The influence of two spatially distinct primers and attribute priming on motion induction

In a series of experiments, we demonstrate the effects of two spatially distinct primers on motion induction (MI) and the influence of attribute characteristics on the resulting collision site. MI means that a primer such as a spot produces a motion sensation in a subsequently presented geometrical pattern such as a line or a rectangle. This pattern will appear to grow out of the spot. In the present paper we report that when two different locations of the visual field are activated simultaneously by presenting two spots prior to a bar between these spots, there is a motion sensation of two bars growing away from the spots and colliding in the centre (split priming effect). Attribute characteristics can have profound effects on this illusion. When two differently coloured isoluminant spots are presented and the subsequent bar is composed of either one of these colours, the induced motion is away from the spot of identical colour. We call this effect attribute priming. Manipulating the delay between the spot presentations (SOA) showed that timing had a strong effect on split priming, but very little on attribute priming. For split priming experiments with dichoptic presentations, we show that at shorter SOAs there is a dominant effect of the primer which is presented to the same eye as the bar, as opposed to the usual dominance of the later primer. For longer SOAs, however, the temporal sequence of the primers also plays a role in motion induction. Further, we report that geometrical arrangements can strongly influence the direction of perceived motion when more than a single primer is used. Generally, in motion induction with two primers, unlike what is found with a single primer, there appears to be a dominance of low-level effects such as geometry, attributes, and eye of presentation. For dichoptic presentations, however, this can be overcome for longer SOAs. The differences between the single and split priming paradigms are discussed in terms of the differential contribution of bottom-up and top-down processes.