How numerical magnitude affects kinematics of reach to grasp actions
The SNARC (spatial-numerical association of response codes) effect is a well-studied phenomenon showing a spatial organisation of the magnitude of numbers. Smaller numbers (0-4) are associated with the left side of an individuals perceived surroundings, while larger numbers (6-9) are associated with the right side of an individuals perceived surroundings. The goal of our study was to determine if a larger numerical value on an object will increase the maximum distance between the thumb and index finger when reaching for the object also known as the maximum grip aperture. Further, it was of interest if the effect would be seen when using a cluster of small shapes as an indicator of numeracy as opposed to an Arabic numeral.
Two sets of blocks were used: one with Arabic numerical values (1, 2, 8, 9) written on them and the other with heart-shaped stickers on them. For each set of blocks the values 1 and 9 were on the faces of the smaller block, while the values 2 and 8 were on faces of the larger block which served as a foil. A control block the same size as the smaller blocks with nothing on its face was also used. University students were recruited for the study, each participant was only tested using one set of blocks. Participants were tasked with grasping blocks after an audio cue. While reaching for the block, participants were instructed to say the number of hearts or Arabic numeral on the block. This was done for both the left and right hand of each participant. During each grasp of the block maximum grip aperture was recorded. Research is still undergoing with results to be finalized in the coming weeks.
Based on prior experiments we hypothesize that maximum grip aperture should be altered depending on the size of the numerical value on the object. A tendency to have a larger maximum grip aperture when reaching for the larger number should occur, even though the objects are the same size. Using a cluster of shapes as an indicator of numeracy should also result in a similar difference to the one seen with numerical values. Since numerical processing occurs in the right hemisphere of the brain, the effect should be more pronounced in the left hand than the right.