Initiation of smooth-pursuit eye movements by real and illusory contours

Abstract

It is well established that elementary motion detectors are only able to code for the movement of a contour perpendicular to its orientation. This shortcoming explains why the initial direction of smooth-pursuit eye movements is directed orthogonal to the orientation of a moving contour independent of its veridical direction of motion. Here, we replicated this finding and asked whether this directional error can be reduced by subjects' prediction of upcoming target moving direction and whether this directional error also occurs during tracking of an illusory contour. Our results show that prediction did not abolish the directional error, it was only slightly reduced. On the other hand, the directional error was considerably diminished during pursuit initiation towards illusory contours and most likely reflected the amount of real stimulation defining the specific illusory contour. We conclude that pursuit initiation is driven by raw retinal image motion signals, which are not yet processed for figure completion.

Linking brain to behavior for the visual perception of figures and objects

“…Psychophysical studies that directly investigated the effect of eccentricity on sensitivity to texture pop-out found that detection was optimal in the periphery (Fiorentini, 1989; Meinecke, 1989). Related to this, an eye-tracking study by Biber and Ilg (2008) found that pursuit initiation to illusory contour stimuli occurs before contour completion can take place, suggesting that segmentation facilitates fixation upon a salient region and that the perception of a figure’s contours requires the high spatial precision afforded by central viewing (Hirsch & Curcio, 1989).…”

Evaluating Motion Estimation Models from Behavioural and Psychophysical Data

“…Translating Bars In [20,8] the authors consider tilted translating bars. Pursuing a translating bar which true motion direction is not normal to its orientation leads to initial deviation in the smooth pursuit eye movement direction.…”

“…• [8]. To obtain a model evaluation procedure, the slope of the directional errors could be analysed with respect to bar length, number of bar tiles.…”

“…Indeed, as the bar length is increased it becomes more complicated to recover its true direction. Likewise it easier to pursue one long bar, if it is tiled into several sub bars [20,8].…”

The analysis of visual motion and smooth pursuit eye movements.

“…There has been some debate over the years whether pursuit correlates better with physical or perceived stimulus motion. When physical and perceived motions are different, the oculomotor system mostly follows the percept rather than the physical stimulus (Beutter & Stone, 1998Biber & Ilg, 2008;Hafed & Krauzlis, 2006Ilg & Thier, 2003;Madelain & Krauzlis, 2003;Ringach, Hawken, & Shapley, 1996;Steinbach, 1976;Wyatt, Pola, Fortune, & Posner, 1994). One particularly interesting case of perceived motion is the illusory motion caused by the motion aftereffect (MAE) in which there is no physical motion at all.…”