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Seminarium: The modularity of high-level colour processing

Zapraszamy na seminarium otwarte w C-Lab, Laboratorium Badania Świadomości.

Prowadzenie: dr Katarzyna Siuda-Krzywicka
Kiedy: 30.10, g. 11:30
Gdzie: sala 2.04

 

"The modularity of high-level colour processing: evidence from brain damage"
 

Abstract:
Colour provides valuable information about the environment, yet the exact mechanisms explaining how colours appear to observers remain poorly understood. Retinal signals are transformed the visual cortex through the high-level mechanisms that link colour perception with top-down expectations and knowledge. Here, we examined the effects of focal brain lesions in humans on these mechanisms. Studies on brain damage suggest that high-level colour processing may be divided into at least three modules: conscious perception, naming and knowledge. We studied the interdependences of those modules by focusing on colour categorisation - a case-in-point of the interplay between colour perception and language.

Based on the evidence from cognitive development, comparative psychology and cognitive neuroscience we propose that colour categorisation originate from neither perception nor language, as assumed by the Nature-Nurture debate. Instead, colour categories may reflect relevant objects in the environment. To empirically assess the causal relationship between colour categorization and naming, we investigated a stroke patient, RDS. Despite severe difficulties in naming chromatic colours (excluding white, black and grey) resulting from a left occipito-temporal lesion, RDS’s colour categorisation was relatively spared. Multimodal MRI experiments revealed that the connectivity between language system and colour perception is essential for efficient colour naming but not for colour categorisation. Then, we investigated object-colour knowledge in the context of RDS’s colour-naming impairment. RDS could associate colour names with object names; and differentiate typically and atypically coloured objects. He could not, however, associate a visually presented colour to a colour name, nor to the shape of its typical object. Thus, RDS could not link abstract colours to language and semantic knowledge. 

Overall, we demonstrated three novel functional segregations in cortical colour processing: (1) between colour categorisation and colour naming, (2) between the naming of chromatic and achromatic colours and (3) between knowing about coloured objects and knowing about abstract colours. We propose that the main purpose of high-level cortical colour mechanisms is to provide sensory and semantic information to guide object-related behaviour, by achieving (1) stable colour perception, (2) ecologically relevant colour categories, and (3) joint mental representations of shapes and colours. These neural computations may have been recycled in cultural evolution to isolate colour from object and label it with colour names. We suggest that research on high-level vision could benefit from incorporating the role of colour in object-related behaviour within models of object recognition and colour perception.

 

 

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