Contextual modulation induced by contrast and speed on direction perception.

We examined the direction perception in centre-surround multielement configurations with varying contrast and velocity to better understand the consequences of surround interactions of orientation and motion direction perception. The stimuli consisted of Gabor elements moving either parallel or orthogonal to their orientation with two different speeds. The surround motion direction varied from 0 degrees to 315 degrees with a step of 45 degrees . The relative contrast in the centre and periphery was varied. The subject's task was to discriminate whether the central motion was to the left or to the right from the vertical downward. The results suggest complex interactions between the speed, contrast, and the texture elements' orientation on both sensitivity and precision of motion direction estimation in the centre and different effects of the experimental factors on the bias and discriminability of motion direction. The potential contribution of different normalization circuits on motion direction estimation is discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).