PSYCHOPHYSICAL METHOD COMPARISON TO ESTIMATE PSYCHOMETRIC FUNCTIONS FOR VISUALLY PERCEIVED SIZES
The choice of psychophysical method to accesses the psychometric functions for visually perceived size is still controversial. To address the question, observers compared the sizes of two circles displayed on a vertical meridian of a computer screen by three procedures: method of constant stimuli, staircase procedures (1up-1down and 1up- 2down) and four-point sampling method. Slopes and points of subjective equality (PSE) were estimated on normal cumulative curves. Results indicated no significant difference for calculating PSE among these methods, but significant differences among slope computations. Slope was higher for four-pointing sampling method, intermediate for constant stimuli method, and lower for the staircase. We concluded that the three methods are similar for PSE estimation, but some care should be taken into account for choosing the method to estimate the slope.