Developmental dysphasia: a defect of perception, not language?

Abstract

Developmental dysphasia may result from a primary impairment in the rate of processing acoustic stimuli, regardless of whether stimuli are verbal or nonverbal. Subjects were tested for their ability to perceive binary sequences of (1) complex tones, (2) synthesized steady-state vowels, (3) synthesized stop-consonants with formant transitions of normal duration (43 msec), and (4) synthesized stop-consonants with formant transitions extended in duration (95 msec). With nonverbal stimuli, dysphasics were adversely affected by decreases in duration of stimulus elements and interval between elements, and by increases in total number of elements. Total duration of stimulus patterns proved critical to dysphasics' performance. With verbal stimuli, dysphasics proved unimpaired in their discrimination of steady-state vowels, but grossly impaired in their discrimination of stop-consonants comprising a 43-msec transitional period. However, when the transitional period of the same stop-consonants was extended to 95 msec, the dysphasics performed as well as normals. It is suggested that developmental dysphasia is not a language disorder, but results from failure to develop a nonverbal auditory perceptual process which is necessary for speech perception.