Objectives: The present study aims to examine in depth the nature and characteristics of the P300 response reflected in the processing of across-category speech stimuli by determining whether the P300 is different for the extent of deviancy of stimuli and a scalp distribution; the behavioral response is different for the extent of deviancy of stimuli; and the P300 is correlated with the behavioral response. Methods: The P300 and behavioral data were measured in an oddball paradigm from twenty

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... rmal-hearing adults. From behavioral labeling test results of a nine-step series /bi/-/pi/ continuum, one within-category CV was selected as a standard stimulus and two across-category CVs were selected as weak (WD) and strong deviant stimuli (SD), respectively. Results: The P300 amplitude was larger for SD than for WD and on central and parietal regions than frontal region while the P300 latency was shorter for SD than for WD with no difference for the scalp distribution. The accuracy response was greater and reaction times were faster for SD than for WD. And reaction times were negatively correlated with P300 amplitude and positively correlated with P300 latency. Conclusion: The results suggest that the P300 amplitude and latency can reflect perceptual processing of subtle phonetic changes in across-category speech stimuli, and they are correlated with reaction times.