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Marcus Kaiser, Markus Lappe; Perisaccadic compression of space orthogonal to saccade direction. Journal of Vision 2002;2(7):173. doi: 10.1167/2.7.173.
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© ARVO (1962-2015); The Authors (2016-present)
Objects flashed before or during a saccade are perceived as shifted towards the saccade target. A possible interpretation is that the target attracts the object. If that would be the case, one would also expect a vertical shift for horizontal saccades. Here we show that a shift in the object's perceived position orthogonal to saccade direction does occur, but only for stimulus positions beyond the target.
Three subjects made horizontal saccades towards a target (20 deg to the right) in front of a red screen. A green dot (1.2 deg) was presented for 12ms before, during or after the saccade. The dot's position was chosen randomly from a 5×5 grid (8×8 deg) centered around the target. After the saccade, the subject reported the object position by setting a mouse pointer. We found that shortly before and during a saccade dots presented left to the target were shifted in horizontal direction. Dots presented to the right of the target, however, were also shifted vertically towards the target position.
In a second experiment we used vertical saccades (20 deg downwards) to test whether transferring information from one hemisphere to the other during remapping or lateralization could account for different results of left and right hemifield. A component of mislocalization orthogonal to saccade direction (i.e. horizontal) occured below the target.
We conclude that the shift towards the target can also have a component orthogonal to saccade direction both for horizontal and vertical saccades. This effect is limited to objects presented in the space beyond the target. We propose that different kinds of visual processing occur for spatial areas before and beyond the target.
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