Millisecond Forums

Random red dot, to measure participants attention level?

https://forums.millisecond.com/Topic13511.aspx

By SpoHo - 6/9/2014

Hi!

At the beginning of our Experiment, we present 18 images (7.5 seconds each). 
To keep the participant interested, we want to give him a little extra task, like counting random red dots.

So here's what we came up with:
On random images, a red dot should appear in a random position on the screen. The task would be to count the number of red dots being shown during the presentation.

So here are my questions:
How can I show a red dot, in a random position?
How can I count, how many times the red dot appeared, so I can give the participant a feedback wether he was right or wrong? (custom value++)?

thanks a lot!!

best regards,
Manu
By Dave - 6/9/2014

#1: You display the dot-stimulus just like any other stimulus. Via a <trial>'s /stimulustimes or -frames. Alternatively you can 'inject' the dot-stimulus using the <trial> element's insertstimulustime(), etc. functions, details for which can be found in the language reference for the <trial> element.

#2: /position attributes etc. accept expressions and the like. You can easily randomize a stimulus' onscreen position using <values>, <expressions>, <list>s and/or a bit of /ontrialbegin logic. Which approach turns out to be the most suitable depends on what exactly you want to achieve. A forum search will provide you with numerous examples regarding position randomization.

#3: Whether you need <values> to count dot-instances depends on how you decide to implement them in the first place. But, in general, yes -- using values is a good idea and provides a lot of flexibility.