The Rod-and-Frame Effect: The Whole is Less than the Sum of its Parts

Since the discovery of the influence of the tilted frame on the visual perception of the orientation perceived as vertical (VPV), the frame has been treated as a unitary object—a Gestalt. We evaluated the effect of 1-line, 2-line, 3-line, and 4-line (square frame) stimuli of two different sizes, and asked whether the influence of the square frame on VPV is any greater than the additive combination of separate influences produced by the individual lines constituting the frame. We found that, for each size, the square frame is considerably less influential than the additive combination of the influences of the individual lines. The results conform to a mass action rule, in which the lengths and orientations of the individual line components are what matters and the organization of the lines into a square does not—no higher-level Gestalt property is involved in the induction effect on VPV.

Large Errors in the Perception of Verticality are Generated by Luminance Borders (Integrated across Space) Not by Subjective Borders

The rod-and-frame illusion shows large errors in the judgment of visual vertical in the dark if the frame is large and there are no other visible cues (Witkin and Asch, 1948 Journal of Experimental Psychology38 762–782). Three experiments were performed to investigate other characteristics of the frame critical for generating these large errors. In the first experiment, the illusion produced by an 11° tilted frame made by luminance borders (standard condition) was considerably larger than that produced by a subjective-contour frame. In the second experiment, with a 33° frame tilt, the illusion was in the direction of frame tilt with a luminance-border frame but in the opposite direction in the subjective-contour condition. In the third experiment, to contrast the role of local and global orientation, the sides of the frame were made of short separate luminous segments. The segments could be oriented in the same direction as the frame sides, in the opposite direction, or could be vertical. The orientation of the global frame dominated the illusion while local orientation produced much smaller effects. Overall, to generate a large rod-and-frame illusion in the dark, the tilted frame must have luminance, not subjective, contours. Luminance borders do not need to be continuous: a frame made of sparse segments is also effective. The mechanism responsible for the large orientation illusion is driven by integrators of orientation across large areas, not by figural operators extracting shape orientation in the absence of oriented contours.

Frame-of-Reference and Hierarchical-Organisation Effects in the Rod-and-Frame Illusion

Two hypotheses proposed as alternatives by Rock—frame of reference and hierarchical organisation of perception—were tested in a series of experiments with the use of the rod-and-frame illusion. This illusion produces errors in the apparent vertical due to the presence of a tilted frame surrounding the test rod. The apparent vertical is shifted in the direction of the frame tilt. When an upright square was added inside the tilted frame, rod-setting errors varied according to the visual characteristics of the display. In the case of a large display presented in the dark (experiment 1), there continued to be large errors in the direction of the outer-square tilt. This finding supports the frame-of-reference hypothesis, which proposes that the orientation of all objects in the visual field is dominated by the most peripheral reference. In the case of a small display presented in a lit environment (experiments 2 and 3), the direction of errors was the opposite. This latter finding was taken to indicate that the rod was set with reference to the perceived tilt of the inner upright square. Thus, according to a hierarchical-organisation hypothesis, the orientation of an object in the visual field is influenced by objects in the immediate surroundings not by outermost reference. Overall, the results confirm the presence of two qualitatively different classes of orientational phenomena: one is concerned with the definition of egocentric coordinates and one with an object-centred visual representation.

Field Dependence and Distraction Revisited

An attempt is made to replicate a former study of the relationship of field dependence as measured by rod-and-frame errors to distraction in an RT paradigm. For two groups of Ss ( n = 14) who differed specifically in their dependence upon the tilted frame and were classified as frame-dependent and frame-independent, no relationship of frame (or field) dependence to susceptibility to distraction was found.