Physiological studies of auditory perception have not yet clearly distinguished sensory from decision processes. In this experiment, human participants identified speech sounds masked by varying levels of noise while blood oxygenation signals in the brain were recorded with functional magnetic resonance imaging (fMRI). Accuracy and response time were used to characterize the behavior of sensory and decision components of this perceptual system. Oxygenation signals in a cortical subregion just anterior and lateral to primary auditory cortex predicted accuracy of sound identification, whereas signals in an inferior frontal region predicted response time. Our findings provide neurophysiological evidence for a functional distinction between sensory and decision mechanisms underlying auditory object identification. The present results also indicate a link between inferior frontal lobe activation and response-selection processes during auditory perception tasks.
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