Space is at a premium in most labs, so we have developed a computer-based system that can test visual acuity and visual recognition memory in one unit of modest footprint.
Testing the visual acuity of pre-verbal subjects, or non-verbal subjects such as animals, presents unique challenges -- one cannot simply ask the subject whether or not they can read an eye chart.
To test such subjects, a black-and-white striped grating is
introduced onto one side or another of a field of grey. If the subject cannot resolve the grating
stripes, the grating will appear uniformly grey, disappearing into the
background. If the subject can resolve
the grating, they are typically struck by the novelty of the introduced image,
and study it, at least casually.
A video camera monitors the subject's face, and an experimenter watches the video feed, looking for such hints of interest. When the experimenter suspects that the subject has seen the grating, they press a footpedal corresponding to the direction the subject is looking. If the experimenter is cued accurately in this way a large percentage of the time, it can be inferred that the subject has adequate visual acuity to see the gratings.
The other test that the system performs is that of visual recognition memory. In this test, the subject is shown an image long enough for the subject to become quite familiar with it:
The subject is then shown both the now-familiar image and a new image:
A subject with a normal, healthy brain will be quite bored with the familiar image, and turn their attention to the new object. A subject with impaired functioning may either not remember the original image, or not register that a new image has appeared, and will show less such preference.
In a manner similar to that for visual acuity, the experimenter monitors a video feed of the subject's face, and notes gazes to the left and right with the footpedals as the subject studies the images. If the subject favors the new image, it may be inferred that the subject remembers the original image, and has a normal reaction to novelty.
Construction details are available here.