Nonveridical Perception

Visual Misperceptions

In a visual illusion, the observer may perceive a visual object or scene that is different from the veridical one. Alternatively, the observer may perceive an object that is not physically present, or fail to perceive an object that is extant in the world. In the scintillating grid illusion (a type of brightness illusion; Figure 1), the subject perceives an illusory darkening of veridical white circles at the intersections of a grid.

Another well-known visual illusion is the perception of apparent movement. In this illusion, one object turns off while another object, in a separate spatial location, turns on. The perception is of a moving object that travels from the location of the first object to that of the second object. Movie marquees and motion pictures are practical applications of this principle.

Size illusions exemplify the importance of context in visual perception. In the Ebbinghaus illusion, a central circle will appear larger or smaller depending on the size of the circles surrounding it (the central circle will look large when the surrounding circles are small, and vice versa).

Figure 1 The Scintillating Grid Illusion

Source: Modified from Schrauf et al., 1997.

Notes: As you move your gaze around the image, observe the white circles on the intersections of the grey bars. Illusory dark dots seem to appear and disappear on top of the white circles, except for the one that you focus your gaze on at any given time.

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