The dynamics of the construction of auditory perceptual representations: MEG studies in humans

This chapter concerns the processes through which auditory sensory information is converted into a perceptual representation relevant for behavior. We describe a series of experiments where subjects listened to faint tones appearing amidst background noise, and were instructed to respond as fast as possible when they detect the tonal objects. Simultaneous psychophysical and brain imaging (MEG) measures were employed to study the mechanisms by which auditory objects are detected and separated from their surroundings. The results demonstrate a striking incongruence between behavioral responses and pre-attentive brain responses, and therefore dissociation between higher level mechanisms related to conscious detection of tones amidst the noise and the lower level, pre-attentive cortical mechanisms that sub-serve the physical extraction of the tonal targets. The implications of these data for the processes that underlie the creation of perceptual representations are discussed. These finding may also provide a methodological tool to study the heuristics humans employ in the course of conscious decision making about events in the world.