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

Abstract

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.

Processing Speed in the Motion-Induction Effect

“…It has also been suggested that attention could be the general underlying factor, which causes the increase in processing speed (Hikosaka et a1 1993a). In the case of double motion induction (split priming), a split of attention must be assumed or a shift of attention from the first to the second stimulus (Faubert and von Grunau 1995). With the present experiments, however, we cannot discriminate between these possibilities, nor can we resolve the questions of where the effect is produced (early vs late) or whether it is mainly bottom -up or top -down.…”

“…This might indicate the percept of collision near the middle of the bar (perhaps somewhat closer to the first spot), since observers were forced to choose only one direction on every trial. It could also indicate that no motion was perceived within the bar, but previous research has shown unequivocally that a (more o r less) central collision is perceived in this case (von Grunau et a1 1994b;Faubert and von Grunau 1995). As stimulus delay increased, the proportion of responses for motion away from the second spot increased and then remained steady.…”

“…On the other hand, the classic motion-induction effect is believed to depend on high-level, perhaps attentional, processes (Hikosaka et a1 1993a;von Grunau and Faubert 1994;Faubert and von Grunau 1995).…”

“…(') That is, motion induction could be made stronger or weaker, according to whether gradient motion would occur in the same or opposite direction. In the present experiments, we investigated the existence of the gradient motion effect and its influence on motion induction in the two paradigms of simplemotion (one inducing spot) and double-motion (two inducing spots) induction (split priming; Faubert and von Grunau 1995). The main goal in this study was the following: given the inconclusive evidence for processing-speed differences in motion induction, (I) Strictly speaking, an interaction between the two effects may also occur if they share only a later stage of processing.…”

The complementary brain: unifying brain dynamics and modularity

“…Independent modules should be able to fully compute their particular processes on their own. Much perceptual data argue against the existence of independent modules, however, because strong interactions are known to occur between perceptual qualities [2][3][4][5][6] . For example, changes in perceived form or color can cause changes in perceived motion, and conversely; and changes in perceived brightness can cause changes in perceived depth, and conversely.…”