Selective adaptation by context-conditioned fricatives

Abstract

The role of vowel context and consonant labeling in the selective adaptation of voiceless fricatives was examined in three experiments. This approach was designed to determine whether selective adaptation effects occurred with voiceless fricative stimuli and to determine whether any such effects had a linguistic basis as opposed to a purely auditory basis. Two synthetic fricative-vowel continua were used; one ranged from [si] to [∫i] and the other from [su] to [∫u]. Identification of the consonant portion of the syllables in these continua, as either [s] or [∫], depended on both the frequency of the friction noise and on the vowel quality. In experiment 1, the end points of the continua were used as adaptors, and the identification boundary shifted toward the adapting stimulus. In experiment 2, an ambiguous frication noise (that was identified as [s] before [u] and as [∫] before [i]) adapted the identification boundary in opposite directions, depending on which of the two vowels followed the noise. Thus the direction of adaptation depended on the perceptual identity of the consonant. In the final experiment, the isolated [i] and [u] vowels, and the isolated ambiguous frication noise, were demonstrated to be ineffective adaptors. The selective adaptation effects observed in these experiments were not determined by the acoustical information in the consonant or the vowel alone, but rather by the context-conditioned percept of the fricative. These results extend the reports of other research that has attempted to dissociate auditory from linguistic adaptation, provide further evidence that selective adaptation effects have multiple loci, and establish for the first time a selective adaptation effect which is unambiguously, not acoustically based.