Position-dependent and position-independent attention shifts: evidence against the spotlight and premotor assumption of visual focussing.

One implication of the spotlight metaphor of visual-attention shifts is that attention moves from position to position, from one object in the visual field to another. According to this view, attention shifts start at the last-focussed position, their spatiotemporal course therefore being position dependent. A different, yet also position-dependent, formulation is implied in the so-called "premotor hypothesis of attention" (Rizzolatti et al., 1987; Umiltà et al., 1991). In this paper these two accounts are tested against an alternative, position-independent conception. It is maintained that in the case of onset-triggered processes, the course of the attentional shifts is independent of the last-focussed position. On the basis of these considerations, three experiments measure choice-reaction times of stimuli at different spatial positions after peripheral cuing of the same or another position within the visual field. Results show no evidence for the position-dependent conception of the spotlight metaphor or the premotor hypothesis with a long SOA (stimulus-onset asynchrony) between cue and stimulus. Only with a short SOA is the premotor hypothesis supported by the data. As an alternative interpretation, a position-independent thesis is favored, in which it is assumed that attention shifts can be adjusted during an early stage of processing.