Speech-sound perception in normal and learning-disabled children: Effect of lengthened CV transition duration

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Previous research has established that many children with learning problems exhibit perceptual deficits in response to certain auditory stimuli, such as stop consonants in CV context. In order to investigate the precise acoustic features of stop consonants that pose perceptual difficulties for these children, discrimination thresholds were compared for normal and learning-disabled children along two separate synthetic /da/–/ga/ continua that differed only in the duration of the formant transitions. Results showed that simply lengthening the formant transition duration from 40 to 80 ms did not result in improved discrimination thresholds for the learning-disabled children. Similarly, an electrophysiologic response that is known to reflect the brain’s preconscious ability to detect a change from one auditory stimulus to another indicated diminished responses in these children to /da/ versus /ga/, regardless of transition duration. This finding suggests that the brevity of the CV formant transitions is not the sole acoustic basis for the observed perceptual deficits. Furthermore, signal processing techniques aimed at enhancing perception of stop consonants likely need to consider other acoustic features, such as relative amplitude and frequency characteristics, instead of (or in addition to) CV transition duration. [Work supported by NIH R01 DC 01510.]