Stimulus intensity modifies saccadic reaction time and visual response latency in the superior colliculus.
Performance in a reaction time task can be strongly influenced by the physical properties of the stimuli used (e.g., position and intensity). The reduction in reaction time observed with higher-intensity visual stimuli has been suggested to arise from reduced processing time along the visual pathway. If this hypothesis is correct, activity should be registered in neurons sooner for higher-intensity stimuli. We evaluated this hypothesis by measuring the onset of neural activity in the intermediate layers of the superior colliculus while monkeys generated saccades to high or low-intensity visual stimuli. When stimulus intensity was high, the response onset latency was significantly reduced compared to low-intensity stimuli. As a result, the minimum time for visually triggered saccades was reduced, accounting for the shorter saccadic reaction times (SRTs) observed following high-intensity stimuli. Our results establish a link between changes in neural activity related to stimulus intensity and changes to SRTs, which supports the hypothesis that shorter SRTs with higher-intensity stimuli are due to reduced processing time.
Bell
A H
AH
Centre for Neuroscience Studies, CIHR Group in Sensory-Motor Systems, Department of Physiology, Queen's University, Kingston, ON, Canada, K7L 3N6. doug@eyeml.queensu.ca.
Meredith
M A
MA
Van Opstal
A J
AJ
Munoz
D P
DP
D000818:Animals; D008253:Macaca mulatta; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D013477:Superior Colliculi / Q000502:physiology*