title: Neuronal nonlinearity explains greater visual spatial resolution for darks than lights.
abstract: Astronomers and physicists noticed centuries ago that visual spatial resolution is higher for dark than light stimuli, but the neuronal mechanisms for this perceptual asymmetry remain unknown. Here we demonstrate that the asymmetry is caused by a neuronal nonlinearity in the early visual pathway. We show that neurons driven by darks (OFF neurons) increase their responses roughly linearly with luminance decrements, independent of the background luminance. However, neurons driven by lights (ON neurons) saturate their responses with small increases in luminance and need bright backgrounds to approach the linearity of OFF neurons. We show that, as a consequence of this difference in linearity, receptive fields are larger in ON than OFF thalamic neurons, and cortical neurons are more strongly driven by darks than lights at low spatial frequencies. This ON/OFF asymmetry in linearity could be demonstrated in the visual cortex of cats, monkeys, and humans and in the cat visual thalamus. Furthermore, in the cat visual thalamus, we show that the neuronal nonlinearity is present at the ON receptive field center of ON-center neurons and ON receptive field surround of OFF-center neurons, suggesting an origin at the level of the photoreceptor. These results demonstrate a fundamental difference in visual processing between ON and OFF channels and reveal a competitive advantage for OFF neurons over ON neurons at low spatial frequencies, which could be important during cortical development when retinal images are blurred by immature optics in infant eyes.
authors: Graduate Center for Vision Research, Department of Biological and Visual Sciences, State University of New York College of Optometry, New York, NY 10036.
authors: Jens
authors: J
authors: Kremkow
authors: Jianzhong
authors: J
authors: Jin
authors: Stanley J
authors: SJ
authors: Komban
authors: Yushi
authors: Y
authors: Wang
authors: Reza
authors: R
authors: Lashgari
authors: Xiaobing
authors: X
authors: Li
authors: Michael
authors: M
authors: Jansen
authors: Qasim
authors: Q
authors: Zaidi
authors: Jose-Manuel
authors: JM
authors: Alonso
mesh_terms: D000818:Animals; D002415:Cats; D003623:Dark Adaptation / Q000502:physiology*; D003624:Darkness; D005074:Evoked Potentials, Visual / Q000502:physiology; D006801:Humans; D008027:Light; D008959:Models, Neurological; D010775:Photic Stimulation; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
keywords: LFP; area V1; irradiation illusion; lateral geniculate nucleus; neuronal coding