SCOTOPIC CENTER-SURROUND ORGANIZATION IN 10-WEEK-OLD INFANTS

The large critical areas for complete spatial summation in infants may be due to immaturities of receptive field organization in both dark a nd light adapted scotopic conditions. Scotopic lateral excitatory/inhi bitory interactions have been previously studied in adults using Westh eimer's [(1965) Journal of Physiology, London, 181, 881-894] paradigm. We modified this paradigm to investigate scotopic receptive field org anization in infants. Detection thresholds for probe flashes of consta nt diameter and duration presented on steady backgrounds of various di ameters were determined for 10-week-old infants and adults. Infants' t hresholds increased up to background diameters of 3 degrees to 3.5 deg rees and then decreased at greater background diameters. Adults' thres holds increased for backgrounds up to about 0.75 degrees diameter and then decreased at greater background diameters. These results suggest that the excitatory, central receptive field size is larger in infants than adults, and that a balanced center-surround mechanism is operati ve.