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DotStim doesn't create a homogeneous dots distribition

Hi everyone,

I am using psychopy to generate a RDK experiment. I am using a field size covering all screen with a 250 pixel aperture in the middle of the screen where dots moving across. For experimental requirements I have to use an infinite dot life (-1) generating inhomogeneities in the dots distribution across the field (empty spots in distribution). This is the stimulus:

 stimA_2 = visual.DotStim(
    win=win, name='stimA_2',
    nDots=NUM_OF_DOTS, dotSize=DOT_SIZE,
    speed=DOT_SPEED, dir=1.0, coherence=1.0,
    fieldPos=[0.0,0.0], fieldSize=CLOUD_SIZE,fieldShape='circle',
    signalDots='different', noiseDots='direction',dotLife=DOT_LIFETIME,
    color=BLUE, colorSpace='hsv', opacity=1,
    depth=-4.0)```

I have tried to manipulate the noiseDots without results. Any suggestion? Thank you in advance!!

Best

Daniele

Don’t use an infinite dot life. Basically, whichever way you cut it that create artefacts in the stimulus. The reason that most people use short dot lives (like 5 frames) is to cut down those artefacts.

Thank you for your answer! Basically I use infinite dot life because I am focused on the saturation changes detection. If I use a finite dot life I suspect that the continuous pop up of new dots could affect the detection task. Do you think that manipulating directly dotStim.py could I find a way to changing the dot distribution?