Random dots blinking: a new approach to elucidate the activities of the extrastriate cortex in humans

To investigate cortical activities related to the visual recognition of cha racters, we recorded the magnetoencephalography (MEG) in six normal subject s who were encouraged to discriminate capital English letters displayed for a brief period. To reduce the primary responses evoked by the luminance ch ange in the striate cortex (V1), we used a novel stimulus method, random do ts blinking (RDB), by means of the temporal changes of patterns using a lar ge number of small random dots. Along with the MEG recording, we also measu red the discrimination accuracy rate (%) to know how well the subjects reco gnized the letters. One clear component, about 300 ms in peak latency, was identified in all six subjects. Its peak amplitude and the discrimination a ccuracy rate increased similarly as the character display duration became l onger. Its signal source was estimated in the extrastriate cortex, around t he fusiform gyrus, in the right hemisphere. We suspect that the activity in these cortical areas has strong relation to the conscious perception of ch aracters. NeuroReport 9: 3961-3965 (C) 1998 Lippincott Williams & Wilkins.