The role of foveal and extrafoveal vision in the processing of scene semantics
This thesis investigated the ability to process semantic information from foveal and extrafoveal vision during scene viewing. Existing research suggested that object semantics could be detected from extrafoveal vision. This suggestion was investigated using three experimental paradigms. Semantic inconsistency was defined as a target semantically incompatible with scene gist. In Experiments 1 to 4, fixation position during a brief scene presentation was manipulated relative to a target object. The target's semantic inconsistency, presented foveally or extrafoveally, influenced performance on an object identification task. Extrafoveally presented semantically inconsistent targets were facilitated when simple line drawings were displayed, although this effect was unlikely to be mediated by semantic processing. No similar effect was found with complex line drawings or photographic stimuli. Experiments 5 and 6 attempted to replicate significant advantages for inconsistent targets in a change detection paradigm. However, no significant difference was found between performance for consistent and inconsistent targets in a two-exposure, forced-choice change detection task or an alternating display change detection task. There was no evidence that changing inconsistent targets were detected more reliably or earlier than changing consistent targets. Experiment 7 investigated the proposal that the extrafoveal processing of inconsistent objects could influence saccade patterns by attracting earlier fixations. Participants freely scanned both line drawings and photographs of scenes with no task. Again, no evidence was found supporting the earlier fixation of inconsistent objects in scenes. Therefore, this thesis could not confirm previous evidence of an inconsistent object advantage in either brief scene presentations, change detection or natural scene viewing. The evidence suggested that the preferential processing of inconsistent scene objects could occur under very limited circumstances, but would be unlikely to be mediated by semantic processing. When viewing complex, realistic scenes, there was no evidence of differential processing for consistent and inconsistent objects.