Abstract

The visual consequences of melanopsin photoreception in humans are not well understood. Here we studied melanopsin photoreception using a technique of photoreceptor silent substitution with five calibrated spectral lights after minimising the effects of individual differences in optical pre-receptoral filtering and desensitising penumbral cones in the shadow of retinal blood vessels. We demonstrate that putative melanopsin-mediated image-forming vision corresponds to an opponent S-OFF L + M-ON response property, with an average temporal resolution up to approximately 5 Hz, and >10x higher thresholds than red-green colour vision. With a capacity for signalling colour and integrating slowly changing lights, melanopsin-expressing intrinsically photosensitive retinal ganglion cells maybe the fifth photoreceptor type for peripheral vision.

Highlights

  • Melanopsin photoreception in intrinsically photosensitive retinal ganglion cells has fundamental roles in light dependent, non-imaging forming functions such as circadian photoentrainment and pupil light responses[1,2,3,4]

  • Penumbral cones can be desensitised with temporal white noise that modulates the L-cone, M-cone, S-cone and rod photoreceptor excitations to provide a direct measure of melanopsin photoreception in humans

  • A known neurophysiological correlate of the intrinsically photosensitive retinal ganglion cells (ipRGC) response property in humans is the characteristic opponent melanopsin and S-cone pupil response[9,28] and we confirm that melanopsin inputs to the pupil response are unaffected by temporal white noise (Fig. 2a)

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Summary

Introduction

Melanopsin photoreception in intrinsically photosensitive retinal ganglion cells (ipRGC) has fundamental roles in light dependent, non-imaging forming (i.e. non-visual) functions such as circadian photoentrainment and pupil light responses[1,2,3,4]. Functional magnetic resonance imaging studies in humans to high contrast melanopsin directed stimuli elicit a response in the visual cortex (area V1) which are associated with a brightening of visual percepts and distinct from the perceptual response to cone luminance directed stimuli[5]. To measure the perceptual correlate of melanopsin signalling in humans, the behavioural effects of melanopsin activation must be separated from visually detectable L- and M-cone signals arising through inadvertent stimulation of penumbral cones in the shadow of retinal blood vessels[10]. Conditions designed to modulate the melanopsin response, we estimate the visual detection threshold for melanopsin, its temporal contrast response and characterise its purported colour opponent response property

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