Deep tectal cells in pigeons respond to kinematograms

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Abstract
Deep tectal neurons in pigeons respond selectively to moving visual stimuli, and are inhibited by large background patterns moved in-phase with these stimuli. In this investigation we demonstrate that these same deep tectal neurons respond equally well to kinematograms as they do to traditional luminance contrast stimuli typically employed in visual experiments. Computer generated kinematograms, the motion domain equivalents of random dot stereograms, were used as stimuli in these experiments. These kinematograms, where a small centrally located set of random dots is moved coherently in one direction while the remaining dots are moved in a different direction, thus constitute a pure motion stimulus where the stimulus form is only visible in the dynamic pattern, but does not exist on any single frame. Both ‘object’ configured and ‘hole’ configured kinematograms were employed; the former appearing as regions of texture moving over, or in front of, the background texture, while the latter appear as windows through which a more distant textured surface is revealed. Extracellular recordings from isolated deep tectal cells showed that all units responded in a very similar manner whether the stimulus was an ‘object’ configured kinematogram or the more traditional luminance contrast variety. This similarity included directional selectivity, the in-phase inhibition anti-phase facilitation effect, and sensitivity to opposed motion independent of direction. However, when the kinematograms were configured as ‘holes’ none of the units tested responded to these stimuli. The significance of these observations for tectal functioning, image segmentation through motion and animal camouflage is discussed.