motion integration and segmentation within and across apertures

[Stephen Grossberg]

The following article is now available at 
http://www.cns.bu.edu/Profiles/Grossberg in HTML, PDF, and  Gzipped 
Postscript.

Grossberg, S., Mingolla, E., and Viswanathan, L.
Neural Dynamics of Motion Integration and Segmentation Within and 
Across Apertures
  Vision Research, in press.

Abstract

A neural model is developed of how motion integration and 
segmentation processes, both within and across apertures, compute 
global motion percepts. Figure-ground properties, such as occlusion, 
influence which motion signals determine the percept. For visible 
apertures, a line's terminators do not specify true line motion. For 
invisible apertures, a line's intrinsic terminators create veridical 
feature tracking signals. Sparse feature tracking signals can be 
amplified before they propagate across position and are integrated 
with ambiguous motion signals within line interiors. This integration 
process determines the global percept. It is the result of several 
processing stages: Directional transient cells respond to image 
transients and input to a directional short-range filter that 
selectively boosts feature tracking signals with the help of 
competitive signals. Then a long-range filter inputs to directional 
cells that pool signals over multiple orientations, opposite contrast 
polarities, and depths. This all happens no later than cortical area 
MT. The directional cells activate a directional grouping network, 
proposed to occur within cortical area MST, within which directions 
compete to determine a local winner. Enhanced feature tracking 
signals typically win over ambiguous motion signals. Model MST cells 
which encode the winning direction feed back to model MT cells, where 
they boost directionally consistent cell activities and suppress 
inconsistent activities over the spatial region to which they 
project. This feedback accomplishes directional and depthful motion 
capture within that region. Model simulations include the barberpole 
illusion, motion capture, the spotted barberpole, the triple 
barberpole, the occluded translating square illusion, motion 
transparency and the chopsticks illusion. Qualitative explanations of 
illusory contours from translating terminators and plaid adaptation 
are also given.