Speech perception by the chinchilla Identification functions for synthetic VOT stimuli Patrica K Kuhl James D Miller JASA 1977 Introduction To account for the data in speech experiment it is useful to distinguish between auditory levels of processing and phonetic levels of processing The evidence supporting a dichotomy between the two levels a lack of acoustic invariance between the acoustic cues and our percepts Liberman et al 1967 the discovery of perceptual behaviors like categorical perception evidence from studies of selective adaptation Questions about the dichotomy Invariant cues for stop consonants may be found in the dynamic configurations of spectral energy over time Fant 1973 Stevens 1975 Perceptual behaviors have been demonstrated for complex nonspeech signals Pisoni 1977 The effects of selective adaptation thought to provide evidence for phonetic feature detectors now appear to be attributed to auditory Solution A direct test of the distinction between auditory and phonetic levels of processingusing animal listener who has no phonetic resources The rationale for this comparative approach is to tease out the perceptual effects from those that are unique to speech sound processing Previous Analyses Liberman et al 1967 categorical perception is considered unique to the processing of speech sounds For nonspeech stimuli Cutting and Rosner 1974 plucked or bowed Pisoni 1977 Eimas 1974b Infants perceives the stimuli in a linguistic mode and may categorically discriminate voicing contrasts that are not phonemic in the infant s linguistic environment Kuhl 1978 While the infant s perceptual proclivities are linguistically relevant their origins may reflect constraints that are psychoacoustic rather than specifically linguistic Goals In an attempt to differentiate perceptual effects that are attributable to auditory and phonetic levels of processing in speech perception Kuhl Moller 1977 undertook a series of experiments with animal listener The results obtained with alveolar stimuli are reported in experiment I results obtained with labial and velar stimuli are reported in experiments II and III Experiment IV is a report of results obtained when the stimuli from all three continua were used Experiment I A Stimuli The speech sounds were synthesized at the Haskins Laboratories on the parallel resonance synthesizer For a specified VOT the upper two formants were excited with thermal noise for the duration of the interval at the end of this interval the two formants were excited with periodic pulses The first formant was off throughout the VOT interval 5ms for b p and d t 20ms for g k stimuli VOT s from 0 to 80ms in 10 ms steps was recorded on a full track tape recorder and then re recorded onto a disk pack of RAP Subjects Four chinchillas each about two years of age Two of the four animals had been previously trained to categorize naturally produced alveolar tokens as either d or t syllables The other two animals had never been trained Four English speaking adults Apparatus A double grille cage with a loudspeaker in a sound treated booth The cage divided by a midline barrier and having a door buzzer at one end Presentation of a speech sound was initiated by the experimenter and controlled by punched paper tape and a high speed paper tape reader The punched tape was prepared according to the randomization speifications Discriminating training On positive trials the animal had to cross the midline barrier to avoid a mild shock and the surrounding of the buzzer On negative trials the animal could remain at the drinking tube If the animal successfully inhibited the crossing response it was rewarded with free water At the end of that experiment two animals had learned to classify correctly the voiced and voiceless CV syllables produced by eight different talkers in six different vowel context Randomization of positive and negative trials by computerpunched paper tapes Generalization testing On half of the trials the endpoint stimuli 0 and 80 ms VOT On the other half of trials the stimuli between these endpoints 10 to 70 ms VOT During generalization testing shock was never presented and all feedback was arranged to tell the animal he was always correct Testing human subjects Four human subjects with the same sound treated booth the same trial structure instructed to label the stimuli as da or ta Results Experiment I Location of the phonetic boundaries The phonetic boundaries of the fitted curves 35 2 ms VOT for English speaking adults 33 3 ms VOT for chinchillas The boundary value range 29 9 ms 42 0 ms for humans 26 7 ms 36 ms for chinchilla Exposure to natural speech had no effect on the location of the boundary a the two animals trained 31 4 ms VOT b the two animals having no training 32 8 ms VOT Experiment II Subjects Two of the four chinchillas used in experiment I served as subject One had originally been trained on natural speech while the other had been trained only on the synthetic tokens The same four English speaking adults Results Experiment II 1 Transfer from the alveolar stimuli to the stimuli with a labial place of articulation 2 Location of the phonetic boundaries phonetic boundaries of the fitted curves are 26 8 ms VOT for English speaking adults and 23 3 ms for chinchillas 3 Boundary width Each subject s fitted curve was matched at the 50 Experiment III Subject same subjects in experiment II Procedure a Discrimination training b Generalization testing Results a Transfer to stimuli with a velar place of articulation b The 50 points of the fitted curves 42 3 ms VOT for English speaking adults 42 5 ms VOT for chinchillas c Each subject s fitted curve was matched at the 50 point Experiment IV Stimuli The labial alveolar and velar stimuli previously described were used Subject A single animal the one for whom voiced stimuli were positive Procedure a Discrimination training with the endpoint stimuli 0 ms VOT and 80 ms VOT of all three continua b Generalization testing six endpoint stimuli and 21 stimuli between the endpoints 10 ms VOT to 70 ms VOT from labial alveolar and velar continua Results Experiment IV Location of the phonetic boundaries The relative locations of the three boundaries did not change when place of articulation was varied randomly Boundary width The boundary widths of the fitted curves from experiment I II and III are very similar to those from experiment IV Statistical Analyses Phonetic boundary two factor Analysis of Variance species x place of
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