Interaction space of Müller-Lyer with filled-unfilled illusion: An explanation of Müller-Lyer asymmetry

Abstract

The filled-unfilled space illusion was investigated as a possible explanation for the asymmetry (difference in strength) between tails-out and tails-in versions of the Miiller-Lyer illusion. Previous work has shown that removal ofthe horizontal shaft makes both configurations look shorter, but affects them unequally and only partially reduces the asymmetry. In two experiments, illusion strength was varied by use of either different tail lengths or single-vs. double-ended figures. Subjects used method of adjustment with stimuli presented by computer. When the Miiller-Lyer was sufficiently weak, shaft removal had equal effects on both tails-in and tails-out configurations, but less effect on plain lines. This produced a reversal of the usual asymmetry, that is, tails-in was stronger than tails-out. It is concluded that the asymmetry is caused by the filledunfilled illusion. This may require reassessment of the view that the two Miiller-Lyer versions are different illusions.As early as 1909, Lewis argued that the Miiller-Lyer illusion could not be explained by any single principle. This view is now supported by a variety of studies, which have found differences between the tails-out and tails-in versions of the illusion. Of these, the best known difference is an asymmetry of strength. When tested separately, the tails-out (long) version is almost always stronger than the tails-in (short) version. In addition, the tails-out and tails-in versions respond differently to changes in such variables as the angle between shaft and tail, distance between tail tips (Sekuler & Erlebacher, 1971), and viewing duration (Erlebacher &Sekuler, 1974;Pollack, 1964). Finally, the two versions also respond differently to amputation of one or more of the tails (Day & Dickinson, 1976;Greist-Bousquet & Schiffman, 1981). Sekuler and Erlebacher noted that such differences are not easily handled by any single theory. They recommended that the two versions of the Millier-Lyer be treated as separate illusions.A slightly different strategy is to analyze the multiple causes of the illusion in such a way that factors responsible for the differences between versions can be separated from those that contribute similarly to both versions. The present study pursues this strategy by searching for the factor or factors that cause the asymmetry of strength.The most promising lead comes from Cooper and Runyon (1970), who reported that elimination of the horizontal shaft connecting the two sets of tails causes a I thank David Dexter and the Alma College Computer Center for technical support, Douglas Boyne and Steve Neff for help with data collection, and Carol Slater for a critique of the writing. Requests for reprints may be sent to Walter Beagley, Department of Psychology, Alma College, Alma, MI48801. 45 reduction in the strength of the tails-out illusion and an increase in the strength of the tails-in version. Although they did not include a plain-line control from which to measure asymmetry, the direction of change they reported should produce a reduc...

Evaluating Müller-Lyer effects using single fin-set configurations

“…The overall magnitude of the metric distortion was reduced with these configurations, but they still observed contraction for concave versions and expansion for convex versions. Similar results were reported by Beagley (1985) and Greist-Bousquet and Schiffman (1981 b). In the work that follows, we have studied whether the distortion differs when the shaft is present or absent and describe this as a manipulation of"shaft state.…”

A quantitative analysis of illusion magnitude predicted by several averaging theories of the Müller-Lyer illusion

“…It has been reported that asymmetries in the data may be partly due to a methodological artifact of the standard or control line (Beagley, 1985;Christie, 1975; see also Adam & Bateman, 1980), to the different spatial locations of the contextual stimuli in the two ML forms (Pressey & Smith, 1986), or to differences in attention between the two ML forms (Pressey & Pressey, 1992). Indeed it has been suggested that a single mechanism underlies the apex-in and apex-out ML illusion (Brigell & Uhlarik, 1979;Jordan & Uhlarik, 1986;Worrall & Firth, 1974).…”

A continuously lit stimulus is perceived to be shorter than a flickering stimulus during a saccade

“…The former is referred to as filled space, and the latter as unfilled space. This phenomenon is referred to as an illusion of filled-unfilled space or an illusion of interrupted distance (Beagley, 1985;Lewis, 1912). If a line works as the unfilled space, the perceptual system of the phantom array or line could be identical to the function underlying the illusion of filled-unfilled space.…”