Response probabilities and “same-different” reaction times

A “same-different” reaction-time (RT) task with multidimensional stimuli was used with a 50:50 and a 75:25 proportion of “different” to “same” response. The “different” RTs to each dimension were similar for the two proportions. However, the “same” RT in the 50:50 condition was faster than the “same” for the 75:25 condition and faster than the slowest “different” RT. Interpretations of the results in terms of response bias and processing criteria are offered.     

Hemispheric asymmetry of auditory evoked potentials to comparisons within and across phonetic categories

In 10 right-handed Ss, auditory evoked responses (AERs) were recorded from left and right temporal and parietal scalp regions during simple discrimination responses to binaurally presented pairs of synthetic speech sounds ranging perceptually from /ba/ to /da/. A late positive component (P3) in the AER was found to reflect the categorical or phonetic analysis of the stop consonants, with only left scalp sites averaging significantly different responses between acoustic and phonetic comparisons. The result is interpreted as evidence of hemispheric differences in the processing of speech in respect of the level of processing accessed by the particular information processing task.     

Matching patterns vs matching digits: The effect of memory dependence and complexity on “same”-“different” reaction times

Two experiments are reported in which “same”-“different” reaction times (RTs) were collected to pairs of stimuli. In Experiment 1 stimuli were matrix patterns, and in Experiment 2 stimuli were digits. In both experiments, the pairs were presented simultaneously (discrimination task) and successively (memory task) for a set of nine simple and a set of nine complex stimuli. The following results were obtained: discrimination RTs were longer than memory RTs; RTs to complex stimuli were longer than RTs to simple stimuli; “same” RTs were faster than “different” RTs across all conditions except simple pattern discrimination, for which “different” RTs were faster than “same” RTs; and discrimination RTs for complex patterns were longer than would be predicted from the other conditions. Some evidence was obtained that the form of encoding for both patterns and digits in the memory task was visual. These results are discussed in terms of encoding and comparison strategies.     

Perceptual equivalence of acoustic cues in speech and nonspeech perception

Trading relations show that diverse acoustic consequences of minimal contrasts in speech are equivalent in perception of phonetic categories. This perceptual equivalence received stronger support from a recent finding that discrimination was differentially affected by the phonetic cooperation or conflict between two cues for the /slIt/-/splIt/contrast. Experiment 1 extended the trading relations and perceptual equivalence findings to the /sei/-/stei/contrast. With a more sensitive discrimination test, Experiment 2 found that cue equivalence is a characteristic of perceptual sensitivity to phonetic information. Using “sine-wave analogues” of the /sei/-/stei/stimuli, Experiment 3 showed that perceptual integration of the cues was phonetic, not psychoacoustic, in origin. Only subjects who perceived the sine-wave stimuli as “say” and “stay” showed a trading relation and perceptual equivalence; subjects who perceived them as nonspeech failed to integrate the two dimensions perceptually. Moreover, the pattern of differences between obtained and predicted discrimination was quite similar across the first two experiments and the “say”-“stay” group of Experiment 3, and suggested that phonetic perception was responsible even for better-than-predicted performance by these groups. Trading relations between speech cues, and the perceptual equivalence that underlies them, thus appear to derive specifically from perception of phonetic information.     

Holistic and analytic processes in the comparison of letters

College students made “same-different” judgments about successively presented pairs of letters whose degree of difference, in terms of the number of line segments out of register, was systematically varied. Reaction time was found to decrease with increases in the degree of difference in “different” responses, as well as to depend on the number of line segments present in the second (probe) letter. “Same” responses were much faster than different responses and were unaffected by the number of segments in the probe letter. This pattern of results suggests analytic (component-by-component) processing of “different” letters and holistic processing of “same” letters. The results have important implications for studies of multi-letter comparisons, in which it is commonly assumed that letter comparisons are holistic in nature.     

Pitch as a phonemic cue

Three experiments that were designed to determine how pitch information is represented in auditory memory are reported. A same-different reaction time was used in all three experiments. Previous experiments have interpreted the finding of faster “same” responses to acoustically identical pairs than to pairs that are phonemically identical but acoustically distinct as indicating that there is a memory that preserves auditory information. It has been assumed that this can be used to match “same” pairs only if the formant frequencies of the members of the pair are the same. In the first experiment, the size of this matching advantage for pairs with identical formant frequencies was not altered when the members of the pair were on different pitches. This indicates that pitch is represented separately from the formants at the auditory level. The second and third experiments used a bigger pitch difference when the pairs were on a different pitch, which, for one of the stimulus sets, resulted in a change in vowel quality but not in the identity of the consonant. In the other stimulus set, both phonemes of the syllable remained the same when presented on different pitches. The matching advantage was reduced when the stimuli were on different pitches for both stimulus sets. This indicates that a difference in pitch can prevent matching at the auditory level under some circumstances. An additional finding, a reduced residual matching advantage when the syllable changes, indicates that at least a syllable-length representation is held in auditory memory. The results are discussed with respect to how the representation in auditory memory might be used in the perception of speech produced by different speakers.     

Some experiments on perceptual learning of mirror-image acoustic patterns

It is well known that the formant transitions of stop consonants in CV and VC syllables are roughly the mirror image of each other in time. These formant motions reflect the acoustic correlates of the articulators as they move rapidly into and out of the period of stop closure. Although acoustically different, these formant transitions are correlated perceptually with similar phonetic segments. Earlier research of Klatt and Shattuck (1975) had suggested that mirror image acoustic patterns resembling formant transitions were not perceived as similar. However, mirror image patterns could still have some underlying similarity which might facilitate learning, recognition, and the establishment of perceptual constancy of phonetic segments across syllable positions. This paper reports the results of four experiments designed to study the perceptual similarity of mirror-image acoustic patterns resembling the formant transitions and steady-state segments of the CV and VC syllables /ba/, /da/, /ab/, and /ad/. Using a perceptual learning paradigm, we found that subjects could learn to assign mirror-image acoustic patterns to arbitrary response categories more consistently than they could do so with similar arrangements of the same patterns based on spectrotemporal commonalities. Subjects respond not only to the individual components or dimensions of these acoustic patterns, but also process entire patterns and make use of the patterns’ internal organization in learning to categorize them consistently according to different classification rules.     

Temporal changes in visual and acoustic codes in a letter-matching task

The objective of the present experiment was to examine the nature of the coding process in a letter-matching task. Letter pairs that were either visually confusable or acoustically confusable or both visually and acoustically confusable were presented tachistoscopically with a variable interval between the first letter and the comparison letter. The dependent measure was RT for the “different” responses to the three types of confusable items which were each assessed at four interstimulus intervals ranging from 0 to 2 sec. The results indicate that a visual code appears to be emphasized for approximately 1 sec, after which an acoustic code seems to be dominant. There is also evidence which indicates that the acoustic code does not immediately replace the visual code and that both may coexist for a brief period of time.     

Auditory evoked potential correlates of speech sound discrimination

An electrophysiological correlate of the discrimination of stop consonants drawn from within and across phonetic categories was investigated by an auditory evoked response (AER) technique. Ss were presented a string of stimuli from the phonetic category [ba] (the standard stimulus) and were asked to detect the occurrence of a stimulus from the same phonetic category (within-category shift), or the occurrence of a stimulus from a different phonetic category [pa] (across-category shift). Both the across- and within-category shift stimuli differed equally from the standard stimulus in the time of onset of the first formant and in the amount of aspiration in the second and third formants. The NIP2 response of the AER was larger to the across-category shift than to the within-category shift. The within-category shift did not differ from a no-shift control. These findings suggest (1) that the AER can reflect the relative discriminability of stop consonants drawn from the same or different phonetic categories in a manner similar to other behavioral measures; (2) that the detailed acoustic representation of stop consonants is transformed into a categorized phonetic representation within 200 msec after stimulus onset.     

Enhanced discriminability at the phonetic boundaries for the voicing feature in macaques

Discrimination of speech sounds from three computer-generated continua that ranged from voiced to voiceless syllables (/ba-pa/, /da-ta/, and ga-ha/ was tested with three macaques. The stimuli on each continuum varied in voice-onset time (VOT). Paris of stimuli that were equally different in VOT were chosen such that they were either within-category pairs (syllables given the same phonetic label by human listeners) or between-category paks (syllables given different phonetic labels by human listeners). Results demonstrated that discrimination performance was always best for between-category pairs of stimuli, thus replicating the “phoneme boundary effect” seen in adult listeners and in human infants as young as I month of age. The findings are discussed in terms of their specific impact on accounts of voicing perception in human listeners and in terms of their impact on discussions of the evolution of language.     

塞辅音范畴通达的时间进程：来自语境效应的证据

采用语境效应范式,以汉语听者为被试,在三个实验中考察了塞辅音声学信息和语音信息激活的时间进程。实验1语境刺激是/ta/、/ka/音节和/ta/、/ka/塞音段的声学模拟音,目标刺激是/ta/-/ka/对比连续体,结果发现,塞音声学信息激活没有产生语境效应。实验2语境刺激是/ta/、/ka/音节和/ta/、/ka/塞音段,结果发现塞音语音信息激活产生了显著的对比语境效应。实验3变化塞音段和目标刺激之间的间隔,系统考察塞音范畴通达的时间进程,结果发现,塞音知觉中听觉加工阶段向语音加工阶段的转变约发生于刺激加工后120 ms。实验结果揭示了塞辅音知觉中音位范畴通达的时间进程。     

Categorical perception of speech stimuli in children at risk for reading difficulty

Children determined to be at risk (n = 24) or not at risk (n = 13) for reading difficulty listened to tokens from a voice onset time (VOT) (/ga/-/ka/) or tone series played in a continuous unbroken rhythm. Changes between tokens occurred at random intervals and children were asked to press a button as soon as they detected a change. For the VOT series, at-risk children were less sensitive than not-at-risk children to changes between tokens that crossed the phonetic boundary. Maps of group stimulus space produced using multidimensional scaling of reaction times for the VOT series indicated that at-risk children may attend less to the phonological information available in the speech stimuli and more to subtle acoustic differences between phonetically similar stimuli than not-at-risk children. Better phonological processing was associated with greater sensitivity to changes between VOT tokens that crossed the phonetic boundary and greater relative weighting of the phonological compared to the acoustic dimension across both groups.     

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.     

Evidence for a central representation of instrument timbre

An information processing account of perception seeks to delineate the stages of processing through which a stimulus passes and determine the properties of the representation at each stage. Research in phonetic perception has identified two stages, the second of which is thought to encode abstract acoustic attributes of sounds. The present study provided a further test of this proposal by assessing whether nonphonetic stimuli could yield results similar to those obtained with phonetic stimuli. Five selective adaptation experiments were carried out with a trumpet—piano timbre continuum. Two manipulations were used to measure abstract encoding: cross-ear presentation of adaptor and test series, and the use of adaptors that were acoustically different from the continuum endpoints. The results provide evidence for an abstract representation of timbre. The similarity of the findings to those in the phonetic adaptation literature is discussed.     

The effect of irrelevant surround on speeded visual discriminations varying in complexity

To measure the effect of varying stimulus material on visual matching, a three-factor experimental design was employed, with “same”-“different” RT as the main dependent variable. Pairs of sequences of meaningless shapes served as stimuli, varying in discriminability (high or low), complexity (sequence lengths of 1, 2, 5, or 8 shapes), and level of pair difference (identical sequences or sequences with one pair differing). All independent variables significantly affected RT, with (a) high-discriminability stimuli being reacted to faster than low, (b)RT increasing with sequence pair length, and (c)“same”-response RTs interacting with “different”-response RTs. A significant triple-order interaction component implied that, while a single-process self-terminating feature testing model could accommodate data from the low-discriminability condition, the high-discriminability data did not fit this model. The results are taken as support for a dual-process model to account for the data from “same”-“different” RT tasks. epaxtment of     

Stimulus-specific processing consequences of pattern goodness

Two issues concerning the effects of visual pattern goodness on information processing time were investigated: the role of memory vs. encoding and the role of individual stimulus goodness vs. stimulus similarity. A sequential “same-different” task was used to provide differentiation of target item or memory effects from display item or encoding effects. Experiment 1 used four alternative stimuli in each block of trials. The results showed that good patterns were processed faster than poor patterns for both “same” and “different” responses. Furthermore, the goodness of the target item had a greater effect on reaction time than did the goodness of the display item, indicating that memory is more important than encoding in producing faster processing of good stimuli. Effects of interstimulus similarity on processing time were minimal, although isolation of good stimuli in a similarity space could explain many of the results. Experiment 2 replicated the results of Experiment 1, despite the fact that differences in similarity space had been minimized by using only two alternative stimuli in each block. In addition, the speed of processing a “same” pair was essentially independent of the particular alternative stimulus in a block. These results suggest that in this task, there is a processing advantage for good stimuli that is stimulus specific, with the effect operating primarily in memory.     

Motor activation from visible speech: evidence from stimulus response compatibility

In speech perception, phonetic information can be acquired optically as well as acoustically. The motor theory of speech perception holds that motor control structures are involved in the processing of visible speech, whereas perceptual accounts do not make this assumption. Motor involvement in speech perception was examined by showing participants response-irrelevant movies of a mouth articulating /ba/ or /da/ and asking them to verbally respond with either the same or a different syllable. The letters "Ba" and "Da" appeared on the speaker's mouth to indicate which response was to be performed. A reliable interference effect was observed. In subsequent experiments, perceptual interference was ruled out by using response-unrelated imperative stimuli and by preexposing the relevant stimulus information. Further, it was demonstrated that simple directional features (opening and closing) do not account for the effect. Rather, the present study provides evidence for the view that visible speech is processed up to a late, response-related processing stage, as predicted by the motor theory of speech perception.     

Auditory and phonetic coding of the cues for speech: Discrimination of the [r-l] distinction by young infants

Infants, 2 and 3 months of age, were found to discriminte stimuli along the acoustic continuum underlying the phonetic contrast [r] vs. [l] in a nearly categorical manner. For an approximately equal acoustic difference, discrimination, as measured by recovery from satiation or familiarization, was reliably better when the two stimuli were exemplars of different phonetic categories than when they were acoustic variations of the same phonetic category. Discrimination of the same acoustic information presented in a nonspeech mode was found to be continuous, that is, determined by acoustic rather than phonetic characteristics of the stimuli. The findings were discussed with reference to the nature of the mechanisms that may determine the processing of complex acoustic signals in young infants and with reference to the role of linguistic experience on the development of speech perception at the phonetic level.

     

Effect of speaking rate on the perceptual structure of a phonetic category

When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener's adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.     

How long to get to the “gist” of real-world natural scenes?

This study aimed at assessing the processing time of a natural scene in a fast categorization task of its context or “gist”. In Experiment 1, human subjects performed 4 go/no-go categorization tasks in succession with colour pictures of real-world scenes belonging to 2 natural categories: “Sea” and “mountain”, and 2 artificial categories: “Indoor” and “urban”. Experiment 2 used colour and grey-level scenes in the same tasks to assess the role of colour cues on performance. Pictures were flashed for 26 ms. Both experiments showed that the gist of real-world scenes can be extracted with high accuracy (>90%), short median RT (400-460 ms) and early responses triggered with latencies as short as 260-300 ms. Natural scenes were processed faster than artificial scenes. Categories for which colour could have a diagnostic value were processed faster in colour than in grey. Finally, processing speed is compared for scene and object categorization tasks.