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.

Comprehension of synthetic speech produced by rule: word monitoring and sentence-by-sentence listening times.

Previous comprehension studies using postperceptual memory tests have often reported negligible differences in performance between natural speech and several kinds of synthetic speech produced by rule, despite large differences in segmental intelligibility. The present experiments investigated the comprehension of natural and synthetic speech using two different on-line tasks: word monitoring and sentence-by-sentence listening. On-line task performance was slower and less accurate for passages of synthetic speech than for passages of natural speech. Recognition memory performance in both experiments was less accurate following passages of synthetic speech than of natural speech. Monitoring performance, sentence listening times, and recognition memory accuracy all showed moderate correlations with intelligibility scores obtained using the Modified Rhyme Test. The results suggest that poorer comprehension of passages of synthetic speech is attributable in part to the greater encoding demands of synthetic speech. In contrast to earlier studies, the present results demonstrate that on-line tasks can be used to measure differences in comprehension performance between natural and synthetic speech.

Loss in pattern-elicited electroretinograms in optic nerve dysfunction.

Both flash- and pattern-elicited electroretinograms and visual-evoked potentials were recorded from a patient with well-documented unilateral optic nerve dysfunction. Although the flash-elicited electroretinograms from the left and right eyes did not differ in amplitude or latency, the flash-elicited visual-evoked potentials were greatly attenuated. Prominent pattern-elicited electroretinograms and visual-evoked potentials, were recorded from the better eye, but neither could be obtained from the affected eye. These results supported the contention that pattern-elicited electroretinograms are derived from optic nerve activity and that the absence of such responses may be diagnostic of loss of optic nerve function. This suggests that testing protocols aimed at assessing optic nerve function might benefit from the inclusion of pattern-elicited electroretinographic recordings. We also obtained contrast sensitivity functions from both eyes. Although considerably suppressed, the contrast sensitivity of the affected eye exhibited a 3-octave range, indicating some pattern-processing capability.