Dot Probe

I am programming a dot probe task and I am unsure of how to randomize the location of the dot. Basically, within a trial I have two words on the left and right side of the screen (matched for length and freq. – so these words will always be paired together). A picture of a dot replaces one of the words, and the participant is to indicate the location of the dot. I want the dot to randomly replace either the left or right word as opposed to having the dot replace the same word for each participant. How do I go about randomizing dot location (left or right) within a given trial?
Any comments are welcome!

Hmm. Perhaps, you could use the randomization functions to set the location values when DirectRT reads your input file--i.e., randomize the actual LOC values of the DOT image. Take a look at this link and see if it's helpful:

[URL]http://www.empirisoft.com/directrt/help/directrt_using_random_values.htm[/URL]

For example, when placing a stimulus image of a dot, you might try the following for a [URL="http://www.empirisoft.com/directrt/help/directrt_loc_stimulus_location.htm"]LOC[/URL] value:

[I]rand(.25,.75),.5,0[/I]

That would randomly place it on the left or right side of the screen, and half way down. Does that make sense?

Thank you!
This is exactly the function I need,
-D

Although not a major concern, I am now unsure as to what values I should be using for a response. I have participants pressing left (203) and right (205) arrows to indicate the location of the (now randomized) dot. Is there an easy way to set the response option so that in the output 'true' and 'false' values will be accurate? In other words, will I be able to easily see if participants made a correct response if the dot is randomly placed on the left or right side?
Thanks,
D

If the correctness will be determined on the fly via the random function, then the "Correct" column won't be of much help. It would have to be determined later on as a function of the stimulus placement. Which I think you can get from the actual input file used because DirectRT saves the post-randomization individual input files when you use those functions.

I am also programming a dot probe task and I was wondering would it be possible to use rand() to select from 3 LOC choices? I want to display an object in a quadrant that I have not previously used for a trial. Thanks.