Relative strength of central and peripheral fusion as a function of stimulus parameters

We investigated the role of various stimulus parameters that influence motor fusion responses for peripheral as compared to central fusional stimuli. Results from the initial experiment indicated that a central stimulus equal in size to a peripheral fusion stimulus dominated the response independent of the amount of retinal eccentricity of the peripheral target. A second experiment indicated that the central stimulus dominated even when the peripheral stimulus was larger. However, when the peripheral stimulus was changed in shape so that it became an annulus surrounding the central stimulus, the peripheral stimulus was always stronger. In another phase of the experiment, we found that the extent to which a peripheral stimulus surrounded the central one determined which controlled the response. We concluded that the surrounding perceptual gestalt produced by the peripheral stimulus was the most significant variable determining the relative strengths of central and peripheral fusion stimuli. Clinical implications are discussed.