Читать книгу The Handbook of Speech Perception - Группа авторов - Страница 75

As described earlier, phonetic segments are composed of a set of features. Comparing the feature composition of segments provides a means of specifying how many features they share. It has been assumed that the more features two segments share, the more similar they are to each other. Behavioral studies support this notion (Bailey & Hahn, 2005). In particular, studies examining ratings of similarity between syllable pairs differing in consonants have shown that listeners rate pairs of syllables that are distinguished by one feature as more similar to each other than stimuli distinguished by two or more features (Greenberg & Jenkins, 1964). Discrimination studies using same/different or two auditory forced choice paradigms show that subjects take longer to discriminate and make more errors for syllable pairs distinguished by one feature (e.g. [p] and [b] differ by voicing or [p] and [t] differ by place of articulation) than stimuli distinguished by several features (e.g. [b] and [t] differ by both voicing and place of articulation) (Wickelgren, 1965; 1966; Wang & Bilger, 1973; Blumstein & Cooper, 1972). Thus, the number of features shared appears to reflect the psychological distance or space between and within phonetic segments.

It is the case that not only the number of features but the particular features present also influence speech perception. Thus, differences also emerge in the perception of single feature contrasts. In general, there is a hierarchy of performance, with increasing numbers of errors occurring for place of articulation contrasts compared to voicing contrasts, and the fewest errors occurring for manner of articulation contrasts (Miller & Nicely, 1955; Blumstein & Cooper, 1972).

Different neural responses have also been shown for features. Given a set of voiced and voiceless stop consonants and fricatives ([b d f p s t v z] in the context of the vowels [a i u]), neural regions encompassing the dorsal speech pathway have been identified that respond to the features place of articulation and to manner of articulation. In particular, Correia, Jansma, and Bonte (2015) trained a classifier to discriminate labial and alveolar place of articulation in the stop consonant syllables [pa] vs. [ta]. They demonstrated generalization in the same neural areas to fricatives distinguished by the same labial vs. alveolar contrast, [fa] vs. [sa]. Similarly, they showed generalization across manner of articulation. Training on a stop vs. fricative pair, [pa] vs. [fa], generalized to [ta] vs. [sa] (see also Guediche et al., 2018 for similar generalization results for the feature voicing).

Aphasic patients show patterns consistent with these findings. In particular, they have more difficulties discriminating minimal pair nonwords and minimal pair words that differ by a single feature compared to stimulus pairs distinguished by two features. Additionally, they have greater difficulties discriminating stimuli distinguished by place of articulation compared to voicing (Blumstein, Baker, & Goodglass, 1977).