Equiluminant Border Ownership Cells as a Missing Link in Color Form Perception

We propose the existence of a sub-population of border ownership neurons that signal figure side along equiluminant borders, those defined purely by color contrast. We postulate that these neurons, similar to primate equiluminant V1 [26] and V4 [5] cells, are strongly activated by equiluminant contrast on their preferred side, with diminished response for strictly luminance contrast. To test this hypothesis, we propose a hierarchical and mechanistic model that explains how equiluminant border ownership signals can be achieved in the ventral stream. Our simulation results suggest that model equiluminant neurons are highly color-selective while exhibiting similar orientation and border ownership selectivity as their luminance counterparts. Additionally, our model equiluminant cells indeed exhibited the above postulated pattern of responses. We suggest that these neurons are the missing links in the equiluminance channels in the ventral stream that transform equiluminant oriented edge signals in V1 to equiluminant object-centered shape representations in V4. Our findings point to the importance of re-examining the border ownership neuron population to further detail their role in equiluminant channels in the ventral stream.