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Paul Moon, Evangelia Diplas, Anusha Kheraj, Hillary Rodman; The impact of lighting on the categorization of facial expressions. Journal of Vision 2020;20(11):1313. doi: https://doi.org/10.1167/jov.20.11.1313.
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Blue light can impact mood, emotion, and cognition through retinal projections, including from intrinsically photosensitive retinal ganglion cells (ipRGCs), to neurological structures such as the suprachiasmatic nucleus, limbic regions including the amygdala, and the lateral habenula, among others. Solar illumination has been consistent throughout human existence. However, modern cities expose us to blue-enriched lighting environments that do not necessarily mimic sun light. ipRGCs in particular may play an important role as they are especially sensitive to blue light and are involved in many non-image forming processes. Here, we examined the impact of blue light on the interpretation of facial expressions in the late morning and early evening. One-hundred and fifty undergraduate students (44 male, 106 female) completed a facial expression processing task under either brighter (131.4 lux) blue-enriched, broad-spectrum illumination (ipRGC driving), or dimmer (13.76 lux), warm illumination with little blue light (ipRGC neutral). Participants viewed happy, sad, angry, fearful, and neutral expressions from two models (one male, one female) for 100 ms and 1,500 ms at 40%, 75%, and 100% expressiveness, and then identified each emotion in a forced choice format. There were no mean differences between the lighting-condition groups for accuracy of expression identification, either overall or for individual expressions. However, by examining the pattern of errors, we determined that, in blue compared to warmer light, when participants were wrong on any given trial, they tended to be wrong towards negative expressions, and away from positive or neutral expressions. Additionally, there was a similar trend for neutral target expressions, such that participants tended to misidentify neutral targets as negative rather than happy expressions in blue light. These data suggest that, when exposed to blue-enriched light, people are subtly biased towards mistaking any expression for a negative one.
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