Puntiroli, Michael

2016, Puntiroli, Michael

Our visual system is fovea-heavy, which means that in-depth processing occurs only in the centre of the retina, forcing the eyes to make constant movements in order to bring visual elements into focus. Despite this, eye movements go largely unnoticed and the environment is perceived as visually stable. Pre-saccadic shifts of attention might be guaranteeing this stability by easing the transition from one foveated image to another. Before an eye movement attention shifts to the location where the eyes will land and visual elements presented there are preferentially processed. A similar mechanism, also based on the allocation of attention in eye-centred coordinates, is known as remapping. It allows attention to be maintained on locations of interest across eye movements, while accounting for the retinal displacement caused by each upcoming movement. In the current thesis, we are concerned with how the visual elements present in the environment shape the allocation of attention before eye movements. We first aimed to determine whether pre-saccadic shifts of attention are a precondition of all saccades, irrespective of goals. We showed that whether the saccade was goal-directed, to the intended target, or involuntary, erroneously directed to a capturing distractor, made little difference to the pre-saccadic shift of attention. Retinal displacement cause by involuntary saccades was also accounted for by the visual system. Next the project focused on how the presented visual elements affect the programming of eye movements, by investigating how the decision to make an eye movement is affected by the number of target alternatives. We saw evidence that a larger set-size can reduce saccadic reaction times without increasing the error rate, a finding not predicted by a popular model. Further, whether the presence of visual elements in and around the saccade landing point influences the shifts of attention was investigated. We demonstrate that objects and their arrangement shape the distribution of attention, and that the effect is not driven by saccade metrics alone. Finally, we look at the spatial and temporal distribution of visual attention when a saccade target is removed shortly before the eye movement.