Effects of the Orientation of Moving Objects on the Perception of Streaming/bouncing Motion Displays

Article excerpt

In this study, we examined the contribution of the orientation of moving objects to perception of a streaming/bouncing motion display. In three experiments, participants reported which of the two types of motion, streaming or bouncing, they perceived. The following independent variables were used: orientation differences between Gabor micropattems (Gabors) and their path of motion (all the experiments) and the presence/absence of a transient tone (Experiment 1), transient visual flash (Experiment 2), or concurrent secondary task (Experiment 3) at the coincidence of Gabors. The results showed that the events at coincidence generally biased responses toward the perception of bouncing. On the other hand, alignment of Gabors with their motion axes significantly reduced the frequency of bounce perception. The results also indicated that an object whose orientation was parallel to its motion path strengthened the spatiotemporal integration of local motion signals along a straight motion path, resulting in the perception of streaming. We suggest that the effect of collinearity between Gabors and their motion path is relatively free from the effect of attention distraction.

A fundamental task of the perceptual system is to spatially and temporally identify external objects. In other words, it is necessary for the perceptual system to discriminate which objects in a present scene correspond to objects in the next scene. So far, research has suggested that dynamic changes in visual objects are detected by several visual mechanisms, such as low-level motion sensors (Adelson & Bergen, 1985; Lu & Sperling, 2001), attentive tracking (Cavanagh, 1992; Pylyshyn & Storm, 1988; Verstraten, Cavanagh, & Labianca, 2000), and spatiotemporal integration of moving objects (Alais & Lorenceau, 2002; Gepshtein & Kubovy, 2000).

The visual ability to identify objects in space and time has been assessed by examining perception, using ambiguous, bistable motion displays, a good example of which is a streaming/bouncing motion display in which two identical objects move toward each other, coincide, and then move away from each other. In this display, either of two types of motion is perceived; streaming, where each object continues to move along its own trajectory, or bouncing, where the two objects change trajectories as though colliding with each other at the point of coincidence (Bertenthal, Banton, & Bradbury, 1993; Goldberg & Pomerantz, 1982; Sumi, 1995). In general, streaming motion is dominantly perceived, perhaps because local motion integration through temporal motion recruitment occurs more easily along the same trajectory than between different trajectories (Anstis & Ramachandran, 1986; Watamaniuk, McKee, & Grzywacz, 1995).

Previous studies have reported that auditory signals can alter visual perception of streaming/bouncing displays. Sekuler, Sekuler, and Lau (1997) found that the perception of bouncing became dominant when a transient sound was presented at the coincidence of moving objects (hereafter, we will simply refer to this as at coincidence). They suggested that auditory signals at coincidence might be utilized to interpret an ambiguous streaming/bouncing display when combined with a visual signal; their results have been replicated and supported in later studies (Bushara et al., 2003; Scheier, Lewkowicz, & Shimojo, 2003; Watanabe & Shimojo, 200Ia, 200Ib). Recently, Shimojo et al. (2001) suggested that multimodal attention might be involved in the perception of streaming/bouncing displays; multimodal transient signals, such as auditory tones and tactile vibrations, at coincidence reliably increased the perception of bouncing. It seems that a deprivation of the attentional resources to be allocated to vision might interfere with the recruitment of local motion signals along a straight motion path.

In line with the findings above, it has been suggested that bouncing is dominantly perceived when observers track moving objects with insufficient visual attentional resources. …