Category Archives: psychophysics

Dynamic Color Stimuli

I’m currently doing some human psychophysics experiments using some dynamic color stimuli that my PI Rich Krauzlis and I developed. The stimuli were inspired by a variant of Random Dot Kinematograms (RDKs), which were initially popularized by Bill Newsome. The variant was used by Rich and his former post-doc Alex Zénon in work that resulted in this paper. The underlying motivation for both is the use of stimuli that lend themselves to the application of Signal Detection Theory (SDT). Here’s a (somewhat low quality) example of the color version:

What’s going on here is that each check’s color is drawn from Gaussian distribution on the DKL plane. Further, each check only lives for 8 frames; once the check’s lifetime is over, it is recolored with a value drawn from the underlying distribution. Finally, halfway through the video, the mean saturation of the distribution increases.

In our experiments, we present these stimuli in the periphery while subjects fixate a spot in the center of the screen, and ask them to report these changes in saturation. We vary the magnitude of the saturation change and see how this affects their ability to detect the change. Here’s the code I used to generate the sequence of images in MATLAB (note that this is optimized for a particular display, in a later post I’ll explain how to modify for other displays).