THE RELATIONSHIP BETWEEN THE STEADY-STATE PUPIL RESPONSE AND BRIGHTNESS SENSITIVITY

OBTAINED BY DIRECT HETEROCHROMATIC BRIGHTNESS MATCHING BASED ON MELANOPSIN STIMULATION

Tomoe Ito* and Sei-ichi Tsujimura*

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

*Corresponding author: Tomoe Ito and Sei-ichi Tsujimura, itto1016@gmail.com

Keywords: Pupillary light reflex, Brightness, Luminance, Melanopsin, Non-image forming pathway, Direct heterochromatic brightness matching

Poster presentation video: https://youtu.be/cXu3e_WktzE

In this study, we investigated the relationship between the steady-state pupil response and brightness sensitivity obtained by direct heterochromatic brightness matching. A recently discovered photoreceptor, ipRGC (intrinsically photosensitive retinal ganglion cell, or melanopsin cell) contributes to non-image forming pathway such as photoentrainment of circadian rhythms and pupillary light reflex. Although a large number of studies have been made on the investigation of non-image forming pathway in rodents, little is known about humans. It is important what kind of attributes of ambient light (i.e. color luminance and melanopsin stimulation) most influences the non- image forming pathway in humans. In this study, therefore, we measured sustained pupil responses to steady light with various kinds of photoreceptor stimulations including melanopsin cell.

According to the literature, melanopsin cells contribute to steady-state pupil response and brightness perception. The brightness sensitivity is known as luminous efficiency function, V(λ), which is obtained by minimum flicker and the luminance of light is calculated from it. Since minimum flicker uses high-frequency stimuli melanopsin cells cannot respond to it. There is another brightness sensitivity, Vd(λ), for static stimulus, which obtained by so-called direct heterochromatic brightness matching and a luminance with Vd(λ) can also be calculated. The spectral sensitivity of Vd(λ) is broader on the long- and short-wavelength region compared to V(λ). The broad shape of Vd(λ) suggests that S-cones and melanopsin cells contribute to brightness sensitivity as well as L- and M-cones.

In this study, we investigated the relationship between the steady-state pupil response and brightness sensitivity obtained by direct heterochromatic brightness matching. The experiment used a multi-primary stimulation system that can independently stimulate each photoreceptor at retina. We used three stimuli according to stimulation of Vd(λ), which were LdMax, LdMiddle and LdMin stimuli, respectively. These stimuli had the same luminance, whereas had the different luminance by direct heterochromatic brightness matching. In addition, these stimuli had different melanopsin stimulations. The observer’s right eye was exposed to full-field stimulation and the steady-state pupil response of the left eye was measured. The measurement was started after an initial adaption for 5 minutes.

The results showed that a large difference in steady-state pupil response between LdMax and LdMin stimulus. The pupil response to LdMax stimulus was greater than that to LdMin stimulus. These results suggest that steady-state pupil response correlate with brightness sensitivity obtained by direct heterochromatic brightness matching.