Relationships between visual acuity and visual attention measures in rhesus monkey infants

Purpose. Tests of visual attention, particularly visual paired comparisons (VPCs) such as the Fagan test, are increasingly used to assess cognitive development and to screen high-risk human infants. Increased look duration in VPCs, possibly reflecting slower processing, has been found together with slower acuity development in monkey and human infants with low levels of n-3 fatty acids (Reisbick et al., Soc. Neurosci. Abstr., 1994; Werkman & Carlson, Lipids, 1996). We explored the relationship of performance in VPCs to visual acuity development in rhesus infants. Methods. Subjects were 43 nursery-reared rhesus infants involved in three separate studies of nutritional variables (taurine and n-3 fatty acids) in visual and cognitive development. Acuity was estimated by both preferential looking and sweep VEP methods at 4, 8, 12 and 16 weeks. In VPCs, done at 3, 6, 10 and 14 weeks, infants were familiarized with pattern or face stimuli for 10-30 sec and then shown a familiar stimulus paired with a novel one. Average look duration and the proportion of time looking at novel stimuli (%novel) were measured during the novelty test. Results. As previously reported, acuity was lower by ∼1 octave in infants fed n-3 deficient diets, and the two acuity measures were highly correlated (r²=.64); in VPCs, look duration was longer in n-3 deficient infants and %novel was higher in taurine-deprived infants. No correlation was found between acuity and look duration, within each study or age or overall (all r²<.07), but acuity correlated moderately with %novel, more so for faces (r²=.25-.33) than for patterns (r²=. 13-.15). Conclusions. Look duration was unrelated to acuity during development. Similar results were found by Carlson et al. for human infants with differing n-3 fatty acid intakes (ISSFAL, 1995). Thus n-3 fatty acids affect these two outcomes independently. Preference for novel stimuli, a measure of visual recognition memory, showed some relationship to acuity within the normal to mildly low range. Acuity may be important for interpreting human VPC performance, especially when more severe visual deficits may be present.