Neural Formulation of the Effects of Target Size and Shape upon Visual Detection*

A hypothesis is presented, the chief assumptions of which are that neural impulses originating in retinal receptors converge upon neurons in a central area, and that the excitation of the most excited neuron in that area determines the response. The relation of this hypothesis to earlier ideas along similar lines is discussed. It is shown that the hypothesis leads to testable relationships between thresholds for circular targets and for targets of other shapes. Evidence is presented that diffuse neural connections are relatively more important at low background levels, and an interpretation is suggested.