Spiking Bipole Cells
This model attempts to illustrate how visual grouping is performed in a network of spiking layer 2/3 cortical cells. The network topology is based on the bipole circuit present in LAMINART models. Individual model cells consist of two compartments governed by Hodgkin-Huxley equations. The model is shown to perform stable grouping and also to account for a range of relevant single-cell recording profiles.
Perceptual grouping is a process through which object features distributed over the visual field are bound together into coherent object representations. This process is well illustrated in illusory contour stimuli such as the Kanizsa square in Figure 1. Here grouping is evidenced by the fact that the percept of a white surface emerges as a result of signals coming from the four corner inducers.
Figure 1 The percept of a square surface emerges from the grouping of the pacman figures. A layer 2/3 cell (blue ellipse) performs the grouping of signals coming from colinear complex cells placed outside of its classical receptive field.
The BCS/FCS and related LAMINART models postulate that grouping is performed by oriented cells in layer 2/3 of visual cortex that respond to collinear inputs outside of their classical receptive field (Grossberg and Mingolla, 1985). These cells combine cooperating collinear inputs from two sides, as illustrated in Figure 1, where one such cell (blue ellipse) is seen to receive signals from neighboring complex cells (indicated in red).
The bipole property Left) Network representation for a luminance defined boundary contour. Right) Network representation for an illusory contour. In this case, there is inward completion but no outward propagation. This is the bipole property.
The current project extends LAMINART by incorporating Hodgkin-Huxley spiking dynamics in simulated cells. This imposes much more biologically plausible temporal constraints on the model than had been done previously. It also makes possible the comparison of network output with single-cell recordings and the study of synchrony in visual grouping.
Figure 2 shows the firing rate of model cells when the input stimulus is either a real contour (left) or an illusory contour (right). In both cases, layer 2/3 cells form a coherent contour representation, that is, they perform visual grouping. This response is sensitive to stimulus contrast and spatial extent.
This research is supported in part by
Selected Publications
Léveillé J. Grossberg, S., Mingolla, E. and Versace, M. (2008). Perceptual grouping in a spiking laminar cortical model. VSS2008, Naples
