Left and Right Hand Congruency effects on Mental Rotation of Hands
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Previous research suggests that mental rotation of hands involves both visual and motor processes; when we mentally rotate visually presented stimuli of hands, we imagine moving our own corresponding hands to match the presented stimuli. The present study investigated hand congruency in terms of the left or right hand matching the stimulus by view (back or palm). We tested 48 right-handed subjects between the ages of 18 and 30. The stimuli consisted of visually presented photographs of left and right hands in either palm or back view and in six orientations with respect to the upright orientation (0° with fingers pointing upwards). For each trial, subjects made a laterality judgment for presented stimuli, as to whether the stimulus was a left or right hand, by verbal response. The main finding of the study is that right hand congruency affects reaction times (RTs) for right and left hands but that left congruency only affects RTs for left hand stimuli. Our results are discussed in terms of both a parallel processing model and a serial processing model as strategies used to judge the laterality of hand stimuli. Our findings indicate that subjects used a serial processing strategy to mentally rotate stimuli; whereby the dominant (right) hand is checked for a match with the stimuli first, and the left hand is checked for a match after the right. Congruency effects are discussed with respect to proprioception (our sense of the body’s orientation in space) and anatomical constraints on motor imagery.