Trottenberg, C. | bioRxiv Science

bioRxiv2026

Much stronger coarse-to-fine visual processing in primate superior colliculus than primary visual cortex neurons

The visual system optimizes its signal processing properties to efficiently encode natural scenes. The superior colliculus (SC) and primary visual cortex (V1) both play important roles in visual-motor processing, and they both exhibit qualitatively similar visual responses. However, it is not clear whether the SC simply inherits V1s efficient coding image processing optimizations or not, especially given that the SC receives a substantial amount of direct anatomical inputs from V1. Here, by performing matched experiments in the two brain areas, as well as with the same visual stimuli and in the same experimental animals, we show that the dynamics of coarse-to-fine visual image processing in the SC are much stronger than those in V1. In the SC, visual response latencies, being fastest for coarse patterns, are dictated by image spatial frequency, independently of the spatial frequency tuning curves of the neurons. On the other hand, V1 visual response latencies are largely dominated by visual response sensitivity, which is itself much more broadband than in the SC. These observations remain fundamentally unchanged in active vision gaze-shift scenarios eliciting visual reafferent responses in both brain areas. Our results suggest that coarse-to-fine visual image processing dynamics are most observable, and thus most relevant, in visually-responsive neurons driving foveating eye movements, like in the SC. Besides explaining behavioral evidence for saccadic facilitation by images that are consistent with the statistics of natural scenes, these results indicate that coarse-to-fine visual processing dynamics are much more of a collicular than a cortical visual phenomenon.

neuroscience↗

bioRxiv2025

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 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 SC or V1 visual responses may predict eye movement timing variability. 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, our largest predictor of behavioral variability was visual response strength in SC visual-motor neurons. These results suggest that the SC reformats its sensory inputs for exploitation of the SCs proximity to the motor periphery; V1 aids in jumpstarting the sensing process, but the SC much more directly supports visually-driven orienting.

neuroscience↗