Target selection in visual search as revealed by movement trajectories

Abstract

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.

Embodied Effects of Conceptual Knowledge Continuously Perturb the Hand in Flight

“…Regardless of whether rotation was required, during the first half of the reach action, an incongruent object in working memory slowed forward progress and attracted the hand toward the competing response element. The latter result converges nicely with previous demonstrations showing analogous effects for both hand and eye movements in two dimensions (McSorley et al, 2004;Song & Nakayama, 2008).…”

Salient stimuli capture attention and action

“…The temporal parameters in both tasks were equally influenced by variables known to influence search times, such as the feature contrast between target and distractors, repetition of the same target dimension, or cuing of the upcoming target dimension. Similarly, Song and Nakayama (2008) observed that spatial parameters of a reaching movement were influenced by the same perceptual competition mechanisms as buttonpresses. When participants were asked to touch the odd-colored item in a search display, the trajectories of the reaching movements often deviated toward the distractors when the visual search task was difficult because there were only a few distractors (Song & Nakayama, 2006.…”

Response trajectories reveal conflict phase in image–word mismatch

“…In several recent studies, researchers have analyzed the trajectory of a participant's response when selecting the answer with the touch of a finger (Boulenger et al, 2006;Finkbeiner, Song, Nakayama, & Caramazza, 2008;Schmidt & Seydell, 2008;Song & Nakayama, 2008a, 2008b, a saccade (Smit & Gisbergen, 1990) or a computer mouse (Freeman & Ambady, 2009;Spivey, Grosjean & Knoblich, 2005). The response choices are presented at different locations in space so that an in-flight deviation toward the competing, incorrect answer can be revealed.…”