Speech remains intelligible despite the elimination of canonical acoustic correlates of phonemes from the spectrum. A portion of this perceptual flexibility can be attributed to modulation sensitivity in the auditory-to-phonetic projection, though signal-independent properties of lexical neighborhoods also affect intelligibility in utterances composed of words. Three tests were conducted to estimate the effects of exposure to natural and sine-wave samples of speech in this kind of perceptual versatility. First, sine-wave versions of the easy/hard word sets were created, modeled on the speech samples of a single talker. The performance difference in recognition of easy and hard words was used to index the perceptual reliance on signal-independent properties of lexical contrasts. Second, several kinds of exposure produced familiarity with an aspect of sine-wave speech: 1) sine-wave sentences modeled on the same talker; 2) sine-wave sentences modeled on a different talker, to create familiarity with a sine-wave carrier; and 3) natural sentences spoken by the same talker, to create familiarity with the idiolect expressed in the sine-wave words. Recognition performance with both easy and hard sine-wave words improved after exposure only to sine-wave sentences modeled on the same talker. Third, a control test showed that signal-independent uncertainty is a plausible cause of differences in recognition of easy and hard sine-wave words. The conditions of beneficial exposure reveal the specificity of attention underlying versatility in speech perception.
Speech signal components that are desynchronized from the veridical temporal pattern lose intelligibility. In contrast, audiovisual presentations with large desynchrony in visible and audible speech streams are perceived without loss of integration. Under such conditions, the limit of desynchrony that permits audiovisual integration is also adaptable. A new project directly investigated the potential for adaptation to consistent desynchrony with unimodal auditory sine-wave speech. Listeners transcribed sentences that are highly intelligible, with veridical temporal properties. Desynchronized variants were created by leading or lagging the tone analog of the second formant relative to the rest of the tones composing the sentences, in 50-msec steps, ranging from 250-msec lead to 250-msec lag. In blocked trials, listeners only tolerated desynchronies <50 msec, and exhibited no gain in intelligibility to consistent desynchrony. Unimodal auditory and bimodal audiovisual forms of perceptual integration evidently exhibit different temporal characteristics, an indication of distinct perceptual functions.
Speech remains intelligible despite the elimination of canonical acoustic correlates of phonemes from the spectrum. Listeners tolerate distortion or spectral blur in tone analogs, noise band vocoded speech, and acoustic chimeras in utterances ranging from syllables to isolated words and sentences. A portion of this flexibility is attributable to short-term perceptual learning in auditory-to-phonetic projection, though exploiting the properties of lexical neighborhoods plays a role with utterances composed of words. New tests were conducted to estimate talker learning, segmental sensitivity, and lexical knowledge in this kind of perceptual versatility. Sine-wave versions of the easy/hard word lists were created, and the performance-level difference between the two lists was used to index the default reliance on lexical processes. Several kinds of preliminary exposure were used to induce sensitivity to a dimension of perceptual learning: sine-wave speech produced by the same talker, sine-wave speech of a different talker, natural speech of the same talker. A comparison of exposure effects on the performance level of easy/hard word recognition offered a clue about the differential contribution of talker-based, segment-based, and lexically-based attention in speech perception without canonical spectra. Implications for perceptual accounts based on cue likelihood will be discussed. [Work supported by NIDCD.]
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