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Random dots: set number of dots moving in one direction AND number of dots moving in the opposite direction

Hi All,

I need to set up an experiment in which I control, during a random dot motion task, the number of dots moving to the left and those moving to the right, while the remaining dots are moving randomly.

I have been trying to play with some code in order to achieve this but couldn’t quite figure it out yet…anyone has some smart tip to provide?

A silly idea I had was that of superimposing 2 RDKs and control them separately; in one I set right and in the other left motion…but I am sure there should be a more elegant solution :smiley: by doing so the RDK ‘on the background’ is covered by the one on top when two dots overlap so I guess that overall the perception would be of more dots moving in the direction of the RDK on top…
Thanks!

Actually on a second thought I think that having the two RDKs overlapping is not such a bad idea and I realised that what I wrote in the previous message

“the RDK ‘on the background’ is covered by the one on top when two dots overlap so I guess that overall the perception would be of more dots moving in the direction of the RDK on top”

is pretty much nonsense, because actually if both RDKs have the same color and opacity of 1, when 2 dots overlap for a very short period, one cannot understand which of the two is on top of the other…also, even when one has 1 rdk dots can overlap and this does not seem to be a problem. Of course if anyone has any opinion/suggestion/comment I’m all ears!