An anti-inertial motion bias explains people discounting inertial motion of carried objects.

In this paper we propose an anti-inertial motion (AIM) bias that can explain several intuitive physics beliefs including the straight-down belief and beliefs held concerning the pendulum problem. We show how the AIM bias also explains two new beliefs that we explore - a straight-up-and-down belief as well as a straight-out/backward bias that occurs for objects traveling in one plane that are then thrown in another plane, ostensibly affording a greater opportunity for perception of canonical motion. We then show how the AIM bias in general is invariant across perceived/imagined speed of the object carrier, only altering percentages of straight-out from backward responses, and why occluding the carrier once the object is released into a second plane does not result in more veridical perception. The AIM bias serves as a simple explanation for a family of beliefs including those in the current paper as well as those shown in previous work.

Manipulation of expended effort and intent does not affect estimates of slant or distance.

It is well known that people overestimate the orientation of both geographical and man-made sloped surfaces by between 5°-20°. More recently, work has shown that when people are encumbered by wearing a heavy backpack they overestimate hills and distances even more than a group not wearing heavy backpacks; however, the backpack manipulation has since been shown to be a demand effect-that is, being encumbered does not affect perception-it only biases those people influenced by it to give estimates the experimenters are seeking. Here we first show that expended effort and intent have never actually been manipulated between subjects in any of the work on steepness estimates, and expended effort has never been explicitly manipulated between subjects for distance estimates. When they are, they do not affect steepness or distance estimates. Our work is the first to experimentally manipulate effort and intent, to do this between subjects, while controlling for demand characteristics and checking to see whether the effort manipulation was effective. The experimental manipulation of effort and especially intent may be of benefit to parsing out perceptual effects from more cognitive or postperceptual processes in future work. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Pushing people to their tipping point: Phenomenal tipping point is predicted by phenomenal vertical and intuitive beliefs.

Previous work has shown that people overestimate their own body tilt by a factor of about 1.5, the same factor by which people overestimate geographical and man-made slopes. In Experiment 1 we investigated whether people can accurately identify their own and others' tipping points (TPs) - the point at which they are tilted backward and would no longer be able to return to upright - as well as their own and others' center of mass (COM) - the relative position of which is used to determine actual TP. We found that people overestimate their own and others' TP when tilted backward, estimate their own and others' COM higher than actual, and that COM estimation is unrelated to TP. In Experiment 2, we investigated people's intuitive beliefs about the TP. We also investigated the relationship between phenomenal TP and perceived vertical. Whether verbally (conceptually) estimating the TP, drawing the TP, or demonstrating the position of the TP, people believe that the TP is close to 45°. In Experiment 3, we found that anchoring influences phenomenal TP and vertical. When accounting for starting position, the TP seems to be best predicted by an intuitive belief that it is close to 45°. In Experiment 4, we show that there is no difference in phenomenal TP and vertical when being tilted about the feet or waist/hips. We discuss the findings in terms of action-perception differences found in other domains and practical implications.

Pedal and haptic estimates of slant suggest a common underlying representation.

It is well known that people verbally exaggerate the slant of visually perceived geographical, virtual, and man-made hills. More recently it has been shown that haptic and verbal estimates of slant result in similar exaggerations, supporting the proprioception calibration hypothesis-that similar biases exist in both verbal estimates of visually perceived slant and proprioceptively perceived hand orientation. This seems to point to a common underlying representation of slant. However, it is unclear if and how manual proprioceptive estimates might be relevant for perception of ground surface slant or how this might translate to pedal perception of surface orientation. In the current work we tested whether pedal perception is systematically connected to a representational system shared by haptic and visual perception. We did this by having people orient their foot to four different orientations of a ramp (Experiment 1) or to a staircase (Experiment 2) and compared these to estimates made using a free hand measure as well as to verbal estimates. Our results show that verbal, haptic, and pedal measures of visually perceived surface orientation all result in similar estimates of slant and do so across different slanted surfaces. This suggests that verbal and haptic proprioceptive estimates tap into a representational system of visually perceived surface orientation that is relevant for walking up various surface orientations.

Perception of objects oriented downward from a vertical position.

In the present work we investigated people's perceptions of orientation for surfaces that are conceived of as being sloped downward from vertical against a vertical reference frame. In the three conditions of Experiment 1, participants either (1) placed a ladder against a wall at what they thought was the most stable position, and then estimated its orientation; (2) gave a verbal (conceptual) estimate of what the most stable position of a ladder leaned against a wall would be; or (3) drew a line representing the most stable position of a ladder to be placed against a wall, and then gave a verbal estimate of the ladder's orientation. Ladder placement was shallower than the most stable position, as were the verbal estimations of both the positioned and drawn orientations and the verbal (conceptual) estimates of the most stable position for a ladder to be leaned against a wall, relative to the actual orientations. In Experiment 2, participants verbally estimated various ladder orientations. The estimates were again shallower than the actual orientations. For orientations between 60° and 90°, the estimates showed a scale compression effect from horizontal. This perceived exaggeration of the orientation of an object typically oriented down from vertical is similar to the perceived exaggeration of the orientation of hills and ramps, typically thought of as oriented up from horizontal. This may point to a generic perceived exaggeration of slant whose direction depends on the conceptual or actual reference frame being used.

The geometry of consciousness.

Conscious experience implies a reference-frame or vantage, which is often important in scientific models. Control models of ball-interception are used as an example. Models that use viewer-dependent egocentric reference-frames are contrasted with viewer-independent allocentric ones. Allocentric reference-frames serve well for models like Newtonian physics, which utilize static coordinate-systems that allow forces and object-movements to be compartmentalized. In contrast, egocentric reference-frames are natural for modeling mobile organisms or robots when controlling perception-action behavior. Lower-level perception-action behavior is often characterized using egocentric coordinate-systems that optimize processing-speed, while higher-level cognitive-processes use allocentric frames that provide a stationary spatial reference. Brain-behavior models like the Ventral-Stream What System, and Dorsal-Stream Where-How System, also respectively utilize allocentric and egocentric reference-frames. Reference-frame clarification can resolve disputes about models of control-tasks like running to catch baseballs, and can provide insights for biomimetic-robots. Confusion regarding geometry and reference-frames contributes to a lack of clarity between how and when egocentric versus allocentric geometries are imposed, with perception-actions generally being more egocentric and conscious experience more allocentric.

The power law as behavioral illusion: reappraising the reappraisals.

Marken and Shaffer (Exp Brain Res 235:1835-1842, 2017) have argued that the power law of movement, which is generally thought to reflect the mechanisms that produce movement, is actually an example of what Powers (Psychol Rev 85:417-435, 1978) dubbed a behavioral illusion, where an observed relationship between variables is seen as revealing something about the mechanisms that produce a behavior when, in fact, it does not. Zago et al. (Exp Brain Res. https://doi.org/10.1007/s0022-017-5108-z , 2017) and Taylor (Exp Brain Res, https://doi.org/10.1007/s00221-018-5192-8 , 2018) have "reappraised" this argument, claiming that it is based on logical, mathematical, statistical and theoretical errors. In the present paper we answer these claims and show that the power law of movement is, indeed, an example of a behavioral illusion. However, we also explain how this apparently negative finding can point the study of movement in a new and more productive direction, with research aimed at understanding movement in terms of its purposes rather than its causes.

The power law of movement: an example of a behavioral illusion.

The curved movements produced by living organisms follow a power law where the velocity of movement is a power function of the degree of curvature through which the movement is made. The exponent of the power function is close to either 1/3 or 2/3 depending on how velocity and curvature are measured. This power law is thought to reflect biological and/or kinematic constraints on how organisms produce movements. The present paper shows that the power law is actually a statistical artifact that results from mistaking a correlational for a causal relationship between variables. The power law implies that curvature influences the velocity of movement. In fact, the power law is a mathematical consequence of the way that these variables are calculated. The appearance that curvature affects the velocity of movement is shown to be an example of a "behavioral illusion" that results from ignoring the purpose of behavior.

Free hand proprioception is well calibrated to verbal estimates of slanted surfaces.

We investigate the relationship between verbal and hand proprioception of slant. In Experiment 1 we demonstrate that verbally estimating free hand orientation produces overestimates by a factor of 1.67. These values are similar to those seen for verbal overestimates of slanted surfaces. In Experiment 2, participants positioned their hand to a ramp at 1 of 4 different orientations, and then verbally estimated the orientation of either their hand or the ramp. We show that verbal estimates of the ramp are a product of the orientation of their hand and the perception of the orientation of their hand. We discuss how this work is consistent with the proprioception calibration hypothesis that proposes that similar biases exist in both verbal estimates of visually perceived slant and proprioceptively perceived hand orientation and how this may explain free hand estimates to outdoor hills that are greater than actual hill orientation by a factor of ~2, but are still less than verbal (over)estimates.

Pitching people with an inversion table: Estimates of body orientation are tipped as much as those of visual surfaces.

In the current work we investigate people's perception of their own body tilt in the pitch direction. In Experiment 1, we tilted people backward at 1 of 5 different randomly assigned angles using an inversion table. People significantly overestimated the angle at which they were tilted backward at angles from 8° to 45°. The slope of the plotted average overestimates had a gain of 1.46, fitting nicely with previously reported gains of verbal overestimates of visually perceived slant of natural outdoor geographically oriented slopes as well as man-made wooden slopes within and outside of reach in the laboratory. In Experiment 2, we showed participants a 45° line and asked them to indicate when they were positioned at that orientation. Participants again significantly overestimated the angle at which they were tilted backward. This extends work showing that a scale-expanded theory of visual space is multisensory, results in equivalent estimates for both verbal and nonverbal/nonnumeric methods, and can now be expanded to include the perceived orientation of one's own body.

Palm board and verbal estimates of slant reflect the same perceptual representation.

People verbally overestimate the orientation of slanted surfaces, but accurately estimate or underestimate slanted surfaces using a palm board. We demonstrate a fundamental issue that explains why the two different values typically given for palm board and verbal/visual matching estimates express similar perceptual representations of slanted surfaces. The fundamental problem in studies measuring palm board and verbal estimates is that the "measure"-either (1) reproducing a verbally given angle or the orientation of a slanted surface with an unseen hand or (2) verbally or visually estimating a visually perceived surface-has always been confounded with the "surface"-either using (1) a palm board or (2) a hill or ramp. Although reproduction has exclusively been used with palm boards in these studies, at the same time verbal estimation or visual matching has exclusively been used with hills/ramps. In three experiments, we showed that verbally estimating palm board orientations produces overestimates by a factor of 1.5, whereas reproducing the orientation of the surface of a ramp to verbally given angles produces gains of ~0.6. These values are similar to those seen for verbal overestimates of slanted surfaces, and to palm board gains for near surfaces and the relative palm-board-to-verbal gains for outdoor hills, respectively. Eliminating this confound eliminated the difference previously seen across surfaces. We discuss how and why different measures should produce different results if we overestimate slant in general and perceptually represent slant in the same way, both haptically and visually.

Catching objects thrown to oneself: Testing control strategies for object interception in a novel domain.

A considerable amount of research has been performed to determine the strategies people use to intercept moving objects. Much of this research has been done using target objects such as baseballs and Frisbees that are launched to people from distances ranging from 10 m to 50 m. This research has qualified the range of domains in which each strategy is effective, but there is still controversy regarding which strategy has the most general application. The present research sought to further reduce the range of possible domains in which these strategies work by testing object interception in a situation that had never been tested before, where people launch the target objects to themselves. A strategy based on controlling optical velocity--acting to keep the optical velocity of the object at zero--provided the best match to catcher ground movements and optical trajectories. These results suggest that control of optical velocity is currently the best explanation of effective interception of both other- and self-launched objects.

Manual anchoring biases in slant estimation affect matches even for near surfaces.

People verbally overestimate hill slant by ~15°-25°, whereas manual estimates (e.g., palm board measures) are thought to be more accurate. The relative accuracy of palm boards has contributed to the widely cited theoretical claim that they tap into an accurate, but unconscious, motor representation of locomotor space. Recently, it was shown that a bias that stems from anchoring the hand at horizontal prior to the estimate can quantitatively account for the difference between manual and verbal estimates of hill slant. The present work extends this observation to manual estimates of near-surface slant, to test whether the bias derives from manual or visual uncertainty. As with far surfaces, strong manual anchoring effects were obtained for a large range of near-surface slants, including 45°. Moreover, correlations between participants' manual and verbal estimates further support the conclusion that both measures are based on the same visual representation.

Remote haptic perception of slanted surfaces shows the same scale expansion as visual perception.

Previous work has shown that overestimates of geographic slant depend on the modality used (verbal or haptic). Recently, that line of reasoning has come into question for many reasons, not the least of which is that the typical method used for measuring "action" has been the use of a palm board, which is not well calibrated to any type of action toward slanted surfaces. In the present work, we investigated how a remote haptic task that has been well calibrated to action in previous work is related to verbal overestimates of slanted surfaces that are out of reach. The results show that haptic estimates are perceptually equivalent to the verbal overestimates that have been found in numerous previous studies. This work shows that the haptic perceptual system is scaled in the same way as the visual perceptual system for estimating the orientation of slanted surfaces that are out of reach.

Anchoring in action: manual estimates of slant are powerfully biased toward initial hand orientation and are correlated with verbal report.

People verbally overestimate hill slant by approximately 15° to 25°, whereas manual estimates (e.g., palm board measures) are thought to be more accurate. The relative accuracy of palm boards has contributed to the widely cited theoretical claim that they tap into an accurate, but unconscious, motor representation of locomotor space. In the current work, 4 replications (total N = 204) carried out by 2 different laboratories tested an alternative anchoring hypothesis that manual action measures give low estimates because they are always initiated from horizontal. The results of all 4 replications indicate that the bias from response anchoring can entirely account for the difference between manual and verbal estimates. Moreover, consistent correlations between manual and verbal estimates given by the same observers support the conclusion that both measures are based on the same visual representation. Concepts from the study of judgment under uncertainty apply even to action measures in information rich environments.

Receivers in American football use a constant optical projection plane angle to pursue and catch thrown footballs.

In the present work we test how well two interceptive strategies, which have been proposed for catching balls hit high in the air in baseball and cricket, account for receivers in American football catching footballs. This is an important test of the domain generality of these strategies as this is the first study examining a situation where the pursuer's locomotor axis is directed away from the origin of the ball, and because the flight characteristics of an American football are far different from targets studied in prior work. The first strategy is to elicit changes in the ball's lateral optical position that match changes in the vertical optical position so that the optical projection plane angle, psi, remains constant, thus resulting in a linear optical trajectory (LOT). The second is keeping vertical optical ball velocity decreasing while maintaining constant lateral optical velocity (generalized optical acceleration cancellation, or GOAC). We found that the optical projection plane angle was maintained as constant significantly more often than maintaining vertical and lateral optical velocities as GOAC predicted. The present experiment extends previous research by showing that the constancy of psi resulting in an LOT is used by humans pursuing American footballs and demonstrates the domain generality of the LOT heuristic.

Chasin' choppers: using unpredictable trajectories to test theories of object interception.

Three theories of the informational basis for object interception strategies were tested in an experiment where participants pursued toy helicopters. Helicopters were used as targets because their unpredictable trajectories have different effects on the optical variables that have been proposed as the basis of object interception, providing a basis for determining the variables that best explain this behavior. Participants pursued helicopters while the positions of both pursuer and helicopter were continuously monitored. Using models to predict the observed optical trajectories of the helicopter and ground positions of the pursuer, optical acceleration was eliminated as a basis of object interception. A model based on control of optical velocity (COV) provided the best match to pursuer ground movements, while one based on segments of linear optical trajectories (SLOT) provided the best match to the observed optical trajectories. We describe suggestions for further research to distinguish the COV and SLOT models.

Sugar and space? Not the case: Effects of low blood glucose on slant estimation are mediated by beliefs.

There is a current debate concerning whether people's physiological or behavioral potential alters their perception of slanted surfaces. One way to directly test this is to physiologically change people's potential by lowering their blood sugar and comparing their estimates of slant to those with normal blood sugar. In the first investigation of this (Schnall, Zadra, & Proffitt, 2010), it was shown that people with low blood sugar gave higher estimates of slanted surfaces than people with normal blood sugar. The question that arises is whether these higher estimates are due to lower blood sugar, per se, or experimental demand created by other aspects of the experiment. Here evidence was collected from 120 observers showing that directly manipulating physiological potential, while controlling for experimental demand effects, does not alter the perception of slant. Indeed, when experimental demand went against behavioral potential, it produced judgmental biases opposite to those predicted by behavioral potential in the low blood sugar condition. It is suggested that low blood sugar only affects slant judgments by making participants more susceptible to judgmental biases.

Blind(fold)ed by science: a constant target-heading angle is used in visual and nonvisual pursuit.

Previous work investigating the strategies that observers use to intercept moving targets has shown that observers maintain a constant target-heading angle (CTHA) to achieve interception. Most of this work has concluded or indirectly assumed that vision is necessary to do this. We investigated whether blindfolded pursuers chasing a ball carrier holding a beeping football would utilize the same strategy that sighted observers use to chase a ball carrier. Results confirm that both blindfolded and sighted pursuers use a CTHA strategy in order to intercept targets, whether jogging or walking and irrespective of football experience and path and speed deviations of the ball carrier during the course of the pursuit. This work shows that the mechanisms involved in intercepting moving targets may be designed to use different sensory mechanisms in order to drive behavior that leads to the same end result. This has potential implications for the supramodal representation of motion perception in the human brain.

To see or not to see: effects of visual feedback on performance and intuitions of quarterbacks in American football.

We investigated the ability of quarterbacks in American football to intercept a moving receiver with a football in occluded and normal viewing conditions, and whether they can accurately predict their own success. Quarterbacks were successful in almost 80% of the trials in the occlusion condition, statistically as successful as in the normal viewing condition. Quarterbacks' predictions of their own success accounted for little variance in actual success. We propose that quarterbacks may attempt to generate a constant target-heading angle between where the football is thrown and the receiver, which may explain the high success rate in the occlusion condition.