PubMed · 14343254
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C R PETERSON, K R HAMMOND, D A SUMMERS. 1965. OPTIMAL RESPONDING IN MULTIPLE-CUE PROBABILITY LEARNING.. https://doi.org/10.1037/h0022261
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There are time delays in visuomanual and oculomotor pathways, and some of these time delays may be due to the finite time required to process visual motion signals and to extract accurate information about the speed and direction of the motion. The present experiments were designed to ascertain the time required to obtain a reliable estimate of the direction of target motion. Subjects were asked to indicate the final direction of a moving target, which abruptly changed direction and shortly thereafter disappeared, by pointing to its expected emergence at the boundary of an occlusion. Subjects made small but consistent errors that overestimated the target's change in direction. These errors depended little on the amount of time the target was visible (ranging from 50 to 400 ms) after it changed direction. Pointing direction was strongly correlated with gaze, which was dominated by a saccade initiated shortly after the target changed direction. The pointing errors were explained by the fact that the saccade always intercepted the (occluded) target, but then continued in the same direction toward the boundary of the occlusion. The analysis reveals that target direction was estimated accurately even at the shortest viewing time.
We demonstrate that the 1st- and 2nd-order characteristics of a visual stimulus can have a profound influence on each other in terms of perceived position. We use the parameter of spatial separation to selectively manipulate the effect of one characteristic upon the other. 1st-order features have their largest effect upon the perceived position of 2nd-order structure when separation is small, whilst the reciprocal effect is maximal at large separations. Implications for models of 1st- and 2nd-order interaction are discussed.
The flash-lag effect occurs when a flash abreast of a smoothly moving object is perceived to spatially lag the moving object. The postdiction accounts of this effect assume either that the flash "resets" motion detectors [Science 287 (2000) 2036], or that position information is not computed for moving objects until it is needed [Trends in the Neurosciences 25 (2002) 293], the latter view having also been proposed by Brenner and Smeets [Vision Research 40 (2000) 1645]. According to these accounts, events occurring before the flash should not change the magnitude of the flash-lag effect. In our experiment, pre-exposure of the moving object as a stationary stimulus, for as little as 50 ms before the flash occurred, significantly reduced the flash-lag effect.