Increased visual sensitivity following periods of dim illumination.
PURPOSE
We measured changes in the sensitivity of the human rod pathway by testing visual reaction times before and after light adaptation. We targeted a specific range of conditioning light intensities to see if a physiological adaptation recently discovered in mouse rods is observable at the perceptual level in humans. We also measured the noise spectrum of single mouse rods due to the importance of the signal-to-noise ratio in rod to rod bipolar cell signal transfer.


METHODS
Using the well-defined relationship between stimulus intensity and reaction time (Piéron's law), we measured the reaction times of eight human subjects (ages 24-66) to scotopic test flashes of a single intensity before and after the presentation of a 3-minute background. We also made recordings from single mouse rods and processed the cellular noise spectrum before and after similar conditioning exposures.


RESULTS
Subject reaction times to a fixed-strength stimulus were fastest 5 seconds after conditioning background exposure (79% ± 1% of the preconditioning mean, in darkness) and were significantly faster for the first 12 seconds after background exposure (P < 0.01). During the period of increased rod sensitivity, the continuous noise spectrum of individual mouse rods was not significantly increased.


CONCLUSIONS
A decrease in human reaction times to a dim flash after conditioning background exposure may originate in rod photoreceptors through a transient increase in the sensitivity of the phototransduction cascade. There is no accompanying increase in rod cellular noise, allowing for reliable transmission of larger rod signals after conditioning exposures and the observed increase in perceptual sensitivity.
['McKeown|Alex S|AS|', 'Kraft|Timothy W|TW|', 'Loop|Michael S|MS|']
D000221:Adaptation, Ocular D000328:Adult D000368:Aged D000818:Animals D002478:Cells, Cultured D003623:Dark Adaptation D004596:Electroretinography D005260:Female D006801:Humans D008029:Lighting D008297:Male D051379:Mice D008810:Mice, Inbred C57BL D008875:Middle Aged D010775:Photic Stimulation D011930:Reaction Time D017948:Retinal Rod Photoreceptor Cells D055815:Young Adult
rods phototransduction hypersensitivity rod vision scotopic sensitivity