A cross-sectional developmental examination of the SNARC effect in a visually-guided grasping task

The present study documents the influence of numerical processing on hand and space use during a reach-to-grasp task. Three questions regarding the SNARC (spatial-numerical association of response codes) effect were asked: (1) would the SNARC effect influence hand and/or space preference for grasping?; (2) would the SNARC effect be demonstrated during the processing of one-digit numbers, two-digit numbers, or both?; and (3) would developmental age influence the strength of the SNARC effect? A total of 84 participants in three age/school level groups (Primary, Secondary, and Post-secondary) took part in the study. Two identical sets of small wooden blocks numbered from 0 to 19 were used. Each set was presented to the right and to the left of each participant. A number was called and participants were asked to find and grasp a block with the corresponding number as fast and accurately as possible. Hand and space used (L/R) was recorded for each grasp. Number magnitude was shown to influence the selection of hand and hemi-space in accordance with the SNARC effect. In the small percentage of trials where the left hand was used, it was more commonly recruited to grasp blocks displaying low numbers than high numbers. Participants grasped blocks from left and right space with equal frequency, but respectively left/right space was accessed more often for blocks displaying low/high numbers. Regression analyses revealed that developmental age is a powerful predictor of the SNARC effect on hand and space selection for grasping. This study provides the first description of the SNARC effect on hand and space preference for the reach-to-grasp action. Results are discussed with relevant literature of numerical processing in the human brain.