Limits in controlling the focus of attention

In a series of five experiments, we attempted to answer three questions concerning the flexibility of visuospatial attention: Is it possible to exert control on the shape of the attentional focus? Can attention be distributed not uniformly but in a gradient fashion within the focus? Does the way in which attentional resources are distributed within the focus affect the way in which they are distributed outside its borders? We provide evidence indicating that observers successfully allocated attention to the cued region. When the cued region was demarcated by a polygon, target detection was speeded up within the polygon. The results also show that the observers were unable to suppress information arising from an irrelevant location falling between two relevant locations (Experiments 1, 2, 3A and 3B). In accord with the zoom lens model, we interpret these results as suggesting that attention forms a unitary zone that may expand to encompass multiple relevant locations but must also include the area between them. In addition, we found that some sort of lateral masking effect occurred when the borders were close to the target location. Tn Experiment 4, we obtained a gradient inside the attentional focus and a symmetrical, but less steep, graded fall-off outside the attentional focus. It was also possible to discriminate attentional effects from effects attributable to retinal eccentricity.