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Richard Vernon, Andre Gouws, Samuel Lawrence, Bruce Keefe, Declan McKeefry, Alex Wade, Antony Morland; Exploring the role of curvature for neural shape representations across hV4 and Lateral Occipital visual field maps. Journal of Vision 2017;17(10):292. doi: 10.1167/17.10.292.
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© ARVO (1962-2015); The Authors (2016-present)
Whilst Macaque V4's role for curvature and shape processing is well documented, the relationship between human Lateral Occipital LO-1/2 and more ventral hV4 retinotopic maps is less clear. The former regions overlap shape-selective Lateral Occipital Complex (LOC), and we previously demonstrated that LO-2 and LOC share similar (potentially curvature-based) neural shape representations. Therefore, we asked more directly whether curvature is explicitly represented in these LO maps, or if instead it is processed by hV4 in line with Macaque literature. We used radial frequency (RF) patterns to test whether degree of curvature (manipulated via amplitude), or simply the number of curves (manipulated via frequency; range 3-5), would most influence neural shape representations. This was tested in a rapid event-related fMRI experiment, using representational similarity analysis to assess patterns of activity across retinotopically- and functionally-defined regions of interest (ROIs). Neural similarity was compared to shape similarity metrics based upon amplitude, frequency, and additional predictors derived from Principal Component Analysis (PCA) on more exploratory stimulus similarity metrics. Those PCA components were 'Lobe-prominence' (degree of curve protrusion) and 'Lobe-curvature' (curvature breadth/acuteness). After controlling for low-level influences, we found three divergent influences in later visual cortex. First, frequency was only influential for LO-1, implying LO-1 is at least partially distinct from other ROIs. Amplitude was well-represented across all Lateral Occipital ROIs (LO-1/2, LO), however this is complicated by our two components. We found that 'Lobe-curvature' was somewhat influential not only for Lateral Occipital ROIs, but also for hV4. Conversely, 'Lobe-prominence' only explained variance in Lateral Occipital regions. This implies that whilst hV4 likely does process shape curvature to some extent, its representation is nevertheless distinct from that of our Lateral Occipital ROIs. On the basis of these results, we suggest the Lateral Occipital shape representation may in part be based upon shape protrusions.
Meeting abstract presented at VSS 2017
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