Background: Understanding the neurophysiological mechanisms of Amblyopia, a neurodevelopmental disorder of the visual cortex, will bring us closer to full recovery. Past findings have been contradictory. Results have shown that despite having severe acuity impairment, amblyopes can nonetheless perceive sharp edges. In this study, we explore the representation of blur through a series of image blur-discrimination and matching tasks, to understand more about the amblyopes’ visual system.
Methods: Monocular image blur-discrimination thresholds were measured in a spatial two-alternative forced-choice procedure whereby subjects had to decide which image was the blurriest. Subjects also had to interocularly match pictures that were identical to those used for the image blur discrimination task. Ten amblyopes, as well as a group of ten controls were under study.
Results: Data on amblyopes and controls will be presented for both experiments. According to previous research that was done on blur-edge discrimination and matching, we predict that subjects’ performance will follow a dipper function, that is, all observers will be better at discriminating between both images when a small amount of blur is applied rather than when the image is either sharp or very blurry. We also predict that amblyopes’ blur discrimination will be noisier, but that they will paradoxically be able to match the sharpness of the images presented in the matching task.
Conclusions: This would confirm our hypothesis about amblyopes’ visual system, that they can represent blur levels defined by spatial frequencies that are beyond their resolution limit, and would also raise interesting questions about the visual system in general regarding the different perceptions driven by images versus edges.
Background: The guiding principle of functional brain mapping is that the cortex exhibits a spatial pattern of response reflecting its underlying functional organization. We know that large-scale patterns are common across individuals—everyone roughly has the same visual areas for example, but we do not know about small patterns, like the distribution of ocular dominance and orientation columns. Studies investigating the temporal aspect of brain-to-brain similarity have shown that a large portion of the brain is temporally synchronized across subjects (Hasson et al., 2004), but spatial pattern similarity has been scarcely studied, let alone at a fine scale. In the current study, we investigated fine-scale spatial pattern similarity between subjects during movie viewing and generated a map of prototypical patterns spanning the visual system. Characteristics of the map, such as spatial pattern size and distribution, reveal properties of the underlying structure and organisation of the visual cortex. These results will guide future brain mapping studies in decoding the informative spatial patterns of the visual cortex and increasing the resolution of current brain maps.
Methods: We had 56 subjects watch two movie clips from “Under the Sea 3D:IMAX” during an fMRI scan. Each clip was 5 minutes in length and was presented in 2D and 3D, in random order. We calculated the intersubject correlation of the spatial pattern inside predefined searchlights of diameter 3, 5, 7, 9 and 11 mm, covering the entire brain. A single threshold permutations test was used to test for significance: we generated 1,000 permutations made from scrambling the spatial patterns inside each searchlight of every subject, pooled these permutations together to generate a large distribution and used the 95th percentile to threshold the actual measurements. We compared these spatial pattern correlations to convexity variance between subjects to determine whether spatial pattern correlation could be explained by differing degrees of alignment across the cortex. We also compared spatial pattern correlation during 2D and 3D movie presentation.
Results: We found significant correlations in spatial pattern between subjects in the majority of early visual cortex, as well as higher visual areas. We found that mean spatial pattern similarity in a visual area tended to decrease as we move up the visual hierarchy. Spatial pattern correlation showed significant positive correlation with convexity variance for most visual areas, meaning that as anatomical misalignment increased, patterns became more similar. Spatial pattern correlation therefore cannot be explained by anatomical misalignment. Lastly, spatial pattern correlations tended to be higher for 3D movie presentation compared to 2D.
Conclusions: Our results suggest that many processes in early visual areas and even higher visual areas process visual information the same way in different individuals. Our results expand past studies by exploring spatial patterns instead of temporal patterns and studying at a fine-scale. This is the first study, to our knowledge, exploring fine-scale spatial patterns across the visual system. Our results show that fine-scale structures underlying activation patterns may be highly similar across subjects, pointing to a more ingrained organisation of the visual system than previously believed. This map we termed the “protoSPACE map”, may one day result in the detection of more subtle abnormalities that arise only during realistic vision in situations such as schizophrenia or mild traumatic brain injury, where traditional anatomical MRI scans report no changes.
