Background, an important factor in visual search.

The ability to detect an object depends on the contrast between the object and its background. Despite this, many models of visual search rely solely on the properties of target and distractors, and do not take the background into account. Yet, both target and distractors have their individual contrasts with the background.

Centre-surround relative motion and the freezing rotation illusion.

In the Freezing Rotation illusion a stimulus rotating with a constant velocity is perceived as stationary on the screen, when it is presented in front of a background pattern that moves with a sinusoidal velocity profile, during the phase in which stimulus and background rotate in the same direction. It has been suggested that this illusion is caused by the interfering effect of induced motion resulting from the relative motion between the centre and the surround. Since the magnitude of such an induced motion component presumably relates to the difference between background and centre velocities, the illusion itself should also be related to the amount of relative motion between the centre and the surround, and it should not occur when this difference is zero.

Search time critically depends on irrelevant subset size in visual search.

In order for our visual system to deal with the massive amount of sensory input, some of this input is discarded, while other parts are processed [Wolfe, J. M. (1994).

Frame of reference transformations in motion perception during smooth pursuit eye movements.

Smooth pursuit eye movements change the retinal image velocity of objects in the visual field. In order to change from a retinocentric frame of reference into a head-centric one, the visual system has to take the eye movements into account. Studies on motion perception during smooth pursuit eye movements have measured either perceived speed or perceived direction during smooth pursuit to investigate this frame of reference transformation, but never both at the same time.

Localization and motion perception during smooth pursuit eye movements.

We investigated the relationship between compensation for the effects of smooth pursuit eye movements in localization and motion perception. Participants had to indicate the perceived motion direction, the starting point and the end point of a vertically moving stimulus dot presented during horizontal smooth pursuit. The presentation duration of the stimulus was varied.

Perceived motion direction during smooth pursuit eye movements.

Although many studies have been devoted to motion perception during smooth pursuit eye movements, relatively little attention has been paid to the question of whether the compensation for the effects of these eye movements is the same across different stimulus directions. The few studies that have addressed this issue provide conflicting conclusions. We measured the perceived motion direction of a stimulus dot during horizontal ocular pursuit for stimulus directions spanning the entire range of 360 degrees.

Vertical object motion during horizontal ocular pursuit: compensation for eye movements increases with presentation duration.

Smooth pursuit eye movements change the retinal image motion of objects in the visual field. To enable an observer to perceive the motion of these objects veridically, the visual system has to compensate for the effects of the eye movements. The occurrence of the Filehne-illusion (illusory motion of a stationary object during smooth pursuit) shows that this compensation is not always perfect.