A new stereoacuity test, the double two rod test, uses a two-alternati
ve forced-choice (2AFC) paradigm. The subject's task is to state which
pair of rods, the left or the right, contains depth information. The
test gives repeatable results; comparison between the depth threshold
measured binocularly and monocularly suggests that monocular cues, if
present, provide only poor depth information, compared to the depth in
formation arising from binocular disparity. As part of an investigatio
n of stereoacuity and ageing, we tested stereoacuity as a function of
viewing time and the number of comparisons made between the two pairs
of rods, Stereoacuity was significantly reduced for viewing times less
than 3s while longer viewing times did not improve stereoacuity. The
number of comparisons made between the two pairs of rods had no effect
on stereoacuity. Copyright (C) 1996 The College of Optometrists. Publ
ished by Elsevier Science Ltd