A generalized sense of number for perception and action

Abstract

Much evidence suggests that humans and many animals possess an abstract sense of approximate quantity: a sense of number. Recently Arrighi et al. (2014) provided behavioral evidence for a generalized number sense by showing that numerosity adaptation occurs cross-modally (from vision to audition and viceversa) and across stimuli presentation format (sequential and simultaneous). Here we extend these findings to show that producing a sequence of motor actions (finger tapping) without tactile feedback (no finger/surface contact during the motor routine) also causes adaptation of numerosity estimation of visual stimuli. In the "high adaptation" condition, participants were asked to tap as quickly as possible (average 5-6 taps/s) whilst in a "low adaptation" condition they were required to tap more slowly (around 1 tap/s). After the adapting phase the test stimulus – either a sequence of flashes or a cloud of dots (tested on separate sessions) – was randomly displayed either to the same side of the screen where the hand had been tapping or to the symmetrically opposite side and participants had to estimate the numerosity of the test stimulus, which varied randomly from trial to trial within the range 6-14. A short period of rapid finger-tapping (without sensory feedback) caused subjects to underestimate the number of visual stimuli presented near the tapping region, and slow tapping caused overestimation. Adaptation to self-produced actions distorted perceived numerosity by about 20%, both for stimuli presented sequentially (series of flashes) and simultaneously (clouds of dots). Importantly, adaptation was spatially selective in external not body coordinates. Taken together these results support previous studies reporting links between perception and action, showing that vision and action share mechanisms that encode number: a generalized number sense, which estimates the number of self-generated as well as external events.

Meeting abstract presented at VSS 2017