A unifying model for discordant and concordant results in human neuroimaging studies of facial viewpoint selectivity
Authors: Revsine Cambria , Gonzalez-Castillo Javier , Merriam Elisha P , Bandettini Peter A , Ramírez Fernando M 
Published: March 2024

Recognizing faces regardless of their viewpoint is critical for social interactions. Traditional theories hold that view-selective early visual representations gradually become tolerant to viewpoint changes along the ventral visual hierarchy. Newer theories, based on single-neuron monkey electrophysiological recordings, suggest a three-stage architecture including an intermediate face-selective patch abruptly achieving invariance to mirror-symmetric face views. Human studies combining neuroimaging and multivariate pattern analysis (MVPA) have provided convergent evidence of view-selectivity in early visual areas. However, contradictory conclusions have been reached concerning the existence in humans of a mirror-symmetric representation like that observed in macaques. We believe these contradictions arise from low-level stimulus confounds and data analysis choices. To probe for low-level confounds, we analyzed images from two face databases. Analyses of image luminance and contrast revealed biases across face views described by even polynomials—i.e., mirror-symmetric. To explain major trends across neuroimaging studies, we constructed a network model incorporating three constraints: cortical magnification, convergent feedforward projections, and interhemispheric connections. Given the identified low-level biases, we show that a gradual increase of interhemispheric connections across network-layers is sufficient to replicate view-tuning in early processing stages and mirror-symmetry in later stages. Data analysis decisions—pattern dissimilarity measure and data recentering—accounted for the inconsistent observation of mirror-symmetry across prior studies. Pattern analyses of human fMRI data (of either sex) revealed biases compatible with our model. The model provides a unifying explanation of MVPA studies of viewpoint selectivity, and suggests observations of mirror-symmetry in humans originate from ineffectively normalized signal imbalances across different face-views.Significance StatementThe recognition of identity regardless of viewpoint is critical for social interactions. In primates, the representation of mirror-symmetric face-views is thought to be a key intermediate processing step leading from strictly view-tuned to viewpoint-invariant representations. Human neuroimaging studies, however, have reached contradictory conclusions regarding the representation of viewpoint information in face-selective areas, despite being concordant in early visual areas. We show that low-level stimulus confounds and data-analysis choices explain these contradictory observations. We propose a network model that replicates observations of view-tuning in early processing stages regardless of analysis choices. The variable observation of mirror-symmetry in later stages is explained by choice of pattern dissimilarity measure and data recentering. Analyses of fMRI data confirmed biases broadly compatible with our model.