Lifting movements in the size-weight illusion

The occurrence of the size-weight illusion is related to the manner in which-objects are lifted. When the SWI occurs, the larger of two objects of equal objective weight is usually lifted with greater acceleration, deceleration, and maximum velocity than the smaller one, but to approximately the same height. These differences are not present when the cans feel equally heavy. The relationship of lifting movements to judgments is consistent with the known behavior of proprioceptors which provide sensory input about muscular and movement events.     

Mechanical advantage in the size-weight illusion

When a hand-held object is lifted by wrist flexion, the lifting system composed of muscles, bones, and the object lifted constitutes a third-class lever. Therefore, objects require greater lifting force as they are supported further distally The small can of the DeMoors size-weight illusion cans is usually supported further distally than the large one, possibly influencing their relative perceived weight When Ss are required to lift the small can through a shorter lever than the large one, there is a significant shift of judgments toward a reversal of the SWI in a paired-comparison situation. It is concluded that mechanical advantage does influence weight judgments and that biomechanical factors should be considered whenever weight judgments are made.     

The role of preparatory muscular tension in the size-weight illusion

Muscle action potentials were recorded from lifting muscles during the foreperiod before lifts of large and small objects when the size-weight illusion occurred. There were increases in tension throughout the foreperiod of both lifts, culminating in a large increase following the instruction to lift. The increases were greater before lifts of the large can, supporting the peripheral theory of comparative weight judgment. The “set to lift” effect was shown to exist in the action potentials before the foreperiod of the second lift when compared to those just prior to the lift of the first can.     

Averaging model applied to the size-weight illusion

A theoretical model was given for the size-weight illusion based on a principle of information integration. Judged heaviness of lifted weights was assumed to be an average of two pieces of information, weight and size, with the latter receiving negative weighting in the model formulation. Two experiments based on a Weight by Size design gave fair support to the parallelism prediction of the integration model. The hypothesis that Ss were really judging density was shown to imply a divergence prediction, contrary to the data. The theoretical analysis was generalized to include negative, positive, and comparative illusions; these were differentiated according to whether the contextual information was integrated with negative weighting, positive weighting, or served as a yardstick of judgment.     

Body-based perceptual rescaling revealed through the size-weight illusion

An embodied approach to the perception of spatial layout contends that the body is used as a 'perceptual ruler' with which individuals scale the perceived environmental layout. In support of this notion, previous research has shown that the perceived size of objects can be influenced by changes in the apparent size of hand. The size-weight illusion is a well known phenomenon, which occurs when people lift two objects of equal weight but differing sizes and perceive that the larger object feels lighter. Therefore, if apparent hand size influences perceived object size, it should also influence the object's perceived weight. In this study, we investigated this possibility by using perceived weight as a measure and found that changes in the apparent size of the hand influence objects' perceived weight.     

Charpentier (1891) on the size-weight illusion

This paper offers background for an English translation of an article originally published in 1891 by Augustin Charpentier (1852-1916), as well as a summary of it. The article is frequently described as providing the first experimental evidence for the size-weight illusion. A comparison of experiments on the judged heaviness of lifted weights carried out by Weber (1834) and by Charpentier (1891) supports the view that Charpentier's work deserves priority; review of other experimental studies on the size-weight illusion in the 1890s suggests that the idea that the illusion depended on "disappointed expectations," especially with respect to speed of lift, became dominant almost immediately following the publication of Charpentier's paper. The fate of this and other ideas, including "motor energy," in 20th-century research on the illusion is briefly described.     

A multidimensional scaling model for the size-weight illusion

The kinds of individual differences in perceptions permitted by the weighted euclidean model for multidimensional scaling (e.g., INDSCAL) are much more restricted than those allowed by Tucker's Three-mode Multidimensional Scaling (TMMDS) model or Carroll's Idiosyncratic Scaling (IDIOSCAL) model. Although, in some situations the more general models would seem desirable, investigators have been reluctant to use them because they are subject to transformational indeterminacies which complicate interpretation. In this article, we show how these indeterminacies can be removed by constructing specific models of the phenomenon under investigation. As an example of this approach, a model of the size-weight illusion is developed and applied to data from two experiments, with highly meaningful results. The same data are also analyzed using INDSCAL. Of the two solutions, only the one obtained by using the size-weight model allows examination of individual differences in the strength of the illusion; INDSCAL can not represent such differences. In this sample, however, individual differences in illusion strength turn out to be minor. Hence the INDSCAL solution, while less informative than the size-weight solution, is nonetheless easily interpretable.This paper is based on the first author's doctoral dissertation at the Department of Psychology, University of Illinois at Urbana-Champaign. The aid of Professor Ledyard R Tucker is gratefully acknowledged.     

The role of haptic versus visual volume cues in the size-weight illusion

Three experiments establish the size-weight illusion as a primarily haptic phenomenon, despite its having been more traditionally considered an example of vision influencing haptic processing. Experiment 1 documents, across a broad range of stimulus weights and volumes, the existence of a purely haptic size-weight illusion, equal in strength to the traditional illusion. Experiment 2 demonstrates that haptic volume cues are both sufficient and necessary-for a full-strength illusion. In contrast, visual volume cues are merely sufficient, and produce a relatively weaker effect. Experiment 3 establishes that congenitally blind subjects experience an effect as powerful as that Of blindfolded sighted observers, thus demonstrating that visual imagery is also unnecessary for a robust size-weight illusion. The results are discussed in terms of their implications for both sensory and cognitive theories of the size-weight illusion. Applications of this work to a human factors design and to sensor-based systems for robotic manipulation are also briefly considered.     

Psychophysical scales of apparent heaviness and the size-weight illusion

The apparent heaviness of a set of 40 cylindrical objects was scaled by the method of magnitude estimation. The objects varied in weight, volume. and density. There were three main conclusions: (1) For any constant volume, heaviness grows as a power function of weight; the larger the volume. the larger the exponent of the power function. The family of such power functions converge at a common point in the vicinity of the heaviest weight that can be lifted. (2) For any constant density (i:e., weight proportional to volume), heaviness does not grow as a power function of weight. (3) For any constant weight, heaviness decreases approximately as a logarithmic function of volume; the constants of the log function depend systematically on the weight of the object. The outcome furnishes a broad quantitative picture of apparent heaviness and of the size-weight illusion (Charpentier’s illusion).     

Independence and separability of volume and mass in the size-weight illusion

Numerous size-weight illusion models were classified in the present article according to general recognition theory (Ashby & Townsend, 1986), wherein the illusion results from a lack of perceptual separability, perceptual independence, decisional separability, or a combination of the three. These options were tested in two experiments in which a feature-complete factorial design and multidimensional signal detection analysis were used (Kadlec & Townsend, 1992a, 1992b). With haptic touch alone, the illusion was associated with a lack of perceptual and decisional separability. When the participant viewed the stimulus in his or her hand, the illusion was associated only with a lack of decisional separability. Visual input appeared to improve the discrimination of mass, leaving only the response bias due to expectation.     

Application of the method of fixed set to the size-weight illusion

Summary The method of fixed set (Uznadze, 1966) was applied to the size-weight illusion. After the repeated lifting of a small, heavy stimulus and a large, light one with both hands simultaneously, the size-weight illusion diminished. It increased after lifting a small, light stimulus and a large, heavy one. These changes in perception were explained as contrast effects caused by the sets which were fixed during the preceding lifts. The same method was applied to the weight-size illusion and the contrast effect was observed in some cases. The results of the application of the fixed-set method to the size-weight illusion and to the visual size perception were compared. All the results showed analogous patterns of conflicting states between the temporarily fixed set and the set that the subject prepares naturally for perception, such as the size-weight illusion. By way of conclusion, the size-weight illusion was assumed to be a kind of contrast effect in the light of Uznadze's theory of set.     

An experimental test of two mathematical models applied to the size-weight illusion.

Two quantitative models, which make different quantitative predictions for the amount of the size-weight illusion, were tested according to the psychophysical methods employed by the respective authors (magnitude estimation versus category ratings). Both models with their corresponding method were supported. This causes uncertainty over Anderson's chaim that the validity of both a model and the applied scale used is sufficiently test by the socalled joint testing procedure.     

3-D processing in the Poggendorff illusion

In the Poggendorff illusion two collinear oblique lines, separated by two vertical lines, appear to be misaligned. 3-D processing of the oblique but not the vertical lines is considered to cause this apparent misalignment. We investigated whether more explicitly triggering 2-D versus 3-D interpretations of the different parts of Poggendorff-like displays would influence the apparent misalignment. In Experiment 1, we found that compared to 2-D controls, 3-D interpretations of the vertical parts did not influence apparent misalignment, while for the oblique parts 3-D processing resulted in more apparent misalignment than 2-D controls. In Experiment 2, the amount of contour convergence of the oblique parts was manipulated resulting in the 3-D blocks, but not the 2-D line patterns, to be perceived as receding in depth. Now, apparent misalignment increased the more the 3-D blocks were perceived as receding in depth. We conclude that apparent misalignment in Poggendorff-like displays can be influenced by different interpretations of its separate parts, while keeping the local junctions between the different elements the same.     

The role of expectancies in the size-weight illusion: A review of theoretical and empirical arguments and a new explanation

The size–weight illusion (SWI) refers to the phenomenon that objects that are objectively equal in weight but different in size or volume are perceived to differ in weight, such that smaller objects feel heavier than larger ones. This article reviews studies trying to support three different viewpoints with respect to the role of expectancies in causing the SWI. The first viewpoint argues for a crucial role; the second admits a role, yet without seeing consequences for sensorimotor processes; and the third denies any causal role for expectancies at all. A new explanation of the SWI is proposed that can integrate the different arguments. A distinctive feature of the new explanation is that it recognizes the causal influence of expectancies, yet combines this with certain reactive and direct behavioral consequences of perceiving size differences that are independent of experience-based expectancies, and that normally result in the adaptive application of forces to lift or handle differently sized objects. The new account explains why the illusion is associated with the repeated generation of inappropriate lifting forces (which can, however, be modified through extensive training), as well as why it depends on continuous visual exposure to size cues, appears at an early age, and is cognitively impenetrable.     

Similarities derived from 3-d nonlinear psychophysics: Variance distributions

Many-one mappings between stimulus properties and pairwise generated similarities are intrinsic to definitions of similarity. This of itself is not sufficient as a basis for predicting the variance associated with any single similarity judgment. An extension to cover this has to be made either by making ancillary assumptions about noise, or by using nonlinear models. The derivation of the variance of similarity judgments is made from the 3 process in nonlinear psychophysics. The idea of separability of dimensions in metric space theories of similarity is replaced by one parameter which represents the degree of a form of interdimensional crosscoupling     

The psychophysics of spending

Several theories of decision making are based, in part, upon the principles of psychophysics (Kahneman and Tversky, 1979; Thaler, 1985). For example, due to the psychophysics of quantity, the difference between $10 and $20 seems greater than the difference between $110 and $120. To determine whether psychophysics influences consumers' decisions, subjects in four studies made real or hypothetical purchases. It was predicted that as the size of the purchase increased, subjects would be more willing to buy additional smaller items. Small extra purchases should seem like minor expenditures when they follow larger purchases. Results of the four studies supported our hypothesis. In addition, it was found that subjects responded not only to actual changes in purchase size but also to changes in the presentation or framing of a purchase.     

The psychophysics of imagery

A series of experiments considers the extent to which the interrelations among subjective magnitudes aroused by images corresponds to those for subjective magnitudes aroused by physical stimuli. In Experiment 1, 68 undergraduates typed phrases in response to graded categories regarding the imagined magnitude of lights, sounds, and smells. In Experiment 2, 5 undergraduates and, in Experiment 3, 3 graduate students then magnitude estimated the image intensity aroused by each of these stimulus phrases. In Experiments 4 and 5, the same subjects performed cross-modality matches between phrases arousing images for different attributes (light, sound, and smell). Statistical analysis indicates that estimates based on images display many of the same patterns as those based on physical stimuli. The major exception involves sequence effects, present for actual stimuli but not for images.