Volume 105, Issue 3, March 1999
Index of content:
- SPEECH PERCEPTION 
105(1999); http://dx.doi.org/10.1121/1.426724View Description Hide Description
Three experiments addressed the question of whether pitch-accent information may be exploited in the process of recognizing spoken words in Tokyo Japanese. In a two-choice classification task, listeners judged from which of two words, differing in accentual structure, isolated syllables had been extracted (e.g., ka from baka HL or gaka LH); most judgments were correct, and listeners’ decisions were correlated with the fundamental frequency characteristics of the syllables. In a gating experiment, listeners heard initial fragments of words and guessed what the words were; their guesses overwhelmingly had the same initial accent structure as the gated word even when only the beginning CV of the stimulus (e.g., na- from nagasa HLL or nagashi LHH) was presented. In addition, listeners were more confident in guesses with the same initial accent structure as the stimulus than in guesses with different accent. In a lexical decision experiment, responses to spoken words (e.g., ame HL) were speeded by previous presentation of the same word (e.g., ame HL) but not by previous presentation of a word differing only in accent (e.g., ame LH). Together these findings provide strong evidence that accentual information constrains the activation and selection of candidates for spoken-word recognition.
105(1999); http://dx.doi.org/10.1121/1.426725View Description Hide Description
The present study measured the recognition of spectrally degraded and frequency-shifted vowels in both acoustic and electric hearing.Vowel stimuli were passed through 4, 8, or 16 bandpass filters and the temporal envelopes from each filter band were extracted by half-wave rectification and low-pass filtering. The temporal envelopes were used to modulate noise bands which were shifted in frequency relative to the corresponding analysis filters. This manipulation not only degraded the spectral information by discarding within-band spectral detail, but also shifted the tonotopic representation of spectral envelope information. Results from five normal-hearing subjects showed that vowel recognition was sensitive to both spectral resolution and frequency shifting. The effect of a frequency shift did not interact with spectral resolution, suggesting that spectral resolution and spectral shifting are orthogonal in terms of intelligibility. High vowel recognition scores were observed for as few as four bands. Regardless of the number of bands, no significant performance drop was observed for tonotopic shifts equivalent to 3 mm along the basilar membrane, that is, for frequency shifts of 40%–60%. Similar results were obtained from five cochlear implant listeners, when electrode locations were fixed and the spectral location of the analysis filters was shifted. Changes in recognition performance in electrical and acoustic hearing were similar in terms of the relative location of electrodes rather than the absolute location of electrodes, indicating that cochlear implant users may at least partly accommodate to the new patterns of speech sounds after long-time exposure to their normal speech processor.
105(1999); http://dx.doi.org/10.1121/1.426726View Description Hide Description
In a series of four experiments, the ability of 3- to 4-month-old infants to form categorical representations to syllable-initial consonants in monosyllabic stimuli (experiments 1 and 2) and to initial and final syllables in bisyllabic stimuli (experiments 3 and 4, respectively) was investigated. Experiment 1 yielded no evidence of categorical representations for the initial consonant. However, the results indicated that the four or six stimuli presented during the initial phase of familiarization had been remembered. The results of experiment 2, which employed a less stringent familiarization criterion, replicated the findings of experiment 1, although there was some evidence for categorization for infants whose familiarization performance more closely matched the weaker criterion. In experiment 3, there was strong evidence for a categorical representation of the initial syllable of bisyllabic stimuli for infants experiencing six familiar stimuli. In experiment 4, there was less robust evidence of categorization of the final syllable of bisyllabic stimuli, but again only when six familiar stimuli were experienced. The results were discussed in terms of the earliest representation of speech being syllables that could be modified by the rhythmic nature of the infant’s native language.