A functional MRI investigation into the neural correlates of the multiple-object tracking deficit in amblyopia.

Amblyopia is a visual developmental disorder defined by reduced visual acuity in one (amblyopic) eye, while the other (fellow) eye has normal visual acuity and is otherwise healthy. Deficits in motion perception – such as multiple object tracking - affect both the amblyopic eye and the fellow eye. This thesis examined the neural correlates of the multiple-object tracking deficit to further understand the cortical deficit in amblyopia. Functional data were collected as participants with and without a history of amblyopia performed the multiple-object tracking task monocularly inside a 3T MRI scanner. Participants were asked to use their attention to track 0, 1, 2 or 4 of 9 moving balls (6 deg/s) for 12 seconds. MR signal change relative to fixation, as a function of target numerosity (track 0, track 1, track 2, track 4), group (control, amblyopia), and eye were examined in six regions of interest: putative V1, MT, superior parietal lobule, frontal eye fields, anterior intraparietal sulcus, and posterior intraparietal sulcus. For all four tracking conditions, area MT was found to be less active in participants with amblyopia with both fellow and amblyopic eye viewing. When tracking 4 balls, the anterior intraparietal sulcus was found to be less active in participants with amblyopia, only with amblyopic eye viewing. This finding suggests the functional differences in this region may be subtle. Future investigations targeting the network involved in sustained attention can determine the extent to which posterior parietal function may be impaired in amblyopia. Overall, this thesis provided neuroimaging evidence that the MT region is affected in human amblyopia, and that both eyes are affected by underlying cortical changes in dorsal extra-striate areas.Medicine, Faculty ofGraduat