Visual search

Hi,

is it possible (and not too complicated) to program visual search experiments with direct rt? This entails, inter alias, the presentation of multiple stimuli at multiple locations, with a random assignment of locations to stimuli. I went through the examples, which however, were not conclusive in this respect.

Thanks,
Gernot

Would need a little more detail, but it sounds like something DirectRT could usually handle. Would depend on your randomization plans/constraints. e.g., with, without replacement. Also, what do you mean by [I]inter alias[/I]?

In a visual search experiment, there are target present and target absent trials. In target present trials, the target (e.g. a happy face, or the letter H or U) is presented within distractors (e.g., an angry face, or other letters, respectively), and in target absent trials, only distractors are presented. The number of stimuli is varied (e.g., 3, 6, and 9) between trials to estimate search efficiency, which is the time needed to process a distractor. There are many ways to layout the stimulus display (e.g., matrix or circle), but very often there are more positions on the screen than stimuli, that is, the positions are irregularily filled. The position of the target and the other stimuli may be controlled, but most often they are simply determined by random. Sometimes distractors are all the same (homogeneous), but of course, sometimes distractors are heterogeneous. Drawing without replacement is probably more typical than with replacement

If randomization without replacement is more common, then you could just create a set of trials with varying location values for the stimuli and then randomize the order of those trials. Would that work for you?