Competition and sharing of processing resources in visual discrimination.
Discrimination thresholds for spatial frequency and contrast tested individually were compared with dual discrimination of contrast and spatial frequency, and dual discrimination of 2 contrast or spatial frequency components. The components were presented overlapping, forming a compound grating or as side-by-side simple gratings. When observers had to judge contrast and spatial frequency simultaneously, discrimination thresholds increased by an amount predicted by a model of stimulus uncertainty for orthogonal dimensions (1.7); when they had to judge 2 frequency or contrast components, discrimination thresholds increased by a factor of 3-6 compared with the single-judgment task. The relative spatial location of the components did not interact with task complexity. The results are consistent with a model assuming a set of parallel special-purpose attentional mechanisms.
Magnussen
S
S
Department of Psychology, University of Oslo, Norway. svein.magnussen@psykologi.uio.no
Greenlee
M W
MW
D000704:Analysis of Variance; D001288:Attention; D015350:Contrast Sensitivity; D006801:Humans; D016015:Logistic Models; D008960:Models, Psychological; D012684:Sensory Thresholds; D013028:Space Perception