Amplitude and spatial-period discrimination in sinusoidal gratings by dynamic touch

We measured discrimination thresholds for sinusoidal gratings using active dynamic touch. In the first experiment we measured the thresholds for ampli tude discrimination as a function of amplitude and spatial period. Threshol ds ranged between 10.8% and 15.8% of the standard amplitude. We showed that amplitude differences as small as 2 mum can be detected. We found that Web er fractions for amplitude discrimination are constant over a range of ampl itudes, but are influenced by the spatial period of the grating; discrimina tion improved with increasing spatial period. In the second experiment we d etermined the thresholds for spatial-period discrimination. We used the sam e design as in the first experiment. Weber fractions ranged from 6.4% to 11 .8%. Amplitude was found to have no effect on the Weber fractions for spati al-period discrimination. However, the spatial period had an effect on the Weber fractions: larger spatial periods yielded lower Weber fractions.