The global processing deficit in amblyopia involves noise segregation

Some studies have reported deficits in amblyopia for global form and motion integration, whereas other studies have shown global integration of form and motion information to be normal in amblyopia. Here, we attempt to resolve this discrepancy by showing that amblyopes only exhibit selective performance deficits on global tasks that contain noise as well as signal. We hypothesized that signal integration is normal, but noise segregation is not. We used comparable global orientation and motion direction discrimination tasks to measure integration performance in the presence of controlled amounts of pedestal noise (i.e., elements whose orientations or directions were randomly selected). We modelled the performance using an equivalent noise model, which has the parameters of internal noise and number of samples. Our results show that amblyopic eyes can integrate form (i.e., orientation) and motion information (i.e., motion direction) similarly to normals when all the information is signal (i.e., no pedestal noise). However, introducing pedestal noise perturbs the performance of the amblyopic eyes significantly more than that of the normal eyes.