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Received November 28, 2003
Revised December 18, 2003
Accepted after revision February 19, 2004
1 Ruhr-University-Bochum
2 Universidade do Minho
* To whom correspondence should be addressed. E-mail: jancke{at}neurobiologie.rub.de.
Psychophysical evidence in humans indicates that localization is different for stationary flashed and coherently moving objects. To address how the primary visual cortex represents object position we used a population approach that pools spiking activity of many neurons in cat area 17. In response to flashed stationary squares (0.4 deg) we obtained localized activity distributions in visual field coordinates, which we referred to as profiles across a "population receptive field" (PRF). We here show how motion trajectories can be derived from activity across the PRF and how the representation of moving and flashed stimuli differs in position. We found that motion was represented by peaks of population activity that followed the stimulus with a speed-dependent lag. However, time-to-peak latencies were shorter by ~16 ms as compared to the population responses to stationary flashes. In addition, motion representation showed a directional bias as latencies were more reduced for peripheral-central motion compared to opposite direction. We suggest that a moving stimulus provides "pre-activation" that allow a more rapid processing than for a single flash event.
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