Color-detection thresholds in rhesus macaque monkeys and humans

Abstract

Macaque monkeys are a model of human color vision. To facilitate linking physiology in monkeys with psychophysics in humans, we directly compared colordetection thresholds in humans and rhesus monkeys. Colors were defined by an equiluminant plane of coneopponent color space. All subjects were tested on an identical apparatus with a four-alternative forced-choice task. Targets were 28 square, centered 28 from fixation, embedded in luminance noise. Across all subjects, the change in detection thresholds from initial testing to plateau performance (''learning'') was similar for þL À M (red) colors and þM À L (bluish-green) colors. But the extent of learning was higher for þS (lavender) than for ÀS (yellow-lime); moreover, at plateau performance, the cone contrast at the detection threshold was higher for þS than for ÀS. These asymmetries may reflect differences in retinal circuitry for S-ON and S-OFF. At plateau performance, the two species also had similar detection thresholds for all colors, although monkeys had shorter reaction times than humans and slightly lower thresholds for colors that modulated L/M cones. We discuss whether these observations, together with previous work showing that monkeys have lower spatial acuity than humans, could be accounted for by selective pressures driving higher chromatic sensitivity at the cost of spatial acuity amongst monkeys, specifically for the more recently evolved L À M mechanism.

Communication efficiency of color naming across languages provides a new framework for the evolution of color terms

“…All people with normal retinal chromatic mechanisms have essentially the same perceptual and discrimination abilities. Indeed, non-human primates have very similar color discrimination mechanisms to humans (Gagin et al, 2014;Horwitz, 2015;Stoughton, Lafer-Sousa, Gagin, & Conway, 2012)-clearly colors can be seen in the absence of language. When presented with a given perceptual space (say Munsell), human observers with normal retinal color mechanisms, regardless of the language they speak, will see the colors similarly, and they will categorize the colors similarly given a specified number of terms (Lindsey & Brown, 2006), even if all people in a population do not all have the words to do so (gathering data from many people in the population and assessing the variability uncovers the universal categorization structure (Gibson et al, 2017;Lindsey et al, 2015)).…”

Neural differences between chromatic- and luminance-driven attentional salience in visual search

“…The approximate step sizes for each condition were ±0.0017 mechanism contrast for reddish and greenish, ±0.020 mechanism contrast for bluish and yellowish, and ±0.012 for dark gray. These step sizes were chosen based on detection thresholds and just noticeable differences for stimuli from the reddish/greenish and bluish/yellowish mechanisms (Gagin et al, 2014;Jennings & Barbur, 2010). It was intended that the initial contrast of the target stimulus would be randomized as (initial contrast ± 5) × step size, but an error in coding resulted in a fixed initial contrast being used for all trials.…”

Mouse hue and wavelength-specific luminance contrast sensitivity are non-uniform across visual space

“…We continued to ask if mice could report a change in hue independent of any luminance change. Instead of explicitly creating a device that normalized total luminance during hue changes 38–40 , we presented sufficient combinations of wavelength-band specific luminance changes to experimentally determine when hue changes occurred independent of luminance changes. We start with the assumption that no change in luminance or hue contrast is not discriminable to the observer.…”