Unimanual SNARC Effect: Hand Matters

Abstract

A structural representation of the hand embedding information about the identity and relative position of fingers is necessary to counting routines. It may also support associations between numbers and allocentric spatial codes that predictably interact with other known numerical spatial representations, such as the mental number line (MNL). In this study, 48 Western participants whose typical counting routine proceeded from thumb-to-little on both hands performed magnitude and parity binary judgments. Response keys were pressed either with the right index and middle fingers or with the left index and middle fingers in separate blocks. 24 participants responded with either hands in prone posture (i.e., palm down) and 24 participants responded with either hands in supine (i.e., palm up) posture. When hands were in prone posture, the counting direction of the left hand conflicted with the direction of the left–right MNL, whereas the counting direction of the right hand was consistent with it. When hands were in supine posture, the opposite was true. If systematic associations existed between relative number magnitude and an allocentric spatial representation of the finger series within each hand, as predicted on the basis of counting habits, interactions would be expected between hand posture and a unimanual version of the spatial–numerical association of response codes (SNARC) effect. Data revealed that with hands in prone posture a unimanual SNARC effect was present for the right hand, and with hands in supine posture a unimanual SNARC effect was present for the left hand. We propose that a posture-invariant body structural representation of the finger series provides a relevant frame of reference, a within-hand directional vector, that is associated to simple number processing. Such frame of reference can significantly interact with stimulus–response correspondence effects, like the SNARC, that have been typically attributed to the mapping of numbers on a left-to-right mental line.

Cross-cultural and intra-cultural differences in finger-counting habits and number magnitude processing: Embodied numerosity in Canadian and Chinese university students

“…A mental simulation account would be consistent with past research by Domahs et al (2012) which indicated that the complexity of finger number gestures may modulate the degree to which counting habits appear to influence cognition. This would also be consistent with a growing literature which suggests that finger-counting direction, as well as hand orientation may impact performance when matching number parity or magnitude with left/right space (Conson, Mazzarella, & Trojano, 2009;Iversen et al, 2006;Michaux, Masson, Pesenti, & Andres, 2013;Riello & Rusconi, 2011).…”

“…Additionally, given the low baseline error-rate in this task, and over-representation of participants whom made no errors in certain comparisons, there was a significant positive skew in the data. Although other studies using these types of data have used a simple arcsine transformation for error proportions (Domahs et al, 2010;Riello & Rusconi, 2011), these transformations actually increase positive skew in error proportions that are close to floor, rendering subsequent analyses excessively liberal. Therefore, all mean error-rate data was normalized using an arcsine square root transformation y = asin(sqrt(x)) prior to data analysis, which better reduced skew and rendered subsequent analyses more conservative.…”

Rear negativity: Verbal messages coming from behind are perceived as more negative

“…There is much evidence that spatial location influences descriptive associations. For example, small numbers are associated with the left position and large numbers with the right position—an effect known as spatial‐numerical association of response codes, SNARC (Dehaene, Bossini, & Giraux, ; Riello & Rusconi, ). In the domain of abstract concepts, a well‐known example is the association of the future and the past with forward or backward motion (Boroditsky, ).…”

The Organization of Spatial Reference Frames Involved in the Snarc Effect

“…Moreover, a recent study showed that a fingerbased reference frame could interact with the SNARC effect. In a parity task where subjects were asked to respond with the index and middle fingers of either their right or their left hand, Riello and Rusconi (2011) observed that unimanual SNARC effects were modulated by participants' hands position. When participants' hands were placed palm down, a unimanual SNARC effect was observed with the right hand, whereas a unimanual SNARC effect with the left hand was observed when the hands were palm up.…”