The effects of attentional spread and attentional effort on orientation discrimination.

The spatial properties of visual attention and its relation to attentional effort have been investigated, and it has been found that stimulus detectability changes as a function of attentional beam width and degree of task difficulty. Using a matching-to-sample paradigm, two Gabor patches were presented simultaneously both as a sample stimulus and a test stimulus, the stimuli set at three different distances. Task difficulty was gradated 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. The detectability, d', differences of probe trials in the two conditions were calculated as a measure of change in attention. Our results show that the detectability of a pair of stimuli decreases with an increase in the distance between stimuli. Furthermore, the results indicate an increase in attentional effort for various attentional beam widths and that r = d'easy/d'difficult of the probe trials is constant throughout the different stimuli separation.