Automaticity in speech perception: some speech/nonspeech comparisons

Three experiments used sine-wave replicas of speech sounds to explore some differences between speech perception and general auditory perception. The experiments compared patterns of behavior in categorization and discrimination tasks for listeners reporting either speech or nonspeech percepts of sine-wave replicas of speech. We hypothesized that the perception of speech sounds is automatized, while the perception of less familiar sounds is not. The first experiment was designed to investigate the perception of relatively long initial consonant transitions using a synthetic /wa/-/ya/ sine-wave analog continuum. Speech listeners perceived the continuum categorically, but nonspeech listeners could not consistently categorize the items in the continuum. In the second experiment, both speech and nonspeech listeners could consistently categorize stimuli having final glides (an/ay/-/aw/ sine-wave replica continuum), but differences between speech and nonspeech listeners were found in the slopes of the identification functions, in reaction times, and in the effect of context. These differences are consistent with the hypothesis that speech perception is automatized. In the third experiment, nonspeech listeners' discrimination sensitivity was greater than speech listeners'. The observed pattern of results suggests that speech perception is accomplished by a fast, obligatory, and thus automatic perceptual mechanism.