Masato Akagi
Psychoacoustic evidence
for the contextual effect model
Abstract:In previous work towards speech recognition (Akagi, 1989), a model was developed which
predicted target formants in reduced vowels based on the interaction between spectral peak
pairs. To substantiate this model, two psychoacoustic experiments were carried out which
measured the amount of phoneme boundary shift with (1) a single formant stimulus as a
preceding anchor and (2) a vowel as a preceding anchor. In the first experiment, a perceptual
boundary shift with a single formant anchor was observed. When the results were compared with
the spectral peak interaction obtained from real speech data using the model, this comparison
showed that the perceptual boundary shift with a single formant anchor is similar to the spectral
peak interaction analyzed by the model. Thus, the contextual effect between single formant
stimuli should play an important role in phoneme neutralization recovery, and the neutralization
recovery model is formulated as the sum of the contextual effects resulting from interaction
between spectral peaks. Additionally, a comparison of these results with those of the second
experiment showed that the phoneme boundary shift with a vowel anchor can be postulated as
the sum of the shift with the single formant anchor and a factor from the preceding anchor. The
factor can be estimated by subtracting the sum of the phoneme boundary shifts with the single
formant anchors estimated by the model from the boundary shift with a vowel anchor. The
difference was represented as a function of the distance between the preceding vowel anchor
and the perceived vowel in a phoneme space.