Color Categorization Independent of Color Naming

Color is continuous, yet we group colors into discrete categories associated with color names (e.g., yellow, blue). Color categorization is a case in point in the debate on how language shapes human cognition. Evidence suggests that color categorization depends on top-down input from the language system to the visual cortex. We directly tested this hypothesis by assessing color categorization in a stroke patient, RDS, with a rare, selective deficit in naming visually presented chromatic colors, and relatively preserved achromatic color naming. Multimodal MRI revealed a left occipito-temporal lesion that directly damaged left color-biased regions, and functionally disconnected their right-hemisphere homologs from the language system. The lesion had a greater effect on RDS’s chromatic color naming than on color categorization, which was relatively preserved on a nonverbal task. Color categorization and naming can thus be independent in the human brain, challenging the mandatory involvement of language in adult human cognition

Ensemble coding of color and luminance contrast

Ensemble coding has been demonstrated for many attributes including color, but the metrics on which this coding is based remain uncertain. We examined ensemble percepts for stimulus sets that varied in chromatic contrast between complementary hues, or that varied in luminance contrast between increments and decrements, in both cases focusing on the ensemble percepts for the neutral gray stimulus defining the category boundary. Each ensemble was composed of 16 circles with four contrast levels. Observers saw the display for 0.5 s and then judged whether a target contrast was a member of the set. False alarms were high for intermediate contrasts (within the range of the ensemble) and fell for higher or lower values. However, for ensembles with complementary hues, gray was less likely to be reported as a member, even when it represented the mean chromaticity of the set. When the settings were repeated for luminance contrast, false alarms for gray were higher and fell off more gradually for out-of-range contrasts. This difference implies that opposite luminance polarities represent a more continuous perceptual dimension than opponent-color variations, and that “gray” is a stronger category boundary for chromatic than luminance contrasts. For color, our results suggest that ensemble percepts reflect pooling within rather than between large hue differences, perhaps because the visual system represents hue differences more like qualitatively different categories than like quantitative differences within an underlying color “space.” The differences for luminance and color suggest more generally that ensemble coding for different visual attributes might depend on different processes that in turn depend on the format of the visual representation

A network-level approach of cognitive flexibility impairment after surgery of a right temporo-parietal glioma

International audienceObjectiveThe right “non-dominant” temporo-parietal junction is usually not considered as a highly eloquent area. This contrasts with its mirrored left “dominant” counterpart, which is known as highly eloquent regarding language function. The question arises about which functions should be monitored when operating lesions of the right temporo-parietal junction under awake conditions.MethodsWe report the case of a patient who underwent a surgical resection of a glioma located in the right temporo-parietal junction. Cognitive evaluations were performed preoperatively and 4 months after surgery, as well as resting state fMRI and diffusion-based tractography.ResultsLong-term postoperative cognitive examination revealed an important deterioration of cognitive control abilities, especially regarding set-shifting abilities as measured by Trail making test part B. Based on pre- and postoperative resting state fMRI and diffusion-based tractography, we demonstrate that surgical resection massively impacted structural and functional connectivity of the right fronto-parieto-temporal network, a network that is classically involved in cognitive control, reasoning and working memory.ConclusionThis case clearly illustrates how a white matter focal lesion can generate a neuropsychological deficit by remotely disconnecting distant cortical areas belonging to a functional network. Furthermore, our observation strongly supports the use of intraoperative cognitive control tests during surgery of the right temporo-parietal junction and promote the interest of pre and postoperative resting state functional connectivity to explore the potential mechanisms causing cognitive deficit