Goozen et al. 2002; Gooren & Giltay 2008; but see Sommer et al.
2008; reviewed in Cherrier 2009).
Spatial ability as such, however, is not a direct measure of
lateralization. A few studies have analysed the relation between
circulating levels of testosterone in human adults and handedness,
a more direct measurement of lateralization. Results from these
studies are, however, ambiguous too: Tan (1991) found higher
levels of circulating testosterone in left-handers, ambidexters and
right-handers with familial sinistrality than in right-handers,
whereas Gadea (2003) and Moffat & Hampson (1996) found lower
levels in left-handers. Other studies found no relation between
testosterone and handedness (Moffat & Hampson 2000; Beaton
et al. 2010). All of these studies assumed that individual differences
in testosterone levels in adulthood reflect organizational
effects of the hormone early in life. However, it is equally likely that
these studies actually tested activating effects of testosterone.