The Hermann grid is a visual illusion developed by Ludimar Hermann in 1870. The original arrangement of the illusion consists of black squares superimposed on a white background. The illusory effect reported by most people is the appearance of faint gray dots at the intersections of the white bars separating the black squares. Many psychologists attribute the explanation of the illusory effect created by the Hermann Grid to a psychologist named Baumgartner in the 1960s. Baumgartner argued that the perception of the faint gray dot was the result of lateral inhibition in the receptive fields of ganglion cells (Blatchley and Moses, 2012). A visual receptive field is the portion of the visual field that allows a given neuron to fire when stimulated. These receptive fields are composed of an inner circular ring and an outer circular ring. The inner ring response is the opposite of the outer ring, whereby an on-center/off-surround receptive field sends an excitatory response with stimulation of the inner ring and an inhibitory response with stimulation of the outer ring ( Blatchley and Moses, 2012). Lateral inhibition is an interaction between the center (inner ring) and the surrounding part (outer ring) of the receptive field (Blatchley and Moses, 2012). Within the Hermann Grid, at the intersections of the white bars, the inhibitory contour of an on-center/off contour in the receptive fields receives more inhibition than the excitatory center of the receptive field, thus creating the perception of faint gray spots (Blatchley and Moses, 2012). This theory proposed by Baumgartner has also been called the “retinal ganglion cell theory” (Schiller and Carvey, 2005). While the retinal ganglion theory has... middle of paper... Baumgartner, as the explanation of the illusory effect created by Hermann's grid was considered the most plausible explanation. Schiller and Carvey (2005), through a series of analytical observations, provided evidence for why the retinal ganglion cell theory is a weak explanation for the illusion. Their research, along with others, sought to refute the untenability of Baumgartner's theory by examining the theory's lack of explanation for several key aspects that influence the perception of the Hermann grid illusion; size, orientation (De Lafuente and Ruiz, 2004), grid manipulation (Levine and McAnany, 2008), color (Blatchley and Moses, 2012) and spatial arrangement (Cox et al., 2007). Each of these aspects has taken aim at the validity of the retinal ganglion cell theory and suggested that there is a possibility that a new explanation will arise and be discovered..