Visual processing of form in human: threshold contrast curves to concentrically symmetric patterns / Processamento visual da forma em humanos: curvas de limiar de contraste para padr es circularmente simétricos

The aim of this work was to measure contrast sensitivity curves to concentrically symmetric patterns in a system of polar coordinates. We measured the contrast thresholds to sine wave gratings, radial frequencies and coupled radial/angular frequencies. Six young adults with corrected-to-normal visual acuity participated in the experiments. The frequencies measured with a forced-choice psychophysical method were 0.2, 0.3, 0.5, 0.8, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 9.0 cpd. Results showed that coupled radial/angular frequencies caused an increase in the sensitivity of at least 1.6 times in relation to radial contrast sensitivity function. These results were in agreement with the model of multiple channels processing of spatial frequencies of stimuli defined in terms of polar coordinates.