Brain and Vision Research Laboratory

 Eye Movements and Motion Perception

The Effect of Lesions on Sensory Motor Integration: 
A study with stroke patients
 

The interaction between the oculomotor system and motion perception systems is a fascinating sensory motor integration issue.  For years it has be known that visual motion processing probably occurs in two cortical areas, the middle temporal region (MT) and the medial superior temporal region (MST).  Little is known about the role of the oculomotor system in visual motion processing.  The goal of this study was to examine sensory motor integration by adapting a measure of eye movement performance, known as an oculomotor difference threshold (ODT), developed by Kowler & McKee, and compare with a psychophysically determined threshold for direction discrimination.  Our hypothesis was that if a subject could match the target velocity of a random dot cinematogram (RDC) stimulus presented at a constant velocity, then, the smallest coherence needed to match the target velocity could be determined.  The ability to match a target velocity would be our measure of smooth pursuit performance.  The measure of smooth pursuit performance could then be compared to psychophysically determined thresholds for direction discrimination.  To measure smooth pursuit performance a software package was developed in Matlab to calibrate and display eye movement data and measure performance of smooth pursuit eye motion.  A stimulus known as a RDC was used to elicit the open loop phase of a smooth pursuit eye motion.  The RDC used, developed by Newsome & Pare contains no net motion, however a sense of coherent motion is perceived due to a spatio-temporal integration over the stimulus region.  Three normal subjects and one patient were tested.  It was shown that it is possible for a normal subject to track an RDC stimulus given a sufficient amount of coherence.  It was also shown that ODT’s are significantly larger than perceptual thersholds.  Data collected from patient JV suggests a problem with her open phase of smooth pursuit motion. The results from this study suggest that RDC's have enormous potential for further investigation into the interaction of processing area in the human brain.

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