Abstract
Although the primate superior colliculus (SC) has a well documented role in the generation of saccadic eye movements, it may also be involved in the control of spatial attention. We have used reversible inactivation to directly test the role of the SC in the allocation of spatial attention.
We performed focal inactivations with muscimol, a GABA agonist, in the SC of a rhesus macaque trained in an attentionally demanding motion discrimination task. After the monkey initially fixated a central dot, four stochastic motion patches were presented in each quadrant of the visual field. One of the four patches was momentarily cued, and after a variable delay, a brief pulse of motion appeared in the cued location. At the same time, a pulse appeared in the diametrically opposite location; the direction of this foil signal was never the same as that of the cued signal. The monkey was rewarded for reporting the direction of the cued signal with a saccade in the same direction as the motion. The direction of the saccade was thus dissociated from the locus of attention.
Focal inactivation in the SC map caused the monkey to preferentially attend to stimuli in the unaffected portion of the visual field. When the monkey was cued to attend into the affected region, he was unable to report the direction of that signal. Instead, he reported the direction of the foil signal despite the fact that this response was never rewarded. In contrast, when the signal appeared in the affected region in the absence of distracters, motion discrimination thresholds were only marginally increased (12% to 17% coherent motion). Therefore inactivation of the SC caused the monkey to neglect visual stimuli in the affected region but only in the presence of distracters (i.e. visual extinction).
Aginsky Estate, Institute for Neural Computation, UCSD (NIH Grant MH20002).