Dissociation of fMRI activation and awareness in auditory perception task.

To investigate the relationship between activity in sensory cortex, and the experience of sensory stimuli, functional magnetic resonance imaging (fMRI) of temporal cortex was performed while subjects indicated their perception of speech sounds combined with noise. Auditory cortex activation was found to decrease with decreasing stimulus saliency. Speech stimuli presented at an intensity level near auditory threshold produced significant activation in temporal cortex even when subjects did not report perception of stimuli. These dissociations between simultaneously recorded neurophysiological and psychophysical measures suggest that stimulus-evoked cortical activity does not necessarily produce conscious perception.