Feature analyzers for the phonetic dimensionstop vs. continuant

Perception of sounds along the phonetic dimensionstop vs. continuant was studied by means of a selective adaptation procedure. Subjects first identified a series of synthetic consonant-vowel syllables whose formant transitions varied in duration, slope, and amplitude characteristics. They were perceived as either [ba] or [wa]. After the initial identification test, an adapting stimulus was presented repeatedly, and then the subjects again identified the original test series. Adapting with a stop (either [ba] or [da]) led to a decrease in the number of test stimuli identified as [ba], whereas adapting with the continuant sound [wa] led to an increase in the number of [ba] identification responses. Removing the vowel portion of an adapting stimulus greatly reduced the identification shift only when the resulting stimulus was no longer perceived as speech-like. A reduction in the number of [ba] identifications occurred even when a nonspeech “stop” (the sound of a plucked string) was used as the adapting stimulus, suggesting that phonetic processing is not a necessary condition for an adaptation effect.     

Functional equivalence of masking and cue reduction in perception of shape at a slant

The present study was undertaken to investigate the effects of syllabic stress and segment structure on selective adaptation in speech. To this end, a CV place of articulation test continuum was selectively adapted by seven different adapting stimuli; the monosyllables [ba] and [ga], two disyllabic stimuli containing equal stress on both syllables, [baga] and [gabal, and three disyllabic stimuli ([baga]) in which stress placement varied and was cued by the acoustic parameters of fundamental frequency and duration. Results for the two adapting stimuli demonstrated significant [b] adaptation for the stimulus [ba] and significant [g] adaptation for [gal. Of the five other adapting stimuli, only [g] adaptation for the stimulus [bagá] was found to be significant. These findings indicate that the operation of detector mechanisms susceptible to fatigue by an adapting stimulus are even more constrained than has heretofore been suggested. It appears that the adapting and test stimuli must not only have the same phonetic and syllable structure, but also the same syllabic organization.     

Contingent feature analysis in speech perception

A contingent adaptation effect is reported for speech perception. Experiments were conducted to test the effects of an alternating sequence of two adapting syllables, [da] and [t^hi], on the perception of two series of synthetic speech syllables, [ba]-[p^ha] and [bi]-[p^hi]. Each of the test series consisted of 11 stimuli varying in voice onset time, a cue which distinguishes voiced from voiceless stop consonants in word-initial position. The [da]-[t^hi] adapting sequence produced opposite shifts in the loci of the phonetic boundaries for the two test series. For the [ba]-[p^ha] series, listeners made fewer identification responses to the [b] category after adaptation, while for the [bi]-[p^hi] series, listeners made more responses to the [b] category. The opposing shifts indicate that the perceptual analysis of voicing in stop consonants is carried out with respect to vowel environment.     

Comparison of consonantal and vocalic cues in selective adaptation

The acoustic cues to the phonetic identity of diphthongs normally include both spectral quality and dynamic change. This fact was exploited in a series of selective adaptation experiments examining the possibility of mutual adaptive effects between these two types of acoustic cues. One continuum of syllables varying from [εi] to [εd] and another varying from [ε] to [εi] were synthesized; endpoint stimuli of both series used as adaptors caused identification boundaries to be shifted. Cross-series adaptation was also attempted on the [ε?εi] stimuli, using [?], [∞], and [ai]. Only [ai] proved effective as an adaptor, suggesting the mediation of a rather abstract auditory level of similarity. The results argue strongly against interpretations in terms of feature detectors, but appear compatible with an “auditory contrast” explanation, which might in turn be incorporated within adaptation level theory in the form recently discussed by Restle (1978). The cross-series results further suggest that selective adaptation might be used to quantify the perceptual distance between auditory cues in speech.     

Contextual effects in vowel perception II: Evidence for two processing mechanisms

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 (before 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-[i] 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 [i]-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.     

A further parallel between selective adaptation and contrast

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.     

The effect of selective adaptation on the identification of speech sounds

An experiment was performed to determine the effect of selective adaptation on the identification of synthetic speech sounds which varied along the phonetic dimensionplace of articulation. Adaptation with a stimulus of a particular place value led to a reduction in the number of test stimuli identified as having that place value. An identification shift was obtained even when the acoustic information specifying place value for the adapting stimulus had virtually nothing in common with the information specifying place value for any of the test stimuli. Removing the vowel portion of an adapting stimulus eliminated identification shift only when the resulting stimulus was no longer perceived as speech-like. The results indicate that at least part of the adaptation effect occurs at a site of phonetic, not merely acoustic, feature analysis.

     

Simple and contingent adaptation effects for place of articulation in stop consonants

Experiments on selective adaptation have shown that the locus of the phonetic category boundary between two segments shifts after repetitive listening to an adapting stimulus. Theoretical interpretations of these results have proposed that adaptation occurs either entirely at an auditory level of processing or at both auditory and more abstract phonetic levels. The present experiment employed two alternating stimuli as adaptors in an attempt to distinguish between these two possible explanations. Two alternating stimuli were used as adaptors in order to test for the presence of contingent effects and to compare these results to simple adaptation using only a single adaptor. Two synthetic CV series with different vowels that varied the place of articulation of the consonant were employed. When two alternating adaptors were used, contingent adaptation effects were observed for the two stimulus series. The direction of the shifts in each series was governed by the vowel context of the adapting syllables. Using the single adaptor data, a comparison was made between the additive effects of the single adaptors and their combined effects when presented in alternating pairs. With voiced adaptors, only within-series adaptation effects were found, and these data were consistent with a on,level model of selective adaptation. However, for the voiceless adaptors, both within- and cross-series adaptation effects were found, suggesting the possible presence of two levels of adaptation to place of articulation. Further, the contingent adaptation effects with the voiceless adaptors seemed to be the result of the additive effects of the two alternating adaptors. This result indicates that previously reported contingent adaptation results may also reflect the net vowel specific adaptation effects after cancellation of other, nonvowel dependent effects and that caution is needed in interpreting such results.     

A “labial” feature analyzer in speech perception

A selective adaptation experiment was conducted to determine the ability of various adapting stimuli to alter the perception of a series of 13 synthetic speech syllables. The synthetic test syllables, which varied acoustically in the starting frequency and direction of second- and third-formant transitions, included stop consonant distinctions ofplace of articulation for the syllable types [bae], [dae], and [gae]. A systematic adaptation effect was produced in the locus of the bae-bae phonetic boundary for these stimuli after repetitive listening to each of the following adapting syllables: [bae], [p^hae], [mae], and [vae], indicating that perception ofplace distinctions among the stop consonants can be altered even by repetitive listening to certain speech sounds not belonging to the stop-consonant class.     

Selective adaptation of English consonants using real speech

Most English consonant-vowel (CV) syllables have other CV syllables embedded within them. For example, splicing sufficient energy from the onset of [k^ha] yields [p^ha], splicing into [ma] or [va] yields [ba], and splicing into [?a] yields [da]. We spliced successively longer segments from naturally spoken CV syllables to produce sequences of CV syllables which varied in discrete acoustic steps from [k^ha] to [p^ha], from [?a] to [da], from [ma] to [ba], from [fa] to [ba], and from [va] to [ba]. Random presentation of syllables in each series resulted in identification functions with typically sharp phoneme boundaries. For example, in the seven-syllable [?a]-[da] series (where [?a] was the original or first syllable), there were98% [?a] responses to Syllable 3, but only 12% [?a] responses (88% [da] responses) to Syllable 5. Following the identification test, subjects listened to 180 repetitions of either the first or last syllable in the test series, and were again required to identify randomly presented syllables from the test series. A shift in the phoneme boundary toward the repeated (adapting) syllable was observed for 11 of the 12 repeated syllables. Repeated presentation of [?a], for example, resulted in fewer [?a] responses to syllables in the [?a]-[da] series, compared to performance on the previous identification test. Likewise, repeated listening to [da] resulted in a decrease in [da] responses. Adaptation was selective in that syllables near the phoneme boundary were most affected by the adapting syllable. A shift in the phoneme boundary was also observed for two different continua when the adapting stimulus contained an acoustic feature identical to syllables in the test series. Thus, selective adaptation was found along a [ma]-[ba] continuum following repeated presentation of [na] and following repeated presentation of nasal resonance removed from its syllable context. A second major result, observed in five different experiments, was an asymmetrical adaptation effect. A greater shift in the phoneme boundary was observed following repeated presentation of the first syllable in each series (e.g., [?a]) than for the final embedded syllable (e.g., [da]). The results were discussed in terms of two different models of-selective adaptation.     

The role of duration and rapid temporal processing on the lateral perception of consonants and vowels

This study explored the extent to which rapid temporal processing and duration contribute to the right-ear advantage (REA) and presumably left-hemisphere processing for stop consonants and the lack of clear-cut laterality effects for vowels. Three sets of synthetic stimuli were constructed: consonant vowel stimuli [ba da ga bi di gi bu du gu] of 300 msec duration (full stimuli) and two shortened stimuli consisting either of a noise burst and 40-msec transitions (40-msec stimuli), or a noise burst and 20-msec transitions (20-msec stimuli). Stimuli were presented dichotically for consonant, vowel, and syllable identification. Results indicated a significant REA for consonants in the full and 40-msec conditions and a non-significant REA in the 20-msec condition. Nevertheless, the magnitude of laterality did not change across the three conditions. These results suggest that although transition information including duration contributes to lateralization for stop consonants, it is the presence of abrupt onsets which crucially determines lateralized processing. For vowels, there was a significant REA only in the full stimulus condition, and a significant decrement in the magnitude of the laterality effect in the two shortened stimulus conditions. These results suggest that for vowel perception, it is the nature of the acoustic cue used for phonetic identification and not duration that seems to be the critical determinant of lateralization effects.     

Human adults and human infants show a “perceptual magnet effect” for the prototypes of speech categories,monkeys do not

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel /i/ on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the /i/ vowels as best instances, or prototypes. The perceived goodness of Iii vowels declined systematically as stimuli were further removed from the prototypic Iii vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic IM vowel was used as the referent stimulus and adults’ generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other /i/ vowels, relative to the situation in which the nonprototype served as the referent. The notion of aperceptual magnet was introduced. The prototype of the category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants’ perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype’s magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code     

Auditory property detectors and processing place features in stop consonants

The effects of selective adaptation on the perception of consonant-vowel (CV) stimuli varying in place of production was studied under two conditions. In the first condition, repeated presentation of a CV syllable produced an adaptation effect resulting in a shift in the locus of the phonetic boundary between [ba] and [da]. This result replicated previously reported findings. However, in the second condition, an adaptation effect was obtained on this same test series when the critical acoustic information (i.e., formant transitions) was present in final position of a VC speech-like syllable. These latter results support an auditory account of selective adaptation based on the spectral similarity of the adapting stimuli and test series rather than a more abstract linguistic account based on phonetic identity.     

Human adults and human infants show a "perceptual magnet effect" for the prototypes of speech categories, monkeys do not

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel i parallel on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the i parallel vowels as best instances, or prototypes. The perceived goodness of i parallel vowels declined systematically as stimuli were further removed from the prototypic i parallel vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic i parallel vowels was used as the referent stimulus and adults' generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other i parallel vowels, relative to the situation in which the nonprototype served as the referent. The notion of a perceptual magnet was introduced. The prototype of the category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants' perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype's magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code.     

Intrinsicf0 differences in spoken and sung vowels and their perception by listeners

We explore how listeners perceive distinct pieces of phonetic information that are conveyed in parallel by the fundamental frequency (f0) contour of spoken and sung vowels. In a first experiment, we measured differences inf0 of /i/ and /a/ vowels spoken and sung by unselected undergraduate participants. Differences in “intrinsicf0” (withf0 of /i/ higher than of /a/) were present in spoken and sung vowels; however, differences in sung vowels were smaller than those in spoken vowels. Four experiments tested a hypothesis that listeners would not hear the intrinsicf0 differences as differences in pitch on the vowel, because they provide information, instead, for production of a closed or open vowel. The experiments provide clear evidence of “parsing” of intrinsicf0 from thef0 that contributes to perceived vowel pitch. However, only some conditions led to an estimate of the magnitude of parsing that closely matched the magnitude of produced intrinsicf0 differences.     

辅音和元音知觉中的启动效应差异

采用启动范式,在两个实验中分别考察了辅音范畴和元音范畴知觉中的启动效应。启动音是纯音和目标范畴本身,目标音是辅音范畴和元音范畴连续体。结果发现辅音范畴连续体知觉的范畴反应百分比受到纯音和言语启动音影响,辅音范畴知觉的反应时只受言语启动音影响;元音范畴连续体知觉的范畴反应百分比不受两种启动音影响,但元音范畴知觉的反应时受到言语启动音影响。实验结果表明辅音范畴和元音范畴知觉中的启动效应存在差异,这为辅音和元音范畴内在加工机制的差异提供了新证据。     

Influence of vowel context on the audio‐visual speech perception of voiced stop consonants

The work reported here investigated whether the extent of McGurk effect differs according to the vowel context, and differs when cross‐modal vowels are matched or mismatched in Japanese. Two audio‐visual experiments were conducted to examine the process of audio‐visual phonetic‐feature extraction and integration. The first experiment was designed to compare the extent of the McGurk effect in Japanese in three different vowel contexts. The results indicated that the effect was largest in the /i/ context, moderate in the /a/ context, and almost nonexistent in the /u/ context. This suggests that the occurrence of McGurk effect depends on the characteristics of vowels and the visual cues from their articulation. The second experiment measured the McGurk effect in Japanese with cross‐modal matched and mismatched vowels, and showed that, except with the /u/ sound, the effect was larger when the vowels were matched than when they were mismatched. These results showed, again, that the extent of McGurk effect depends on vowel context and that auditory information processing before phonetic judgment plays an important role in cross‐modal feature integration.     

Identification of argentine Spanish vowels

The acoustical spectrum of the five Spanish vowels |a, e, i, o, u| has been delimited to show the areas covered by F ₁ , F ₂ , and F ₃ and the relative distribution energy among the formants. Through the analysis of the spectral components of vowels, isolated and in consonantal context, it is possible to estimate the different weight of each formant in vowel identification. At least for isolated vowels,F ₂ andF ₃ seem to be effective for the identification of [i] and [e] while theF ₁ andF ₂ carry the weight for the identification of [o] and [u]. The cue to differentiate [a] seems to beF ₂. Spanish vowels are compared with cardinals and North American English vowels. There is no correlation with cardinal vowels while similarities are found with English vowels.     

Selective adaptation effects on end-point stimuli in a speech series

Recent experiments in speech perception using the selective adaptation paradigm have found that the phonetic boundary of a test series shifts following adaptation. However, no changes within the phonetic category have been found. In the present experiment, a series of voiced CV syllables which varied along the feature of place was used in a selective adaptation paradigm. The end-point stimuli trom the test series were used as adaptors. Subjects used a 6-point rating scale to respond to the stimuli instead of the usual two-category identification. The average rating for end-point stimuli from the same category as the adaptor, as well as the boundary stimuli, shifted as a function of adaptation. In all cases, the average rating response shifted toward that of the unadapted category. The average rating for stimuli in the opposite category from that of the adaptor remained relatively unchanged. These results indicate that the entire category of the adapting stimulus changes as a function of selective adaptation and that the effect is not confined to stimuli near the phonetic boundary.     

Contextual effects in vowel perception I: Anchor-induced contrast effects

Results from recent experiments using a selective adaption paradigm with vowels have been interpreted as the result of the fatigue of a set of feature detectors. These results could also be interpreted, however, as resulting from changes in auditory memory (auditory contrast) or changing response criteria (response bias). In the present studies, subjects listened to vowels under two conditions: an equiprobable control, with each of the stimuli occurring equally often, and an anchoring condition, with one vowel occurring more often than any of the others. Contrast effects were found in that vowel category boundaries tended to shift toward the category of the anchor, relative to the equiprobable control. Results from these experiments were highly similar to previous selective adaptation results and suggest that neither feature detector fatigue nor response criterion changes can adequately account for the adaptation/ anchoring results found with vowels.