ZASPiL 40 = Speech production and perception : Experimental analyses and models
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In this paper the issue of the nature of the representations of the speech production task in the speaker's brain is addressed in a production-perception interaction framework. Since speech is produced to be perceived, it is hypothesized that its production is associated for the speaker with the generation of specific physical characteristics that are for the listeners the objects of speech perception. Hence, in the first part of the paper, four reference theories of speech perception are presented, in order to guide and to constrain the search for possible correlates of the speech production task in the physical space: the Acoustic Invariance Theory, the Adaptive Variability Theory, the Motor Theory and the Direct-Realist Theory. Possible interpretations of these theories in terms of representations of the speech production task are proposed and analyzed. In a second part, a few selected experimental studies are presented, which shed some light on this issue. In the conclusion, on the basis of the joint analysis of theoretical and experimental aspects presented in the paper, it is proposed that representations of the speech production task are multimodal, and that a hierarchy exists among the different modalities, the acoustic modality having the highest level of priority. It is also suggested that these representations are not associated with invariant characteristics, but with regions of the acoustic, orosensory and motor control spaces.
A fundamental question in the study of speech is about the invariance of the ultimate percepts, or features. The present paper gives an overview of the noninvariance problem and offers some hints towards a solution. Examination of various data on place and voicing perception suggests the following points. Features correspond to natural boundaries between sounds, which are included in the infant's predispositions for speech perception. Adult percepts arise from couplings and contextual interactions between features. Both couplings and interactions contribute to invariance. But this is at the expense of profound qualitative changes in perceptual boundaries implying that features are neither independently nor invariantly perceived. The question then is to understand the principles which guide feature couplings and interactions during perceptual development. The answer might reside in the fact that: (1) adult boundaries converge to a single point of the perceptual space, suggesting a context-free central reference; (2) this point corresponds to the neutral vocoïd, suggesting the reference is related to production; (3) at this point perceptual boundaries correspond to the natural ones, suggesting the reference is anchored in predispositions for feature perception. In sum, perceptual invariance seems to be grounded on a radial representation of the vocal tract around a singular point at which boundaries are context-fee, natural and coincide with the neutral vocoïd.
This paper presents the results of Open Quotient measurements in EGG signals of young (18 to 30 year old) and elderly (59 to 82 year old) male and female speakers. The paper further presents quantitative results on the relation between the OQ and the perception of a speaker's age. Higgins & Saxman (1991) found a decreased OQEGG with increasing age for females, whereas the OQEGG in sustained vowel material increased for males as the speakers age increased. In Linville (2002), however, the spectral amplitudes in the region of F0 (obtained by LTAS-measurements of read speech material) increased with increasing age independent of gender; this could be interpreted indirectly as an increasing OQ. We measured the OQEGG not only for sustained vowels, but also in vowels taken from isolated words. In order to analyse the relation between breathiness in terms of an increased OQ and the mean perceived age per stimulus a perception test was carried out in which listeners were asked to estimate speaker's age based on sustained /a/-vowel stimuli varying in vocal effort (soft - normal - loud) during production. The results indicated the following: (i) The decreased OQ for elderly females originally found by Higgins & Saxman is not apparent in our data for sustained /a/-vowels. For our female speakers no significant difference between the OQ of young and old speakers was found; for elderly males, however, we also found an increasing OQ with increasing age.(ii) In addition, a statistically significant increased OQEGG occurs for the group of the elderly males for the vowels from the word material. (iii) Our results show a strong positive relation between perceived age and OQ in male voices. Regarding (i) and (ii), at least the male speaker's voice becomes more breathy as age increases. Considering (iii), increased breathiness may contribute to the listener’s perception of increased age.