On a changing perspective illusion within Vermeer's The Music Lesson.

The effect of line of sight on the perception of spatial configuration has been investigated in a well-known painting (The Music Lesson by Vermeer) and in two control patterns. In experiment 1, subjects indicated the perceived inclination of two major contours which defined the sidewall-floor and backwall-floor joints in (i) a projected image of the painting, (ii) a three-line representation of the major spatial elements of the painting, and (iii) a three-dimensional wire model of these same contours, when standing in each of eighteen positions on a line running parallel to the surface of the screen. Results indicated a significant change in the perception of the sidewall-floor, but not of the backwall-floor contour, as viewing angle changed, in both the painting and the three-line representation. However, the angular setting in the latter case was significantly less than when the painting was used, ie subjects underestimated the depicted inclination. Settings for the wire model did not deviate with viewing angle and reflected geometrically correct adjustments. In experiment 2, the results of experiment 1 were confirmed using enantiomorphs. These findings are discussed in the light of other view-dependent illusions in paintings.