title: Can responses to basic non-numerical visual features explain neural numerosity responses?
abstract: Humans and many animals can distinguish between stimuli that differ in numerosity, the number of objects in a set. Human and macaque parietal lobes contain neurons that respond to changes in stimulus numerosity. However, basic non-numerical visual features can affect neural responses to and perception of numerosity, and visual features often co-vary with numerosity. Therefore, it is debated whether numerosity or co-varying low-level visual features underlie neural and behavioral responses to numerosity. To test the hypothesis that non-numerical visual features underlie neural numerosity responses in a human parietal numerosity map, we analyze responses to a group of numerosity stimulus configurations that have the same numerosity progression but vary considerably in their non-numerical visual features. Using ultra-high-field (7T) fMRI, we measure responses to these stimulus configurations in an area of posterior parietal cortex whose responses are believed to reflect numerosity-selective activity. We describe an fMRI analysis method to distinguish between alternative models of neural response functions, following a population receptive field (pRF) modeling approach. For each stimulus configuration, we first quantify the relationships between numerosity and several non-numerical visual features that have been proposed to underlie performance in numerosity discrimination tasks. We then determine how well responses to these non-numerical visual features predict the observed fMRI responses, and compare this to the predictions of responses to numerosity. We demonstrate that a numerosity response model predicts observed responses more accurately than models of responses to simple non-numerical visual features. As such, neural responses in cognitive processing need not reflect simpler properties of early sensory inputs.
authors.affiliation: Faculty of Psychology and Education Sciences, University of Coimbra, Rua do Colégio Novo, 3001-802 Coimbra, Portugal; Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 1, Utrecht 3584 CS, Netherlands.
authors.forename: Ben M
authors.initials: BM
authors.lastname: Harvey
authors.affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 1, Utrecht 3584 CS, Netherlands; Spinoza Centre for Neuroimaging, Amsterdam, Netherlands.
authors.forename: Serge O
authors.initials: SO
authors.lastname: Dumoulin
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D003071:Cognition / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D055641:Mathematical Concepts; D010296:Parietal Lobe / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult