MENTAL ROTATION TEST PERFORMANCES AND FAMILIAL SINISTRALITY IN DEXTRALS, WITH SPECIAL REFERENCE TO THE BENT TWIG THEORY

Recently, in this journal, Casey (1995) and McKeever (1996) noted that they have reached opposite conclusions regarding the effect of famili al sinistrality on mental rotation ability in dextral females. Casey a nd colleagues concluded that those dextral women with a family history of left handedness (the FS+) are comparable to men in mental rotation ability and that the overall male superiority on such tasks is a func tion of the poor performances of dextral women who lack left handednes s (the FS-) in their families. McKeever and colleagues had come to the exact opposite conclusion. We restudied this question and eliminated three possible methodological factors that might conceivably have acco unted for the different outcomes. The results of the present study fai led to find any relationship of FS status to mental rotation ability. These findings raise serious questions as to the replicability of any FS status/mental rotation ability relationships.