1. Program in Neurobiology and Behavior,
2. Howard Hughes Medical Institute and,
3. Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA
4. Functional Neurobiology and Helmholtz Institute, Utrecht University, 3584 CH Utrecht, The Netherlands

Correspondence to: Fred Rieke^2,3 Correspondence and requests for materials should be addressed to F.R. (Email: rieke@u.washington.edu).

We see over an enormous range of mean light levels, greater than the range of output signals retinal neurons can produce. Even highlights and shadows within a single visual scene can differ 10,000-fold in intensity—exceeding the range of distinct neural signals by a factor of 100. The effectiveness of daylight vision under these conditions relies on at least two retinal mechanisms that adjust sensitivity in the 200 ms intervals between saccades¹. One mechanism is in the cone photoreceptors (receptor adaptation)^{2, 3, 4, 5} and the other is at a previously unknown location within the retinal circuitry that benefits from convergence of signals from multiple cones (post-receptor adaptation)^{6, 7}. Here we find that post-receptor adaptation occurs as signals are relayed from cone bipolar cells to ganglion cells. Furthermore, we find that the two adaptive mechanisms are essentially mutually exclusive: as light levels increase the main site of adaptation switches from the circuitry to the cones. These findings help explain how human cone vision encodes everyday scenes, and, more generally, how sensory systems handle the challenges posed by a diverse physical environment.

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