Abstract not found

Abstract not found

Abstract not found

scintillating grid illusion in stereo-depth

We attempted to resolve an apparent conflict between the lack of psychophysical evidence of collinear facilitation at the nearperiphery and physiological evidence from the monkey showing collinear effects extra-fovealy. We compared collinear and orthogonal configurations to discount facilitation due to reduced positional uncertainty. Detection thresholds were measured for Gabor targets at eccentricities of 0°–4°, flanked by collinear or orthogonal flankers. Like in previous reports in the literature, results varied among subjects when the stimulus position was off-fixation. We found reduced facilitation at eccentricities as small as 1°–2°. Moreover, facilitation did not increase when the stimuli were M-scaled or when observers received more practice. However, a larger proportion of subjects showed collinear facilitation when attention was directed to the tested configurations. The results suggest that differences in allocation of attention along the visual field may affect the underlying lateral interactions, consequently resulting in eccentricity effects as well as inter-observer variability.

, 411–420; Katkov, M., Tsodyks, M., & Sagi, D. (2006b). Singularities in the inverse modeling of 2AFC contrast discrimination data. Vision Research, 46, 256–266; Katkov, M., Tsodyks, M., & Sagi, D. (2007). Singularities explained: Response to Klein. Vision Research, doi:10.1016/j.visres.2006

Targets that are flashed during smooth pursuit are mislocalised in the direction of the pursuit. It has been suggested that a similar mislocalisation of moving targets could help to overcome processing delays when hitting moving objects. But are moving targets really mislocalised in the way that flashed ones are? To find out we asked people to indicate where targets that were visible for different periods of time had appeared. The targets appeared while the subjectsÕ eyes were moving, and were either moving with the eyes or static. For flashed targets we found the usual systematic mislocalisation. For targets that moved with the eyes the mislocalisation was at least as large, irrespective of the presentation time. For static targets the mislocalisation decreased with increasing presentation time, so that by the time the presentations reached about 200ms the targets were not mislocalised at all. A simple model that combines smooth retinal motion with information about the velocity of smooth pursuit could account for the measured tapping errors. These findings support the notion that the systematic mislocalisation of flashed targets is related to the way in which people intercept moving objects. Ó 2004 Elsevier Ltd. All rights reserved. 1.

Human observers had to point to the location of a briefly presented target by means of a mouse after a brief delay following target offset. It was found that observers systematically mislocalized the target closer to the center of gaze, and to visually salient markers in the visual display. A

). Shifting visual attention between objects and locations: evidence from normal and parietal lesion subjects. Journal of Experimental Psychology: Human Perception and Performance, 123, 161–177]). We show that this object-based mediation of attention is disrupted when a pointing movement is prepared

Image motion is initially detected locally. Local motion signals are then integrated across space in order to specify the global motion of objects or surfaces. It is well known that prolonged exposure to motion causes adaptation at the local motion level. We have investigated whether adaptation also occurs at the global motion level. We have devised a global motion stimulus (a random dot kinematogram) which has equal motion energy in opposite directions but nonetheless gives rise to global motion perception. At the local motion level, adaptation to this stimulus should cause equal adaptation in both directions and should not give rise to an aftereffect. Any aftereffect seen must therefore be attributable to adaptation at the global motion level. We find that following adaptation to this stimulus, judgements of the perceived direction of a test pattern are systematically biased towards the direction opposite to the adapting direction, suggesting that adaptation does occur at a level of visual processing at which