Underlying mechanism for categorical perception: tone-onset time and voice-onset time evidence of Hebrew voicing.
The nature of the mechanism responsible for the categorical labeling of stimuli is not clear. One hypothesis suggests that categorization is limited by the 'natural sensitivities' of the auditory system. The alternative hypothesis suggests that categorization is mediated by a special speech mode and is influenced by how speech is produced. The present study attempts to provide some insight into this dilemma by evaluating categorical perception (CP) in speech and non-speech stimuli and across languages. Specifically, the goals of the present study were (1) to compare phonetic boundaries of Hebrew voicing to categorical boundaries (CB) of a two-tone complex which varies in the relative timing of the two tones (TOT) [TOT stimuli are considered be the non-speech analog to voice-onset time (VOT)], and (2) to re-establish the CB values of non-speech analog to voicing in American-English speakers using the same TOT continua as the Hebrew speakers and to compare them to CB of Hebrew-speaking subjects. Our assumption was that if CP is mediated by basic auditory sensitivity then we expect similar CB for speech and non-speech stimuli and no effect of language on CB. If, however, a special speech code determines CP, then phonetic boundaries are expected to be different from CB of non-speech stimuli and across languages. Of particular interest is the special case of Hebrew whose voice-voiceless distinction in production is very different from that in English. Twelve Hebrew-speaking adults and 12 American-English speaking adults participated in this study. Stimuli consisted of (a) a two-tone complex continuum that varied in the relative onset time of the lower tone from a lead of -100 ms to a lag of +50 ms in 10 ms steps, and (b) a /ba-pa/ continuum which varied in VOT values similar to (a). Subjects identified TOT stimuli as belonging to one of three categories: leading, simultaneous, or lagging. VOT stimuli were labeled as /ba/ or /pa/. Results show (a) different phonetic boundary for Hebrew voicing compared to published data on English voicing, (b) different category boundaries for speech and non-speech stimuli in Hebrew, (c) a phonetic boundary for Hebrew voicing that does not align with the VOT values of production, and (d) very similar CB for TOT stimuli in Hebrew- and American-English-speaking subjects. The data support the influence of both general auditory abilities and unique speech processes on categorical perception of speech.
Kishon-Rabin
Liat
L
Department of Communication Disorders, Sheba Medical Center, Tel-Hashomer, Israel 52621. Irabin@post.tau.ac.il
Rotshtein
Shira
S
Taitelbaum
Riki
R
D000161:Acoustic Stimulation; D000328:Adult; D001307:Auditory Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D011930:Reaction Time / Q000502:physiology; D013067:Speech Perception / Q000502:physiology*; D014831:Voice / Q000502:physiology