Columnar Processing & Feedback Involved in Border Ownership in V4 of the Macaque Visual Cortex

Article: Which side is which?: How the brain perceives borders
Source: Salk Institute
Published: November 30, 2021 

Rubin’s vase optical illusion illustrating
different interpretations of object borders

To interpret a visual scene, the brain must differentiate object from background. It does so by deciphering borders. Neuroscientists at the Salk Institute are studying how neurons assign border ownership. Individual neurons in the brain's visual cortex only receive information about a minuscule region of a scene. As such, neurons that receive information at the border of objects do not have information about the overall context of the scene. Yet, researchers have discovered sets of neurons that specifically signal border ownership, that is, which side of the border belongs to the object. Some scientists have hypothesized a feedforward mechanism, wherein successively more complex computations are added as visual information travels from the retina into increasingly higher-order areas of the brain, until the brain builds an overall interpretation of the visual scene. Other scientists emphasize the importance of feedback mechanisms, in which downstream areas of the brain process some of the information before sending clues to upstream brain areas to facilitate deciphering borders. The present study sought to determine which hypothesis was correct.

The researchers used multielectrode probes to investigate different layers of area V4 of the macaque visual cortex as the monkeys views squares on blank backgrounds. The authors report, "We find that border ownership selectivity occurs first in deep layer units," which lends evidence to feedback pathways being involved. They also observed a columnar selectivity for borders, such that neurons stacked in the same vertical penetration (by the probe), through multiple horizontal layers, shared the same border ownership preference. Some columns preferred scenes where the left side of the border was the object and other columns preferred scenes where the right side was the border of the the object, suggesting a systematic organization. The authors conclude, "Together our data reveal a columnar organization of border ownership in V4 where the earliest border ownership signals are not simply inherited from upstream areas, but computed by neurons in deep layers, and may thus be part of signals fed back to upstream cortical areas or the oculomotor system early after stimulus onset." They next plan to investigate how information conveyed by feedback contributes to the processing of borders, perhaps aiding in brain disorders where perception is distorted.

My rating of this study: ⭐⭐⭐

Franken TP and Reynolds JH. "Columnar processing of border ownership in primate visual cortex." eLife.  10:e72573. 30 November 2021. https://doi.org/10.7554/eLife.72573