Poster Session B, Sunday, March 24, 8:00 – 10:00 am, Pacific Concourse
How to separate extraction of numerical and non-numerical magnitude information in the visual stream with a frequency-tagging approach?
Amandine Van Rinsveld1, Mathieu Guillaume1, Christine Schiltz2, Wim Gevers1, Alain Content1; 1Université Libre de Bruxelles, 2University of Luxembourg
The ability to handle approximate large quantities has been identified as a building block of mathematical skills but the mechanism allowing to extract numerical magnitudes (i.e., numerosity) from visual environments is still debated. Many authors agree that humans have an Approximate Number System that specifically processes numerosity. However, a set of objects is not only characterized by its numerosity but also by non-numerical visual information related to its continuous dimensions (e.g., total area, dot size). Accordingly, the alternative theory argues that the numerosity is extracted through a weighting of continuous dimensions. Until now the opposite view could not be tested properly due to the intrinsic correlations between numerosity and continuous dimensions. We aimed at isolating the specific cerebral responses to numerosity and to continuous dimensions by using Steady-State Visual Evoked Potentials (SSVEP). Participants (N=21) were presented dot collections that varied randomly along all dimensions but one, which entailed a systematic change at the rate of 1.25 Hz. This periodic dimension was either the numerosity or one of the continuous dimensions (size, area, convex hull or density). Electrophysiological recording showed a neural synchronization on the numerosity but also on the total area of the collections. In contrast, no synchronization was observed for the other continuous dimensions. In conclusion, we provide evidence that not only numerosity but also some continuous properties can be extracted rapidly along the visual stream. Our study bypasses the recurrent problem of intrinsic correlations between numerosity and continuous dimensions, providing novel insights to existing theories of numerosity extraction.
Topic Area: PERCEPTION & ACTION: Vision