Psychophysical measurement of marmoset acuity and myopia

Abstract

The common marmoset has attracted increasing interest as a model for visual neuroscience. A measurement of fundamental importance to ensure the validity of visual studies is spatial acuity. The marmoset has excellent acuity that has been reported at the fovea to be nearly half that of the human (Ordy and Samorajski, 1968), a value that is consistent with them having similar photoreceptor densities combined with their smaller eye size (Troilo et al, 1993). Of interest, the marmoset exhibits a higher proportion of cones than rods in peripheral vision than human or macaque, which in principle could endow them with better peripheral acuity depending on how those signals are pooled in subsequent processing. Here we introduce a simple behavioral paradigm to measure acuity and then test how acuity in the marmoset scales with eccentricity. We trained subjects to fixate a central point and detect a peripheral Gabor by making a saccade to its location. First, we found that accurate assessment of acuity required correction for myopia in all subjects. This is an important point because marmosets raised in laboratory conditions often have mild to severe myopia (Graham and Judge, 1999), a finding that we confirm, and that would limit their utility for studies of vision if uncorrected. With corrected vision, we found that their acuity scales with eccentricity similar to that of humans and macaques, having roughly half the value of the human and with no clear departure for higher acuity in the periphery.