Different magnitude representations in left and right hemisphere: evidence from the visual half field technique

The differences between left and right hemispheric magnitude representations were investigated in two lateralised priming experiments using single-digit (Experiment 1) and two-digit numbers (Experiment 2). Based on recent brain-imaging and TMS studies, some authors have argued that the magnitude representation in the left hemisphere (LH) is more precise than the one in the right hemisphere (RH). In two experiments a prime number preceded a target number that had to be classified as smaller or larger than a fixed standard. In order to reveal hemispheric differences in magnitude representation, the priming distance effect, i.e., faster responses to targets preceded by numerically closer primes, was analysed in both visual half fields (VHF). Using single-digit numbers no hemispheric differences were found for the priming distance effect, supporting an equally precise magnitude representation in both hemispheres. However, the experiment using two-digit numbers revealed a significantly steeper priming curve when targets were presented in the left visual field (LVF) compared to targets presented in the RVF. These results suggest a less precise magnitude representation in the RH, due to a larger overlap of magnitude representations.