Migration of objects during rapid serial visual search
This thesis is concerned with the various factors determining the apparent migration of targets during rapid serial visual presentation (RSVP). This migration effect occurs when an observer reports a target as being present in a scene other than the one in which it was actually presented, usually the immediately preceding or following scene - the "host" scene. An experimental technique was developed based on Intraub's (1985;1989) work on these migration errors, and an improved computer-based system was developed. This allowed flexibility in the manipulation of experimental variables and also used a recognition memory paradigm to identify targets. Ten experiments were completed in total which examined three major issues concerning RSVP: contextual effects, low-level cues and the effects of apparent contrast. Using the newly developed software, Intraub's original results were replicated and extended. Manipulation of contextual information surrounding a host scene showed that the direction of apparent target migration, to the scene either succeeding or preceding the host scene, could be influenced by using a pre- or post-host bias in the visual context. For example, preceding an outdoor host-scene with another outdoor scene and following it with an indoor scene led to more migration errors to the preceding scene, i.e. there was a tendency for errors to be biased to structurally similar scenes. In another set of experiments, it was found that low-level binding cues could effectively aid the cohesiveness of host and target and thus reduce the number of migration errors. Furthermore, in a third set of experiments evidence that the direction of migration errors could be influenced by the apparent contrast of the search target was found. Higher apparent contrast could produce a predominance of pre-host migration errors. However, caution is called for in the interpretation of this final set of results since they are somewhat ambiguous and need further clarification. Taken as a whole the results found in these experiments have shown that an overall presentation rate of 8.33 Hz, subjects are able to effectively grasp the gist of the background to the target.