Abstract Motor‐driven prism stereoscope vergence tests, base in break, base in recovery, base out break, and base out recovery, repeated three times (BIB, BIR, BOB, BOR x 3) were given to three separate groups. Two instruments with different speeds were used. Repeated testing shows a slight trend to convergence in slower machines. The results from both machines are still comparable. Means are similar to previously published norms from hand‐turned instruments, but the variance of scores is about twice as large and there is an eso trend at near. The motor drive aids discrimination, since Ss who are capable can now follow with smooth vergences over a wider range. In general, there is no substantial trend with age between 3 and 25 years other than those which may be due to decreasing response times. Vergence scores can be adequately reduced to two independent factors, loading on convergence and divergence, respectively, which suggests that there are two processes varying independently in maturation and therapy as well as assessment.
Vaegan et al. (Thu,) studied this question.