inlables One set ranged perceptually from [sis] (as in cease) to [sis] (as in sister), while the other ranged from [bit] (beetj to vowel anchoring effects Reducing the information [blt[ (bit) In the [sVs] series, 250-msec steady-state vowels were in auditory memory could have its primary influence embedded between initial and final Is] fricatives The Is] fricaon the magnitude of either the [i]-anchor contrasttives were both 200 msec in duration and consisted of bandlimited noise between 3,400 and 5,000 Hz The seven syllables effects or the [I]-anchor effects varied only in the first three formants for the vowel The actual If auditory memory underlies the influence of the frequencies, bandwidths, and fundamental frequency [i] anchor and the [I] anchor induces changes at aformant were identical to those of the isolated vowels used in Experilater, response, stage, then reducing available auditoryments and (see also Pisoni, 1971) Thus, the [sis]-[slsl memory should also reduce the size of the contraststimuli represent the embedding of vowels similar to our original effects found for [i] In addition, we might alsoisolated vowels in an [sVs] context The [bit]-[blt] series varied both the initial consonantal transiexpect the size o.~ the [I]-induced contrast effects to tions and the formant frequencies for the vowel in equal decrease, since reducing available auditory memorylogarithmic steps All seven stimuli were 200 msec in duration renders perception more categorical (Pisoni, 1973, and consisted of an initial 30-msec consonantal transitional 1975) and previous results have shown that categori- followed by a 90-msec dynamic vowel During the vowel, the first three formants gradually changed from their values at the end cally perceived speech stimuli usually show smaller the consonant to "target" values The target values were contrast effects than noncategorically perceivedof attained 60 msec into the vowel and held for the last 30 msec stimuli (Eimas, 1963; Sawusch & Pisoni, Note 3).of the vowel The formant frequencies for the first three formants Thus, if the CVC series show less influence of audi-of the [bit] and [blt] endpoints at onset (0 msec); end of consonantal transitions (30 msec); and end of the vowel transit:ons tory memory in ABX discrimination and both the msec) are shown in Table The values between these p~3ints CiC and CIC anchor effects are drastically reduced (90 were determined by linear interpolation The first 35 msec of in magnitude, we will have evidence that some form each vowel contained vocalic excitation, while the last 55 nasec of auditory memory underlies the [i| (and [I]) vowelanchoring effects Table On the other hand, if auditory memory is not aFormant Frequency Values for the [bit] (Stimulus 1) and [bit] major factor in [i] anchoring, then a different pattern (Stimulus 7) Endpoints of the [bit] -[bit] Series at Onset (0 msec), 30 msec, and 90 msec of results would be expected According to this [bit] explanation, reducing the available auditory memory Time [bit] should reduce the contrast effects only for a CIC (msec) F1 F2 F3 F3 F1 F2 anchor (as outlined above) The effects of CiC 200 1600 2200 200 1400 2000 anchoring would be relatively unaffected by auditory 450 1900 2600 2200 2800 30 300 memory and should remain despite decreases in 120 2050 2800 3040 424 273 2450 available auditory memory CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II 429 [bit] [blt] 200 400 200 400 TIME (msec) Figure Sound spectrograms of the [bit] and [bit] endpoints of the [bit]-[blt] series used in Experiment were aspirated in preparation for the voiceless final stop In all seven stimuli, the vowels were followed by a 60-msec silent period and then a 20-msec burst appropriate for the voiceless stop It] The endpoints of the [bVt] series were patterned after sound spectrograms of utterance of one of the authors Spectrograms of these two endpoints are shown in Figure All stimuli were generated using a software cascade synthesizer (Klatt, Note 7, or see Kewley-Port, Note 8) in the Speech Perception Laboratory at the State University of New York at Buffalo The stimuli were converted to analogue form and recorded to make four test tapes for each of the two stimulus series The baseline identification tape contained 10 occurrences of each stimulus from a series in random order The [sis] and [bit] endpoint anchor tapes each contained 40 occurrences of the [sis] or [bit] endpoint stimulus and 10 occurrences of each of the other six stimuli in random order The [sls] and [blt] anchor tapes were constructed in a similar fashion The final tape for each series was an ABX discrimination tape This tape consisted of two-step comparisons (i.e., Stimuli and 3, and 4, etc.) with 500 msec between stimuli within a triad This tape was constructed in a fashion similar to the baseline ABX tape for Experiment In all four tapes, there were sec between trials (triads) All stimuli were presented in random order, with the restriction that no stimulus (or stimulus pair for ABX) could occur more than three times in succession Procedure The tapes were reproduced and played to the subjects on the same equipment and in a fashion similar to that used in Experiments and Eight of the subjects listened to the [bit]-[blt] series and 12 listened to the [sis]-[sls] series All subjects were run in small groups of from two to six at a time Each subject participated in two l-h sessions on separate days On each day, the subjects listened to one presentation of the baseline identification tape followed by the ABX discrimination tape Following these, two presentations of the [bit] ([sis]) anchoring tape were presented on one day and two presentations of the [bit] ([sis]) anchoring tape on the other The order of these tapes was counterbalanced across subjects The subjects used the same identification plus rating response for the identification tapes that was used in Experiment For the ABX tapes, the subjects also used the same response procedure that was used in Experiment By the end of the experiment, each subject had provided at least 20 responses to each stimulus in each of the three identification conditions and 32 responses to each stimulus pair for the ABX discrimination tapes Results The baseline identification and ABX discrimination results for the [sis]-[sls] group are shown in Figure on the right For comparison purposes, the ABX results for these same vowels in isolation are shown (from Pisotfi, 11973), as are the predictions of the Haskins categorical perception model for our [sis]-[sls] series.4 The ABX results for this series are clearly not categorical [X2(4) = 28.7, p < 001].s However, the obtained [sis]-[sls] discrimination is not as continuous as the long, isolated vowel data of Pisoni [X2(4) = 7.79, 05 < p < 1] Thus, the [sis]-[sls] series seems to allow some use of auditory memory but less than that for the vowels used in Experiments and The identification plus rating data was also converted into the same 8-point rating scale used in 430 SAWUSCH, NUSBAUM, AND SCHWAB [sis]-[sls] Series Ioo r~ 5o la.I 4- 234 234 567 STIMULUS VALUE Figure Rating functions (left) and ABX discrimination (right) data for the [sis]-[sls] series in Experiment Control (solid triangles), [sis]-anchor (open circles) and [sls]-anchor (open squares) rating functions are shown on the left Control rating data (solid triangles), obtained ABX discrimination data (solid circles), Haskins predicted ABX discrimination (open circles), and obtained ABX discrimination for isolated vowels (open squares) are shown on the right Experiment The baseline rating, [sis] anchor, and Isis] anchor functions appear on the left in Figure each of the anchoring conditions caused a significant shift in the category boundary toward the anchored end of the series [t(ll) = 7.72, p < 001, for the [sis] anchor and t(ll) = 2.93, p < 02, for the [sis] anchor] Furthermore, the [sis]-anchor-induced shift was significantly larger than the Isis] anchor shift [t(ll) = 3.73, p < 01] Thus, since the [sis]Isis] series shows less use of auditory memory than the isolated vowels and contrast effects at the [I] end of this series seems to have been reduced, it appears that auditory memory is the mediating factor in the anchoring effects of [I] but not of [i] A similar pattern of results was found for the [bit][bit] series The ABX results are shown on the right side of Figure Again, the predictions of the Haskins model and the data of Pisoni (1971) are shown for comparison The [bit]-[bIt] data were significantly less categorical than the Haskins predictions [X2(4) = 26.7, p < 001] Also, as before, the obtained [bit]-[blt] discrimination data were not as continuous as the isolated vowels [X2(4) = 6.01, < p < 2] The baseline, [bit]-anchor, and [bIt]-anchor rating functions are shown on the left side of Figure Both anchors produced significant shifts in the category boundary toward the category of the anchor It(7) = 7.04, p < 001, and t(7) = 3.12, p < 02, for the [bit] and [bit] anchors, respectively] As with the [sis]-|sIs] series, the [bit] anchor produced a significantly larger shift than the [bit] anchor [t(7) = 3.45, p < 02] Discussion The reduction in available auditory memory for both of these two test series when compared to the long, isolated vowels clearly indicates that this series is intermediate between categorical and continuous perception Furthermore, both the [i] and the [I] ends of the series appear to have equal amounts of auditory memory information available, since they have equal within-category discriminability (approximately 65% correct) However, only the anchoring at the [I] end of the series appears to have been affected by this reduction in auditory memory In Experiments and 2, the [i] and [I] anchoring effects were approximately equal, with a slightly larger [i] effect in Experiment and a slightly larger [I] effect in Experiment Although direct comparison of the magnitudes of the shifts across experiments is inappropriate because the stimuli are different and hence the category boundary shifts (measured in stimulus units) are not strictly comparable,6 the results of Experiment are clearly different from those of Experiments and and from those of Sawusch and Nusbaum (1979) The results with both the [bit]-[bIt] series and the [sis]-[sIs] series indicate that reducing the available auditory memory for vowel information reduces the contrast effects for the [I]-anchor stimuli Thus, the contrast effects found with [I]-vowel anchoring appear to be mediated by auditory memory for vowel information As auditory memory was reduced, the contrast effects for [I] anchors were reduced correspondingly These results are inconsistent with the model proposed by Fujisaki and Shigeno (1979) as outlined earlier The effect of the [i] anchors however, was not related to the use of auditory memory Instead, the [i] effect appears to represent a change in early perceptual processing, separate from auditory memory, possibly the rerunning of a prototype from long-term memory [bit]-[blt] Series IOO -~ m m z 567 12345671234 STIMULUS VALUE Figure Rating functions (left) and ABX discrimination (right) data for the [bit]-[bit] series in Experiment Control (solid triangles), [bitl-anchor (open circles) and [blt]-anchor (olden squares) rating functions are shown on the left Control rating data (solid triangles), obtained ABX discrimination data (solid circles), Haskins predicted ABX discrmination (olden circles), and obtained ABX discrimination for isolated vowels (open squares) are shown on the right CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II 431 results have a number of implications for theories of vowel perception and studies showing contrast Taken together, the results of these experiments effects with speech stimuli provide evidence for the involvement of two distinct In terms of the auditory ground explanation outperceptual processes in the contrast effects found forlined earlier, the [i] anchoring results may be seen vowels One of these processes is the major factor as reflecting an alteration or retuning of one or more in contrast effects found with the [i]-vowel stimuli prototypes used in processing vowels The auditory on our various [i]-[I] series, while the other processground would reflect two sources of information: seems to underlie the [I]-anchor contrast effects prototype information from long-term memory and Our experiments showed changes in within-categorycertain information from the stimuli being preABX discriminability for the [i] end of our series assented These are combined in a fashion similar to a function of [i] anchoring No such changes inthat proposed in adaptation level theory (see Helson, within-category ABX discrimination were found for1964; Restle, 1978) to form an auditory ground This [1] anchoring Using a signal detection analysis, theauditory ground has a longer duration than PAS contrast effects for an [i] anchor were found to be (Crowder, 1973), and changes in it seem to reflect largely the result of changes in sensitivity between a buildup of critical information over time Synvarious vowel pairs By comparison, the [I]-anchorthesized auditory memory, as proposed by Massaro effects were largely the result of criterion shifts (1972), may represent this auditory ground The Finally, when available auditory memory for vowelauditory ground would then be used in evaluating information was reduced by placing the vowels ineach succeeding vowel in our identification proCVC syllables, only the contrast effects induced bycedure From the results of the present experiments, [1] anchors decreased The reduction in auditory it is clear that [i] and [I] vowels have substantially memory had no influence on the [i]-anchor contrastdifferent effects on this auditory ground The [i] effects Thus, two processes are involved in vowel anchor seems to alter or retune the prototype space anchoring in the present experiments This modification would lead to different processing The process underlying [I] anchoring appears to be for vowels that nominally fall within the [il category, a shift in the criterion used for applying an [I] labeland would lead to changes in discriminability within to a stimulus From the lack of a within-categorythe [i] category, as were found in Experiments and discrimination change in Experiment 1, this criterion The effect of the [I] anchor, however, does not seem placement process operates after the storage of to involve much, if any, alteration in the vowel proinformation in auditory memory Furthermore, thetotype space Rather, [I] anchoring may affect the shift in criterion placement seems to be dependentcriteria used for mapping regions in the prototype on auditory memory information for precedingspace onto phonetic categories This would be convowel stimuli, since the reduction of auditory mem-sistent with the general lack of change in discriminory information for the vowels in Experiment alsoability for [I] anchoring in Experiments and reduced the contrast effects found with the [I]-vowelFrom the results of Experiment 3, some form of anchor auditory memory which contains information about Although the actual processes responsible for thethe quality of the stimulus may underlie the changes effects of [i] anchoring are still not known, a numberin criterion for [I1 anchoring In addition, memory of characteristics of this process are known One is of the phonetic label assigned to this auditory trace that the [i] anchoring effect occurs at a stage ofmay also influence [I] criteria placements This outperceptual processing prior to phonetic labeling Thisline of a model for vowel processing is consistent is clearly the case, since [i] anchoring was found towith both our vowel results and the contrast effects increase discriminability within the [i] category in in vowel perception recently reported by Repp et al both Experiment and Experiment Furthermore, (1979) reducing the available auditory memory for vowel What remains to be explained is why the [i] information had no influence upon [i] anchoring vowel would cause a prototype space retuning when Thus, [i] anchoring may represent changes in the[I] does not There are a number of differences auditory processing of vowel information However,between the [i] and [I1 vowels The [i] vowel has the [il anchoring does not represent the fatigue of featurephonetic feature tense and is intrinsically long in detectors tuned to formant frequencies or other such duration, while [I] is lax and intrinsically short The information Feature detector fatigue can be ruledvowel [i] is also a "point" vowel while [I] is not out because in the anchoring procedure used in theseAlthough the tense-lax distinction may be important, experiments, all stimuli are separated by at leastvowel length does not seem to be sufficient In Ex4 sec and no single stimulus occurred more than threeperiment 3, both long ([SiSI-[SISI) and short ([bit]times in succession (see also Sawusch & Nusbaum, [bit]) versions of the vowels were used and no dif1979; Simon & Studdert-Kennedy, 1978) These ferences were found in the results as a function of GENERAL DISCUSSION 432 SAWUSCH, NUSBAUM, AND SCHWAB vowel duration However, the point-nonpoint difference between [i] and [I] presents an intriguing possibility The retuning process proposed above may represent a form of "normalization" (see Lieberman, Crelin, & Klatt, 1972) The vowel [i] represents an extreme vowels in terms of both its production and its acoustic structure Thus, our subjects may have been using this vowel to retune or normalize their perceptual vowel space Although this explanation is speculative, it is consistent with various proposals for normalization processes in speech perception (Gerstman, 1968; Ladefoged & Broadbent, 1957; Lieberman, 1973; Lieberman et al., 1972) Our results might also help to explain why previous experiments designed to investigate normalization influences have found largely negative results (see Verbrugge, Strange, Shankweiler, & Edman, 1976) In the present studies, the influence of an anchoring stimulus is almost entirely confined to ambiguous, boundary stimuli Little, if any, influence of the anchor was found near the endpoints of the various series using the identification-plus-rating procedures Only the ABX procedure and the signal detection analysis revealed within-category changes, and then only for the anchored, [i] category Thus, if the present results represent the operation of a normalization process, then they indicate that future tests of normalization should include ambiguous test items (cf Ladefoged & Broadbent, 1957) The present results also have important implications for models of contrast effects in general Experiments and clearly demonstrate that anchoring can produce changes in vowel discriminability This is consistent with previous studies showing similar results for nonspeech signals (e.g., Cuddy et al., 1973) These discriminability changes are important in light of recent diverse interpretations of selective adaptation results (Diem et al., 1978, in press; Rosen, iNote 4) Our results indicate that anchoring procedures (and paired comparison procedures) can produce changes in discriminability as well as criterion shifts for speech stimuli Given the present results, the interpretation of any particular anchoring or adaptation result as being due to changes in response processes seems to be unwarranted Although anchoring results can not be readily explained in terms of feature detector fatigue, they not necessarily constitute support for responselevel interpretations of adaptation and anchoring either A more comprehensive set of results, involving procedures and/or stimuli that can potentially separate the influence of sensitivity changes from response bias, is necessary before the contrast effects found with consonant adaptation and anchoring can be interpreted within an information processing framework REFERENCE NOTES Fujisaki, H., & Kawashima, r On the modes and mechanisms of speech perception Annual Report of the Engineerin~ Researck,, Institute, University of Tokyo, Tokyo, 1969, 28, 67-73 Fujisaki, H., & Kawashima, T Some experiments on speecl’t perception and a model for the perceptual mechanism Annual Report Qf the Engineering Research Institute, University of Tokyo, Tokyo, 1970, 29, 207-214 Sawnsch, J R., & Pisoni, D B ,4nchoring, contra~t effects and the perception of speech Manuscript in preparation Rosen, S M Range and frequency effects in consonam’ categorization Manuscript submitted for publication Nusbaum, H C., & Sawusch, J R The role of assimilation and contrast in vowel perception Paper presented at the 20th meeting of the Psychonomic Society, Phoenix, Arizona, November 1979 Sachs, R M Vowel identification and discrimination in isolation vs work context (Quarterly Progress Report No 93 pp 220-229) Cambridge, Mass: Research Laboratory of Electronics, Massachusetts Institute of Technology, 1969 Klatt, D H A cascade/parallel terminal analog speech synthesizer and a strategy for consonant-vowel synthests Paper presented at the 93rd meeting of the Acoustical Society of America, University Park, Pennsylvania, June 1977 Kewley-Port, D KL TEXC: Executive program to implement the KLA TT software speech synthesizer (Research on Speech Perception, Progress Report 4) Bloomington, Ind: Indiana University, 1978 REFERENCES BRAIDA, L D., & DURLACH, N I Intensity perception I1 Resolution in one-interval paradigsm Journal of the Acoustical Society of America, 1972, 51,483-502 BROAD~ZNV, D E., & LA~VO~ED, P Vowel judgments and adaptation level Proceedings of the Royal Society, B, 1960., 151,384-399 CnOWD~R, R G The sound of vowels and consonants in immediate memory Journal of Verbal Learning and Verbal Behavior, 1971, 10, 587-590 CROWDER, R G Representation of speech sounds in precategorical acoustic storage Journal of Experimental Psychology, 1973, 98, 14-24 CROWDER, R G., & MORrON, J Precategorical acoustic storage (PAS) Perception & Psychophysics, 1969, 5,365-373 Cuo~v, L L., PINN, J., & SIMONS, E Anchor effects with biased probability of occurrence in absolute judgment of pitch Journal of Experimental Psychology, 1973, 100, 218-220 DARWIN, C J Ear differences in the recall of fricatives and vowels Quarterly Journal of Experimental Psychology, 1971, 23, 46-62 DARWIN, C T., TURVEY, M T., & CROWDER, R G An auditory analogue of the Sperling partial report procedure: Evidence for brief auditory storage Cognitive Psychology, 1972, 3, 255-267 D~nL, R L., ELMAN, J L., & McCus~R, S B Contrast effects in stop consonant identification Journal of Erperimental Psychology: Human Perception and Performance, 1978, 4, 599-609 DIEHL, R L., LANG, M., & PARKER, E M A further parallel between selective adaptation and response contrast Journal of Experimental Psychology: Human Perception and Performance, in press Dun~AO~, N I., & BRAtDA, L D Intensity perception I Preliminary theory of intensity resolution Journal of the Acoustical Society of America, 1969, 46, 372-383 E~MAS, P D The relation between identification and discrimination along speech and non-speech continua Language & Speech, 1963, 6, 206-217 CONTEXTUAL EFFECTS IN VOWEL PERCEPTION II 433 FRY, D B., ABRAMSON, A S., EIMAS, P D., & LIBERMAN, of the Acoustical Society of America, 1978," 64, 1338-1357 A M The identification and discrimination of synthetic vowels SanVENS, K N On the relations between speech movements and L angua~e and Speech, 1962, 5, 171 - 189 speech perception Zeitschrift fiir Phonetik, Sprachwissenschaft FuJxsaK~, H., & StIIGENO, S Context effects in the categoriundKommunikationsforschung, 1968, 21,102-106 zation of speech and non-speech stimuli In J J Wolf & D H STUDDERT-KENNEDY, M., & SHANKWEILER, D Hemispheric Klatt (Eds.), Speech communication papers presented at the specialization for speech perception Journal of the Acoustical 97th meeting of the Acoustical Society of America New York: Society of America 1970, 41t, 579-594 Acoustical Society of America, 1979 VERBRUGGE, R R., STRANGE, W., SHANKWEILER, D P., & GEaSTMAN, L Classification of self-normalized vowels IEEE EDMAN, T R What information enables a listener to map a Transactions on Audio and Electroacoustics, 1968, A U-16, 78-80 talker’s vowel space? Journal of the Acoustical Society of GREEN, D M., & SWETS, J A Signal detection theory and America, 1976, 60, 198-212 psychophysics Huntington, New York: Krieger, 1974 HAGGARD, M P Encoding and the REA for speech signals Quarter(v Journal of Experimental Psychology, 1971, 23, 34-45 HELSON H Adaptation level theory New York: Harper & Row, NOTES 1964 HELSOr~, H., & KOZAKI, A Anchor effects using numerical All statistical tests, unless otherwise indicated, were twoestimates of simple dot patterns Perception & Psychophysics, tailed t tests for correlated measures 1968, 4, 163-164 The increase in the average rating of Stimulus as a funcLADEFO(;ED, P., & BROADaENT, D E Information conveyed by tion of [i] anchoring was not significant [t(5) = 2.37, 05 < vowels Journal of the Acoustical Society of America, 1957, p < 1, for a mean increase of 69 rating units) Furthermore, 29, 98-104 the Haskins model of categorical perception (Liberman et al., LIBERMAN, A M., HARRIS, K S., HOFFMAN, H S., & GRIFFITH, 1957; Pollack & Pisoni, 1971), after modification for use with B C The boundaries Journal of Experimental Psychology, rating data, predicted a within-category discrimination score of 1957, 54, 5,358-368 50.5°7o for the Stimulus 1,2 pair following anchoring This was LIEUERMAN, P On the evolution of language: A unified view well below the obtained 68.2070 correct discrimination Thus, the Cognition, 1973, 2, 59-94 increase in within-category discriminability is not predictable from L~EaERMAN, P., CRELIN, E S., & KLATT, D H Phonetic the identification plus rating data ability and related anatomy of the newborn, adult human, The appropriateness of the Durlach and Braida (1969) TSD Neanderthal man, and the chimpanzee American Anthropolmodel for the data in Experiment was evaluated using two ogist, 1972, 74, 287-307 criteria The first was whether the obtained ROC curves were MASSARO, D W Preperceptual images, processing time and perlinear when plotted on normal-normal coordinates The hit and ceptual units in auditory perception Psychological Review, false-alarm percentages in the range from 008 to 992 were con1972, 79, 124-1.45 verted to z scores The best fitting regression lines were calculated MORSE, P A., KASS, J E., & TURK1ENICZ, R Selective for each stimulus pair (6) for each subject (12) in each conadaptation of vowels Perception & Psychophysics, 1976, 19, dition (2), yielding a total of 144 cases 137-143 In 40 of these cases, fewer than three points were available in PARDUCCI, A Range-frequency compromise in judgment Psy- the ROC curves, so the normal distribution assumption could not chological Monographs, 1963, 77, 2, 1-50 be checked Of the remaining 104 cases, a significant correlation PAaDUCCL A Category judgment: A range-frequency model (between the z scores of hits and false alarms) was found for 90 Psychological Review, 1965, 72,407-418 instances, indicating that in these cases, a significant linear comPARDVCCI, A Contextual effects: A range-frequency analysis In ponent was present The 90 out of 104 cases was significant E C Carterette & M P Friedman (Eds.), Handbook of per(z = 7.35, p < 001, using a z-score approximation to the sign ception (Vol IlL New York: Academic Press, 1975 test) In addition, the 90 cases where the normal distribution P~soNi, D B On the nature of categoricalperception of speech assumption held was significant when compared to the 144 total sounds Unpublished doctoral dissertation, University of cases (z = 2.92, p < 002, using the z approximation to the sign Michigan, 1971 test) The equal variance assumption was checked by computing P~SONI, D B Auditory and phonetic memory codes in the disa 5% confidence interval for the slope of the regression line crimination of consonants and vowels Perception & Psycho- In the 90 of the 104 cases that could be checked, the confiphysics, 1973, 13, 253-260 dence interval bracketed a slope of 1.0 (which would indicate P[SONL D B Auditory short-term memory and vowel perception equal variance) For the 104 cases where the equal variance, Memory & Cognition, 1975, 3, 7-18 normal assumptions could be checked, the linear component in POLLACK, I., & PISONI, D B On the comparison between identithe ROC plot accounted for an average of 9507o of the variance fication and discrimination tests in speech perception PsychoThus, the vowel data to a considerable extent, seem to meet nomic Science, 1971, 24,299-300 the assumptions of the Durlach and Braida model REPP, B H., HEALV, A F., & CROWDER, R G Categories and The ABX discrimination data from Experiment are not an context in the perception of isolated steady-state vowels Journal appropriate comparison for the CVC discrimination results in of Experimental Psychology: Human Perception & Performance, Experiment In Experiment 1, one-step ABX triads with sec 1979, 5, 129-145 between items within a triad were used This set of parameters RESTLE, F Assimilation predicted by adaptation-level theory with was used to insure that no ceiling effects would occur in the variable weights In N J Castellan & F Restle (Eds.), isolated vowel ABX discrimination In Experiment 3, our requireCognitive theory (Vol 3) Hillsdale, N.J: Erlbaum, 1978 ments were just the opposite We wanted a situation where isoSAWUSCH, J R., & NUSBAUM, H C Contextual effects in vowel lated vowel ABX discrimination was excellent Therefore, twoperception l: Anchor-induced contrast effects Perception & step triads with 500 msec between items within a triad were used Psychophysics, 1979, 25,292-302 Thus, the ABX data from Experiments and are not comparable SHANKWEILER, D., & STUDDERT’KENNEDY, M Identification of and Pisoni’s (1973) vowel data represent an appropriate comconsonants and vowels presented to left and right ears Quarterly parison Journal qf Experimental Psychology, 1967, 19, 59-63 Using a two-tailed chi-square goodness-of-fit test SIMON, H J., & "STUOOEaT-KENNED’~, M Selective anchoring The closest comparison that can be mae between previous, and adaptation of phonetic and nonphonetic continua Journal isolated vowel results and the CVC stimuli is between the isolated 434 SAWUSCH, NUSBAUM AND SCHWAB vowels of Sawusch and Nusbaum (1979) and Experiment and the [sisl-[sls] results of Experiment The [sVs] stimuli did have formant frequencies and bandwidths which were identical to those of the isolated vowels In Experiment 1, there was no significant difference between the magnitudes of the category boundary shifts induced by the [i] and [I] anchors It(10) = 1.29, p < 20] In comparing the [sis]-anchor contrast effect with the [i] effects in Experiment 1, no significant difference was found [t(16) = p > 20 using a two-tailed, independent t test] However, when the Isis]- e.nd [l]-anct~or shill~ were compared, a sig~fificantl5 smaller effect for [sis] was found It(16) = 2.52, p < 05, u~ing a two-tailec[, independent t test] Thus, reducing auditory merr ory does seem to reduce the contrast effects for [I]-vowel anchors while leaving the [i]-anchor effects largely unchanged (Received for publication September 10, 1979; revision accepted February 26, 1980.) ... [i] and [I] anchoring effects reflect the involvement of distinct perceptual processing mechanisms EXPERIMENT If two distinct processes are involved in anchoring effects with vowels, and one of... memory for vowelauditory ground would then be used in evaluating information was reduced by placing the vowels ineach succeeding vowel in our identification proCVC syllables, only the contrast effects. .. Contextual effects in vowel lated vowel ABX discrimination was excellent Therefore, twoperception l: Anchor-induced contrast effects Perception & step triads with 500 msec between items within