Perceptual contributions to problem solving: Chunk decomposition of Chinese characters.

Chunk decomposition is the decomposing of familiar patterns into their component elements so that they can be regrouped in another meaningful manner. Such a regrouping is sometimes critically required in problem solving because during initial encoding the problem elements become automatically grouped into familiar chunks and this may prohibit finding a novel or efficient solution to problems [G. Knoblich, S. Ohlsson, H. Haider, D. Rhenius, Constraint relaxation and chunk decomposition in insight problem solving, J. Exp. Psychol. Learn. Mem. Cogn. 25 (1999) 1534-1556]. In order to elucidate the brain mechanisms underlying the process of chunk decomposition, we developed a task that uses Chinese character as materials. Chinese characters are ideal examples of perceptual chunks. They are composed of radicals, which in turn, are composed of strokes. Because radicals are meaningful chunks themselves but strokes are not meaningful in isolation, it is much easier to separate a character by its radicals than to separate a character by its strokes. By comparing the stroke-level decomposition and the radical-level decomposition, we observed activities in occipital, frontal, and parietal lobes. Most importantly, during the moment of chunk decomposition, we found the early visual cortex showed a tendency of negative activation whereas the higher visual cortex showed a tendency of positive activation. This suggests that in order to successfully decompose a chunk, the higher visual areas must at least partly be 'disconnected' from the input provided by early visual processing in order to allow simple features to be rearranged into a different perceptual chunk. We conclude that early perceptual processes can crucially affect thinking and problem solving.