The impact of hand dominance on haptic and visual size comparisons.

The present study investigated the impact of handedness on haptic and visual size comparisons. Moreover, we sought to determine whether strength differences between the hands are correlated with lateral differences between judged sizes. Therefore, 80 left-handed and 80 right-handed young adults (without additional constraints on individual characteristics except for those required by the experimental tasks) completed a bimanual haptic size-comparison task, a visual size-comparison task, and strength measurements of fingers, hands, and arms. In the haptic size-comparison task, we observed an impact of handedness: Both left- and right-handers underestimated the size of an object in their dominant hand relative to an object in their non-dominant hand. This hand-related bias was confined to the haptic modality; in the visual size-comparison task, we observed a small overestimation of stimulus size in the right visual hemifield, as compared to the left visual hemifield, in right-handers, but not in left-handers. The strength measurements revealed the expected superiority of the dominant effector over the non-dominant effector, but the strength asymmetries were not correlated with the bias in haptic size-comparisons. The observed impact of handedness on haptic size judgments represents a case of embodied perception in the haptic modality.