Adaptation and multivoxel codes in high-level visual cortex

University Of Pennsylvania, Philadelphia PA

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Abstract

DESCRIPTION (provided by applicant): A core concern of cognitive neuroscience is understanding the representational distinctions made by different brain regions. Two techniques are commonly used in functional magnetic resonance imaging (fMRI) studies to investigate this issue: multivoxel pattern analysis (MVPA) and fMRI adaptation (fMRIa). Whereas MVPA examines the voxelwise response patterns elicited by different stimuli to determine which items elicit patterns that are distinguishable, fMRIa examines the effect of repeating items over time under the hypothesis that repetition of representationally-similar items will elicit a reduced response. Although MVPA and fMRIa have become part of the central toolkit of cognitive neuroscience, little is known for certain about the neuronal mechanisms that underlie these two techniques. Consequently, it has been difficult to relate results obtained through MVPA to results obtained through fMRIa. Indeed, previous work from our lab has shown that apparently inconsistent results can be obtained from fMRIa and MVPA, even when these techniques are applied to the same dataset. The main goal of the current project is to test several hypotheses about the different neuronal mechanisms that might underlie MVPA and fMRIa. Specifically, we will test whether fMRIa indexes neuronal or subneuronal tuning (Exp. 1), stimulus similarity or perceptual expectations (Exp. 2), and we will test the spatial scale of functional organization indexed by MVPA (Exp. 3). The focus of this preliminary project will be on fMRI signals in the parahippocampal place area (PPA) during viewing of real-world visual scenes and in the lateral occipital complex (LOC) during the viewing of objects. Although the current experiments do not directly examine recovery or disease, they will, if successful, provide important analytical tools for such investigations. For example, attempts to use MVPA and fMRIa to understand plasticity and cortical reorganization in amblyopia, or after recovery of sight in the blind, can only bear fruit if the interpretation of the findings in terms of underlying neural mechanisms is fully understood.