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Aoi Takasu* and Sei-ichi Tsujimura

Graduate school of design and architecture, Nagoya City University, Japan

*Corresponding author:

Keywords: brightness perception, melanopsin, heterochromatic brightness matching, photoreceptor stimulation

Poster presentation video:

Melanopsin cells, a type of photoreceptor in the retina, were discovered around 2000. In the literature, they contribute to the regulation of circadian rhythms and pupil's response to light. They receive inputs from three types of cones and rods and contribute to the non-imaging forming pathway such as pupil response and photoentrainment of circadian rhythm. In addition, the melanopsin cells contribute to brightness perception.

Brightness sensitivity is expressed as specific visual sensitivity. Luminance is defined by CIE (Commission international de l'éclairage) to provide the amount of brightness. Luminance is derived from minimum flicker method, which uses high-temporal frequency stimuli. Several studies have shown that L and M cones, but not S cones, can contribute in minimum flicker. On the other hand, another brightness sensitivity, particularly to static stimuli, has also been proposed. This luminous efficiency function is derived from direct heterochromatic brightness matching.

The visual sensitivity derived by direct heterochromatic brightness matching has a wide bandwidth in wavelength compared to that derived by minimum flicker. The direct heterochromatic brightness matching uses static stimuli, which has a low-frequency component, suggesting that S cones and melanopsin cells could contribute. It is, therefore, important to investigate how melanopsin cells and cones contribute to the brightness sensitivity derived by direct heterochromatic brightness matching. The purpose of this study was to investigate the contribution of melanopsin cells in brightness sensitivity derived by direct heterochromatic brightness matching.

In the experiment, a multi-primary illumination system was used, which allows the independent stimulation of each photoreceptor. Before the session, observers had the initial adaptation for 5 minutes. We used two-intervals alternative forced choice procedure (2IAFC) to measure brightness perception. The test and reference stimuli were presented for 1 second. The reference and test stimuli were switched gradually to avoid artefacts due to rapid changes in the stimuli. The order of the test and reference stimuli was counterbalanced. All stimuli had equal luminance in minimum flicker, but different brightness based on direct heterochromatic brightness matching.

The results showed that test stimuli of the same luminance caused different brightness perceptions. Brightness perception increased as luminance derived by direct heterochromatic brightness matching increased. In addition, brightness perception increased as melanopsin stimulation in the stimuli increased. These results suggest that melanopsin cells as well as cones contribute to brightness perception based on direct heterochromatic brightness matching.

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