Chunking Patterns Reflect Effector-dependent Representation of Motor Sequence

Sequential organization is central to much of human intelligent behavior ranging from everyday skills such as lacing shoes to using a computer. It is well known that such sequential skills involve chaining a number of primitive actions together.. A robust representation of skills can be formed by chunking together several elements of a sequence. We demonstrate, using a 2x6 finger movement task, that during the process of acquiring visuomotor skills the chunking patterns remained unaltered when utilizing an effector dependent representation of the sequence. In the 2x6 task, subjects learned a sequence of 12 visual cues displayed as six sets of two elements each and performed finger movements on a keypad.Two experiments Normal-Motor and Normal-Visual were conducted on nine subjects and two observations were collected from each subject. Each experiment consisted of a Normal and a Rotated condition. In the Rotated (Motor and Visual) conditions, subjects were required to rotate the visual cues by 180 degrees and press the corresponding keys. The display sequence was also rotated for the Motor condition, requiring an identical set of effector movements to be performed as in the Normal condition. Chunking patterns were identified using the response times (RTs) for individual sets of the sequence. A pause between set RTs demarcates an ensuing chunk. We demonstrate that usage of an effector dependent representation is supported by the observation of identical chunking patterns between the Normal and Motor conditions, and the lack of similarity in chunking patterns between the Normal and Visual conditions.