A grating is an oriented 2D stimulus characterized by parallel and alternating light and dark bars whose relative amplitudes define the contrast of the stimulus. This luminance modulation typically follows a sine-wave or square-wave function. Gratings have been frequently used as stimuli in psychophysical experiments to measure many visual functions such as visual acuity, contrast sensitivity, orientation discrimination or motion selectivity. More important, they have been used to investigate neurophysiologically the nature and properties of the spatial frequency channels in the visual system. They can be presented in isolation like in this example or combined with other gratings of different orientation to form plaid stimuli or of different spatial frequency to form more complex gratings with multiple harmonics.

References:

  Campbell & Robson (1968) Application of Fourier analysis to the visibility of gratings. Journal of Physiology 197(3): 551–566

  Shapley & Tolhurst(1973) Edge detectors in human vision. Journal of Physiolology 229(1):165–183

  De Valois et al (1979) Responses of striate cortex cells to grating and checkerboard patterns. Journal of Physiolology 291:483–505

  Albrecht & De Valois (1981) Striate cortex responses to periodic patterns with and without the fundamental harmonics. Journal of Physiolology 319:497–514

  Adelson & Movshon (1982) Phenomenal coherence of moving visual patterns. Nature 300:523–525

  Burr et al (1989) Evidence for edge and bar detectors in human vision. Vision Research 29(4):419–431

Here is the math behind this stimulus:

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