Anna Franklin

Categorical perception of color is lateralized to the right hemisphere in infants, but to the left hemisphere in adults

Both adults and infants are faster at discriminating between two colors from different categories than two colors from the same category, even when between- and within-category chromatic separation sizes are equated. For adults, this categorical perception (CP) is lateralized; the category effect is stronger for the right visual field (RVF)–left hemisphere (LH) than the left visual field (LVF)–right hemisphere (RH). Converging evidence suggests that the LH bias in color CP in adults is caused by the influence of lexical color codes in the LH. The current study investigates whether prelinguistic color CP is also lateralized to the LH by testing 4- to 6-month-old infants. A colored target was shown on a differently colored background, and time to initiate an eye movement to the target was measured. Target background pairs were either from the same or different categories, but with equal target-background chromatic separations. Infants were faster at initiating an eye movement to targets on different-category than same-category backgrounds, but only for targets in the LVF–RH. In contrast, adults showed a greater category effect when targets were presented to the RVF–LH. These results suggest that whereas color CP is stronger in the LH than RH in adults, prelinguistic CP in infants is lateralized to the RH. The findings suggest that language-driven CP in adults may not build on prelinguistic CP, but that language instead imposes its categories on a LH that is not categorically prepartitioned.

Further evidence that Whorfian effects are stronger in the right visual field than the left

The Whorf hypothesis holds that differences between languages induce differences in perception and/or cognition in their speakers. Much of the experimental work pursuing this idea has focused on the domain of color and has centered on the issue of whether linguistically coded color categories influence color discrimination. A new perspective has been cast on the debate by recent results that suggest that language influences color discrimination strongly in the right visual field but not in the left visual field (LVF). This asymmetry is likely related to the contralateral projection of visual fields to cerebral hemispheres and the specialization of the left hemisphere for language. The current study presents three independent experiments that replicate and extend these earlier results by using different tasks and testing across different color category boundaries. Our results differ in one respect: although we find that Whorfian effects on color are stronger for stimuli in the right visual field than in the LVF, we find that there are significant category effects in the LVF as well. The origin of the significant category effect in the LVF is considered, and two factors that might account for the pattern of results are proposed.

New evidence for infant colour categories

Bornstein, Kessen, and Weiskopf (1976) reported that pre-linguistic infants perceive colour categorically for primary boundaries: Following habituation, dishabituation only occurred if the test stimulus was from a different adult category to the original. Here, we replicated this important study and extended it to include secondary boundaries, with a crucial modification: The separations between habituated and novel stimuli were equated in a perceptually uniform metric (Munsell), rather than in wavelength. Experiment 1 found Categorical Perception and no within-category novelty preference for primary boundary blue-green and secondary boundary blue-purple. Experiment 2 replicated the categorical effect for blue-purple and found no within-category novelty preference with increased stimulus separation. Experiment 3 showed category effects for a lightness/saturation boundary, pink-red. Novelty preference requires a categorical difference between the habituated and novel stimulus. The implications for the origin of linguistic colour categories are discussed.

Lateralization of categorical perception of color changes with color term acquisition

Categorical perception (CP) of color is the faster and more accurate discrimination of two colors from different categories than two colors from the same category, even when same- and different-category chromatic separations are equated. In adults, color CP is lateralized to the left hemisphere (LH), whereas in infants, it is lateralized to the right hemisphere (RH). There is evidence that the LH bias in color CP in adults is due to the influence of color terms in the LH. Here we show that the RH to LH switch in color CP occurs when the words that distinguish the relevant category boundary are learned. A colored target was shown in either the left- or right-visual field on either the same- or different-category background, with equal hue separation for both conditions. The time to initiate an eye movement toward the target from central fixation at target onset was recorded. Color naming and comprehension was assessed. Toddlers were faster at detecting targets on different- than same-category backgrounds and the extent of CP did not vary with level of color term knowledge. However, for toddlers who knew the relevant color terms, the category effect was found only for targets in the RVF (LH), whereas for toddlers learning the color terms, the category effect was found only for targets in the LVF (RH). The findings suggest that lateralization of color CP changes with color term acquisition, and provide evidence for the influence of language on the functional organization of the brain.

Color Perception in Children with Autism.

This study examined whether color perception is atypical in children with autism. In experiment 1, accuracy of color memory and search was compared for children with autism and typically developing children matched on age and non-verbal cognitive ability. Children with autism were significantly less accurate at color memory and search than controls. In experiment 2, chromatic discrimination and categorical perception of color were assessed using a target detection task. Children with autism were less accurate than controls at detecting chromatic targets when presented on chromatic backgrounds, although were equally as fast when target detection was accurate. The strength of categorical perception of color did not differ for the two groups. Implications for theories on perceptual development in autism are discussed.

Neurophysiological evidence for categorical perception of color

The aim of this investigation was to examine the time course and the relative contributions of perceptual and post-perceptual processes to categorical perception (CP) of color. A visual oddball task was used with standard and deviant stimuli from same (within-category) or different (between-category) categories, with chromatic separations for within- and between-category stimuli equated in Munsell Hue. CP was found on a behavioral version of the task, with faster RTs and greater accuracy for between- compared to within-category stimuli. On a neurophysiological version of the task, event-related potentials (ERPs) showed earlier latencies for P1 and N1 components at posterior locations to between- relative to within-category deviants, providing novel evidence for early perceptual processes on color CP. Enhanced P2 and P3 waves were also found for between- compared to within-category stimuli, indicating a role for later post-perceptual processes.

Reduced chromatic discrimination in children with autism spectrum disorders

Atypical perception in Autism Spectrum Disorders (ASD) is well documented (Dakin & Frith, 2005). However, relatively little is known about colour perception in ASD. Less accurate performance on certain colour tasks has led some to argue that chromatic discrimination is reduced in ASD relative to typical development (Franklin, Sowden, Burley, Notman & Alder, 2008). The current investigation assessed chromatic discrimination in children with high-functioning autism (HFA) and typically developing (TD) children matched on age and non-verbal cognitive ability, using the Farnsworth-Munsell 100 hue test (Experiment 1) and a threshold discrimination task (Experiment 2). In Experiment 1, more errors on the chromatic discrimination task were made by the HFA than the TD group. Comparison with test norms revealed that performance for the HFA group was at a similar level to typically developing children around 3 years younger. In Experiment 2, chromatic thresholds were elevated for the HFA group relative to the TD group. For both experiments, reduced chromatic discrimination in ASD was due to a general reduction in chromatic sensitivity rather than a specific difficulty with either red-green or blue-yellow subsystems of colour vision. The absence of group differences on control tasks ruled out an explanation in terms of general task ability rather than chromatic sensitivity. Theories to account for the reduction in chromatic discrimination in HFA are discussed, and findings are related to cortical models of perceptual processing in ASD.

Color categories affect pre-attentive color perception.

Categorical perception (CP) of color is the faster and/or more accurate discrimination of colors from different categories than equivalently spaced colors from the same category. Here, we investigate whether color CP at early stages of chromatic processing is independent of top-down modulation from attention. A visual oddball task was employed where frequent and infrequent colored stimuli were either same- or different-category, with chromatic differences equated across conditions. Stimuli were presented peripheral to a central distractor task to elicit an event-related potential (ERP) known as the visual mismatch negativity (vMMN). The vMMN is an index of automatic and pre-attentive visual change detection arising from generating loci in visual cortices. The results revealed a greater vMMN for different-category than same-category change detection when stimuli appeared in the lower visual field, and an absence of attention-related ERP components. The findings provide the first clear evidence for an automatic and pre-attentive categorical code for color.

Categorical encoding of color in the brain

Significance Humans group the millions of discriminable colors into discrete categories, such as “blue” and “green.” There has been much debate about where color categories come from; for example, whether color categories are inbuilt into the visual system. We use functional MRI to identify regions of the brain that categorize color. Color categories are encoded by regions of the frontal lobes, which also categorize other information (e.g., sounds). Interestingly, the visual cortex responds only to the size of color differences, but not color categories. We conclude that color categories occur at the level of attention rather than being inbuilt into the visual system. The findings shed light on how the brain categorizes information and how it processes color. The areas of the brain that encode color categorically have not yet been reliably identified. Here, we used functional MRI adaptation to identify neuronal populations that represent color categories irrespective of metric differences in color. Two colors were successively presented within a block of trials. The two colors were either from the same or different categories (e.g., “blue 1 and blue 2” or “blue 1 and green 1”), and the size of the hue difference was varied. Participants performed a target detection task unrelated to the difference in color. In the middle frontal gyrus of both hemispheres and to a lesser extent, the cerebellum, blood-oxygen level-dependent response was greater for colors from different categories relative to colors from the same category. Importantly, activation in these regions was not modulated by the size of the hue difference, suggesting that neurons in these regions represent color categorically, regardless of metric color difference. Representational similarity analyses, which investigated the similarity of the pattern of activity across local groups of voxels, identified other regions of the brain (including the visual cortex), which responded to metric but not categorical color differences. Therefore, categorical and metric hue differences appear to be coded in qualitatively different ways and in different brain regions. These findings have implications for the long-standing debate on the origin and nature of color categories, and also further our understanding of how color is processed by the brain.

The relationship between color–object associations and color preference: Further investigation of ecological valence theory

Ecological valence theory (EVT; Palmer & Schloss, Proceedings of the National Academy of Sciences 107:8877–8882, 2010) proposes that color preferences are due to affective responses to color-associated objects: That is, people generally like colors to the degree that they like the objects associated with those colors. Palmer and Schloss found that the average valence of objects associated with a color, when weighted by how well the objects matched the color (weighted affective valence estimates: WAVE) explained 80% of the variation in preference across colors. Here, we replicated and extended Palmer and Schloss’s investigation to establish whether color–object associations can account for sex differences in color preference and whether the relationship between associated objects and color preference is equally strong for males and females. We found some degree of sex specificity to the WAVEs, but the relationship between WAVE and color preference was significantly stronger for males than for females (74% shared variance for males, 45% for females). Furthermore, analyses identified a significant inverse relationship between the number of objects associated with a color and preference for the color. Participants generally liked colors associated with few objects and disliked colors associated with many objects. For the sample overall and for females alone, this association was not significantly weaker than the association of the WAVE and preference. The success of the WAVE at capturing color preference was partly due to the relationship between the number of associated objects and color preference. The findings identify constraints of EVT in its current form, but they also provide general support for the link between color preference and color–object associations.