In addition to rods and cones, the human retina contains melanopsin which has been identified recently in the body and dendrites of a few ganglion cells. The intrinsically photosensitive retinal ganglion cells (ipRGCs) are good candidates for controlling the tonic pupil aperture but their spectral sensitivity is close to those of rods and S-cones which are other candidates. Our study aims at identifying the stimulus for the pupil response when the luminance is constant and the spectrum of the light changes. A light booth was equipped with five types of coloured light emitting diodes (LEDs): Blue, Cyan, Green, Orange and Red. The intensity of each LED type could be adjusted to control the light spectrum. Illumination pairs were prepared ensuring the exclusive variation of excitation of one receptor type and silent substitution for others. Because the range of the possible controlled changes of excitation was narrow, we also prepared illumination pairs ensuring silent substitution for luminance rather than for L-cones and M-cones independently. Photographs of the observer's eyes were taken following one minute of adaptation to each illumination and the ratio of pupil to iris diameter was measured. No differential pupillary response was observed with a variation of rod, melanopsin or S-cone excitation alone. A differential pupillary response could only be obtained with a variation of the melanopsin stimulus of sufficient high contrast with or without a concurrent variation of rods.

In everyday life, the visual system is remarkably good at recognizing materials across a wide range of viewing conditions. This paper addresses the problem of identifying real samples of materials from appearance. Here, we consider gloss as an appearance attribute that could reveal certain information about object properties. We prepared twelve samples of glass and PMMA and eroded these using different agents. The gloss and haze of the samples were measured at 60 degrees via a gloss meter. For all samples, the surface roughness properties were measured. Microfacet distributions were derived from measured BRDFs using an inverted microfacet model. We conducted a visual ranking experiment using the pair comparison method. The psychophysical gloss ratings correlate well with the 60 degrees gloss index. Principal component analysis of the psychophysical results revealed a somewhat more complicated picture in which three components seem to play a role. We conclude that observers can apprehend the physical nature of the surface of real objects from features that are included in the BRDF and available in the gloss appearance.

Any stimulus can be described as composed of two components-a fundamental color stimulus that controls the three cone responses and a metameric black that has no effect on cones but can drive photoreceptors other than cones [e.g., rods and melanopsin expressing retinal ganglion cells (ipRGCs)]. The Cohen and Kappauf [Am. J. Psychol. 95, 537 (1982)] method is extended to calculate the black metamer basis for a limited set of band spectra. Using seven colored LEDs, the method is exploited to produce real metamer illuminations that stimulate in parallel melanopsin expressing ipRGCs and rods, at most or at least. We have verified that the pupil diameter increases when the ipRGC and rod excitation is at a minimum. For 14 observers, the average relative increase is 12%.