Transcranial magnetic stimulation over MT/MST fails to impair judgments of implied motion |
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Authors: | James L Alford Paul van Donkelaar Paul Dassonville Richard T Marrocco |
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Institution: | University of Oregon, Eugene, Oregon 97403, USA. |
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Abstract: | The medial temporal and medial superior temporal cortex (MT/MST) is involved in the processing of visual motion, and fMRI
experiments indicate that there is greater activation when subjects view static images that imply motion than when they view
images that do not imply motion at all. We applied transcranial magnetic stimulation (TMS) to MT/MST in order to assess the
functional necessity of this region for the processing of implied motion represented in static images. Area MT/MST was localized
by the use of a TMS-induced misperception of visual motion, and its location was verified through the monitored completion
of a motion discrimination task. We controlled for possible impairments in general visual processing by having subjects perform
an object categorization task with and without TMS. Although MT/MST stimulation impaired performance in a motion discrimination
task (and vertex stimulation did not), there was no difference in performance between the two forms of stimulation in the
implied motion discrimination task. MT/MST stimulation did, however, improve subjects’ performance in the object categorization
task. These results indicate that, within 150 msec of stimulus presentation, MT/MST is not directly involved in the visual
processing of static images in which motion is implied. The results do, however, confirm previous findings that disruption
of MT/MST may improve efficiency in more ventral visual processing streams. |
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