Maxwell J. Greene¹, Ramon Bartolo Orozco¹, Felix Bartsch^1,2, Jasper C. Hood², Daniel A. Butts², Bevil R. Conway¹; ¹Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, ²Program in Neuroscience and Cognitive Science and Dept. of Biology, University of Maryland

Neurons in V1 optimize their ability to signal spatiotemporal patterns by bringing their dynamic range into register with the prevalent scene contrast. Prior studies have also shown that contrast can influence receptive field (RF) spatial structure in V1, though this work has been largely limited to the parafovea and periphery. Here, we describe the effect of varying luminance contrast on the space, time, and color RFs of V1 cells receiving input from the center-of-gaze. We measured the responses of foveal V1 units in awake fixating macaques to dynamic noise, which consisted of a luminance (L+M) component as well as L-M and S-varying components. In one condition (“high-contrast”), the luminance contrast spanned the full range permitted by the display, which approximates the statistics of natural scenes in which luminance variation exceeds chromatic variation. To investigate the dependence of V1 color sensitivity on environmental color statistics, we included a second condition (“low-contrast”) where the luminance contrast was restricted to ~10% of the maximum to match the L-M and S contrast of the high-contrast condition. Fine-grained spatiochromatic RFs were determined using linear and quadratic data-driven models of each neuron, which incorporated eye tracking to precisely estimate the retinal location of the stimulus. Under low contrast, the population mean firing rate was 12.4+/-9.0 Hz (s.d.), whereas under high contrast it was 16.7+/-11.0 Hz (N = 33). This firing rate increase of only ~0.13 log units over a log unit increase in luminance contrast is clear evidence of contrast adaptation. Across contrast levels, chromatic and achromatic RF structure remained largely unchanged, although the magnitude of the luminance filter increased in low contrast. Our results are consistent with early visual mechanisms that preserve foveal RF structure across large variations in illumination, which is likely important for the maintenance of high acuity vision.

Acknowledgements: BRC: NIH IRP 1ZIAEY000558; NSF 0918064; NIH R01 EY023322; DAB: NSF IIS-2113197; NIH R01 EY037347-01. Contributions of NIH authors are considered Works of the United States Government. The findings and conclusions are those of the authors and do not necessarily reflect the views of the NIH or the U.S. Department of Health and Human Services.