Examination of apparent extent as an explanation of the Poggendorff effect

Abstract

The explanation of apparent misalignment in the Poggendorff figure, based on underestimation of the intertransversal distance, was investigated in two experiments. In Experiment 1, subjectsjudged the intertransversal distance in the traditional Poggendorfffigure and two of its variants. The size of the acute angle and the intertransversal distance were manipulated. Half of the subjects made the judgments with the method used by Wilson and Pressey (1976) and the other half made their judgments with the method used by Greist-Bousquet and Schiffman (1981). The results indicated that perceived intertransversal distance was greater with the former method. In Experiment 2, subjects adjusted the transversals to apparent collinearity in the same displays as were used in Experiment 1. The collinearity judgments were transformed to allow comparison with the results of Experiment 1. Comparison of the collinearity judgments with the distance judgments indicated that they did not follow similar trends. For each Poggendorff variant, proportional distance judgments increased as the size of the acute angle increased, and decreased as the intertransversal distance increased. Collinearity judgments did not vary as a function of intertransversal distance. As the size of the acute angle increased, collinearity judgments increased for two of the Poggendorff variants but decreased for the third. It was concluded that the findings did not support the explanation of apparent misalignment based on underestimation ofthe intertransversal distance.The traditional Poggendorff figure, as seen in Figure lA, consists of a transversal separated by two vertical parallel lines. Although the two portions of the transversal are objectively collinear, subjectively they do not appear so. In the example shown in Figure lA, the upper right transversal is judged higher than the linear extension of the lower left transversal. This apparent misalignment of the transversals is referred to as the Poggendorff effect.Judd (1899) was one of the first investigators to discard the popular belief that the Poggendorff effect was one of direction and instead proposed that it was caused by a misjudgment of linear extent or distance. Specifically, Judd suggested that the perceived noncollinearity of the transversals was due to underestimation of the intertransversal distance. The underestimation, according to Judd, was caused by the influence of the components of the Miiller-Lyer figure found within the Poggendorff display. As seen in Figures lB and lC By studying these variations of the Poggendorff figure, Judd (1899) discovered that the wings-in variation resulted in a stronger effect than the wings-out variation. Because This research is based on a Master's thesis submitted to the University of New Brunswick by M. T. Trueman.

Common factors versus uncommon variability in comparisons of the Poggendorff and Müller-Lyer illusions

“…*Converted to intertransversal extent (see Weintraub & Krantz , 1971 Despite this research on the relationship between the Poggendorff and Miiller-Lyer illusions and controversy regarding a common causal basis in these illusions (e.g. , Day , Jolly , & Duffy, 1987;Trueman & Wilson , 1989), it must be stressed here that we have consistently encountered differences in the variability of the two illusory effects. In the correlational study noted above, the variability in the responses to the wings-in and wings-out MullerLyer figures was substantially greater than the variability observed for Poggendorff alignment judgments (see Table 1).…”

The logic of misperceived distance (or location) theories of the Poggendorff illusion

“…Greist-Bousquet and associates (e.g., Greist-Bousquet & Schiffman, 1981, 1985Greist-Bousquet, Schiffman, Dorsett, & Davis, 1989a) have been actively promoting a distance-misperception hypothesis grounded on the Milller-Lyer (arrowhead) display, arguing that misperception of the distance between the arrowheads is applicable to the Poggendorff display. They have been challenged by Trueman and Wilson (1989) and Day, Jolly, and Duffy (1987). Some years ago, my decision was to reject a parallels-attract version of the distance-misperception hypothesis .…”

“…(The two physical distances, each with an associated perceived distance must be distinguished; cf. Trueman & Wilson, 1989). Greist-Bousquet and Schiffman (1981), Trueman and Wilson (1989), and Weintraub and Tong (1974) have employed a dot-setting task that permits the observer to set the distance and orientation between a pair of free-standing dots to match perceptually the intertransversal slant distance and direction in a Poggendorff display.…”

“…Trueman & Wilson, 1989). Greist-Bousquet and Schiffman (1981), Trueman and Wilson (1989), and Weintraub and Tong (1974) have employed a dot-setting task that permits the observer to set the distance and orientation between a pair of free-standing dots to match perceptually the intertransversal slant distance and direction in a Poggendorff display. Wilson and Pressey's (1976) method precludes perceived orientation judgments by requiring all dot settings to be oriented horizontally.…”

Illusion decrement and transfer of illusion decrement in obtuse- and acute-angle variants of the Poggendorff illusion

“…For example, Finlay and Caelli (1975) and Wilson and Pressey (1976) reported overestimation of interparallel extent. Recently, Trueman and Wilson (1989) found that apparent alignment judgments and judgments of intertransversal distance did not follow similar trends, and others (Day, Jolly, & Duffy, 1987;Wenderoth & O'Connor, 1987) In this experiment, the magnitude of the Poggendorff illusion was monitored at I-min intervals over a 5-min period. The primary issue investigated here was whether or not inspection of the obtuse-and the acute-angle Poggendorff variants differentially affected the magnitude of the Poggendorff illusion over the 5-min inspection period, as might be expected from Greist-Bousquet and Schiffman's apparent distance theory.…”