The role of structural components in the Mueller-Lyer illusion

In order to assess the role of the structural components of the Mueller-Lyer illusion, subjects reproduced the central extent of standard Mueller-Lyer figures and configural variations. Illusory magnitude of the underestimated wings-in and overestimated wings-out figures was examined with selective amputations of the oblique wings and central line segment (shaft). Variations were presented at 0, 45, 90, and 135 deg from vertical. Orientation had no reliable effect on illusory magnitude. Elimination of the shaft effected a decrease in the apparent extent for all variations, presumably due to the addition of the filled-unfilled space illusory effect to the standard Mueller-Lyer effect. A second study corroborated this finding The decrease in apparent extent consequent to shaft removal occurred independently of any response factor. Selective wing removal differentially decreased the illusory magnitude of the standard Mueller-Lyer figures; this was discussed with regard to a dual-illusion hypothesis. Finally, variations that contained no intersecting lines produced a significant illusion in the direction of the standard Mueller-Lyer figures, suggesting the involvement of higher level, nonperipheral distortion mechanisms.     

A Mueller-Lyer illusion induced by selective attention

Subjects estimated the length of a horizontal line which was flanked by oblique angles pointing both inside and outside (this figure would be created by superimposing the wings-in and wings-out figures of the Mueller-Lyer illusion). Ignoring the outside wings resulted in an underestimation of the line length of comparable magnitude to that obtained for the wings-in Mueller-Lyer figure. Ignoring the inside wings caused an overestimation of the line length only when the inner and outer wings were of non-corresponding orientations. These results emphasize the role of cognitive factors in the Mueller-Lyer illusion.     

Morinaga’s paradox and figure-ground organization

Morinaga’s paradox of displacement is constructed by setting several copies of the two Mueller-Lyer figures one above the other. The Mueller-Lyer illusion is that the wings pointing out seem farther apart than wings pointing in, and Morinaga’s paradox is that when one looks down a column of wings pointing alternately one way and the other, they appear misaligned but in the opposite direction from the Mueller-Lyer illusion. The hypothesis of this paper is that the subject, under instructions to align the vertical array of wings, sets up a vertical figure-ground organization different from that used in judging the horizontal distance between wings, and that the two illusions are contingent upon the two organizations. The experiment showed that Morinaga’s paradox occurs when only one column of wings is shown, in agreement with the figure-ground hypothesis, and also shows that Morinaga’s paradox disappears when short line segments are introduced which disrupt the vertical figure-ground organization.     

An increase in strength of tilt aftereffect associated with tryptophan depletion

The effects of a tryptophan-free amino acid mixture on tilt aftereffect, movement aftereffect, and the Mueller-Lyer illusion were studied. 12 male subjects ingested either a balanced amino acid mixture or a tryptophan-free mixture which causes a marked depletion of brain tryptophan and serotonin. The tryptophan-free mixture significantly increased the strength of tilt aftereffect but had no effect on movement aftereffect or the Mueller-Lyer illusion. These results were discussed with reference to the pharmacological activity of serotonin and its influence on the strength of lateral inhibition in mammalian brains.     

The hydra-headed Mueller-Lyer effect: A theoretical puzzle

Three experiments were conducted to examine the effects of multiple fins on the magnitude of the Mueller-Lyer illusion. All studies showed that the multiple form of the elongation illusion was greater than the average of the components and that the multiple form of the shrinkage illusion was smaller than either of the components. The pattern of results failed to support either simple addition models or more complex averaging theories of illusions. A cross-attribute summation hypothesis and a filled space hypothesis were proposed as possible explanations for the results.     

Differentiation and decrement in the Mueller-Lyer illusion

Two experiments were conducted to test the hypothesis that decrement of the Mueller-Lyer illusion with inspection is due to learning to differentiate the test element from the accessory lines. In one experiment, the test element is predifferentiated for the observer by means of configurational variations and in the other by restriction of attention. Although the initial magnitude of the illusion is found to be inversely proportional to the amount of predifferentiation, the slopes of the decrement curves are not affected.     

A mathematical theory of optical illusions and figural aftereffects

If it is assumed that spurious enhancement of receptive field excitations near the intersection of image lines on the retina contributes to the cortical determination of the geometry of two-dimensional figures, an equation based on the least-squares fit of data points to a straight line-can be obtained to represent theapparent line. Such a fit serves as anextreemum on the precision with which a data set can be represented by a straight line. The disparity between theapparent line and the actual line that occurs in the case of peripheral (and to a lesser degree in more central regions of the retina) vision is sufficient to produce the perceptual errors that occur in the Poggendorff, Hering, and Mueller-Lyer illusions. The magnitude of the Poggendorff illusion as a function of the line angle is derived and experimentally tested. Blakemore, Carpenter, and Georgeson’s (1970) experimental data on angle perception are shown to fit this same function. Theapparent curve is derived for the Hering illusion. The Mueller-Lyer illusion is found to be a variation of the Poggendorff illusion. The equations are further developed and used to derive Pollack’s (1958) experimental results on figural aftereffects. The results involve onlyone experimentally determined coefficient that can be evaluated, within the limits of experimental error, in terms of physiological data. The use of these concepts provides a foundation for the abstract modeling of the initial phases of the central nervous system data reduction processes, including receptive field structure, that is consistent with the physiological limitations of the retina as a source of visual data, as well as with the findings of Hubel and Wiesel (1962).     

A comparison of five methods of illusion measurement

The relative efficiency of five techniques of illusion measurement were tested on parametric variations of the Mueller-Lyer and Ebbinghaus figures. The methods of average error, reproduction, and selection from a graded series all showed significant effects of configurational variations. The subjective scaling techniques each failed to measure adequately changes in illusion magnitude for one illusion configuration. The suitability of the tested measures for group administration is also discussed.     

Mueller-Lyer decrement: practice or prolonged inspection?

Noting the similarity between the illusion decrement and selective adaptation paradigms, Long has challenged the view that illusion decrement effects reflect a strategic--as opposed to a structural--underlying mechanism, and has called for further research on this issue. To investigate the confound between prolonged free inspection and repeated trials in the standard decrement procedure, the effects of three inspection conditions (continuous, intermittent, and immediate) on the magnitude of the overestimation Mueller-Lyer illusion have been assessed under two levels of trials (a total of two or six judgments). Significant illusion decline was found only under conditions of repeated trials, with either continuous or intermittent inspection. These findings do not support the predictions of purely structural theories (including neural adaptation and efferent readiness theories), according to which degree of decrement should be determined solely by viewing time. Instead, the data demonstrate that illusion decrement is a product of practice, providing converging evidence for the view of decrement as involving a cognitive 'recalibration' or learning process.     

The case for misapplied constancy scaling: depth associations elicited by illusion configurations

It has been suggested that many visual-geometric illusions arise from inappropriate evocation of size-constancy by depth cues implicit in illusion configurations. Observers gave free association responses while viewing illusion figures. Analysis of these responses provides weak but consistent evidence for the elicitation of depth in the Sander parallelogram, Mueller-Lyer, Zoellner, and Ehrenfels variant of the Ponzo illusion. No evidence for depth is found in the normal form of the Ponzo, Poggendorff, and horizontal-vertical illusions, and the evidence is ambiguous in the Orbison configurations. These results indicate that depth processing may be evoked by some, but not all, classical illusion forms.     

Altering Mueller-Lyer illusion magnitude using figural additions at the wing-shaft intersections

The Mueller-Lyer (ML) illusion has been used to study the way in which perceived length is affected by processes of information extraction when a visual target of interest (the ML shaft) is surrounded by other nontarget figural elements (inward-or outward-turning wings). It is argued that the perception of length is computed in terms of the center of gravity or centroid of figural elements at the wing-shaft intersection. The outward-turning wings shift the computational centroid away from the shaft end, giving rise to an erroneous overestimation of shaft length, while the inward-turning wings have the opposite effect. In three experiments, we observed that figural changes, which theoretically shifted the center of gravity of figural elements at the wing-shaft intersection, also increased or decreased the magnitude of the ML illusion.     

Communication deviances in parents of schizophrenics

In an attempt to make a multimethod assessment of communication deviance in parents of schizophrenics, a communication conflict situation (CCS) and the TAT were used to obtain qualitative and quantitative measures of communication for a sample of 50 parental couples, 21 of which were parents of schizophrenics, 9 were parents of nonpsychotic psychiatric patients, and 20 were parents of normals. The results were a general confirmation of earlier reports that communication deviance is an outstanding characteristic in families with a schizophrenic offspring. The most important finding, however, was that parents of paranoid and nonparanoid schizophrenics score very differently on a majority of the communication variables. Parents of nonparanoid schizophrenics form one extreme on a continuum of communication deviance, and parents of paranoid schizophrenics and normals the other. Egocentrism, measured by CCS, turned out to be the single qualitative variable with best discriminating power across all groups.     

The Draw-A-Person Test and Process-Reactive Schizophrenia

The Draw-A-Pcrson test was administered to three matched groups of 32 male Ss each: reactive schizophrenics, process schizophrenics, and normal control subjects. Patients were rated for prognosis using the Premorbid Subscale of the Phillips Scale. Drawings were rated by two judges on 80 diagnostic signs culled from the literature. No signs were found to significantly differentiate reactive and process schizophrenics, and only three signs significantly differentiated normals from schizophrenics. It was concluded that a sign approach to the DAP is insensitive to the reaction-process dimension of schizophrenia, and of only limited value in differentiating between normals and schizophrenics in general.     

Pursuit Rotor Reminiscence in Schizophrenics and Normals

Normal and schizophrenic Ss (N=24 each) did pursuit rotor tracking and reminiscence was the score of interest; rest pauses of 2, 12, and 30 min., and 1, 6, and 24 hr. were interpolated in counterbalanced order after 5 min. of practice. It was predicted, on the basis of previous work, that schizophrenics would show greater reminiscence after the longer rest pauses, normals after the shorter rest pauses. The expected cross-over effect was found, but at a non-significant level only. There were no order effects. A discussion is given of the relation of these results to the interpretation of schizophrenia in terms of ‘‘arousal.”     

Peripheral and central components in variants of the Mueller-Lyer illusion

Illusion decrement with prolonged inspection was used as a technique to assess the relative amount of central component in seven variants of the Mueller-Lyer illusion. Results indicate that all of the variant forms share a common, central component, while the peripheral components, such as lateral inhibition, vary as a function of the presence of converging lines in the illusion configurations.     

Speech competence of children vulnerable to psychopathology

Verbal productivity and cohesion and reference patterns of children of schizophrenics (N=23), unipolars (N=43), bipolars (N=38), and normals (N=53) were assessed using the Rochester and Martin (1979) evaluation system. Children of all offspring groups could be discriminated from one another, with children of schizophrenics showing the most deviant speech performance across all dependent measures. Children of schizophrenics were less verbally productive and had poorer patterns of cohesion between ideas than children of normals. In addition, they produced more unclear and ambiguous references to previously mentioned ideas than did children of normals. The consistency of deviance and performance on specific dependent variables in these children at risk for schizophrenia was similar to the speech performance of thought-disordered schizophrenics. Possible explanations for these similarities were discussed and evaluated.This research was supported by grant number MH21145 from the National Institute of Mental Health and by funds from the William T. Grant Foundation. The authors would like to thank Lina Jandorf for her invaluable assistance in data collection and scoring.     

Some aspects of verbal conditioning in psychiatric patients

Using a modification of a verbal conditioning technique reported by Tafiel (1955) it was found that only schizophrenics and normals showed evidence of conditioning, neurotics and depressives showing changes not differing from chance. There was greater evidence of conditioning among Ss aware of the contingency between response and reinforcement, and some tentative evidence for relationships of anxiety and extraversion with verbal conditioning.     

The assessment of components involved in illusion formation using a long-term decrement procedure

Available evidence seems to indicate that illusion decrement represents reorganization of cognitive components involved in visual-geometric illusions. Observers viewed one of the two forms of the Mueller-Lyer illusion, containing differential opportunities for peripheral structural interactions, for a 10-min test session on each of 5 successive days. The magnitude of the distortion decreased to a different asymptotic level in each of the two configurations with the form, with more opportunity for structural interactions showing the higher asymptote. Thus, this asymptote probably represents the structural or physiological contribution to the illusory distortion.     

Schizophrenic reactions in the Serial Spiral After-Effect Test

A group of 52 schizophrenics, 13 neurotics and 30 normals were studied by means of the Serial Spiral After-Effect Test. Schizophrenics with classical overt symptoms showed significantly higher values compared to neurotics, normals and latent schizophrenics on the residual variability in ten consecutive durations of the after-effect, i.e. the total variability minus the variability ascribable to linear change. Significant correlations were obtained between residnal variability in the Serial Spiral After-Effect Test and psychosis, as assessed by a psychiatric rating scale for the schizophrenics with classical overt symptoms, when the mean level in the Serial Spiral After-Effect Test was checked.     

Schizophrenia and automatic processing: an exploratory study

This study deals with the schizophrenic deficit as one of automatic processing. To test the idea, a special experimental task was designed on which 21 schizophrenics, 21 depressives, and 21 normal subjects had to complete a series of simple geometric figures. When the subjects had thoroughly learned this activity, another information source, a brief story, was introduced, and the subjects had to pay attention to the story while they did the task. Two dependent variables were considered, execution time and performance. There were no differences among the three groups in the first experimental condition; but in the second condition, when the distractor was introduced, schizophrenics needed more time to do the task and their performance was noticeably worse than those of both normals and depressives. This outcome is explained in terms of a failure in the internal mechanisms which regulate the automatic, parallel, and unconscious processing.