RAMESES publication standards: meta-narrative reviews

PMCID: PMC3558334This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Getting a grip on heaviness perception: a review of weight illusions and their probable causes

Weight illusions--where one object feels heavier than an identically weighted counterpart--have been the focus of many recent scientific investigations. The most famous of these illusions is the 'size-weight illusion', where a small object feels heavier than an identically weighted, but otherwise similar-looking, larger object. There are, however, a variety of similar illusions which can be induced by varying other stimulus properties, such as surface material, temperature, colour, and even shape. Despite well over 100 years of research, there is little consensus about the mechanisms underpinning these illusions. In this review, I will first provide an overview of the weight illusions that have been described. I will then outline the dominant theories that have emerged over the past decade for why we consistently misperceive the weights of objects which vary in size, with a particular focus on the role of lifters' expectations of heaviness. Finally, I will discuss the magnitude of the various weight illusions and suggest how this largely overlooked facet of the topic might resolve some of the debates surrounding the cause of these misperceptions of heaviness

Examining the size-weight illusion with visuo-haptic conflict in immersive virtual reality.

This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.When we experience our environment, we do so by combining sensory inputs with expectations derived from our prior knowledge, which can lead to surprising perceptual effects such as small objects feeling heavier than equally weighted large objects (the size-weight illusion (SWI)). Interestingly, there is evidence that the way in which the volume of an object is experienced can affect the strength of the illusion, with a SWI induced by exclusively haptic volume cues feeling stronger than a SWI induced with only visual volume cues. Furthermore, visual cues appear to add nothing over and above haptic size cues in terms of the strength of the induced weight illusion-findings which are difficult to reconcile with work using cue-conflict paradigms where visual cues usually dominate haptic cues. Here, virtual reality was used to place these senses in conflict with one another. Participants ( N = 22) judged the heaviness of identically weighted cylinders across three conditions: (1) objects appeared different sizes but were physically the same size, (2) objects were physically different sizes but appeared to be the same size, or (3) objects which looked and felt different sizes from one another. Consistent with prior work, haptic size cues induced a larger SWI than that induced by visual size differences. In contrast to prior work, however, congruent vision and haptic size cues yielded a larger still SWI. These findings not only add to our understanding of how different modalities combine to influence our hedonic perception but also showcase how virtual reality can develop novel cue-conflict paradigms

Dimensional analysis using toric ideals: Primitive invariants

© 2014 Atherton et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Classical dimensional analysis in its original form starts by expressing the units for derived quantities, such as force, in terms of power products of basic units M, L, T etc. This suggests the use of toric ideal theory from algebraic geometry. Within this the Graver basis provides a unique primitive basis in a well-defined sense, which typically has more terms than the standard Buckingham approach. Some textbook examples are revisited and the full set of primitive invariants found. First, a worked example based on convection is introduced to recall the Buckingham method, but using computer algebra to obtain an integer K matrix from the initial integer A matrix holding the exponents for the derived quantities. The K matrix defines the dimensionless variables. But, rather than this integer linear algebra approach it is shown how, by staying with the power product representation, the full set of invariants (dimensionless groups) is obtained directly from the toric ideal defined by A. One candidate for the set of invariants is a simple basis of the toric ideal. This, although larger than the rank of K, is typically not unique. However, the alternative Graver basis is unique and defines a maximal set of invariants, which are primitive in a simple sense. In addition to the running example four examples are taken from: a windmill, convection, electrodynamics and the hydrogen atom. The method reveals some named invariants. A selection of computer algebra packages is used to show the considerable ease with which both a simple basis and a Graver basis can be found.The third author received funding from Leverhulme Trust Emeritus Fellowship (1-SST-U445) and United Kingdom EPSRC grant: MUCM EP/D049993/1

Size matters: a single representation underlies our perceptions of heaviness in the size-weight illusion.

PublishedJournal ArticleResearch Support, Non-U.S. Gov'tIn the size-weight illusion (SWI), a small object feels heavier than an equally-weighted larger object. It is thought that this illusion is a consequence of the way that we internally represent objects' properties--lifters expect one object to outweigh the other, and the subsequent illusion reflects a contrast with their expectations. Similar internal representations are also thought to guide the application of fingertip forces when we grip and lift objects. To determine the nature of the representations underpinning how we lift objects and perceive their weights, we examined weight judgments in addition to the dynamics and magnitudes of the fingertip forces when individuals lifted small and large exemplars of metal and polystyrene cubes, all of which had been adjusted to have exactly the same mass. Prior to starting the experiment, subjects expected the density of the metal cubes to be higher than that of the polystyrene cubes. Their illusions, however, did not reflect their conscious expectations of heaviness; instead subjects experienced a SWI of the same magnitude regardless of the cubes' material. Nevertheless, they did report that the polystyrene cubes felt heavier than the metal ones (i.e. they experienced a material-weight illusion). Subjects persisted in lifting the large metal cube with more force than the small metal cube, but lifted the large polystyrene cube with roughly the same amount of force that they used to lift the small polystyrene cube. These findings suggest that our perceptual and sensorimotor representations are not only functionally independent from one another, but that the perceptual system represents a more single, simple size-weight relationship which appears to drive the SWI itself.G. Buckingham was funded with a Banting Postdoctoral Fellowship awarded from the Natural Sciences and Engineering Council of Canada (NSERC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Move on up: Fingertip forces and felt heaviness are modulated by the goal of the lift

This is the final version. Available on open access from Springer via the DOI in this recordWhen we interact with objects, we usually do so for a purpose. It is well known that the specific goal of an action can have a substantial effect on initial reach kinematics. No research, however, has examined the effect that the goal of a lift can have on the fingertip forces and perception of object weight when picking up an object to move it. Here, we report a study in which participants were asked to move objects laterally to a higher platform, to a lower platform, or to a platform of the same height. The objects were rated, on average, as feeling heavier after they were moved to a higher platform than after they were moved to a lower platform or to a platform of the same height. Furthermore, participants gripped and lifted with more force, and used higher rates of force, when moving objects to a higher platform compared with moving it to a platform of the same height. These findings suggest that the goal of movement in the context of object interaction may affect how heavy an object feels and the way in which it is lifted

Bimanual Lifting: Do Fingertip Forces Work Independently or Interactively?

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this record.Bimanual coordination is a commonplace activity, but the consequences of using both hands simultaneously are not well understood. The authors examined fingertip forces across 4 experiments in which participants undertook a range of bimanual tasks. They first measured fingertip forces during simultaneous lifts of 2 identical objects, noting that individuals held the objects with more force bimanually than unimanually. They then varied the mass of the objects held by each hand, noting that when both hands lifted together performance was equivalent to unimanual lifts. The authors next measured one hand's static grip force while the other hand lifted an object. They found a gradual reduction of grip force throughout the trial, but once again no evidence of one hand influencing the other. In the final experiment the authors tested whether tapping with one hand could influence the static grip force of its counterpart. Although the authors found no changes in static grip force as a direct consequence of the other hand's actions, they found clear differences from one task to the other, suggesting an effect of task instruction. Overall, these results suggest that fingertip forces are largely independent between hands in a bimanual lifting context, but are sensitive to different task requirements

Perceiving and acting upon weight illusions in the absence of somatosensory information

This is the author accepted manuscript. The final version is available from the American Physiological Society via the DOI in this record.When lifting novel objects, individuals’ fingertip forces are influenced by a variety of cues such as volume and apparent material. This means that heavy-looking objects tend to be lifted with more force than lighter-looking objects, even when they weigh the same amount as one another. Expectations about object weight based on visual appearance also influence how heavy an object feels when it is lifted. For instance, in the "size-weight illusion," small objects feel heavier than equally weighted large objects. Similarly, in the "material-weight illusion," objects that seem to be made from light-looking materials feel heavier than objects of the same weight that appear to be made from heavy-looking materials. In this study, we investigated these perceptual and sensorimotor effects in IW, an individual with peripheral deafferentation (i.e., a loss of tactile and proprioception feedback). We examined his perceptions of heaviness and fingertip force application over repeated lifts of objects that varied in size or material properties. Despite being able to report real weight differences, IW did not appear to experience the size- or material-weight illusions. Furthermore, he showed no evidence of sensorimotor prediction based on size and material cues. The results are discussed in the context of forward models and their possible influence on weight perception and fingertip force control

The National Football League-225 Bench Press Test and the Size-Weight Illusion

This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.The purpose of this study was to test reports that size and arrangement manipulations of weight plates (i.e., inducing a size-weight illusion [SWI]) would have an effect on athletic weightlifting performance. The participants were 72 experienced, weight-trained collegiate American football players. Across 3 weeks, each athlete performed three different repetitions-to-fatigue bench press tests (NFL-225, SWI-225, and SWI-215). A multiple regression revealed a positive association between participants' strength relative to the test load and repetitions for NFL-225 and SWI-215, but no association with SWI-225. To explore these results, players were ranked into quartiles based on their one-repetition maximum relative to 102.27 kg (225 lb), and a 3 × 4 repeated measures analysis of variance was conducted. The primary finding was a significant Test Condition × Quartile interaction ( p = .004). Bonferroni-corrected pairwise comparisons revealed that Quartile 4 (those with lowest strength relative to test load) completed more repetitions for SWI-225 compared with NFL-225 ( p = .049). These results suggest that alternate weight plate arrangements may be beneficial for those whose bench press load is near the lifter's one-repetition maximum. However, variations of the SWI do not appear to affect the performance of repetitions-to-fatigue bench press tests for the majority of collegiate American football players