Spatial properties of flicker adaptation

Prolonged viewing of a flickering region reduces sensitivity to a subsequently flickered test patch of identical extent, but the spatial properties of this adaptation are unknown. What happens to the sensitivity to a smaller flickered test patch completely contained in, but inset from, the adapted region? We show that sensitivity to the inset test patch is only slightly affected by adaptation of the larger region. This suggests that neurons that respond to the edges of the smaller test patch are not adapted by the larger flickering region. We then show that an annulus adapter designed specifically to adapt only those edges only slightly reduces sensitivity, demonstrating that neurons that do not adapt to the flickered edges are also involved in detecting flicker. This gives further evidence that flicker detection depends on at least two mechanisms – one sensitive to flickering edges and one sensitive to local flicker, and shows that these mechanisms can operate in isolation.

► Flicker adaptation is strong when the test and adapt regions are spatially aligned.
► Adaptation is weak when the test region is inset relative to the adapter.
► Adaptation is weak when the adapter only modulates the edge of the test region.
► Our results suggest two different mechanisms for flicker detection.
► These mechanisms can operate in isolation with minimal loss in sensitivity.