Mechanisms of Approximate Numerosity Processing: Approximate Number Tasks in the Haptic and Visual Modality

Abstract

The perception and processing of number is an essential ability of humans and animals to interact with their environment. The Approximate Number System (ANS) is assumed to be a part of the perception and cognitive processing of distinct numerical magnitude without counting. Non-symbolic perception of numerosity in an imprecise manner allows advantageous real-life decision making. A modern example from everyday life might be that if you want to get to a checkout faster, it makes sense to join a queue with fewer people. This decision, based on the number of people in the line, can be made in a fraction of a second without actually counting the number of people. The Approximate Number System is thought to allow extracting the approximate number of items in scenes, such as the number of people in a queue. One popular assumption about the ANS is that number is an abstract representation and not tied to a sensory modality, since stimulus-related features that go along with discrete entity (like the occupied area) are removed. Although widely accepted, this assumption of an amodal percept lacks on profound empirical evidence. Only very few studies have explored approximate numerosity in other modalities than the visual. Furthermore, different factors regarding the methodology for assessing ANS-acuity and recent findings indicate that other influences (e.g., spatial attributes of visual stimuli) also affect a numerosity percept, questioning the theoretical ANS assumptions. This work contributes in forthcoming and understanding the nature of the ANS by utilizing intra- and cross-modal paradigms adapted to the visual and haptic modality. In Study 1, we used a dot comparison task in both the visual modality and the haptic modality to measure the non- symbolic numerical discrimination ability of 67 participants. We found that a) besides number, participants were also influenced by spatial factors in their performance, and b) even though the performance was ratio-dependent, indicating ANS involvement, the performance between the modalities was not correlated. In Study 2, we investigated in 50 participants whether their discrimination performance was affected by spatial information of numerical stimuli in an approximate number-matching task. We let participants perceive numerosity from haptic source stimuli and then let them match it to one of two visually presented dot patterns. We found that the spatial configurations of the (dot) stimuli in the haptic source modality significantly affected the numerosity matching performance in the visual modality. The findings of both studies are in conflict with the strong assumptions of the so-called “direct” ANS model, which is currently state-of-the-art. Due to our results, there is reason to widen the perspective of how the percept of numerosity arises and to consider competing ANS perspectives or alternative approaches for empirical testing. Furthermore, we emphasize that the measurement of ANS-acuity requires better standardization and sensitivity for specific implementations in the future.