Area-threshold relations at controlled retinal locations in 1-month-old infants

A fixation-and-flash technique has been developed to provide control over the retinal eccentricities of stimuli presented to infant subjects, to within a few degrees of visual angle. The technique is a variant of forced-choice preferential looking (FPL). An adult observer triggers presentation of the test stimulus when she judges that the infant is fixating a centrally located fixation target. The stimuli are short in relation to the infant's refixation latency. Auxiliary experiments confirmed that on most trials the stimuli fell within +/- 4 degrees of the designated eccentricity. Test fields of two sizes, 3.1 and 17 degrees, were presented to 1-month-old infants at one of four retinal locations, 9, 18, 27 and 36 degrees eccentric. The infants' data show a perfect area-intensity tradeoff at all four locations. Adult control subjects showed summation over areas of only 1-2 degrees. The results are discussed in relation to other evidence of coarse spatial processing in human infants and other immature mammalian systems.