Second-order motion refers to temporal contrast variations along some spatial direction. The contrast (or more generally texture-defined) information is believed to be processed at a later stage of the visual system, typically through the analysis of a bank of non-linear filters, though it is still unclear where in the visual cortex.

References:


   Schofield & Georgeson (1999) Sensitivity to modulations of luminance and contrast in visual white noise: Separate mechanisms with similar behaviour. Vision Research 39(16):2697–2716

   Dumoulin et al. (2003) Cortical specialization for processing first- and second-order motion. Cerebral Cortex 13(12):1375–1385

   Hutchinson & Ledgeway (2006) Sensitivity to spatial and temporal modulations of first-order and second-order motion. Vision Research Cortex 46: 324–335

   Ashida et al. (2007) fMRI adaptation reveals separate mechanisms for first-order and second-order motion. Journal of Neurophysiology 97(2):1319–1325

Here is the math behind this stimulus:

  noise = unoise(x,1,1)
  xrot = x*cos(angle)-y*sin(angle)
  smod = cos(2*pi*xrot*sf+phase+2*pi*speed*time)
  tmod = cos(2*pi*time*tf)
  env = r<radius
  z = noise*(1+(cnt/100)*smod*tmod)*env

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 using 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 !