Visual response of posterior parietal neurons and saccadic reaction time during a visual detection task Abbreviated title: Neuronal and behavioral performance during visual detection

This is the pre-peer reviewed version of the following article: Visual response of neurons in the lateral intraparietal area and saccadic reaction time during a visual detection task. Eur J Abstract Luminance is important in visual detection. A target with higher luminance is detected with reduced saccadic reaction times. However, little is known about how stimulus luminance affects the visual response in the posterior parietal cortex (PPC), and how luminance-related activity modulations are correlated with changes in reaction time. To address these issues, we recorded single-cell activity from visually responsive PPC neurons of monkeys required to make a saccade to an isolated target over five luminance levels. We found that as stimulus luminance increased, visual response strength increased, and response onset latency decreased. These luminance-related changes in activity were significantly correlated with changes in reaction time. Particularly, changes in response onset latency accounted for a substantial part of the observed changes in reaction time. However, the length of time from response onset to saccade onset was not constant but increased as luminance was reduced, suggesting the existence of other luminance-dependent processing in downstream and/or parallel pathways before saccade generation. Additionally, we failed to find strong covariance between response strength or latency and reaction time when the effect of luminance changes was removed. These results suggest that luminance-related changes in response strength and latency of PPC visual neurons may propagate to the saccade generation process, leading to substantial changes in reaction time. However, these response variables in the visual activity in PPC may contribute less directly to saccade generation itself during visual detection.