Tabandeh, N. | Search bioRxiv

bioRxiv2025

Photoreceptor-specific scene statistics reveal melanopic structure in natural environments

Natural scenes shape visual perception and non-visual responses, yet the melanopsin pathway, the retinas key circadian input, is rarely quantified in this context. We measured spectral and spatial properties of 671 natural scenes: indoor scenes without windows (n=115), indoor scenes with windows (n=194), and outdoor scenes (n=362), across all five human photoreceptors. Radiance and photometric metrics increased systematically from windowless indoor view (mean melanopic EDI 280 lx) to indoor scenes with window view (2386 lx) to outdoor scenes (12,142 lx), with melanopic and photopic illuminance strongly correlated (r {approx} 0.9, p < 10-5). Beyond overall -opic exposure, melanopic input exhibited structured spatial variation. RMS contrast ranged from 0.001 to 0.365, lowest without windows and highest outdoors, and correlated with melanopic luminance indoors with windows (r = 0.495) and outdoors (r = 0.477) but not windowless scenes (r = 0.026). Melanopic amplitude spectra followed 1/f -like power laws, steeper slopes indoors (modal{approx} -1.4) and flatter outdoors (modal{approx} -1.1), revealing photoreceptor-resolved regularities in natural melanopic input.

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bioRxiv2025

Regulation of eye movements and pupil size in natural scenes

The visual diet of humans is complex in space, time, spectrum, and conse- quently the activation of the retinal photoreceptors. While analyses of natural scenes have yielded valuable insights, the naturalistic natural stimulus on the retina is not very well understood. In the present study, we performed eye tracking in naturalistic indoor and outdoor real-world scenes. We recorded pupil size, several saccade and fixation metrics, as well as subjective scene perception ratings derived from subjective questionnaires. For the first five seconds of eye tracking, the descriptive data analysis revealed significantly increased average saccade frequency (p =.0025), amplitude (p =.0049), peak velocity (p =.0072), as well as pupil size (p = 1.307e-09) in the indoor environ- ments. After this initial phase, these differences vanished, except for pupil size. Using an exploratory analysis on the whole 4-minute measurement, we found that saccade and fixation metrics, along with scene ratings, showed significantly different correlations between indoor and outdoor conditions. Despite the inherent constraints of such a naturalistic study (reduced ability to exert control over the precise task and the environmental conditions), we contend that the dataset holds substantial value for field of eye movement research, as it has effectively minimized confounding factors that have been prevalent in previous eye tracking studies. HighlightsO_LIIncreased amplitude, frequency, and peak velocity of saccades in real- world indoor environments within the initial 5 seconds of eye tracking C_LIO_LIDifferent correlations of eye movement metrics and subjective scene per- ception between real-world indoor and outdoor environments C_LIO_LIEstablishing an eye movement dataset of various saccade in fixation metrics in naturalistic real-world environments with reduced confounding factors C_LI

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