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Re: Location of phonemic boundaries

Dear List:
Richard Warren suggests using the Gating Paradigm to define the perceptual beginning and end of phonemes. This paradigm is used quite widely. However, the validity of Gating Paradigm results depends upon the implicit assumption that later or earlier portions of the stimulus are perceptually irrelevant to the needed recognition process. Specifically, this is an assumption that there is minimal Backward Recognition Masking (BRM) and Forward Recognition Contrast (FRC), phenomena largely studied in the 1970s. We have a manuscript coming out in the next issue of Perception & Psychophysics that, at least for relative pitch judgment of tones, challenges this assumption. We measured the duration threshold for judgment of tones separated by a Musical Fifth. When asked to judge relative pitch for tones in isolation, the target tones need to be about 8 ms in duration. When followed by one or more contextual tones, the target tones need to be at least 25 ms, and sometimes as long as 45 ms., in duration. The relevance to the Gating Paradigm is discussed in the manuscript. We currently are preparing a manuscript describing a completed follow-up study where the task was to judge the direction of (pitch) change for linear frequency glides, measuring thresholds in terms of size of glide frequency change. Compared to threshold for isolated glides, there are very significant (and very large) amounts of BRM when the glide is followed by one or more steady-state tones, and there can be significant FRC when the glide is preceded by such a tone. If these findings with simple stimuli generalize in any way to the processes needed for phoneme identification, then Gating Paradigm results may not be accurate indicators of the perceptual boundaries of phonemes.
  Dick Pastore

Richard Pastore
Distinguished Service Professor
Department of Psychology
Binghamton University
Binghamton, NY 13902-6000

----- Original Message ----- From: "Richard Warren" <rmwarren@xxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Tuesday, August 12, 2008 12:42 PM
Subject: Location of phonemic boundaries

Dear List,

     Jim Miller pointed out on 8 August that “It is well established
that the acoustic information used by a listener to identify a
consonant or a vowel is overlapping and distributed acoustically
across a considerable span of time.”  He indicated that although some
have attempted to identify the acoustic locations of consonants and
vowels in running speech, they have for the most part failed since
coarticulation extends well into adjacent phonemes.  But if the
question is changed from “acoustic” boundaries to “perceptual”
boundaries, the task becomes rather easy.

      When a sentence is abruptly terminated, the last speech sound
is easily perceived.  By using an arbitrary starting point before the
beginning of a recorded sentence, and moving the time of the cutoff
through the sentence, it is easy to map the perceptual beginning and
end of each phoneme within a few milliseconds.  We have been using
this procedure for several decades.