DotStim doesn't create a homogeneous dots distribition

Coding
1

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
2

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.

3

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?