Perceptual Organization of Speech

Abstract

How does a perceiver resolve the linguistic properties of an utterance? This question has motivated many investigations within the study of speech perception and a great variety of explanations. In a retrospective summary 15 years ago, Klatt (1989) reviewed a large sample of theoretical descriptions of the perceiver's ability to project the sensory effects of speech, exhibiting inexhaustible variety, into a finite and small number of linguistically defined attributes, whether features, phones, phonemes, syllables, or words. Although he noted many distinctions among the accounts, with few exceptions they exhibited a common feature. Each presumed that perception begins with a speech signal, well-composed and fit to analyze. This common premise shared by otherwise divergent explanations of perception obliges the models to admit severe and unintended constraints on their applicability. To exist within the limits set by this simplifying assumption, the models are restricted to a domain in which speech is the only sound; moreover, only a single talker ever speaks at once. Although this designation is easily met in laboratory samples, it is safe to say that it is rare in vivo. Moreover, in their exclusive devotion to the perception of speech the models are tacitly modular (Fodor, 1983), whether or not they acknowledge it.Despite the consequences of this dedication of perceptual models to speech and speech alone, there has been a plausible and convenient way to persist in invoking the simplifying assumption. This fundamental premise survives intact if a preliminary process of perceptual organization finds a speech signal, follows its patterned variation amid the effects of other sound sources, and delivers it whole and ready to analyze for linguistic properties. The indifference to the conditions imposed by the common perspective reflects an apparent consensus that perceptual organization of speech is simple, automatic, and accomplished by generic means. However, despite the rapidly established perceptual coherence of the constituents of a speech signal, the perceptual organization of speech cannot be reduced to the available and well-established principles of auditory perceptual organization.

Constraints on Sensitivity to Auditory Modulation in the Perceptual Organization of Speech

“…The function of perceptual organization obliges a perceiver, young or old, to resolve the time-varying pattern of a speech spectrum independent of the specific physical characteristics of the carrier, as studies of sine-wave speech (Remez, 2005), noiseband vocoded speech (Shannon, Zeng, Kamath, Wygonski, & Ekelid, 1995) and chimerical speech (Smith, Delgutte & Oxenham, 2002) have shown. Further, this sensitivity to pattern irrespective of the spectral elements which compose it is arguably a key feature of the robustness of speech to distortion.…”

“…Indeed, in order to group time-varying sinusoids into a coherent signal, a listener must tolerate the absence of natural acoustic products of vocalization and the familiar timbres these spectral elements evoke. Moreover, the listener must disregard the nonvocal quality of the contrapuntal tones in resolving the coherence among the auditory constituents of an evolving utterance (Remez, 2005). …”

“…In this function, the whistles, clicks, hisses buzzes and hums composing speech cohere perceptually despite their acoustic variety and discontinuity. By meeting this fundamental challenge, a second perceptual function becomes possible, namely, to analyze a coherent sensory stream for its linguistic and personal attributes (Remez, 2005; Remez, Rubin, Berns, Pardo & Lang, 1994). Auditory sensory samples of speech fade rapidly (Cowan, 1984), yet perceivers are exquisitely sensitive to the spectrotemporal pattern of a speech spectrum.…”

The auditory organization of complex sounds

“…According to Bregman's proposal, schemas can only select among the potential groupings of frequency components that have been generated by general-purpose grouping processes (4). The opposite view is that speech processes have the ability to extract frequency components from the input independently of the operation of general-purpose grouping processes (50)(51)(52). Even though the studies reviewed in the following sections demonstrate that phonetic perception is affected by auditory organization principles, it is still necessary to explain why speech percepts are sometimes formed in apparent violation of the principles of general-purpose grouping processes.…”

“…Moreover, the sinusoidal components for a given word may have asynchronous onsets, and there can be sudden discontinuities in the frequencies of successive portions of the same sine-wave formant tracks. There is little doubt that speech processes can derive intelligible speech from such unusual stimuli because correct phoneme identification rates of about 70 % can be achieved (51). The crucial question is how can this happen in spite of the violation of some of the most effective principles of auditory organization?…”