combination of A and MT. As you can see, in Fig. 8.9, the distance Wes line up pretty closely on a line as the model says it should. One thing worth noting is the three points that have 200-msec movement times. One of the things we expect to happen is that, as the movement times become slower and people begin to use feedback (at around 200 msec), the slope of the line should begin to decrease. Perhaps these data are saying that subjects are just beginning to use feedback when the movement time is 200 msec; this agrees well with the data presented earlier from Keele and Posner ( 1968). Next, consider the direction errors--errors directly perpendicular to overall movement direction. Figure 8.10 shows a plot of We for direction as a function of the ratio of A/MT. Again, we see that error in hitting the target is linearly related to the difficulty of the movement, A/MT.
I'm excited about this line of research. It seems to say that by taking into consideration the fact that programs cause impulses that cause movement, and that when impulses are more noisy the movement is more noisy, we can account for the relationships among such important variables as MT, A, and errors. Motor behaviorists have not been able to do this before now.
The project was supported in part by Grant No. BNS 7910672 from the National Science Foundation to the author.
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