Numbers in Action

Abstract

Humans show a remarkable tendency to describe and think of numbers as being placed on a mental number line (MNL), with smaller numbers located on the left and larger ones on the right. Faster responses to small numbers are indeed performed on the left side of space, while responses to large numbers are facilitated on the right side of space (spatial-numerical association of response codes, SNARC effect). This phenomenon is considered the experimental demonstration of the MNL and has been extensively replicated throughout a variety of paradigms. Nevertheless, the majority of previous literature has mainly investigated this effect by means of response times and accuracy, whereas studies considering more subtle and automatic measures such as kinematic parameters are rare (e.g., in a reaching-to-grasp movement, the grip aperture is enlarged in responding to larger numbers than in responding to small numbers). In this brief review we suggest that numerical magnitude can also affect the what and how of action execution (i.e., temporal and spatial components of movement). This evidence could have large implications in the strongly debated issue concerning the effect of experience and culture on the orientation of MNL.

Act on Numbers: Numerical Magnitude Influences Selection and Kinematics of Finger Movement

“…In fact, a growing number of studies are now using motion capture and detailed kinematic analyses to parameterize behavior and to deeply examine questions relating to cognitive processing in naturalistic protocols (for reviews, see Castiello, 2005 ; Krishnan-Barman et al, 2017 ). From this fascinating perspective, an essential improvement of the actual knowledge would be obtained by combining a “free response” task with a kinematic analysis of movement, which may allow to understand how the responses are executed ( Rugani and Sartori, 2016 ). In fact, given that cognitive representations of perceptual and semantic information cannot be fully understood without considering their impact on actions ( Gallese and Lakoff, 2005 ), the existing knowledge on MNL will be advantaged by studies that analyze the motor action while responding to a number.…”

“…In everyday life, we often perceive and act on spatially organized numbers: rulers, keyboards, and objects ordered by their dimensions by different labels (e.g., small, medium large) or Arabic digits (1, 2, 3, 4) to indicate their sizes, are clear examples of this bias. These frequent experiences could induce us to respond to small numbers with the left hand and to larger number with the right one, as well as to prepare a smaller grasping action in relation to smaller digits ( Rugani and Sartori, 2016 ).…”

Peer Review #1 of "Compatibility between object size and response side in grasping: the left hand prefers smaller objects, the right hand prefers larger objects (v0.1)"

“…However, this concept cannot be readily applied to the (horizontal) spatial domain PeerJ reviewing PDF | (2018:09:31015:1:1:NEW 24 Oct 2018) Manuscript to be reviewed (i.e., left and right). Similarly, in the context of numerical-spatial interactions (e.g., SNARC effect), the origin of the orientation of the mental number line (MNL) remains a debated topic (Rugani and Sartori, 2016).…”

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“…However, this concept cannot be readily applied to the (horizontal) spatial domain (i.e., left and right). Similarly, in the context of numerical-spatial interactions (e.g., SNARC effect), the origin of the orientation of the MNL remains a debated topic (Rugani and Sartori, 2016).…”

“…For example, even 3-day old domestic chicks, after being familiarized with a target number, associated a smaller number with left space and a larger number with right space to obtain a food reward (Rugani et al, 2015). Given that the numerical magnitude influenced the chicks' response selection (i.e., go to the left vs. go to the right), it might constitute a link between (numerical) magnitude processing and action (Rugani and Sartori, 2016). These findings suggest that the MNL, rather than being "culturally learned", originated from pre-linguistic and biologically determined precursors, maybe imposed by hemispheric asymmetries related to visuospatial attention (Rugani et al, 2015).…”