Much higher covariation with foveation timing by superior colliculus than primary visual cortical neuronal activity
The superior colliculus (SC) is a potent driver for orienting movements, but it also possesses robust, short-latency visual responses. Even though such responses largely derive from direct primary visual cortical (V1) input, their relationship to V1 activity has never been analyzed with the same experimental subjects and stimuli. Here, we revisited pioneering observations that trial-by-trial variability in either the SC or V1 may predict variability in eye movement timing. We found that V1 covariation with behavioral variability was virtually non-existent in comparison to the SC, whether with respect to visual response onset latency, visual response strength, or pre-stimulus state. By far, the largest predictor of behavioral variability was visual response strength in SC visual-motor neurons. These results suggest that the SC reformats its inputs for exploitation of the SC's proximity to the motor periphery; V1 aids in jumpstarting the sensing process, but the SC much more directly supports visually-driven orienting.