Anu Sharma Thomas D. Carrell Nina Kraus
Dept. of Commun. Sci. and Disord., Northwestern Univ., Searle Bldg., 2299 N. Campus Dr., Evanston, IL 60208
Speeded classification of stimuli varying along two independent acoustic dimensions is frequently used to study perceptual processing of dependencies in speech perception. Reaction times are compared for different presentation sequences to infer perceptual dependencies. Initially, Wood [J. Exp. Psychol. 1, 3--20 (1975)] observed a unidirectional dependency relation demonstrating that the processing of place of articulation is dependent on the earlier processing of pitch. Subsequently, other investigators reported diverse patterns of dependencies for different stimulus parameters. However, it is not clear if these dependencies are specific only to the speeded-classification paradigm. The purpose of this experiment was to try to generalize Wood's (1975) results using a different paradigm. The processing dependencies between pitch and place of articulation using a speeded-discrimination paradigm were chosen for examination. The basic principle of the experiment was the same, however instead of classifying the sounds, subjects had to discriminate pairs of sounds using a two-choice (``same'' or ``different'') discrimination task. The overall pattern of results was similar to Wood's study, i.e., there exists an asymmetric dependency between pitch and place of articulation. Furthermore, this pattern of results was observed for ``same'' as well as ``different'' reaction times. A second finding (not reported by Wood) was that the error rate data showed the same pattern of results as the reaction time data. Finally, it appears that speeded discrimination requires a greater level of selective attention and cognitive processing for the decision making process than speeded classification.