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J Neurophysiol (July 9, 2008). doi:10.1152/jn.00747.2007
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Submitted on July 5, 2007
Accepted on July 4, 2008

Smooth pursuit eye movements to isoluminant targets

Doris I Braun1, Neil Mennie1, Christoph Rasche1, Alexander C Schutz1, Michael J Hawken2, and Karl R Gegenfurtner1*

1 Abteilung Allgemeine Psychologie, Justus-Liebig-Universitat, Giessen, Germany
2 Center for Neural Science, New York University, New York, New York, United States

* To whom correspondence should be addressed. E-mail: gegenfurtner{at}uni-giessen.de.

At slow speeds chromatic isoluminant stimuli are perceived to move much slower than comparable luminance stimuli. We investigated whether smooth pursuit eye movements to isoluminant stimuli show an analogous slowing. Beside pursuit speed and latency, we studied speed judgments to the same stimuli during fixation and pursuit. Stimuli were either large sine wave gratings or small Gaussians blobs moving horizontally at speeds between 1 and 11 deg/s. Targets were defined by luminance contrast or color. Confirming prior studies, we found that speed judgments of isoluminant stimuli during fixation showed a substantial slowing when compared to luminance stimuli. A similarly strong and significant effect of isoluminance was found for pursuit initiation: compared to luminance targets of matched contrasts latencies of pursuit initiation were delayed by 50 ms at all speeds and eye accelerations were reduced for isoluminant targets. A small difference was found between steady-state eye velocities of luminance and isoluminant targets. For comparison we measured latencies of saccades to luminance and isoluminant stimuli under similar conditions, but the effect of isoluminance was only found for pursuit. Parallel psychophysical experiments revealed that, different from speed judgments of moving isoluminant stimuli made during fixation, judgments during pursuit are veridical for the same stimuli at all speeds. Therefore, information about target speed seems to be available for pursuit eye movements and speed judgments during pursuit, but is degraded for perceptual speed judgments during fixation and for pursuit initiation.




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A. Tavassoli and D. L. Ringach
Dynamics of Smooth Pursuit Maintenance
J Neurophysiol, July 1, 2009; 102(1): 110 - 118.
[Abstract] [Full Text] [PDF]




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