Dissociation between the focal and orientation component of spatial attention in detection, discrimination and reading tasks

In our daily life, attention plays a fundamental role in governing our visual experience. Indeed, every visual experience consists in an overwhelming amount of visual information reaching our visual system. Selective attention allows us to select the relevant information, which is important for our goals, while ignoring the irrelevant information in our environment. However, selective attention is not a unitary notion, but a multi-faceted concept constituted by different components. Several models on how the attentional resources can be allocated in the space identify two distinct components: an orientation component, which moves the attentional resources to relevant locations for further processing, and a focal component, which allows us to converge our resource on a limited amount of space. The present dissertation inquires the classical view of these two components of selective attention, providing a characterization of both and their mutual relationship. Using a combination of behavioural and neuropsychological evidence, I investigated how these two components operate in different viewing conditions, with different temporal trends and different task demands. Finally, I examined how a deficit in the ability to adjust the attentional focus can condition the reading process in brain-damaged patients. By measuring the cue-size effect in healthy participants, the first set of studies characterizes how the focal component is deployed in the centre of the visual field. These studies show that, even if detectable in both exogenous and endogenous conditions, the facilitatory effect of the focal component is best revealed and more effective in exogenous conditions. Moreover, I elucidated the role played by the task demands and the stimuli used in evoking this facilitatory effect. The second set of studies, always on healthy participants, further extends these findings by showing that the focal and the orientation component are two independent components, which displayed their effects in different viewing conditions and with different temporal trends. The dissociation of these two components is evident not only in simple tasks, as single letter detection or discrimination, but also in a more reading-related task, consisting in discriminating a letter among others. At complement with evidence in healthy participants, the third set of studies investigates how a deficit in the control of the focal component could be responsible for the substitution errors that brain-damage patients affected by Neglect Dyslexia (ND) make in reading texts and single words. The substitution errors would depend on the difficulty to perceptually segregate the letters between each other, and a deficit in the control of the focal component would play a main role in increasing this phenomenon, by preventing the adjustment of the integration field necessary to identify and read the letter correctly. Overall, this set of experiments illustrates a dissociation between the focal and the orientation component of selective attention and suggests the existence of a causal link between the former one and the substitution errors in reading.