The role of spatial information in an approximate cross-modal number matching task

Abstract

The approximate number system (ANS) is thought to be an innate cognitive system that allows humans to perceive numbers (>4) in a fuzzy manner. One assumption of the ANS is that numerosity is represented amodally due to a mechanism, which filters out nonnumerical information from stimulus material. However, some studies show that nonnumerical information (e.g., spatial parameters) influence the numerosity percept as well. Here, we investigated whether there is a cross-modal transfer of spatial information between the haptic and visual modality in an approximate cross-modal number matching task. We presented different arrays of dowels (haptic stimuli) to 50 undergraduates and asked them to compare haptically perceived numerosity to two visually presented dot arrays. Participants chose which visually presented array matched the numerosity of the haptic stimulus. The distractor varied in number and displayed a random pattern, whereas the matching (target) dot array was either spatially identical or spatially randomized (to the haptic stimulus). We hypothesized that if a "numerosity" percept is based solely on number, neither spatially identical nor spatial congruence between the haptic and the visual target arrays would affect the accuracy in the task. However, results show significant processing advantages for targets with spatially identical patterns and, furthermore, that spatial congruency between haptic source and visual target facilitates performance. Our results show that spatial information was extracted from the haptic stimuli and influenced participants' responses, which challenges the assumption that numerosity is represented in a truly abstract manner by filtering out any other stimulus features.

Keywords: Haptics; Multisensory processing; Visual perception.

Fig. 1

Illustration of the experimental setup. Note. Left image shows a top-down view of the setup. Right image shows a cross-section view of the setup and how the participants engaged in the task. a Participant’s screen for visual stimuli; b curtain that prevents the participant from visually inspecting the haptic stimulus; c haptic stimulus

Fig. 2

Examples of haptic and visual stimuli used in the experiment. Note. (a) Haptic stimulus. (b) Visual stimulus. Haptic pattern matches the visual stimulus on the right side, which displays the identical pattern of dots (SI condition). (Color figure online)

Fig. 3

Illustration of the procedure in the cross-modal matching task

Fig. 4

Mean percentage correct per ratio and pattern in the complete sample. Note. “SI” refers to the spatially identical pattern condition when the haptic dowel array and the correct visual dot array match in numerosity and also in spatial arrangement. “SR” refers to the spatially randomized pattern condition, when the haptic dowel array and the correct visual dot array solely match in numerosity but not in spatial arrangement. N = 50