Impact of early visual experience on later usage of color cues

Human visual recognition is remarkably robust to chromatic changes. In this work, we provide a potential account of the roots of this resilience based on observations with 10 congenitally blind children who gained sight late in life. Several months or years following their sight-restoring surgeries, the removal of color cues markedly reduced their recognition performance, whereas age-matched normally sighted children showed no such decrement. This finding may be explained by the greater-than-neonatal maturity of the late-sighted children's color system at sight onset, inducing overly strong reliance on chromatic cues. Simulations with deep neural networks corroborate this hypothesis. These findings highlight the adaptive significance of typical developmental trajectories and provide guidelines for enhancing machine vision systems.

Facial expressions affect the memory of facial colors

Facial color influences the perception of facial expressions, and emotional expressions bias how facial color is remembered. However, it remains unclear whether facial expressions affect daily facial color memory. The memory color effect demonstrates that knowledge about typical colors affects the perception of the actual color of given objects. To investigate the effect of facial color memory, we examined whether the memory color effect for faces varies depending on facial expression. We calculated the subjective achromatic point of the facial expression image stimulus and compared the degree to which it was shifted from the actual achromatic point between facial expression conditions. We hypothesized that if the memory of facial color is influenced by the facial expression color (e.g., anger is a warm color, fear is a cold color), then the subjective achromatic point would vary with facial expression. In Experiment 1, we recruited 13 participants who adjusted the color of facial expression stimuli (anger, neutral, and fear) and a banana stimulus to be achromatic. No significant differences in the subjective achromatic point between facial expressions were observed. Subsequently, we conducted Experiment 2 with 23 participants because Experiment 1 did not account for the sensitivity to color changes on the face; humans perceive greater color differences in faces than in non-faces. Participants selected which facial color they believed the expression stimulus appeared to be, choosing one of two options provided to them. The results indicated that the subjective achromatic points of anger and fear faces significantly shifted toward the opposite color direction compared with neutral faces in the brief presentation condition. This research suggests that the memory color of faces differs depending on facial expressions and supports the idea that the perception of emotional expressions can bias facial color memory.

Color-hierarchies in executive control of monkeys' behavior

Processing advantages for particular colors (color-hierarchies) influence emotional regulation and cognitive functions in humans and manifest as an advantage of the red color, compared with the green color, in triggering response inhibition but not in response execution. It remains unknown how such color-hierarchies emerge in human cognition and whether they are the unique properties of human brain with advanced trichromatic vision. Dominant models propose that color-hierarchies are formed as experience-dependent learning that associates various colors with different human-made conventions and concepts (e.g., traffic lights). We hypothesized that if color-hierarchies modulate cognitive functions in trichromatic nonhuman primates, it would indicate a preserved neurobiological basis for such color-hierarchies. We trained six macaque monkeys to perform cognitive tasks that required behavioral control based on colored cues. Color-hierarchies significantly influenced monkeys' behavior and appeared as an advantage of the red color, compared to the green, in triggering response inhibition but not response execution. For all monkeys, the order of color-hierarchies, in response inhibition and also execution, was similar to that in humans. In addition, the cognitive effects of color-hierarchies were not limited to the trial in which the colored cues were encountered but also persisted in the following trials in which there was no colored cue on the visual scene. These findings suggest that color-hierarchies are not resulting from association of colors with human-made conventions and that simple processing advantage in retina or early visual pathways does not explain the cognitive effects of color-hierarchies. The discovery of color-hierarchies in cognitive repertoire of monkeys indicates that although the evolution of humans and monkeys diverged in about 25 million years ago, the color-hierarchies are evolutionary preserved, with the same order, in trichromatic primates and exert overarching effects on the executive control of behavior.

The impact of housing environment color on zebrafish anxiety-like behavioral and physiological (cortisol) responses

Color of the environment is an important factor modulating human and animal behavior and physiology. Animal models are a valuable tool to understand how colors affect social, cognitive and affective responses. The zebrafish (Danio rerio) is rapidly emerging as an important organism in neuroscience and physiology. Here, we examine whether the color of housing environment influences zebrafish anxiety-like behavior and whole-body cortisol levels. Overall, housing for 15 days in transparent and white holding tanks increases, and in black or blue tanks decreases, baseline anxiety-like behavior in adult zebrafish. Housing in blue tanks (vs. white) also reduced their whole-body cortisol levels. Taken together, our data suggest that color of the housing environment affects neurobehavioral and endocrine responses in zebrafish, with multiple implications for behavioral phenomics and animal welfare. Our study also reinforces zebrafish as a promising model organism to study neurobiology of compex brain-environment interactions.