Target selection in visual search as revealed by movement trajectories

We examined target selection for visually guided reaching movements in visual search, in which participants reached to an odd-colored target presented with two homogenous distractors. The colors of the target and distractors were randomly switched for each trial between red and green, and the location of the target was varied. Therefore either color could be a distractor or target, and the identity was resolved by grouping two distractors having the same color. Thus, there was ongoing competition between a target and distractors. In some trials, reaches were directed to the target, and in other trials, reaches were initially directed towards a distractor and corrected in mid-flight, showing highly curved trajectories. Interestingly, trials with highly curved trajectories were no less efficient in terms of accuracy or total time. The extra time taken up in movement duration was offset by shorter initial latencies. By analyzing curved trajectories, we demonstrated that corrective movements occur shortly after the onset of initial movement, suggesting that a corrective new target is selected even before initial movement is executed. This provides an explanation as to why misdirected reaches, hastily initiated, can be corrected with minimal loss in overall efficiency. In addition, our results show that the details of movement trajectories allow us to visualize the dynamics of target selection as they unfold in time. (c) 2007 Elsevier Ltd. All rights reserved.