Spatial representation of time during motor preparatory information processing in humans

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The planned research aims to clarify the characteristics of sensorimotor transformations in humans. Recent findings have shown that cognitive mental representations of stimuli, such as numerals (from 1 to 9), auditory pitch (from low to high), and letters of the alphabet (from A to Z) have spatial characteristics, and that this influences speed of responses. With respect to the evidence of an interaction between numerals and spatial information, for example, smaller numbers (e.g., 1 & 2) facilitate left-side manual responses compared to right-side responses, whereas larger numbers (e.g., 8 & 9) facilitate right-side responses compared to left-side responses. This suggests the existence of the ‘mental number line,’ i.e., spatial representations of the magnitude of numbers, and such a representation interacts with motor preparation in space. Recently, neuropsychological studies and brain imaging studies revealed that the inferior parietal lobule (IPL) reflects the common need for space, time, and quantity information to be used in sensorimotor transformations, suggesting that the IPL is a generalized magnitude system for action. Therefore, it can be hypothesized that temporal information (e.g., from early to late) would interact with spatial information during motor preparation. Based on this hypothesis, I am planning to run experiments in order to clarify the characteristics of spatial-temporal associations in sensorimotor transformation. Preliminary experiments which I have conducted showed promising results: temporal information interacts with spatial information in action. This novel finding invites further investigations on the ‘mental time line’ in relation to the sensorimotor transformation. The planned research includes investigations in both normal subjects and brain injured patients who show unilateral neglect.