Brouwer Anne-Marie, Middelburg Tom, Smeets Jeroen B J, Brenner Eli
Erasmus MC, Rotterdam, Netherlands.
Exp Brain Res. 2003 Oct;152(3):368-75. doi: 10.1007/s00221-003-1556-8. Epub 2003 Jul 30.
Previous work has indicated that people do not use their judgment of a target's speed to determine where to hit it. Instead, they use their judgment of the target's changing position and an expected speed (based on the speed of previous targets). In the present study we investigate whether people also ignore the target's apparent direction of motion, and use the target's changing position and an expected direction of motion instead. Subjects hit targets that moved in slightly different directions across a screen. Sometimes the targets disappeared after 150 ms, long before the subjects could reach the screen. This prevented subjects from using the target's changing position to adjust their movements, making it possible to evaluate whether subjects were relying on the perceived or an expected (average) direction to guide their movements. The background moved perpendicular to the average direction of motion in some trials. This influences the target's perceived direction of motion while leaving its perceived position unaffected. When the background was stationary, subjects hit disappearing targets along their trajectory, just as they hit ones that remained visible. Moving the background affected the direction in which subjects started to move their hand, in accordance with the illusory change in direction of target motion. If the target disappeared, this resulted in a hit that was systematically off the target's trajectory. If the target remained visible, subjects corrected their initial error. Presumably they did so on the basis of information about the target's changing position, because if the target disappeared they did not correct the error. We conclude that people do use the target's perceived direction of motion to determine where to hit it. Thus the perceived direction of motion is treated differently than the perceived speed. This suggests that the motion of an object is not broken down into speed components in different directions, but that speed and direction are perceived and used separately.
先前的研究表明，人们不会依据对目标速度的判断来确定击打目标的位置。相反，他们会依据对目标位置变化的判断以及预期速度（基于先前目标的速度）来做出决策。在本研究中，我们探究人们是否也会忽略目标的视在运动方向，而是使用目标的位置变化和预期运动方向来替代。受试者需要击打在屏幕上沿略有不同方向移动的目标。有时目标在150毫秒后消失，远早于受试者能够到达屏幕的时间。这使得受试者无法利用目标位置的变化来调整他们的动作，从而有可能评估受试者是依靠感知到的方向还是预期（平均）方向来指导他们的动作。在某些试验中，背景沿与平均运动方向垂直的方向移动。这会影响目标的视在运动方向，而不影响其视在位置。当背景静止时，受试者会沿着目标的轨迹击打消失的目标，就如同击打那些保持可见的目标一样。移动背景会影响受试者开始移动手部的方向，这与目标运动方向的错觉变化一致。如果目标消失，这会导致击打偏离目标轨迹。如果目标保持可见，受试者会纠正他们最初的误差。据推测，他们是基于目标位置变化的信息来这样做的，因为如果目标消失，他们就不会纠正误差。我们得出结论，人们确实会利用目标的视在运动方向来确定击打位置。因此，视在运动方向与视在速度的处理方式不同。这表明物体的运动不是被分解为不同方向的速度分量，而是速度和方向是分别被感知和使用的。
