A quantitative analysis of the contribution of melanopsin to brightness perception

Masahiko Yamakawa,Katsunori Okajima,Sei-Ichi Tsujimura

doi:10.1038/s41598-019-44035-3

Masahiko Yamakawa, Katsunori Okajima + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-44035-3

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Abstract

In the retina, intrinsically photosensitive retinal ganglion cells (ipRGCs) which express photopigment melanopsin have been identified as photoreceptors which differ from cones and rods. It has been established that such melanopsin-expressing RGCs are involved in the circadian photo-entrainment and pupillary light reflexes. An additional projection from ipRGCs to the lateral geniculate nucleus has been identified, which indicates the association of ipRGCs with visual perception induced by the image-forming pathway. Reportedly, ipRGCs modulate brightness perception but quantitative analysis of brightness perception involving melanopsin and cones-based signals has not been elucidated. We conducted brightness perception experiments that involved melanopsin using a novel projector with six primary colors and formulated the results for melanopsin and cone stimuli. The white visual stimuli (5 degrees in size) that we used had a single xy-chromaticity values but melanopsin stimuli were modulated by designing different spectral distributions. Perceived brightness was measured using a magnitude estimation method at several luminance levels in the near periphery (7 degrees). Additionally, pupil diameter was measured for estimating the intensity of visual stimuli on the retina. The results showed that the perceived brightness of a white visual stimulus with different spectral distributions can be described by a summation of the nearly linear melanopsin response and the non-linear cone response with weighted coefficients, and the contribution ratio of melanopsin in brightness perception increased to 50% and more with increasing visual stimulus. These suggest that melanopsin signals play a crucial role in the estimation of the absolute intensity of the light environment by obtaining absolute brightness information even when cones are adapted by light.

Highlights

The photoreceptors in the retina that are responsible for forming images typically comprise cones and rods
Statistical tests were conducted to investigate the difference in brightness perception between stimuli C (M/P ratio 9.3) and E (M/P ratio 5.6), between stimuli C and G (M/P ratio 2.6), and between stimuli E and G for 102 cd/m2
The determination coefficient between the experimental value and the calculated value was 0.57 when formulated only with the cone term. This is greatly inferior to the determination coefficient (0.94) when formulated with the sum of the melanopsin term and the cone term. This clearly demonstrated that melanopsin are involved in brightness perception

Summary

Introduction

The photoreceptors in the retina that are responsible for forming images typically comprise cones and rods. The RGCs and the LGN neurons respond to the inputs produced in time or in space projected upon their receptive fields[1] This pathway is called the image forming pathway. Studies have found that light signals received by the melanopsin-expressing RGCs are projected to the suprachiasmatic nucleus (SCN), which entrains circadian rhythms[14], and to the olivary pretectal nucleus (OPN), which controls the pupillary light reflex[15]. This pathway is called the non-image forming pathway. These results showed that melanopsin is not a minor contributor in brightness perception but, rather present as a critical factor for the formulation

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