Consistent with our expectation, fish treated with testosterone
showed a population bias to look at a predator with the right eye,
thus using the left hemisphere (one-sample t test: t19¼2.268,
P ¼ 0.035), whereas in the control treatment no such bias was
found (one-sample t test: t18 ¼ 0.181, P ¼ 0.858; Fig. 1a). Testosterone
treatment did not affect the absolute value of the laterality
index (Wald c1
2 ¼ 0.071, P ¼ 0.790; Fig. 1b)