The mechanism for processing random-dot motion at various speeds in early visual cortices

PLoS One. 2014 Mar 28;9(3):e93115. doi: 10.1371/journal.pone.0093115. eCollection 2014.

Abstract

All moving objects generate sequential retinotopic activations representing a series of discrete locations in space and time (motion trajectory). How direction-selective neurons in mammalian early visual cortices process motion trajectory remains to be clarified. Using single-cell recording and optical imaging of intrinsic signals along with mathematical simulation, we studied response properties of cat visual areas 17 and 18 to random dots moving at various speeds. We found that, the motion trajectory at low speed was encoded primarily as a direction signal by groups of neurons preferring that motion direction. Above certain transition speeds, the motion trajectory is perceived as a spatial orientation representing the motion axis of the moving dots. In both areas studied, above these speeds, other groups of direction-selective neurons with perpendicular direction preferences were activated to encode the motion trajectory as motion-axis information. This applied to both simple and complex neurons. The average transition speed for switching between encoding motion direction and axis was about 31°/s in area 18 and 15°/s in area 17. A spatio-temporal energy model predicted the transition speeds accurately in both areas, but not the direction-selective indexes to random-dot stimuli in area 18. In addition, above transition speeds, the change of direction preferences of population responses recorded by optical imaging can be revealed using vector maximum but not vector summation method. Together, this combined processing of motion direction and axis by neurons with orthogonal direction preferences associated with speed may serve as a common principle of early visual motion processing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cats
  • Female
  • Male
  • Motion
  • Motion Perception / physiology*
  • Neurons / physiology
  • Orientation / physiology
  • Photic Stimulation / methods
  • Visual Cortex / physiology*
  • Visual Fields / physiology
  • Visual Pathways / physiology*
  • Visual Perception / physiology*

Grant support

This work was supported by the National ‘973’ Program 2011CBA00400, 2009CB941303, and the Fundamental Research Funds for the Central Universities (WK2070000007). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.