Point spread functions and detail detection

Point spread functions, intended to characterize local spatial transfer of the visual system, can be obtained psychophysically using a perturbation technique. Data of such point spread functions are shown for three experimental conditions: foveally at adaptation levels of 1200 and 10 Td, and in the parafovea at an eccentricity of 2 deg using a 1200 Td adaptation level. The results are consistent with earlier findings (Blommaert, F. J.J. and Roufs, J.A.J. 1981, Vision Res. 21, 1223-1233). On the basis of such point spread functions a simplified multiple unit model was constructed, the parameters of which were fitted to thresholds of discs with varying diameter. Threshold predictions from this model for annuli, thin lines and broad lines were found to be in fair quantitative agreement with experimental results. It is argued that for a certain class of slender stimuli, including alphanumeric characters, thresholds can be described with a single channel model containing only the experimentally determined point spread function as a basic component.