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Ken Nakayama, Joo-Hyun Song, Matthew Finkbeiner, Alfonso Caramazza; Hand trajectories reveal cognitive states. Journal of Vision 2007;7(9):568. doi: 10.1167/7.9.568.
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© ARVO (1962-2015); The Authors (2016-present)
We report two studies which demonstrate that motor behavior can reveal hidden cognitive states.
In our first study, observers were faced with a row of three squares on a screen. Single digits were presented on the middle square. The observers were instructed to touch the left square if the digits were between 1–4, the right square if the digits were between 6–9 and to press the middle square if the digit was a 5. Even though the response required was categorical (touch one of 3 squares), detailed measurement of hand trajectories revealed clear differences within categories. The initial direction of the trajectory reflected the numerical magnitude of the digit, with more leftward directions seen for smaller numbers.This provides strong support for an underlying analogue representation of digitally presented numbers and indicates that it is activated very quickly after the presentation of the digit.
In our second study, observers were required to touch a right (green) or left (red) square according to the object color designated by a target word at fixation (spinach, ketchup). The words were preceded by an unseen prime (red, green, boy), forward and backward masked. Highly curved trajectories were seen when the prime was incompatible with the color of the target word. The hand was directed to the wrong square and corrected mid-flight. These results reveal the existence of competing motor commands triggered by unseen words.
Taken together, the results challenge the assumption that behavior can be analyzed as a set of sequential stages, simply reflecting the outcome of earlier completed decisions. Motor behavior begins much earlier than has been previously assumed, thus providing a new window to view otherwise hidden cognitive states as they unfold over time (see also Spivey et al. PNAS, 2005).
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