On the bistability of sine wave analogues of speech.

Our studies revealed two stable modes of perceptual organization, one based on attributes of auditory sensory elements and another based on attributes of patterned sensory variation composed by the aggregation of sensory elements. In a dual-task method, listeners attended concurrently to both aspects, component and pattern, of a sine wave analogue of a word. Organization of elements was indexed by several single-mode tests of auditory form perception to verify the perceptual segregation of either an individual formant of a synthetic word or a tonal component of a sinusoidal word analogue. Organization of patterned variation was indexed by a test of lexical identification. The results show the independence of the perception of auditory and phonetic form, which appear to be differently organized concurrent effects of the same acoustic cause.

Perceiving the sex and identity of a talker without natural vocal timbre.

The personal attributes of a talker perceived via acoustic properties of speech are commonly considered to be an extralinguistic message of an utterance. Accordingly, accounts of the perception of talker attributes have emphasized a causal role of aspects of the fundamental frequency and coarse-grain acoustic spectra distinct from the detailed acoustic correlates of phonemes. In testing this view, in four experiments, we estimated the ability of listeners to ascertain the sex or the identity of 5 male and 5 female talkers from sinusoidal replicas of natural utterances, which lack fundamental frequency and natural vocal spectra. Given such radically reduced signals, listeners appeared to identify a talker's sex according to the central spectral tendencies of the sinusoidal constituents. Under acoustic conditions that prevented listeners from determining the sex of a talker, individual identification from sinewave signals was often successful. These results reveal that the perception of a talker's sex and identity are not contingent and that fine-grain aspects of a talker's phonetic production can elicit individual identification under conditions that block the perception of voice quality.

Talker identification based on phonetic information.

Accounts of the identification of words and talkers commonly rely on different acoustic properties. To identify a word, a perceiver discards acoustic aspects of an utterance that are talker specific, forming an abstract representation of the linguistic message with which to probe a mental lexicon. To identify a talker, a perceiver discards acoustic aspects of an utterance specific to particular phonemes, creating a representation of voice quality with which to search for familiar talkers in long-term memory. In 3 experiments, sinewave replicas of natural speech sampled from 10 talkers eliminated natural voice quality while preserving idiosyncratic phonetic variation. Listeners identified the sinewave talkers without recourse to acoustic attributes of natural voice quality. This finding supports a revised description of speech perception in which the phonetic properties of utterances serve to identify both words and talkers.

On the intonation of sinusoidal sentences: contour and pitch height.

A sinusoidal replica of a sentence evokes a clear impression of intonation despite the absence of the primary acoustic correlate of intonation, the fundamental frequency. Our previous studies employed a test of differential similarity to determine that the tone analog of the first formant is a probable acoustic correlate of sinusoidal sentence intonation. Though the typical acoustic and perceptual effects of the fundamental frequency and the first formant differ greatly, our finding was anticipated by reports that harmonics of the fundamental within the dominance region provide the basis for impressions of pitch more generally. The frequency extent of the dominance region roughly matches the range of variability typical of the first formant. Here, we report two additional tests with sinusoidal replicas to identify the relevant physical attributes of the first formant analog that figure in the perception of intonation. These experiments determined (1) that listeners represent sinusoidal intonation as a pattern of relative pitch changes correlated with the frequency of the tonal replica of the first formant, and (2) that sinusoidal sentence intonation is probably a close match to the pitch height of the first formant tone. These findings show that some aspects of auditory pitch perception apply to the perception of intonation; and, that impressions of pitch of a multicomponent nonharmonic signal can be derived from the component within the dominance region.

On the perception of speech from time-varying acoustic information: contributions of amplitude variation.

The cyclic variation in the energy envelope of the speech signal results from the production of speech in syllables. This acoustic property is often identified as a source of information in the perception of syllable attributes, though spectral variation can also provide this information reliably. In the present study of the relative contributions of the energy and spectral envelopes in speech perception, we employed sinusoidal replicas of utterances, which permitted us to examine the roles of these acoustic properties in establishing or maintaining time-varying perceptual coherence. Three experiments were carried out to assess the independent perceptual effects of variation in sinusoidal amplitude and frequency, using sentence-length signals. In Experiment 1, we found that the fine grain of amplitude variation was not necessary for the perception of segmental and suprasegmental linguistic attributes; in Experiment 2, we found that amplitude was nonetheless effective in influencing syllable perception, and that in some circumstances it was crucial to segmental perception; in Experiment 3, we observed that coarse-grain amplitude variation, above all, proved to be extremely important in phonetic perception. We conclude that in perceiving sinusoidal replicas, the perceiver derives much from following the coherent pattern of frequency variation and gross signal energy, but probably derives rather little from tracking the precise details of the energy envelope. These findings encourage the view that the perceiver uses time-varying acoustic properties selectively in understanding speech.

Perceptual normalization of vowels produced by sinusoidal voices.

When listeners hear a sinusoidal replica of a sentence, they perceive linguistic properties despite the absence of short-time acoustic components typical of vocal signals. Is this accomplished by a postperceptual strategy that accommodates the anomalous acoustic pattern ad hoc, or is a sinusoidal sentence understood by the ordinary means of speech perception? If listeners treat sinusoidal signals as speech signals however unlike speech they may be, then perception should exhibit the commonplace sensitivity to the dimensions of the originating vocal tract. The present study, employing sinusoidal signals, raised this issue by testing the identification of target /bVt/, or b-vowel-t, syllables occurring in sentences that differed in the range of frequency variation of their component tones. Vowel quality of target syllables was influenced by this acoustic correlate of vocal-tract scale, implying that the perception of these nonvocal signals includes a process of vocal-tract scale, implying that the perception of these nonvocal signals includes a process of vocal-tract normalization. Converging evidence suggests that the perception of sinusoidal vowels depends on the relation among component tones and not on the phonetic likeness of each tone in isolation. The findings support the general claim that sinusoidal replicas of natural speech signals are perceptible phonetically because they preserve time-varying information present in natural signals.

Coding of the speech spectrum in three time-varying sinusoids.

Recent perceptual experiments with normal adult listeners show that phonetic information can readily be conveyed by sinewave replicas of speech signals. These tonal patterns are made of three sinusoids set equal in frequency and amplitude to the respective peaks of the first three formants of natural-speech utterances. Unlike natural and most synthetic speech, the spectrum of sinusoidal patterns contains neither harmonics nor broadband formants, and is identified as grossly unnatural in voice timbre. Despite this drastic recoding of the short-time speech spectrum, listeners perceive the phonetic content if the temporal properties of spectrum variation are preserved. These observations suggest that phonetic perception may depend on properties of coherent spectrum variation, a second-order property of the acoustic signal, rather than any particular set of acoustic elements present in speech signals.

Speech perception without traditional speech cues.

A three-tone sinusoidal replica of a naturally produced utterance was identified by listeners, despite the readily apparent unnatural speech quality of the signal. The time-varying properties of these highly artificial acoustic signals are apparently sufficient to support perception of the linguistic message in the absence of traditional acoustic cues for phonetic segments.