WorldViz User Forum - Logging an RT with a window of time

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hfarmer

07-02-2014 10:22 AM

Logging an RT with a window of time

Hi,

I'm currently trying to get a study set up using vizard 4 and am having a bit of a problem. I want to set up some code to measure reaction times after the presentation of a stimuli. However I want the program to move on to the next trial after 3 seconds regardless of whether a key is pressed or not. However this doesn't seem to be possible using the standard way of measuring reaction times given in the Vizard tutorial e.g:

Code:

                d = yield viztask.waitDraw() #Set Display time

                displayTime = d.time #Log display time

                d = yield viztask.waitKeyDown(None) #Log keypress time

                pressTime = d.time

                reactionTime = pressTime- displayTime #Calculate reaction time

Basically I want to know if there's a way to set up two parallel processes, one which is waiting for a key press to log reaction times and the other which just runs a timer and moves on the program after 3 seconds. Any help would be much appreciated.

Jeff	07-02-2014 04:48 PM

You can use the viztask.waitAny command to wait for one condition, out of a list of conditions, to occur.

hfarmer

07-07-2014 02:53 AM

Hi Jeff,

Thanks for your help.

I found that command but the problem is that I want the program to always wait 3 seconds before moving on regardless of whether a key is pressed or not. But it seems like to log the reaction time I need to make if a yield command and that means the program will wait until a key is pressed before moving on. Is there a way to log reaction time without using the yield command?

Best,

Harry

Jeff	07-07-2014 03:23 PM

You could log the reaction time and then yield for an additional amount of time equal to 3 seconds minus the reaction time:

Code:

import viz

import viztask

viz.go()



def MyTask():

        

        waitKey = viztask.waitKeyDown(' ')

        waitTime = viztask.waitTime(3)

        

        while True:

                

                print 'start'



                #Wait for next frame to be drawn to screen

                d = yield viztask.waitDraw()



                #Save start time

                startTime = d.time



                d = yield viztask.waitAny( [ waitKey, waitTime ] )

                

                if d.condition is waitKey:

                        keyData = d.data

                        elapsed = keyData.time - startTime

                        print 'The spacebar was pressed after {:.2f} seconds'.format(elapsed)

                        yield viztask.waitTime(3-elapsed)

                        

                elif d.condition is waitTime:

                        print '3 seconds passed, the spacebar was not pressed'



viztask.schedule( MyTask() )

hfarmer

07-18-2014 05:38 AM

Hi Jeff,

Sorry for the delay in getting back to you, thanks for the example code, I didn't know about the condition command before but can see that it would be very useful. However I have one more question which is how to remove the "True" condition after each trial so that the program moves on to the next trial.

At the moment I am getting the information logged but the program seems to stick on the first condition rather than timing out after 3 seconds. Could you let me know what the "while True" part of the code refers to? I assume it just means while in that function but am a bit unclear on how to end the function with a command.

Best,

Harry

Jeff	07-18-2014 02:28 PM

The while True line always evaluates to True so the loop keeps repeating. To run that code a set number of times you could use a for loop or have an expression following while that evaluates to False after several loops. Try replacing:

Code:

while True

with:

Code:

for i in range(1,5):

        

        print 'start trial {}'.format(i)

hfarmer

07-21-2014 06:15 AM

Dear Jeff,

Just wanted to let you know that I tried what you suggested and the program works perfectly now.

Many Thanks,

Harry

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