ABSTRACT
In the widely known visual illusion called the Hermann grid, perceptual ‘smudges’ appear on the intersections of a white grid superimposed on a black background or on the intersections of a black grid superimposed on a white background (Brewster, 1844; Hering, 1920; Hermann, 1870). The Hermann grid is a staple for introductory psychology and perception textbooks and is one of the most frequently investigated visual illusions (e.g. Baumgartner, 1960; Geier et al., 2004, 2008; Hamburger et al., 2012; Jung and Spillmann, 1970; Levine et al., 1980; Oehler and Spillmann, 1981; Spillmann, 1971; Spillmann and Levine, 1971; for an overview see Schiller and Carvey, 2005 or Spillmann, 1994). Spillmann and Levine (1971) produced an ingenious display for investigating the contrasts of the grid's vertical and horizontal bars with respect to the background.
