14.01.2014

New abstract by Heiko Schütt and Felix Wichmann

Heiko and Felix's abstract was acceppted as a poster at TeaP in Giessen from 30.03.-02.04.2014. Title: "Uncertainty effects in visual psychophysics"

Abstract:

"Uncertainty effects in visual psychophysics"

Uncertainty effects refer to decreased sensitivity in detection experiments when the subject is uncertain about the physical properties of the stimulus (such as its size, position or spatial frequency). In particular, uncertainty about the spatial frequency of a sinusoidal grating is thought to cause a large drop in detectability (Davis & Graham, 1980).
The uncertainty model of Pelli (1985) and a recent model by Goris, Putzeys, Wagemans, and Wichmann (2013) both account for this effect. However, the models make different predictions on the slope of the psychometric function. Pelli’s model predicts a rise of the slope when the threshold rises, while the model of Goris et al. predicts a pure shift without any slope change.
We measured psychometric functions for detection of sinusoidal gratings with spatial frequencies of 3, .75 and 12 cyc/deg, alone and intermixed under uncertainty.
Surprisingly, we do not find a sizeable uncertainty effect in our data. We measured at least 13800 trials per subject. With the statistical power due to this large number of trials we can exclude effect sizes of the magnitude found in the literature. We discuss different explanations for this lack of effect in our data compared to previous studies.