Factors limiting the postnatal development of visual acuity in the monkey.

A major factor underlying the prolonged postnatal improvement of visual acuity in primates is an increase in the sampling limit imposed by the photoreceptor mosaic, which may be as much as 5-fold. Further factors operating peripheral to neurons of the lateral geniculate nucleus, which might include changes in neural connectivity, appear to contribute at most 1.5 octaves, between 3 weeks and 6 months of age. Neural factors at the geniculo-cortical synapse may add another half-octave between 10 weeks and 1 yr. Factors operating after the level of the striate cortex (changes in spatial degradation, attention, motivation, etc.) contribute up to another octave or more to the increase in behavioural acuity between birth and about 11 weeks of age. The foveal image is substantially undersampled in young animals and therefore aliasing could occur over a wide range of spatial frequencies.