Stimulus position has been found to affect the ability
of the horse to perform tasks involving visual discriminations.
In a study by Gardner (1937b), horses were
trained to select a feed box covered with a black cloth
from two other plain feed boxes. The effect of repositioning
the black cloth either above or below the box containing
the food reward was then investigated (Gardner,
1937a). The latter study found that more errors
were made with the black cloth in the high vs. low
position. However, more errors were made in both of
the new positions compared with the original position
that was over the food box (i.e., in the same location
as the reward). In a more recent study using a visual
discrimination task to assess intelligence and learning
in horses, the reward was presented in the same location
as the stimulus, but both were at nose height (Sappington
and Goldman, 1994). The results of an early
study into equine color vision where stimuli were presented
at ground level (Grzimek, 1952) differ from findings
of subsequent studies involving stimulus presentations
at a higher level (Pick et al., 1994; Macuda and