Temporal tuning and the development of lateral interactions in the human visual system.

PURPOSE The authors examined the development of lateral interactions between neurons in the human visual system through the use of visual evoked potentials (VEPs) elicited by windmill-dartboard stimuli. Previously, these VEPs have revealed two distinct types of lateral interactions (short-range and long-range) in adults. This study aims to track the development of these interactions in the first 6 months of life. METHOD Windmill-dartboard stimuli were generated by a computer-controlled visual stimulator and presented on an oscilloscope display. VEPs to these stimuli were obtained from a group of human infants between 14 days and 6 months of age and from a group of adults who served as a basis for comparison. Fourier analysis was used to retrieve amplitude and phase measures of the relevant frequency components of the response. RESULTS Amplitude measures of the VEP components elicited by the windmill-dartboard stimulus showed that the attenuation of the second harmonic frequency component (reflecting long-range lateral interactions) was essentially adultlike at all temporal frequencies for the majority of infants. In contrast, the amplitude of the fundamental frequency component (thought to reflect short-range lateral interactions) exhibited a low-pass temporal tuning function in infants that differed dramatically from adults. Additional immaturities were observable in the phase of the fundamental component of the infant VEPs. CONCLUSIONS Evidence for the presence of some degree of lateral interaction was seen in even the youngest infant. Long-range lateral interactions appear to mature rapidly in infancy, whereas short-range lateral interactions show a much longer developmental time-course, and their properties are dependent on temporal frequency.