Abstract
This study investigated the mechanisms of flicker detection suppression by measuring mesopic rod and cone critical flicker frequencies (CFFs) at different center and surround illuminance levels. Stimuli were generated with a four-primary photostimulator that provided independent control of rod and cone excitations. The results showed that dim surrounds ≤0.2 Td suppressed cone-mediated CFFs at ≥20 Td but not rod-mediated CFFs. These results can be understood in terms of peak amplitudes of photoreceptor impulse response functions under different stimulation conditions.
Highlights
Anatomical and single-unit electrophysiological studies have shown that rods and cones share neural pathways and have joint inputs to retinal ganglion cells [1,2]
Our measurements indicated that critical flicker frequencies (CFFs) with the isolated cone stimuli and with the combined stimuli at ≥20 Td were comparable, suggesting dominating cone contributions to the combined CFFs at these light levels
Given that equiluminantsurround CFFs with the isolated cone stimuli and with the combined stimuli at ≥20 Td were most likely to be reduced by dim surrounds and suppression of rod flicker detection was observed only in one observer at 200 Td, we concluded that dim surrounds suppressed cone CFFs but only at a higher light level
Summary
Anatomical and single-unit electrophysiological studies have shown that rods and cones share neural pathways and have joint inputs to retinal ganglion cells [1,2]. One pathway is via ON rod bipolars, AII amacrine cells, and ON and OFF cone bipolars. This rod bipolar pathway [3] is slow in temporal processing and is hypothesized to mediate rod vision at scotopic light levels. The second pathway transmits rod information via rod– cone gap junctions and ON and OFF cone bipolars. This rod– cone gap junction pathway [3] is faster than the rod bipolar pathway and is hypothesized to mediate rod vision at high scotopic and mesopic light levels. A third insensitive rod pathway between rods and OFF cone bipolars has been identified but so far has been evident only in rodents [4]
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