Abstract
Detection and discrimination of spatial patterns is thought to originate with photoreception by rods and cones. Here, we investigated whether the inner-retinal photoreceptor melanopsin could represent a third origin for form vision. We developed a 4-primary visual display capable of presenting patterns differing in contrast for melanopsin vs cones, and generated spectrally distinct stimuli that were indistinguishable for cones (metamers) but presented contrast for melanopsin. Healthy observers could detect sinusoidal gratings formed by these metamers when presented in the peripheral retina at low spatial (≤0.8 cpd) and temporal (≤0.45 Hz) frequencies, and Michelson contrasts ≥14% for melanopsin. Metameric gratings became invisible at lower light levels (<1013 melanopsin photons cm−2 sr−1 s−1) when rods are more active. The addition of metameric increases in melanopsin contrast altered appearance of greyscale representations of coarse gratings and a range of everyday images. These data identify melanopsin as a new potential origin for aspects of spatial vision in humans.
Highlights
Detection and discrimination of spatial patterns is thought to originate with photoreception by rods and cones
We recently addressed that deficit by recording electrophysiological responses in the mouse dLGN to melanopsin-directed spatial patterns[24]
A conceptually straightforward test of the hypothesis that melanopsin contributes to form vision is to ask whether people can detect patterns that are invisible to cones but contain contrast for melanopsin
Summary
Detection and discrimination of spatial patterns is thought to originate with photoreception by rods and cones. We approached this by using the principles of receptor silent substitution and metamerism to generate carefully calibrated visual stimuli in which spatial contrast for melanopsin can be controlled independent of that for cones This strategy has been effectively applied to describe the contribution of melanopsin to non-image forming visual responses[25,26,27,28] and to reveal melanopsin’s role in perception of scene brightness[12,22], but until now has not been applied to an apparatus capable of presenting spatial patterns. The additional degree of freedom allowed by inclusion of a 4th primary allows us to produce patterns that are indistinguishable for cones (‘metameric’) but contain significant contrast for melanopsin We show that such patterns are detectable when presented at low spatiotemporal frequencies and high radiance, and can augment the appearance of greyscale images when superimposed upon them. These data support the hypothesis that melanopsin can provide form vision, allowing detection and discrimination of patterns at low spatiotemporal frequencies and influencing the appearance of everyday images
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