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Kwesi Sullivan, Jay Edelman; An oculomotor Simon effect. Journal of Vision 2009;9(8):380. doi: 10.1167/9.8.380.
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© ARVO (1962-2015); The Authors (2016-present)
The Simon Effect is traditionally observed in manual responses when a peripheral imperative stimulus, which presumably attracts attention, dictates a response with the contralateral limb. Such “incongruous” responses have been found to have longer latency than “congruous” responses, with an ipsilateral limb response (Simon and Rudell, 1967; Lu and Proctor, 1995). We examined whether such a Simon effect was also evident for saccadic eye movements, such that a saccade directed contraversive to a peripheral imperative stimulus would be of longer latency than a saccade directed ipsiversively (also see Sheliga et al, 1997). Subjects viewed a CRT display controlled by Vision Shell software routines while eye position was monitored by videooculography at 500 frames/s (Eyelink II, SR Research). Trials began with presentation of a central fixation point alongside two white squares, 8 deg. to the left or right of fixation. 500–800 ms later, a red or green “figure 8” appear 8 deg to the left or right of fixation (i.e. superimposed on one of the small peripheral squares). In manual trials, a red (green) figure 8 indicated a left (right) button press (‘z’ or ‘/’ key on a standard keyboard). In the saccade task, stimulus presentation was identical; the red (green) figure 8 indicated a left (right) saccade. Subjects were instructed to respond as quickly and rapidly as possible. Across subjects, saccade and manual response latency depended similarly on response congruity. But, strikingly, the error rate for saccadic responses was considerably higher than that for manual responses. These results indicate that the Simon Effect is stronger for saccadic than manual responses, and suggest that the link between attention and saccade programming is stronger than that between attention and manual motor programming.
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