Effects of absolute luminance and luminance contrast on visual discrimination in low mesopic environments

Abstract

Recent research revealed considerable decline in visual perception under low luminance conditions. However, systematic studies on how visual performance is affected by absolute luminance and luminance contrast under low mesopic conditions (<0.5 cd/m) is lacking. We examined performance in a simple visual discrimination task under low mesopic luminance conditions in three experiments in which we systematically varied base luminance and luminance contrast between stimulus and background. We further manipulated eccentricity of the stimuli because of known rods and cones gradients along the retina. We identified a "deficiency window" for performance as measured by d' when luminance was < 0.06 cd/m and luminance contrast as measured by the luminance ratio between stimulus and background was below < 1.7. We further calculated performance-based luminance as well as contrast efficiency functions for reaction times (RTs). These power functions demonstrate the contrast asymptote needed to decrease RTs and how such a decrease can be achieved given various combinations of absolute luminance and luminance contrast manipulations. Increased eccentricity resulted in slower RTs indicative of longer scan distances. Our data provide initial insights to performance-based efficiency functions in low mesopic environments that are currently lacking and to the physical mechanisms being utilized for visual perception in these extreme environments.

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“…There was a reduction in CS with MTF CL compared to control, and a greater reduction was found when wearing the ND filter. The results agree with findings that CS is reduced with decreased luminance, 29 as would be the case when wearing ND filters. Studies also pointed out that target discrimination and identification are also affected, 30 so that reaction time decreased with low luminance.…”

Effects of absolute luminance and luminance contrast on visual search in low mesopic environments

“…Recently, Hunter and colleagues demonstrated a deficiency window and performance efficiency functions for performance accuracy (d') and reaction time for a simple twotarget discrimination task under low mesopic conditions (Hunter, Godde, & Olk, 2016). Participants had to identify a target within a two-stimuli search array with absolute target luminance, luminance contrast, and target eccentricity being manipulated.…”

“…Because of our previous study being restricted to a simple two-target discrimination task and simplified analyses, it is necessary to apply similar procedures in a more complex visual-search paradigm to obtain a clearer picture of the hypothesized mechanisms and a more robust assessment of the performance efficiency functions (Hunter et al, 2016). In the present study, we therefore raised the questions (1) whether the deficiency window and the performance efficiency functions described in our previous study (Hunter et al, 2016) could be demonstrated under low luminance conditions also in visual-search tasks of different complexity, and, if so, (2) how the introduced efficiency functions describing the contributions of C M or C W to performance need to be adjusted for these conditions.…”

“…Variation of set size (i.e., by increasing the number of distractors) typically does not affect search rates (reaction time per number of stimuli) in such feature-search paradigms, and multiple stimuli are searched simultaneously (Wolfe, 1998; but see Duncan & Humphreys, 1989, who discuss stimulus parameters that elicit set size effects for feature search). However, this research has usually been carried out in photopic environments and the described phenomena may not hold true in lower luminance environments where the visual perception mechanisms are impaired and can ultimately lead to target perception difficulties (Hunter et al, 2016). Furthermore, even though there is sufficient research on the contribution of luminance contrast to parallel search, respective findings on the role of the parvo and magnocellular visual pathways, are potentially confounded by the fact that they were usually performed under ambient light conditions (cf.…”

“…The goal of the present experiment was to fill a gap in research by providing a visual-search paradigm that transitions from the low mesopic to scotopic spectrums expanding off our previous target discrimination task (Hunter et al, 2016). Using the same stimuli, we increased the total number of stimuli to four and 16, aiming to replicate the RT deficiency window, as defined by interaction effects of C W and C M (Hunter et al, 2016). However, in accordance with Wolfe (1994), we expected not to find any effect of set size on RT.…”