Indications for two attentional gradients in endogenous visual-spatial attention

Four experiments were designed to investigate the meridian effect on attentional orienting (characterized by a larger cost when the cue and target fall in different visual fields relative to when they fall in the same fields) when employing an endogenous cue. In Experiment 1 a circular display of eight boxes was employed and no meridian effect was found. In Experiment 2 three displays were compared: Semicircular, vertical, and horizontal. No meridian effect was found in the semicircular display. However, in the two linear displays (vertical, horizontal) there was a significant meridian effect. Experiments 3 and 4 were designed to investigate an attentional gradient hypothesis. In all experiments a distance effect was found. Nevertheless, the distance effect was not directly related to the actual distance between the target positions. The results suggest the existence of two attentional gradients that develop simultaneously in the visual field: an excitation gradient centred at the cued location (the strongest excitation) and an inhibition gradient, centred at the fixation point (the strongest inhibition).