6274 PSYC Laboratory methods of perceptual psychology Winter 2009
Problem set #2
1. Write a function called measurecsf.m that measures a contrast sensitivity function. Measure 2AFC contrast thresholds at spatial frequencies 0.5, 1, 2, 4, 8, and 16 cycles/degree. Use a stimulus duration of 250 ms, an interstimulus interval of 500 ms, and a scale constant of two wavelengths. Measure each 71% threshold in a separate block of 200 trials with a 1-up 2-down staircase. Take the observer's initials as an input argument, and save data trial-by-trial in a file named csf_jfk.txt, where "jfk" is replaced by the observer's initials. Without a high-contrast-resolution video card, you will not be able to show gratings at threshold on a blank background, so show all stimuli in Gaussian white noise with a pixelwise standard deviation of 20...