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Candace L. Eshelman-Haynes, Scott N. Watamaniuk; Background motion affects the perceived direction of a trajectory target. Journal of Vision 2004;4(8):561. doi: https://doi.org/10.1167/4.8.561.
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Spatially close motions can affect each other — one motion may capture/assimilate or repel the other. Here, we studied how coherent background motion affects the perceived direction of a target moving on a fixed trajectory. Straight and curved trajectories were studied but in all experiments observers fixated a central spot and were shown two stimuli, a target trajectory on a background of motion and a comparison trajectory on a blank background. Observers judged the comparison's direction or curvature relative to the target's. Straight trajectory: a single red target dot moved at 9 deg/sec along a consistent trajectory against a background of white dots moving coherently in a common direction differing from the target direction by 10 to 120 degrees. Results showed that when the trajectory was within 30 deg of the background direction, the trajectory was perceived to be moving in a direction more similar to that of the background (assimilation). When the trajectory's direction was beyond 30 deg of the background motion, the trajectory was perceived to be moving in a direction further from that of the background (repulsion). This repulsion effect peaked when the direction difference between the background and trajectory was about 70 deg and declined with larger direction differences. Curved trajectory: a red target dot following a curved trajectory against a background of dots following a curved path with a radius of 18 deg. The 15x15 deg stimulus aperture was positioned so that only a top portion of the rotating background was visible. The target's trajectory either curved in the same (arcing upward) or opposite (arcing downward) way as the visible background or followed a straight path, but all targets traveled in the opposite direction of the background flow. Results showed that there was little effect when target curvature was the same as the background. However, when target curvature was opposite the background, the target's curvature appeared flattened.
NSF Grant IBN-9983563 to SNW
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