Spatial attention and metacontrast unmasking : integration of the two solitudes

This thesis claims that metacontrast unmasking is influenced by attentional orienting towards the target location. This view is contrary to Breitmeyer, Rudd and Dunn (1981), who proposed that metacontrast unmasking is the product of inhibition of the primary mask's transient signal by the sustained signal of a secondary mask. A series of experiments demonstrate the thesis using a task in which observers discriminated the missing corner of a target diamond. Experiments 1 and 2 replicated metacontrast masking and unmasking, respectively, experiment 3 illustrated that contour proximity had no influences on unmasking, contrary to dual-channel inhibition theory. Experiments 4 and 5 indicated that metacontrast unmasking was influenced by spatial orienting. We propose an addition of attention to dual-channel theory as it is incomplete with regards to metacontrast unmasking.Arts, Faculty ofPsychology, Department ofGraduat