Human trichromacy revisited

Abstract

The presence of a photopigment (melanopsin) within certain retinal ganglion cells was a surprising and significant discovery. This pigment is routinely described as "nonvisual" to highlight its signaling role in pupil dilation and circadian rhythms. Here we asked whether light absorbed by melanopsin can be seen by healthy human subjects. To answer this requires delivering intense (above rod saturation), well-controlled lights using four independent primaries. We collected detection thresholds to many four-primary stimuli. Threshold measurements in the fovea are explained by trichromatic theory, with no need to invoke a fourth photopigment. In the periphery, where melanopsin is present, threshold measurements deviate from trichromatic theory; at high photopic levels, sensitivity is explained by absorptions in four, not three, photopigment classes. We consider a series of hypotheses to explain the tetrasensitivity at high photopic levels in the human peripheral field. The most likely hypothesis is that in healthy human subjects melanopsin absorptions influence visibility.color perception | retina | ipRGC | flicker sensitivity

A five-primary photostimulator suitable for studying intrinsically photosensitive retinal ganglion cell functions in humans

“…In contrast, the five-primary approach we used will yield a unique solution for a certain combination of the excitations of the five types of photoreceptors. Thirdly, another group also reported developing a six-primary photostimulator to study the contribution of melanopsin to chromatic discrimination (Horiguchi et al, 2013;Horiguchi, Winawer, Wandell, & Dougherty, 2011). However, they decided not to use all of the six primaries because of the difficulty in accounting for individual variability in the transmission of the cornea and lens.…”

“…IpRGCs project to brain areas associated with non-imageforming functions, such as the SCN for circadian photoentrainment Ruby et al, 2002) and the olivary pretectal nucleus (OPN) for controlling pupil size (Clarke, Zhang, & Gamlin, 2003;Hattar et al, 2002;Lucas et al, 2003). IpRGCs also project to the LGN (Berson, 2003;Dacey et al, 2005) and may contribute to image-forming processes Brown et al, 2012;Horiguchi, Winawer, Dougherty, & Wandell, 2013;Zaidi et al, 2007).…”

Adaptation to steady light by intrinsically photosensitive retinal ganglion cells

“…For nonimage vision, although adaptation is certainly beneficial for increasing the signaling dynamic range, the exact implication of Weber-Fechner behavior is less obvious. Because ipRGCs are now known to also contribute to conscious vision (12,(48)(49)(50)(51)(52), this adaptation behavior may have more to do with the latter function. It would, thus, be useful to know whether the other ipRGC subtypes [which supposedly are more involved in image vision compared with M1 cells (12,15)] show similar adaptation behavior.…”

The importance of intrinsically photosensitive retinal ganglion cells and implications for lighting design

“…It has been reported that humans lacking an outer retina [39] or animals with rods and cones ablated genetically [40] can preserve some light detection functions. In people with normal retinas, melanopsin activation could contribute to brightness discrimination [40], chromatic discrimination [41], color perception [42,43] and contrast sensitivity [4,44]. However, the mechanisms for melanopsin activation affecting conscious visual perception are not well-understood.…”