Academic journal article North American Journal of Psychology

Color and Saturation Effects on Perception: The Hermann Grid

Academic journal article North American Journal of Psychology

Color and Saturation Effects on Perception: The Hermann Grid

Article excerpt

The Hermann Grid is a visual illusion developed in 1870 by Ludimar Hermann. The traditional layout of the grid consists of black squares superimposed on a white background in a grid formation (Figure 1). Most people report seeing a fuzzy dot (also called an "illusory dot"or ID) at the intersections of the white bars that separate the squares. The purpose of this study is to determine if color and saturation affect the perception of the ID using the Hermann Grid.

Much of the previous research that has been conducted on the Hermann Grid has focused on developing an explanation for the perception of the ID that occurs when one looks at the grid (Schiller & Carvey, 2005). Oehler and Spillman (1981) attribute the primary explanation of the Hermann Grid to Baumgartner in 1960. Baumgartner claimed perception of the ID was the result of lateral inhibition in the receptive fields of ganglion cells. A visual receptive field is the portion of the visual field that must be stimulated for a given neuron to fire. These fields are typically circular, composed of an inner circle and an outer ring. The response to stimulation of the inner circle is the opposite of the response to stimulation of the outer ring, so that an "on-center/off-surround" receptive field sends an excitatory response with stimulation of the inner circle and an inhibitory response to stimulation of the outer ring. In an "off-center/on-surround" an inhibitory response would be sent to the ganglion cell layer in response to stimulation of receptors in the center of the field, and an excitatory response would be sent when the surrounding ring is stimulated. Lateral inhibition is a competitive interaction between the center and the surround part of the receptive field. Perception can be complicated by simultaneous stimulation of both center and surround, such as what occurs when you look at the intersection of the white bands of the Hermann Grid. At the intersection of the white bands the inhibitory surround of an on-center/off-surround receptive field receives more inhibition than does the excitatory center of the field. This results in the perception of a "less-than white" (grey) dot at the intersection of the bars. Away from the intersection of the white bars, the inhibitory surround receives less stimulation than does the excitatory center, resulting in the perception of a white bar (see Figure 2). Goldstein (2010) provides an excellent description both of the organization of retinal receptive fields and of lateral inhibition (pages 45-47).

[FIGURE 1 OMITTED]

Several recent studies have suggested that Baumgartner's explanation of the illusion as dependent on lateral inhibition in the retina is not supported by the data (Cox, Ares-Gomez, Pacey, Gilchrist & Mahalingam, 2007; Schiller & Carvey, 2005; Vergeer & van Lier, 2010). Altering the straightness of the lines of the grid (Geier, Bernath, Hudak & Sera., 2004), and the orientation of the grid (De Lafuente & Ruiz, 2004) do not change the amount of lateral inhibition in the signal and so ought not to affect the perception of the ID, yet both manipulations of the grid eliminate the illusion. Increasing the size of the grid (Schiller & Carvey, 2005) and adding diagonal white lines cross the squares of the grid (Lingelbach, Block, Hatzky & Reisinger (1985) cited in Schiller & Carvey, 2005) increase the amount of lateral inhibition and so ought to increase the apparent darkness of the ID, yet neither manipulation does so, and adding the diagonal line actually eliminates the illusion for most viewers.

[FIGURE 2 OMITTED]

Researchers have also examined the role of color with regard to the perception of the Hermann Grid. Oehler and Spillman (1981) investigated color in the Hermann Grid by changing the color of the bars and background. The researchers found that the strongest illusion occurs when the bars and the background were the same color. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.