By aghartley - 3/10/2015
I am designing an experiment in which participants can either earn money (incentive) or lose money (decentive) for correct guess per trial. For example, if it's an incentive block, participants will earn $.15 for each correct guess per trial within that block. But if the next block is a decentive block, they will lose $.05 for each correct guess.
I'm using the counter element so that participants can keep track of their earnings. However, currently, as I've programmed the experiment, if participants lose money below $0, the program records negative numbers, but their counter amount shows $0. So, when participants start earning money again, they need to get out of the negative range before the counter will show anything over $0.
Basically, I need to know how to get the counter to reset the participant's earnings to 0 when they dip into the negative digits (we are not interested in having participants owe money for this task). Would I do this using the reset interval attribute? Or would I need to fix something elsewhere in the code, outside the counter element?
Please let me know if you'd like to see my code. Thank you!
By Dave - 3/10/2015
I'm not sure why you would use a <counter> to keep track of earnings at all. The best-suited element for that is a <values> entry -- you simply update that value by adding or subtracting earnings or losses. Setting that value to zero if it goes negative is trivial.
/ points = 0
/ trials = [1-10 = mytrial]
/ ontrialend = [if (trial.mytrial.response == 17) values.points += 10]
/ ontrialend = [if (trial.mytrial.response == 38) values.points -= 10]
/ ontrialend = [values.points=max(0,values.points)]
/ stimulusframes = [1=mytext, mypoints]
/ validresponse = ("w", "l")
/ items = ("Press 'W' to win points, press 'L' to lose points.")
/ items = ("Your have <%values.points%> points")
/ position = (50%, 10%)
/ erase = false
/ size = (25%, 10%)
A <counter>'s /resetinterval will not help you, nor will explicitly calling the reset() function on it. Neither changes the counter's *contents*, both merely reset it's selection pool.