Temporal cortex activation during speech recognition: an optical topography study

Cortical activity during speech recognition was examined using optical topo graphy (OT), a recently developed non-invasive technique. To assess relativ e changes in hemoglobin oxygenation, local changes in near-infrared light a bsorption were measured simultaneously from 44 points in both hemispheres. A dichotic listening paradigm was used in this experiment, in which target stimuli and non-target stimuli were presented to different ears. Subjects w ere asked to track targets and to press a button when targets shifted from one ear to the other. We compared three tasks: (i) a control task, in which a tone was used as the target; (ii) a repeat task, in which the target was one repeated sentence; (iii) a story task, in which the targets were conti nuous sentences of a story. The activity for the story task, compared with the repeat task, was localized in the left superior temporal cortex. Relati ve to the control task, we observed in this region a larger increase in oxy hemoglobin concentration and a decrease in deoxyhemoglobin concentration in the story task than those in the repeat task. These results suggest that t he activity in the left temporal association area reflects the load of audi tory, memory, and language information processing, (C) 1999 Elsevier Scienc e B.V. All rights reserved.