Declines in Wavelength Discrimination and Shifts in Unique Hue with Hypoxia

INTRODUCTION: Hypoxia can be a problem for warfighters, compromising visual and cognitive performance. One area of study has been hypoxia-induced decrements in color vision.METHODS: The present study examined how hypoxia affected the perception of wavelengths associated with unique green and with unique yellow as well as discriminability by the blue vs. yellow (b-y) and the red vs. green (r-g) spectrally opponent color channels while breathing O2 levels found at sea level and at 5500 m. Measurements of wavelengths producing unique green (minimizing response by the b-y channel) and unique yellow (minimizing response by the r-g channel) preceded measurements of wavelength discriminability near those unique hues.RESULTS: Relative to sea level, unique yellow shifted to shorter wavelengths (0.54 nm) and unique green shifted to longer wavelengths (2.3 nm) under hypoxia. In terms of an equal psychophysical scale, both unique hues shifted by similar magnitudes. Wavelength discriminability of both color channels was compromised by statistically reliable amounts of 16–17% under hypoxia.DISCUSSION: These results were consistent with previous studies and the inference that postreceptor, M-cone neurons were differentially compromised by hypoxia. However, these measurable changes in color vision due to hypoxia were not perceived by the subjects.Bierman A, LaPlumm T, Rea MS. Declines in wavelength discrimination and shifts in unique hue with hypoxia. Aerosp Med Hum Perform. 2020; 91(5):394–402.

Chromatic information processing in the first optic ganglion of the butterfly Papilio xuthus

The butterfly Papilio xuthus has acute tetrachromatic color vision. Its eyes are furnished with eight spectral classes of photoreceptors, situated in three types of ommatidia, randomly distributed in the retinal mosaic. Here, we investigated early chromatic information processing by recording spectral, angular, and polarization sensitivities of photoreceptors and lamina monopolar cells (LMCs). We identified three spectral classes of LMCs whose spectral sensitivities corresponded to weighted linear sums of the spectral sensitivities of the photoreceptors present in the three ommatidial types. In ~ 25% of the photoreceptor axons, the spectral sensitivities differed from those recorded at the photoreceptor cell bodies. These axons showed spectral opponency, most likely mediated by chloride ion currents through histaminergic interphotoreceptor synapses. The opponency was most prominent in the processes of the long visual fibers in the medulla. We recalculated the wavelength discrimination function using the noise-limited opponency model to reflect the new spectral sensitivity data and found that it matched well with the behaviorally determined function. Our results reveal opponency at the first stage of Papilio’s visual system, indicating that spectral information is preprocessed with signals from photoreceptors within each ommatidium in the lamina, before being conveyed downstream by the long visual fibers and the LMCs.

Behavioural evidence for polychromatic ultraviolet sensitivity in mantis shrimp

Stomatopod crustaceans are renowned for their elaborate visual systems. Their eyes contain a plethora of photoreceptors specialized for chromatic and polarization detection, including several that are sensitive to varying wavelength ranges and angles of polarization within the ultraviolet (UV) range (less than 400 nm). Behavioural experiments have previously suggested that UV photoreception plays a role in stomatopod communication, but these experiments have only manipulated the entire UV range. Here, using a behavioural approach, we examine UV vision in the stomatopod Haptosquilla trispinosa . Using binary trained choice assays as well as innate burrow-choice experiments, we assessed the ability of H. trispinosa to detect and respond to narrow-band LED stimuli peaking near 314 nm (UVB) versus 379 nm (UVA) in wavelength. We find that H. trispinosa can discriminate these stimuli and appears to display an aversive reaction to UVB light, suggesting segregated behavioural responses to stimuli within the UV range. Furthermore, we find that H. trispinosa can discriminate stimuli peaking near 379 nm versus 351 nm in wavelength, suggesting that their wavelength discrimination in the UV is comparable to their performance in the human-visible range.