The document summarizes research investigating the role of GABA in visual processing in the retina. It finds that: 1) Horizontal cells in the retina help produce high contrast vision through a complex exchange of chemicals with photoreceptors and bipolar cells. 2) Experiments on isolated catfish horizontal cells found that applying GABA sometimes caused an increase in extracellular acidity and sometimes an alkalization, likely through GABA receptors and transporters on the cells. 3) It is proposed that GABA regulation of pH involves cell depolarization opening calcium channels, increasing intracellular calcium and triggering a calcium pump that moves protons out of the cell.