Conjunctive Coding of Complex Object Features

Critical to perceiving an object is the ability to bind its constituent features into a cohesive representation, yet the manner by which the visual system integrates object features to yield a unified percept remains unknown. Another important aspect of object perception is the ability to represent complex objects across different viewing angles, despite the drastic variability in appearance caused by shifting viewpoints. This dissertation describes a novel application of multivoxel pattern analysis (MVPA) of neuroimaging data that allows a direct investigation of whether neural representations integrate object features into a whole that is different from the sum of its parts and whether these representations are view invariant. Results showed that patterns of activity throughout the ventral visual stream (VVS), extending anteriorly into the perirhinal cortex (PRC), discriminated between the same sets of features when combined into different objects. Despite this sensitivity to the unique conjunctions of features, this activity was invariant to the viewpoints from which the conjunctions were presented. These results suggest that the manner in which our visual system processes complex objects depends on the explicit coding of the feature conjunctions comprising them, and that these representations are invariant to large changes in visual appearance caused by shifting viewpoints. To test whether experience with the objects changed the pattern of conjunctive representations across the VVS, participants were scanned in a separate fMRI study following an extensive behavioural training period. Results showed that both view-dependent and view-invariant conjunctive representations shifted to more posterior regions of the VVS, suggesting that training affected how unique feature conjunctions are represented across the VVS. These results support the representational-hierarchical view of cortical organization and contribute to our understanding of object perception and memory.Ph.D.2018-02-09 00:00:0