Individual differences in auditory abilities

Performance on 19 auditory discrimination and identification tasks was measured for 340 listeners with normal hearing. Test stimuli included single tones, sequences of tones, amplitude-modulated and rippled noise, temporal gaps, speech, and environmental sounds. Principal components analysis and structural equation modeling of the data support the existence of a general auditory ability and four specific auditory abilities. The specific abilities are (1) loudness and duration (overall energy) discrimination; (2) sensitivity to temporal envelope variation; (3) identification of highly familiar sounds (speech and nonspeech); and (4) discrimination of unfamiliar simple and complex spectral and temporal patterns. Examination of Scholastic Aptitude Test (SAT) scores for a large subset of the population revealed little or no association between general or specific auditory abilities and general intellectual ability. The findings provide a basis for research to further specify the nature of the auditory abilities. Of particular interest are results suggestive of a familiar sound recognition (FSR) ability, apparently specialized for sound recognition on the basis of limited or distorted information. This FSR ability is independent of normal variation in both spectral-temporal acuity and of general intellectual ability.     

Individual differences in auditory discrimination of spectral shape and speech-identification performance among elderly listeners

Speech-understanding difficulties observed in elderly hearing-impaired listeners are predominantly errors in the recognition of consonants, particularly within consonants that share the same manner of articulation. Spectral shape is an important acoustic cue that serves to distinguish such consonants. The present study examined whether individual differences in speech understanding among elderly hearing-impaired listeners could be explained by individual differences in spectral-shape discrimination ability. This study included a group of 20 elderly hearing-impaired listeners, as well as a group of young normal-hearing adults for comparison purposes. All subjects were tested on speech-identification tasks, with natural and computer-synthesized speech stimuli, and on a series of spectral-shape discrimination tasks. As expected, the young normal-hearing adults performed better than the elderly listeners on many of the identification tasks and on all but two discrimination tasks. Regression analyses of the data from the elderly listeners revealed moderate predictive relationships between some of the spectral-shape discrimination thresholds and speech-identification performance. The results indicated that when all stimuli were at least minimally audible, some of the individual differences in the identification of natural and synthetic speech tokens by elderly hearing-impaired listeners were associated with corresponding differences in their spectral-shape discrimination abilities for similar sounds.     

Cross-language specialization in phonetic processing: English and Hindi perception of /w/-/v/ speech and nonspeech

This study examined the perceptual specialization for native-language speech sounds, by comparing native Hindi and English speakers in their perception of a graded set of English /w/-/v/ stimuli that varied in similarity to natural speech. The results demonstrated that language experience does not affect general auditory processes for these types of sounds; there were strong cross-language differences for speech stimuli, and none for stimuli that were nonspeech. However, the cross-language differences extended into a gray area of speech-like stimuli that were difficult to classify, suggesting that the specialization occurred in phonetic processing prior to categorization.     

Categorization and discrimination of nonspeech sounds: differences between steady-state and rapidly-changing acoustic cues

Different patterns of performance across vowels and consonants in tests of categorization and discrimination indicate that vowels tend to be perceived more continuously, or less categorically, than consonants. The present experiments examined whether analogous differences in perception would arise in nonspeech sounds that share critical transient acoustic cues of consonants and steady-state spectral cues of simplified synthetic vowels. Listeners were trained to categorize novel nonspeech sounds varying along a continuum defined by a steady-state cue, a rapidly-changing cue, or both cues. Listeners' categorization of stimuli varying on the rapidly changing cue showed a sharp category boundary and posttraining discrimination was well predicted from the assumption of categorical perception. Listeners more accurately discriminated but less accurately categorized steady-state nonspeech stimuli. When listeners categorized stimuli defined by both rapidly-changing and steady-state cues, discrimination performance was accurate and the categorization function exhibited a sharp boundary. These data are similar to those found in experiments with dynamic vowels, which are defined by both steady-state and rapidly-changing acoustic cues. A general account for the speech and nonspeech patterns is proposed based on the supposition that the perceptual trace of rapidly-changing sounds decays faster than the trace of steady-state sounds.     

Differentiation of speech and nonspeech processing within primary auditory cortex

Primary auditory cortex (PAC), located in Heschl's gyrus (HG), is the earliest cortical level at which sounds are processed. Standard theories of speech perception assume that signal components are given a representation in PAC which are then matched to speech templates in auditory association cortex. An alternative holds that speech activates a specialized system in cortex that does not use the primitives of PAC. Functional magnetic resonance imaging revealed different brain activation patterns in listening to speech and nonspeech sounds across different levels of complexity. Sensitivity to speech was observed in association cortex, as expected. Further, activation in HG increased with increasing levels of complexity with added fundamentals for both nonspeech and speech stimuli, but only for nonspeech when separate sources (release bursts/fricative noises or their nonspeech analogs) were added. These results are consistent with the existence of a specialized speech system which bypasses more typical processes at the earliest cortical level.     

Functional neuroimaging of speech perception in six normal and two aphasic subjects.

This positron emission tomography study used a correlational design to investigate neural activity during speech perception in six normal subjects and two aphasic patients. The normal subjects listened either to speech or to signal-correlated noise equivalents; the latter were nonspeech stimuli, similar to speech in complexity but not perceived as speechlike. Regions common to the auditory processing of both types of stimuli were dissociated from those specific to spoken words. Increasing rates of presentation of both speech and nonspeech correlated with cerebral activity in bilateral transverse gyri and adjacent superior temporal cortex. Correlations specific to speech stimuli were located more anteriorly in both superior temporal sulci. The only asymmetry in normal subjects was a left lateralized response to speech in the posterior superior temporal sulcus, corresponding closely to structural asymmetry on the subjects' magnetic resonance images. Two patients, who had left temporal infarction but performed well on single word comprehension tasks, were also scanned while listening to speech. These cases showed right superior temporal activity correlating with increasing rates of hearing speech, but no significant left temporal activation. These findings together suggest that the dorsolateral temporal cortex of both hemispheres can be involved in prelexical processing of speech.     

Acoustic temporal modulation detection and speech perception in cochlear implant listeners

The goals of the present study were to measure acoustic temporal modulation transfer functions (TMTFs) in cochlear implant listeners and examine the relationship between modulation detection and speech recognition abilities. The effects of automatic gain control, presentation level and number of channels on modulation detection thresholds (MDTs) were examined using the listeners' clinical sound processor. The general form of the TMTF was low-pass, consistent with previous studies. The operation of automatic gain control had no effect on MDTs when the stimuli were presented at 65 dBA. MDTs were not dependent on the presentation levels (ranging from 50 to 75 dBA) nor on the number of channels. Significant correlations were found between MDTs and speech recognition scores. The rates of decay of the TMTFs were predictive of speech recognition abilities. Spectral-ripple discrimination was evaluated to examine the relationship between temporal and spectral envelope sensitivities. No correlations were found between the two measures, and 56% of the variance in speech recognition was predicted jointly by the two tasks. The present study suggests that temporal modulation detection measured with the sound processor can serve as a useful measure of the ability of clinical sound processing strategies to deliver clinically pertinent temporal information.     

Auditory temporal acuity in relation to category boundaries; speech and nonspeech stimuli

Experiments were conducted to determine the underlying resolving power of the auditory system for temporal changes at the onset of speech and nonspeech stimuli. Stimulus sets included a bilabial VOT continuum and an analogous nonspeech continuum similar to the "noise-buzz" stimuli used by Miller et al. [J. Acoust. Soc. Am. 60, 410-417 (1976)]. The main difference between these and earlier experiments was that efforts were made to minimize both the trial-to-trial stimulus uncertainty and the cognitive load inherent in some of the testing procedures. Under conditions of minimal psychophysical uncertainty, not only does discrimination performance improve overall, but the local maximum, usually interpreted as evidence of categorical perception, is eliminated. Instead, discrimination performance for voice onset time (VOT) or noise lead time (NLT) is very accurate for short onset times and generally decreases with increasing onset time. This result suggests that "categorization" of familiar sounds is not the result of a psychoacoustic threshold (as Miller et al. have suggested) but rather of processing at a more central level of the auditory system.     

Perceptual coherence in listeners having longstanding childhood hearing losses, listeners with adult-onset hearing losses, and listeners with normal hearing

Perceptual coherence, the process by which the individual elements of complex sounds are bound together, was examined in adult listeners with longstanding childhood hearing losses, listeners with adult-onset hearing losses, and listeners with normal hearing. It was hypothesized that perceptual coherence would vary in strength between the groups due to their substantial differences in hearing history. Bisyllabic words produced by three talkers as well as comodulated three-tone complexes served as stimuli. In the first task, the second formant of each word was isolated and presented for recognition. In the second task, an isolated formant was paired with an intact word and listeners indicated whether or not the isolated second formant was a component of the intact word. In the third task, the middle component of the three-tone complex was presented in the same manner. For the speech stimuli, results indicate normal perceptual coherence in the listeners with adult-onset hearing loss but significantly weaker coherence in the listeners with childhood hearing losses. No differences were observed across groups for the nonspeech stimuli. These results suggest that perceptual coherence is relatively unaffected by hearing loss acquired during adulthood but appears to be impaired when hearing loss is present in early childhood.     

Evaluating the function of phonetic perceptual phenomena within speech recognition: an examination of the perception of /d/-/t/ by adult cochlear implant users

This study examined whether cochlear implant users must perceive differences along phonetic continua in the same way as do normal hearing listeners (i.e., sharp identification functions, poor within-category sensitivity, high between-category sensitivity) in order to recognize speech accurately. Adult postlingually deafened cochlear implant users, who were heterogeneous in terms of their implants and processing strategies, were tested on two phonetic perception tasks using a synthetic /da/-/ta/ continuum (phoneme identification and discrimination) and two speech recognition tasks using natural recordings from ten talkers (open-set word recognition and forced-choice /d/-/t/ recognition). Cochlear implant users tended to have identification boundaries and sensitivity peaks at voice onset times (VOT) that were longer than found for normal-hearing individuals. Sensitivity peak locations were significantly correlated with individual differences in cochlear implant performance; individuals who had a /d/-/t/ sensitivity peak near normal-hearing peak locations were most accurate at recognizing natural recordings of words and syllables. However, speech recognition was not strongly related to identification boundary locations or to overall levels of discrimination performance. The results suggest that perceptual sensitivity affects speech recognition accuracy, but that many cochlear implant users are able to accurately recognize speech without having typical normal-hearing patterns of phonetic perception.     

An auditory basis for the stimulus-length effect in the perception of stops and glides

To investigate possible auditory factors in the perception of stops and glides (e.g., /b/ vs /w/), a two-category labeling performance was compared on several series of /ba/-/wa/ stimuli and on corresponding nonspeech stimulus series that modeled the first-formant trajectories and amplitude rise times of the speech items. In most respects, performance on the speech and nonspeech stimuli was closely parallel. Transition duration proved to be an effective cue for both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets, and the category boundaries along the transition-duration dimension did not differ significantly in the two cases. When the stop/glide distinction was signaled by variation in transition duration, there was a reliable stimulus-length effect: A longer vowel shifted the category boundary toward greater transition durations. A similar effect was observed for the corresponding nonspeech stimuli. Variation in rise time had only a small effect in signaling both the stop/glide distinction and the nonspeech distinction between abrupt and gradual onsets. There was, however, one discrepancy between the speech and nonspeech performance. When the stop/glide distinction was cued by rise-time variation, there was a stimulus-length effect, but no such effect occurred for the corresponding nonspeech stimuli. On balance, the results suggest that there are significant auditory commonalities between the perception of stops and glides and the perception of acoustically analogous nonspeech stimuli.     

Effects of language experience and stimulus complexity on the categorical perception of pitch direction

Whether or not categorical perception results from the operation of a special, language-specific, speech mode remains controversial. In this cross-language (Mandarin Chinese, English) study of the categorical nature of tone perception, we compared native Mandarin and English speakers' perception of a physical continuum of fundamental frequency contours ranging from a level to rising tone in both Mandarin speech and a homologous (nonspeech) harmonic tone. This design permits us to evaluate the effect of language experience by comparing Chinese and English groups; to determine whether categorical perception is speech-specific or domain-general by comparing speech to nonspeech stimuli for both groups; and to examine whether categorical perception involves a separate categorical process, distinct from regions of sensory discontinuity, by comparing speech to nonspeech stimuli for English listeners. Results show evidence of strong categorical perception of speech stimuli for Chinese but not English listeners. Categorical perception of nonspeech stimuli was comparable to that for speech stimuli for Chinese but weaker for English listeners, and perception of nonspeech stimuli was more categorical for English listeners than was perception of speech stimuli. These findings lead us to adopt a memory-based, multistore model of perception in which categorization is domain-general but influenced by long-term categorical representations.     

Effect of age on detection of gaps in speech and nonspeech markers varying in duration and spectral symmetry

Gap detection thresholds for speech and analogous nonspeech stimuli were determined in younger and older adults with clinically normal hearing in the speech range. Gap detection thresholds were larger for older than for younger listeners in all conditions, with the size of the age difference increasing with stimulus complexity. For both ages, gap detection thresholds were far smaller when the markers before and after the gap were the same (spectrally symmetrical) compared to when they were different (spectrally asymmetrical) for both speech and nonspeech stimuli. Moreover, gap detection thresholds were smaller for nonspeech than for speech stimuli when the markers were spectrally symmetrical but the opposite was observed when the markers were spectrally asymmetrical. This pattern of results may reflect the benefit of activating well-learned gap-dependent phonemic contrasts. The stimulus-dependent age effects were interpreted as reflecting the differential effects of age-dependent losses in temporal processing ability on within- and between-channel gap detection.     

Speech categorization in context: joint effects of nonspeech and speech precursors

The extent to which context influences speech categorization can inform theories of pre-lexical speech perception. Across three conditions, listeners categorized speech targets preceded by speech context syllables. These syllables were presented as the sole context or paired with nonspeech tone contexts previously shown to affect speech categorization. Listeners' context-dependent categorization across these conditions provides evidence that speech and nonspeech context stimuli jointly influence speech processing. Specifically, when the spectral characteristics of speech and nonspeech context stimuli are mismatched such that they are expected to produce opposing effects on speech categorization the influence of nonspeech contexts may undermine, or even reverse, the expected effect of adjacent speech context. Likewise, when spectrally matched, the cross-class contexts may collaborate to increase effects of context. Similar effects are observed even when natural speech syllables, matched in source to the speech categorization targets, serve as the speech contexts. Results are well-predicted by spectral characteristics of the context stimuli.     

Using statistical decision theory to predict speech intelligibility. II. Measurement and prediction of consonant-discrimination performance.

The speech recognition sensitivity (SRS) model [H. Müsch and S. Buus, J. Acoust. Soc. Am. 109, 2896-2909 (2001)] was tested by applying it to consonant-discrimination data collected in this study. Normally hearing listeners' abilities to discriminate among 18 consonants were measured in 58 filter conditions using two test paradigms. In one paradigm, listeners chose among all 18 stimuli. In the other, response alternatives were restricted to the correct response and eight consonants that were randomly selected among the 17 incorrect response alternatives. The effect of the number of response alternatives on performance can be described by statistical decision theory. Most filter conditions included one or more sharply filtered narrow bands of speech. Depending on the selection of bands, listeners' performance in multi-band conditions falls short of, equals, or exceeds the performance expected from multiplication of the error rates in the individual bands. The performance advantage in multi-band conditions increases with average band separation. The SRS model provides a good fit to the data and predicts the data more accurately than does the speech intelligibility index.     

Auditory discontinuities interact with categorization: implications for speech perception

Behavioral experiments with infants, adults, and nonhuman animals converge with neurophysiological findings to suggest that there is a discontinuity in auditory processing of stimulus components differing in onset time by about 20 ms. This discontinuity has been implicated as a basis for boundaries between speech categories distinguished by voice onset time (VOT). Here, it is investigated how this discontinuity interacts with the learning of novel perceptual categories. Adult listeners were trained to categorize nonspeech stimuli that mimicked certain temporal properties of VOT stimuli. One group of listeners learned categories with a boundary coincident with the perceptual discontinuity. Another group learned categories defined such that the perceptual discontinuity fell within a category. Listeners in the latter group required significantly more experience to reach criterion categorization performance. Evidence of interactions between the perceptual discontinuity and the learned categories extended to generalization tests as well. It has been hypothesized that languages make use of perceptual discontinuities to promote distinctiveness among sounds within a language inventory. The present data suggest that discontinuities interact with category learning. As such, "learnability" may play a predictive role in selection of language sound inventories.     

Could temporal order differences underlie 2-month-olds' discrimination of English voicing contrasts?

Previous studies have shown that infants discriminate voice onset time (VOT) differences for certain speech contrasts categorically. In addition, investigations of nonspeech processing by infants also yield evidence of categorical discrimination of temporal-order differences. These findings have led some researchers to argue that common auditory mechanisms underlie the infant's discrimination of timing differences in speech and nonspeech contrasts [e.g., Jusczyk et al., J. Acoust. Soc. Am. 67, 262-270 (1980)]. Nevertheless, some discrepancies in the location of the infant's category boundaries for different kinds of contrasts have been noted [e.g., Eilers et al. (1980)]. Because different procedures were used to study the different kinds of contrasts, interpretation of the discrepancies between the studies has been difficult. In the present study, three different continua were examined: [ba]-[pa] stimuli, which differed in VOT; [du]-[tu] stimuli, which differed in VOT but which lacked format transitions; nonspeech formant onset time (FOT) stimuli that varied in the time that lower harmonics increased in amplitude. An experiment with adults indicated a close match between the perceptual boundaries for the three series. Similarly, tests with 2-month-old infants using high amplitude sucking procedure yielded estimates of perceptual category boundaries at between 20 and 40 ms for all three stimulus series.     

Perceptual learning of spectrally degraded speech and environmental sounds

Adaptation to the acoustic world following cochlear implantation does not typically include formal training or extensive audiological rehabilitation. Can cochlear implant (CI) users benefit from formal training, and if so, what type of training is best? This study used a pre-/posttest design to evaluate the efficacy of training and generalization of perceptual learning in normal hearing subjects listening to CI simulations (eight-channel sinewave vocoder). Five groups of subjects were trained on words (simple/complex), sentences (meaningful/anomalous), or environmental sounds, and then were tested using an open-set identification task. Subjects were trained on only one set of materials but were tested on all stimuli. All groups showed significant improvement due to training, which successfully generalized to some, but not all stimulus materials. For easier tasks, all types of training generalized equally well. For more difficult tasks, training specificity was observed. Training on speech did not generalize to the recognition of environmental sounds; however, explicit training on environmental sounds successfully generalized to speech. These data demonstrate that the perceptual learning of degraded speech is highly context dependent and the type of training and the specific stimulus materials that a subject experiences during perceptual learning has a substantial impact on generalization to new materials.     

Some remarks on Pastore (1988)

Pastore [J. Acoust. Soc. Am. 84, 2262-2266 (1988)] has written a lengthy response to Kewley-Port, Watson, and Foyle [J. Acoust. Soc. Am. 83, 1133-1145 (1988)]. In this reply to Pastore's letter, several of his arguments are addressed, and new data are reported which support the conclusion of the original article. That conclusion is, basically, that the temporal acuity of the auditory system does not appear to be the origin of categorical perception of speech or nonspeech sounds differing in temporal onsets.     

Incidental categorization of spectrally complex non-invariant auditory stimuli in a computer game task

This study examined perceptual learning of spectrally complex nonspeech auditory categories in an interactive multi-modal training paradigm. Participants played a computer game in which they navigated through a three-dimensional space while responding to animated characters encountered along the way. Characters' appearances in the game correlated with distinctive sound category distributions, exemplars of which repeated each time the characters were encountered. As the game progressed, the speed and difficulty of required tasks increased and characters became harder to identify visually, so quick identification of approaching characters by sound patterns was, although never required or encouraged, of gradually increasing benefit. After 30 min of play, participants performed a categorization task, matching sounds to characters. Despite not being informed of audio-visual correlations, participants exhibited reliable learning of these patterns at posttest. Categorization accuracy was related to several measures of game performance and category learning was sensitive to category distribution differences modeling acoustic structures of speech categories. Category knowledge resulting from the game was qualitatively different from that gained from an explicit unsupervised categorization task involving the same stimuli. Results are discussed with respect to information sources and mechanisms involved in acquiring complex, context-dependent auditory categories, including phonetic categories, and to multi-modal statistical learning.