Attention acts as a filter to expedite and accentuate the processing of relevant information. This thesis focused on understanding object-based attention, a form of visual attention in which objects are selectively filtered and prioritised. In Chapter 2, using the 'rectangle paradigm' of Egly, Driver and Rafal (1994), a measure of object-based attention was acquired by comparing the differences in reaction times to targets in cued versus uncued objects. While holding the duration of object exposure constant, when the objects appear before the cue does not affect object-based attention. Hence this result combined with other research would suggest that it is not about when the objects appear but rather how long the objects are present for that determines object-based attention. Chapter 3 used a similar method to Chapter 2 under EEG conditions to dissociate the neural basis of space- and object-based attention. It was found that space-based attention modulated the P2 component in the ERP to the target, the N1 component to the cue and the N1 component to the object. Object-based attention only affected the N1 component to the rectangle onset. Crucially, both space- and object-based attention correlated with altered processing of object information (the object onset). However these correlations with the object can be dissociated by their different directionalities and localisations. Therefore space- and object-based attention appear to represent distinct mechanisms. Chapters 2 and 3 together showed that oscillations in the magnitude of space- and object-based attention occur as the time between the cue and target changes, supporting previous work (Fiebelkorn, Saalmann, a Kastner, 2013). Chapter 4, using a motion induced blindness paradigm (Bonneh, Cooperman, a Sagi, 2001), reports that two connected circles can form an object totally outside of awareness. Whilst, the objects that formed likely produced object-based attention this was nonetheless insufficient to bring a previously unconscious stimulus into awareness. Thus object-based attention is insufficient for awareness. Overall this thesis advances the field of object-based attention and establishes a clear role for object-based attention in the visual system.Attention acts as a filter to expedite and accentuate the processing of relevant information.
|Title||:||The Causes, Distinctiveness and Effects of Object-based Attention|
|Author||:||Cameron T. Ellis|