Abstract
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.
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Acknowledgements
The authors thank A. Lablans, D. Hamburger, C. Wellstood, F. Paquin, and K. Moore for their invaluable assistance and technical expertise; M.Van Wanrooij for his help with data collection; and B. Coe, J. Fecteau, S. Boehnke, J. Gore, R. Marino, D. Brien, and I. Cameron for commenting on earlier versions of this manuscript. This work was supported by the Human Frontiers Science Program (RG0174/1998-B) and the Canadian Institutes of Health Research. AHB was supported by a Doctoral Research Award from the Canadian Institutes of Health Research. DPM was supported by the Canada Research Chair Program.
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Bell, A.H., Meredith, M.A., Van Opstal, A.J. et al. Stimulus intensity modifies saccadic reaction time and visual response latency in the superior colliculus. Exp Brain Res 174, 53–59 (2006). https://doi.org/10.1007/s00221-006-0420-z
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DOI: https://doi.org/10.1007/s00221-006-0420-z