![]() ![]() Finally, the melanopsin photopigment has a peak spectral sensitivity at around 480 nm. The photopigments (cone opsins) in the L, M, and S cones peak around 420, 530, and 558 nm, respectively rhodopsin, the pigment in rods, has a peak at around 495 nm. The peak spectral sensitivities (λ max) of the human photoreceptors are distinct. ipRGCs receive synaptic input from cones and rods but, in the absence of those inputs, these cells themselves are photosensitive due to the expression of the melanopsin photopigment in the cell membrane. Photoreception in the human retina is based on the signals produced by the three types of cones-the long-wavelength-sensitive cones, the medium-wavelength-sensitive cones, and the short-wavelength-sensitive cones-, the rods, and the intrinsically photosensitive retinal ganglion cells (ipRGCs), which contain the photopigment melanopsin ( 2– 6). Fundamentals Overlapping Spectral Sensitivities of the Human Photoreceptors We start with the fundamentals underlying the method of silent substitution, provide an overview of studies that have used this method, provide a practical guide and R code to implement silent substitution and highlight a few challenges to the method of silent substitution. The goal of this primer is to describe the method of silent substitution for examining photoreceptor-specific pupil responses. These different photoreceptors differ in many respects: their wavelength tuning (spectral sensitivity), their temporal properties, their operating range and their distribution across the retina. In this primer, we describe the method of silent substitution and provide an overview of studies that have used it to examine inputs to the human pupillary light response.Īt the input level, the size of the pupil is controlled by the activity of the different photoreceptors in the human eye ( 1). ![]() The method of silent substitution uses pairs of lights (“metamers”) to selectively stimulate a given class of photoreceptors while keeping the activation of all others constant. ![]() These photoreceptor classes have distinct but overlapping spectral tuning, and even a monochromatic light with a wavelength matched to the peak spectral sensitivity of a given photoreceptor will stimulate all photoreceptors. The human pupillary light response is driven by all classes of photoreceptors in the human eye-the three classes of cones, the rods, and the intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin. 2Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, Netherlands.1Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom. ![]()
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