Spatial and chromatic properties of numerosity estimation in isolation and context

Abstract

Numerosity estimation around the subitizing range is facilitated by a shape-template matching process and shape-coding mechanisms are selective to visual features such as colour and luminance contrast polarity. Objects in natural scenes are often embedded within other objects or textured surfaces. Numerosity estimation is improved when objects are grouped into small clusters of the same colour, a phenomenon termed groupitizing, which is thought to leverage on the subitizing system. Here we investigate whether numerosity mechanisms around the subitizing range are selective to colour, luminance contrast polarity and orientation, and how spatial organisation of context and target elements modulates target numerosity estimation. Stimuli consisted of a small number (3-to-6) of target elements presented either in isolation or embedded within context elements. To examine selectivity to colour, luminance polarity and orientation, we compared target-only conditions in which all elements were either the same or different along one of these feature dimensions. We found comparable performance in the same and different feature conditions, revealing that subitizing mechanism do not depend on ‘on-off’ luminance-polarity, colour or orientation channel interactions. We also measured the effect of varying spatial organisation of (i) context, by arranging the elements either in a grid, mirror-symmetric, translation-symmetric or random; (ii) target, by placing the elements either mirror-symmetric, on the vertices of simple shapes or random. Our results indicate higher accuracy and lower RTs in the grid compared to all other context types, with mirror symmetric, translation and random arrangements having comparable effects on target numerosity. We also found improved performance with shape-target followed by symmetric and random target arrangements in the absence and presence of context. These findings indicate that numerosity mechanisms around the subitizing range are not selective to colour, luminance polarity and orientation, and that symmetric, translation and random contexts organisations inhibit target-numerosity encoding stronger than regular/grid context.

One step beyond! The conjunction-bias between non-spatial (Color) and spatial Grouping cues over approximate number perception extends to Symmetry and Connectedness.

“…Besides the ANS, it would be interesting to investigate how grouping cues such as symmetry/shape, and the effect of grouping conjunctions, impact the Groupitizing strategies, in order to increment the accuracy during Groupitizing process. For example, it is not unlikely that subsets formed by geometric/symmetrical spatial disposition (e.g., a square) of items would increase the ability to individuate and count this subset, increasing the overall accuracy in counting tasks (e.g., Gheorghiu & Goldschmitt, 2022;Hsin, Lo, & Tseng, 2021). Moreover, if the dots forming the geometrical shape are also similar in color, this conjunction of geometrical and color cues would speed up further the process (e.g., as a linear sum of the single conditions).…”