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 e voked potentials (VEPs) elicited by windmill-dartboard stimuli. Previo usly, these VEPs have revealed two distinct types of lateral interacti ons (short-range and long-range) in adults. This study aims to track t he development of these interactions in the first 6 months of life. Me thod. Windmill-dartboard stimuli were generated by a computer-controll ed 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 ba sis for comparison. Fourier analysis was used to retrieve amplitude an d phase measures of the relevant frequency components of the response. Results. Amplitude measures of the VEP components elicited by the win dmill-dartboard stimulus showed that the attenuation of the second har monic frequency component (reflecting long-range lateral interactions) was essentially adultlike at all temporal frequencies for the majorit y of infants. In contrast, the amplitude of the fundamental frequency component (thought to reflect short-range lateral interactions) exhibi ted a low-pass temporal tuning function in infants that differed drama tically from adults. Additional immaturities were observable in the ph ase of the fundamental component of the infant VEPs. Conclusions. Evid ence for the presence of some degree of lateral interaction was seen i n even the youngest infant. Long-range lateral interactions appear to mature rapidly in infancy, whereas short-range lateral interactions sh ow a much longer developmental time-course, and their properties are d ependent on temporal frequency.