Fig. 1
Stronger premicrosaccadic enhancement of superior colliculus (SC) visual sensitivity for dark contrasts. (a, b) Visual responses of an example SC neuron to 10% contrast stimuli of either positive (a) or negative (b) luminance polarity. The gray curves (dark in b and lighter shade in a) show the stimulus-evoked visual responses of the neuron in the absence of any microsaccades within ± 150 ms from stimulus onset. The neuron preferred the dark stimulus. The colored curves show the same neuron’s visual responses when stimulus onset occurred within < 100 ms before microsaccade onset. Premicrosaccadic enhancement occurred, consistent with our earlier results10, but it was stronger for the dark contrast. (c, d) The same neuron’s responses for 100% contrast stimuli. This time, there was no premicrosaccadic enhancement for bright stimuli (c), but it was present for dark stimuli (d). The inset shows the retinotopic preferred RF location of the neuron (approximately 6° eccentricity in the lower left visual field). (e–h) Another example neuron from the same SC site. This neuron preferred bright stimuli in its baseline curves. Once again, it exhibited premicrosaccadic enhancement. However, the enhancement was weak or absent for bright stimuli, and more robust for dark stimuli (e.g. the 100% contrast condition). Thus, there was stronger premicrosaccadic enhancement of SC visual sensitivity for negative luminance polarity stimuli. Error bars denote SEM. n = 24–33 trials in the baseline curves across panels; n = 5–9 trials in the premicrosaccadic curves across panels (Methods).
