Figure 7. Cartoon of a conceptual model of columnar processing of border ownership, supported by our data.

Two columnar structures are shown, each of which responds to vertical edges in the classical receptive field (cRF), but they have opposite preferred sides of border ownership (indicated by the direction of the arrows on the units in the columns, and by the symbol below each column). Such columns may or may not be adjacent. The earliest occurrence of border ownership selectivity in the deep layers is symbolized by the positon of deep layer units near the left edge of the column. Light and dark gray arrows indicate where different types of stimulus information likely arrive first. Stimulus information in the cRF (gray edge) arrives first in the granular layer. Deep layer neurons may first compute border ownership selectivity by integrating this information with contextual information that arrives in superficial and deep layers, possibly provided by corticocortical feedback and horizontal connections. The content of these context signals is necessarily asymmetric to result in border ownership preference, and different for the two columns shown (indicated by the symbols above the columns). Because of their prominence in deep layers, early border ownership signals may be part of the feedback that projects from V4 to upstream areas (e.g., V2), and to subcortical targets, such as the superior colliculus (black arrows). Later on during the response, after border ownership signals have first been established in V4, the feedforward input from V2 to V4 likely also contains border ownership signals, since roughly half of V2 units are selective for border ownership (Zhou et al., 2000).