Acoustic Cue Discrimination in Adult Aphasia

Discrimination ability of 15 aphasic, 10 normal, and 10 brain-damaged nonaphasic adults was assessed using a specially constructed discrimination test designed to assess ability to discriminate important acoustic cues for distinctive features of phonemes. A single acoustic cue, such as stopgap duration, spectrum of a consonantal burst peak, or direction and extent of a second-formant transition, created the only difference in minimal pairs which were otherwise acoustically identical. Three of the subtests utilized a spectral cue and three a temporal cue. All subtests used human rather than synthesized speech, and each was altered by a variety of dubbing, filtering, and splicing procedures. Of the 15 aphasic subjects studied, seven failed both the discrimination test and a comprehension test, suggesting that their comprehension disturbances may arise from reduced ability to discriminate acoustic cues for speech sounds. In contrast, both the normal and brain-damaged nonaphasic groups were successful on the discrimination test, suggesting that failure on these discrimination tasks was not simply a function of age or brain damage per se. Moreover, discrimination failure by the aphasics was not evenly distributed. Rather, the aphasic subjects experienced significantly more failures on the temporal cues and were generally successful on the subtests involving cues of a spectral nature.