A Gabor patch is a 2D stimulus made of a sinusoidal luminance modulation (grating) with a Gaussian envelope. Gabor patches are frequently used as stimuli in psychophysical experiments to measure many visual functions such as visual acuity, contrast sensitivity, orientation tuning or motion selectivity. They can be presented in isolation like in this example or surrounded by other contextual stimuli. They are thought to be an approximation of the preferred orientation tuning of many cells in the primary visual cortex (V1) in humans. Because any image can be represented by a set of 2D Gabor wavelets, it is even potentially possible to reconstruct a picture of a person’s visual experience from brain activity measurements.

References:

  Daugman (1980) Two-dimensional spectral analysis of cortical receptive field profiles. Vision Research 20(10):847–856

  Jones & Palmer (1987) An evaluation of the two-dimensional Gabor filter model of simple receptive fields in cat striate cortex. Journal of Neurophysiology 58(6):1233–1258

  Lee (1996) Image representation using 2D Gabor wavelets.. IEEE Transactions on Pattern Analysis and Machine Intelligence 18:959–971

  Kay et al (2008) Identifying natural images from human brain activity. Nature 452(7185):352–355

Here is the math behind this stimulus:

  xrot = x*cos(angle)-y*sin(angle)           # Rotation
  gauss = exp(-(r*r)/(2*sigma*sigma))         # Gaussian envelope
  smod = cos(2*pi*xrot*sf+phase+2*pi*speed*time)  # Spatial carrier
  tmod = cos(2*pi*time*tf)              # Temporal carrier
  z = (cnt/100)*gauss*smod*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 !