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Steven L. Prime, Matthais Niemeier, John D. Crawford; Trans-saccadic integration of the orientation and location features of linear objects. Journal of Vision 2004;4(8):742. doi: 10.1167/4.8.742.
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It is currently unclear how and to what extent the visual system is able to integrate information across sequential gaze fixations to form a unified perceptual representation. We have recently found that subjects could retain information about visual features (such as stimulus orientation) across saccades just as well as within fixations (Prime, Niemeier, Yan, & Crawford, Society for Neuroscience Abstracts, 2002). One job for trans-saccadic integration then would be to integrate the locations and orientations of linear stimuli across to construct emergent properties required for object and scene perception. We tested this by having our subjects view two bars of different orientations that appeared briefly, one at a time, at two locations in space. Using a mouse cursor, they then pointed at where the two bars would intersect, providing an indication of whether they were able to synthesize information from the two lines. In the control condition, subjects maintained eye fixation as both bars were presented. In the test condition, the two probes were presented in two fixations separated by a saccadic eye movement. The magnetic search coil technique was used for monitoring eye movements to ensure that subjects did not make extraneous eye movements and stimulus presentation was controlled using on-line eye movement feedback. Results showed that the subjects' accuracy in the saccade condition was the same as in the eyes-fixated condition. In both conditions, subjects underestimated the true intersections' vertical position and these vertical errors increased as a function of intersection position. Moreover, subjects' pointing was biased in the direction of the first presented probe in both conditions. These findings suggest that, apart from minor errors, the brain retains the location and the orientation of lines across saccades and that it can integrate these two sources of information into new percepts.
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