A Gaussian blob is an isotropic 2D stimulus which is characterized by a smooth “blurry” profile. Gaussian blobs are frequently used as stimuli in psychophysical experiments to provide a smooth luminance increment (or decrement) relative to an homogeneous background when measuring various visual functions such as spatial and temporal luminance detection or to create a simple luminance target when measuring saccadic eye movements for example. Gaussian blobs can be presented in isolation like in this example to study some low-level aspects of the visual system (retinal or early cortical) or combined with other Gaussian blobs to form more complex stimuli like random-dot kinematogram (RDK). More important, they are often used to limit the visibility of other stimuli. They are also used as an approximation of the receptive field of non-oriented cells in the retina, lateral geniculate nucleus or primary visual cortex in mammalians. Gaussian blobs are thought to be better stimuli than dots because their Fourier transform is also a Gaussian blob, with a central spatial frequency of 0 cpd.

References:

  Bijl et al (1989) Visibility of blobs with a gaussian luminance profile. Vision Research 29(4):447–456

  Bijl and Koenderink (1993) Visibility of elliptical gaussian blobs. Vision Research 33(2):243–255

  Cellini et al (2010) Saccadic eye movements to Gaussian luminance and color blobs. Journal of Vision 9(8):438–438

Here is the math behind this stimulus:

  gauss = exp(-(r*r)/(2*sigma*sigma))         # Spatial envelope
  tmod = cos(2*pi*time*tf)              # Temporal carrier
  z = (cnt/100)*gauss*tmod

The whole stimulus is generated in real-time using a GLSL shader that runs right inside your WebGL-compatible browser. The plain Math behind the stimulus was converted to this optimized GLSL shader using the new Psykinematix Pro Edition. Translation to Matlab and Python code is also possible !

This whole widget was also fully generated using Psykinematix Pro Edition. The parameters that control the stimulus properties through the sliders are the same as the ones you would define as dependent or independent variables when using the stimulus in an actual psychophysical experiment run in Psykinematix. The widget creation is otherwise fully customizable with your own logo, copyright, links, etc.

To learn more about the widget creation, click on the above "Made With" button !