The Effects of Attentional Spread and Attentional Effort on Orientation Discrimination

Abstract

We investigated the spatial properties of visual attention, and its relation to attentional effort. We show that stimulus detectability changes as a function of attentional beam width and of the degree of task difficulty. We used a matching-to-sample paradigm, presenting two Gabor patches simultaneously as sample stimuli and as test stimulus, the stimuli being at three different distances. Task difficulty was graded by changing the orientation difference of the two Gabor patches on nonmatching trials. ‘Difficult’ nonmatching probe trials were embedded within an easy block of trials (easy condition), and vice versa for ‘easy’ probe trials. Differences in the detectability, d', between probe trials in the two conditions were taken as a measure for the change in attention. Our results show that the detectability of a pair of stimuli decreases with an increase in the distance between stimuli. In addition, the results indicate an increase in attentional effort for different attentional beam widths, and also suggest a decrease in the SD of the internal stimulus representation during the task conditions that require more attention.