Assessing perceptual chromatic equiluminance using a reflexive pupillary response

• Published in: Scientific reports Vol. 14; no. 1; pp. 2420 - 12
• Main Authors: Liu, Ye, Mahony, Bridget W., Wang, Xiaochun, Daye, Pierre M., Wang, Wei, Cavanagh, Patrick, Pouget, Pierre, Andolina, Ian Max
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29-01-2024; Nature Publishing Group; Nature Portfolio
• Subjects: 631/378/2613/1786; 631/378/2613/1875; 631/378/2613/2141; Animals; Cognitive science; Color Perception - physiology; Contrast Sensitivity; Fourier transforms; Humanities and Social Sciences; Humans; Marking and tracking techniques; multidisciplinary; Neurosciences; Oscillations; Perceptions; Photic Stimulation; Physical Examination; Primates; Pupil; Science; Science (multidisciplinary); Time Factors; Training; Visual stimuli; colour perception; pupillometry; colour perception pupillometry no-report paradigm frequency-tagging isoluminance; isoluminance; frequency-tagging; no-report paradigm
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-024-51982-z

Equiluminant stimuli help assess the integrity of colour perception and the relationship of colour to other visual features. As a result of individual variation, it is necessary to calibrate experimental visual stimuli to suit each individual’s unique equiluminant ratio. Most traditional methods rely on training observers to report their subjective equiluminance point. Such paradigms cannot easily be implemented on pre-verbal or non-verbal observers. Here, we present a novel Pupil Frequency-Tagging Method (PFTM) for detecting a participant’s unique equiluminance point without verbal instruction and with minimal training. PFTM analyses reflexive pupil oscillations induced by slow (< 2 Hz) temporal alternations between coloured stimuli. Two equiluminant stimuli will induce a similar pupil dilation response regardless of colour; therefore, an observer’s equiluminant point can be identified as the luminance ratio between two colours for which the oscillatory amplitude of the pupil at the tagged frequency is minimal. We compared pupillometry-based equiluminance ratios to those obtained with two established techniques in humans: minimum flicker and minimum motion. In addition, we estimated the equiluminance point in non-human primates, demonstrating that this new technique can be successfully employed in non-verbal subjects.