Center-surround organisation and interactions in receptive fields of goldfish tectal units

Small spot mapping of the receptive fields (RF's) of tectal units never revealed a truly annular surround. In contrast, a surround enclosing receptive field center (RFC) often appeared if the RFC was illuminated by a small spot of light. The so-called induced surround was found for 21 on units ( N = 36). With flickering spot at a fixed position outside the RFC, the strength of the response to the flickering spot was a function of the position of the adapting spot in the RF and appeared to be proportional to the RFC response profile. The RFC behaved predominantly as an adaptation pool. Electrical stimulation established that ganglion cells as well as tectal neurons can have an induced surround.