Abstract
We asked how the characteristics of a surround could affect the perception of a central component undergoing translational motion. Two adjacent patches of moving dots (100 dots per patch; diameter 2.5 deg) were presented on a VDU screen. A central ‘target’ patch consisted of a combination of signal dots, undergoing left - right translational motion, and noise dots, which moved in random directions at the same speed as the signal dots. To the right of this a ‘probe’ patch contained dots undergoing translational motion. A simple 2IFC task was used to detect the presence of left - right translational motion in the target patch. An adaptive staircase varied the ratio of translating (signal) to noise dots to measure the 79.4% correct point.
Preliminary findings indicate that both the directional characteristics of the probe and the degree of separation between the two patches influence sensitivity to the target motion. At large separations, probe characteristics do not influence target sensitivity. As the two patches become closer together, probe motion parallel to the target patch increases sensitivity, whereas orthogonal probe motion decreases target sensitivity. Surprisingly, as the separation between the patches becomes even smaller, sensitivity to the target motion is reduced by a parallel probe and increased by an orthogonal probe. This suggests that spatial motion integration involves facilitation and inhibition between different motion directions, and that these two effects have different spatial characteristics.
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