A neuromorphic recurrent model for figure - ground
segregation of coherent motion
W H A Beaudot (CSEM--Centre Suisse d'Électronique et de Microtechnique SA, Jaquet-Droz 1, CH 2007, Neuchâtel, Switzerland; e-mail: ; WWW: http://wbeaudot.kybervision.net)
A neuromorphic model of the retino-cortical motion processing stream is proposed which incorporates both feedforward and feedback mechanisms. The feedforward stream consists of motion integration from the retina to the MT area. Retinal spatiotemporal filtering provides X-like and Y-like visual inputs with band-pass characteristics to the V1 area (Beaudot, 1996 Perception25 Supplement, 30 - 31). V1 direction-selective cells respond to local motion resulting from nonlinear interactions between retinal inputs. MT direction-selective cells respond to global motion resulting from spatial convergence and temporal integration of V1 signals. This feedforward stream provides a fine representation of local motion in V1 and a coarse representation of global motion in MT. However, it is unable to deal with the aperture problem.
Solving this problem requires the adjunction of local constraints
related to both smoothness and discontinuity of coherent motion, as well
as some minimisation techniques to obtain the optimal solution. We propose
a plausible neural substrate for this computation by incorporating excitatory
intracortical feedbacks in V1 and their modulation
by reciprocal connections from MT. The underlying enhancement
or depression of V1 responses according to the strength of MT responses
reflects changes in the spatiotemporal properties of the V1 receptive
fields. This mechanism induces a dynamic competition between local and
global motion representations in V1. On convergence of these dynamics,
responses of V1 direction-selective cells provide
a fine representation of `true' motion, thus solving the aperture problem
and allowing a figure - ground segregation based on coherent
motion. The model is compatible with recent anatomical, physiological,
and psychophysical evidence [Bullier et al, 1996 Journal de
Physiologie (Paris) 90 217 - 220].
© 1997 CSEM S.A.