Russell, Charlotte Lisa; (2002) Implicit and explicit measures of visual processing within 'Inattentional Blindness' and 'Change Blindness' paradigms. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis examines two distinct yet interrelated topics. One concerns the role of attention within 'Change Blindness' (CB) phenomena (e.g. Rensink, O'Regan & Clark, 1997). The second contrasts direct and indirect measures, to examine whether aspects of unattended visual stimuli, within CB and Inattentional Blindness' (IB) paradigms, that are seemingly inaccessible to awareness may nevertheless be implicitly extracted. A series of new experiments were conducted on the role of attention in CB. Pre-cueing subjects' attention to the locus of a change greatly reduced change blindness. Moreover, presenting a post-cue could also improve change detection. This evidence supports a role for attention in CB, but further suggests that more detailed visual information can be retained across brief interruptions than previously proposed. Further experiments with a modified CB paradigm examined whether there is a spontaneous attentional bias to attend to foreground rather than background items. These studies consistently found that changes were explicitly reported for foreground but not background items, consistent with default allocation of attention to the foreground. Regarding the second main topic of the thesis, a series of experiments demonstrated that Gestalt grouping may be implicitly extracted under conditions of 'inattention', despite the fact that such grouping may be unavailable for explicit report, as measured by standard IB indices. Such grouping may also be implicitly extracted even across saccadic eye movements. Further experiments showed that undetected background luminance-changes, or background motion, can also be implicitly extracted, and can influence explicit reports of foreground stimuli by inducing illusions for them. Although both IB and CB have been taken to suggest that little visual processing takes place outside the focus of attention, the present experiments suggest that considerable processing does take place, albeit implicitly.

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