Simultaneous Encoding of Direction at a Local and Global Scale

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Assessed whether encoding global motion (the coherent motion of a field of dots) would preclude the encoding of a local trajectory component and vice versa. In 3 experiments with 3 30–52-yr-olds, 100–150 dots were randomly assigned directions from a uniform distribution of directions spanning a range of 160° to create global motion in a single direction. Amidst these background dots, 1 dot moved in a consistent direction (trajectory) for the duration of the display. The direction of this 'trajectory dot' was similar to the mean direction of the distribution of directions determining the movement of the background dots. Direction discrimination for both the global motion and the trajectory was measured, using the method of constant stimuli, under precued and postcued partial report conditions. Direction discrimination thresholds for both global and local motion in the postcued condition were not significantly different from those obtained in the precued condition. Results suggest that direction information for both global and local motion is encoded simultaneously and that the observer has access to either motion signal after the presentation of a stimulus.



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