Influence of rod adaptation upon cone responses to light offset in humans: II. Results in an observer with exaggerated suppressive rod-cone interaction.
In normal observers, sensitivity of cones to rapid sinusoidal flicker decreases by about 0.7 log units as rods progressively dark adapt. However, Arden and Hogg (1985) described a night-vision disorder characterized by normal rod sensitivity but exaggerated suppressive rod-cone interaction (SRCI). We refer to this condition as the exaggerated SRCI syndrome (ESS). The present paper examines the influence of rod-adaptation upon cone-mediated responses to light onset and offset in an observer with ESS. Under all conditions of adaptation examined, sensitivity of cones to rapid-on waveforms is indistinguishable to that of a normal observer tested under identical circumstances; rod sensitivity is also normal. However, the sensitivity of cones to transient decreases in illumination is clearly subnormal under light-adapted conditions. This deficit in cone responsiveness to light offset becomes increasingly subnormal as rods dark adapt and, when completely dark adapted, the ESS observer is nearly blind to 1 Hz rapid-off sawtooth waveforms. These results strongly bolster previous results that suggest that suppressive rod-cone interaction is restricted to the response to transient decreases in illumination.
Lange
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Department of Psychology, Queens College of CUNY, Flushing 11367.
Frumkes
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D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D003119:Color Perception Tests; D003623:Dark Adaptation / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D009755:Night Blindness / Q000503:physiopathology*; D010786:Photoreceptor Cells / Q000503:physiopathology*; D012684:Sensory Thresholds