Connectionists: laminar cortical dynamics of visual form and motion interactions

[Stephen Grossberg]

The following article is now available at 
http://www.cns.bu.edu/Profiles/Grossberg :

Berzhanskaya, J., Grossberg, S., and Mingolla, E.

Laminar cortical dynamics of visual form and motion interactions 
during coherent object motion perception

ABSTRACT
How do visual form and motion processes cooperate to compute object 
motion when each
process separately is insufficient? Consider, for example, a deer 
moving behind a bush. Here the
partially occluded fragments of motion signals available to an 
observer must be coherently
grouped into the motion of a single object. A 3D FORMOTION model 
comprises five important
functional interactions involving the brain's form and motion systems 
that address such
situations. Because the model's stages are analogous to areas of the 
primate visual system, we
refer to the stages by corresponding anatomical names. In one of 
these functional interactions,
3D boundary representations, in which figures are separated from 
their backgrounds, are formed
in cortical area V2. These depth-selective V2 boundaries select 
motion signals at the appropriate
depths in MT via V2-to-MT signals. In another, motion signals in MT 
disambiguate locally
incomplete or ambiguous boundary signals in V2 via MT-to-V1-to-V2 
feedback. The third
functional property concerns resolution of the aperture problem along 
straight moving contours
by propagating the influence of unambiguous motion signals generated 
at contour terminators or
corners. Here, sparse "feature tracking signals" from, e.g., line 
ends, are amplified to overwhelm
numerically superior ambiguous motion signals along line segment 
interiors. In the fourth, a
spatially anisotropic motion grouping process takes place across 
perceptual space via MT-MST
feedback to integrate veridical feature-tracking and ambiguous motion 
signals to determine a
global object motion percept. The fifth property uses the MT-MST 
feedback loop to convey an
attentional priming signal from higher brain areas back to V1 and V2. 
The model's use of
mechanisms such as divisive normalization, endstopping, 
cross-orientation inhibition, and long-range
cooperation is described. Simulated data include: the degree of 
motion coherence of
rotating shapes observed through apertures, the coherent vs. element 
motion percepts separated
in depth during the chopsticks illusion, and the rigid vs. non-rigid 
appearance of rotating ellipses.

Keywords: motion perception, depth perception, perceptual grouping, 
prestriate cortex, V1, V2,
MT, MST