Normal Noise - Is this defined as Michelson Contrast or RMS Contrast?

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1

Hi, I am building an experiment in Builder and want to use a normally distributed noise sample, aka ‘Normal’ noise.

The documentation and states that contrast is defined by Michelson contrast, which I understand would be appropriate for certain types of noise but I thought that Normal noise would be defined by RMS contrast; the contrast value sets the standard deviation (SD) of the normal distribution and then pixel values are randomly assigned a luminance value from that distribution. Does anyone know if this is the case?

Also, further to that I want to vary the contrast of the Normal noise in my experiment, am I correct in thinking that changing the contrast value in the NoiseStim component would vary the SD of the noise distribution?

2

I contacted Becca at OpenScienceTools and thought I would pass on her response:

She said that it seems the ‘Normal Noise’ is taken from a normal distribution where varying the contrast parameter in builder will vary the standard deviation of the pixel values, therefore a contrast value of 1.0 will display pixel values ranging from -1 to +1.

She also very kindly made a demo (link below) and attached the plot of the distribution of the noise sample .

https://gitlab.pavlovia.org/lpxrh6/noise_distribution_demo
NoiseDist