Foot and shoe responsible for majority of soft tissue work in early stance of walking

Soft tissues located throughout the human body are known to perform substantial mechanical work through wobbling and deforming, particularly following foot impacts with the ground. Yet, it is not known which specific tissues in the body are responsible for the majority of the soft tissue work. The purpose of this study was to quantify how much of the soft tissue work after foot contact was due to the foot and shoe, vs. from tissues elsewhere in the body, and how this distribution of work changed with walking speed and slope. We collected ground reaction forces and whole-body kinematics while ten subjects walked at five speeds (0.8–1.6 m/s) and on seven different slopes (9 degrees downhill to 9 degrees uphill). Using a previously-published Energy-Accounting analysis, we found that the majority of the soft tissue work during early stance was due to deformation of the foot and shoe. The percentage of work did not vary significantly with speed but did vary significantly with slope. The foot and shoe were responsible for ∼60–70% of the soft tissue work during level and uphill walking, and 80–90% during downhill walking.     

De-polarizing verbal irony

In three studies participants were asked to rate the degree of irony perceived in comments relating to five variations of a scenario, ranging from one pole to the opposite pole and passing through three in-between states. In study 1, the comments pertained to the polar extremes of a dimension, e.g. “It’s uphill!” stated with reference to varying degrees of steepness both uphill and downhill (i.e. steep, slightly steep, flat, slightly sloping downhill and steeply sloping downhill). In study 2, the comments were of an “intermediate” nature (e.g. “This hill is neither uphill nor downhill!”) and, as in Study 1, they were used to refer to the same five varying degrees of the same dimension. Study 3 involved the stimuli from both of the first two experiments in a between-participants design.

The results consistently demonstrated that verbal irony does not only apply to (weakly or strongly) polarised statements and situations, but it can also apply to intermediate comments and experiences. The perceptual structure of the dimensions involved modulates the effect.     

Why do pitched horizontal lines have such a small effect on visually perceived eye level?

In two experiments, visually perceived eye level (VPEL) was measured while subjects viewed two-dimensional displays that were either upright or pitched 20 degrees top-toward or 20 degrees top-away from them. In Experiment 1, it was demonstrated that binocular exposure to a pair of pitched vertical lines or to a pitched random dot pattern caused a substantial upward VPEL shift for the top-toward pitched array and a similarly large downward shift for the top-away array. On the other hand, the same pitches of a pair of horizontal lines (viewed binocularly or monocularly) produced much smaller VPEL shifts. Because the perceived pitch of the pitched horizontal line display was nearly the same as the perceived pitch of the pitched vertical line and dot array, the relatively small influence of pitched horizontal lines on VPEL cannot be attributed simply to an underestimation of their pitch. In Experiment 2, the effects of pitched vertical lines, dots, and horizontal lines on VPEL were again measured, together with their effects on resting gaze direction (in the vertical dimension). As in Experiment 1, vertical lines and dots caused much larger VPEL shifts than did horizontal lines. The effects of the displays on resting gaze direction were highly similar to their effects on VPEL. These results are consistent with the hypothesis that VPEL shifts caused by pitched visual arrays are due to the direct influence of these arrays on the oculomotor system and are not mediated by perceived pitch.     

Slope estimation and viewing distance of the observer

The overestimation of geographical slant is one of the most sizable visual illusions. However, in some cases estimates of close-by slopes within the range of the observer’s personal space have been found to be rather accurate. We propose that the seemingly diverse findings can be reconciled when taking the viewing distance of the observer into account. The latter involves the distance of the observer from the slope (personal space, action space, and vista space) and also the eye-point relative to the slope. We separated these factors and compared outdoor judgments to those collected with a three-dimensional (3D) model of natural terrain, which was within arm’s reach of the observer. Slope was overestimated in the outdoors at viewing distances between 2 m and 138 m. The 3D model reproduced the errors in monocular viewing; however, performance was accurate with stereoscopic viewing. We conclude that accurate slant perception breaks down as soon as the situation exits personal space, be it physically or be it by closing one eye.     

Visually induced reorientation illusions.

It is known that rotation of a furnished room around the roll axis of erect subjects produces an illusion of 360 degrees self-rotation in many subjects. Exposure of erect subjects to stationary tilted visual frames or rooms produces only up to 20 degrees of illusory tilt. But, in studies using static tilted rooms, subjects remained erect and the body axis was not aligned with the room. We have revealed a new class of disorientation illusions that occur in many subjects when placed in a 90 degrees or 180 degrees tilted room containing polarised objects (familiar objects with tops and bottoms). For example, supine subjects looking up at a wall of the room feel upright in an upright room and their arms feel weightless when held out from the body. We call this the levitation illusion. We measured the incidence of 90 degrees or 180 degrees reorientation illusions in erect, supine, recumbent, and inverted subjects in a room tilted 90 degrees or 180 degrees. We report that reorientation illusions depend on the displacement of the visual scene rather than of the body. However, illusions are most likely to occur when the visual and body axes are congruent. When the axes are congruent, illusions are least likely to occur when subjects are prone rather than supine, recumbent, or inverted.     

On the role of otoliths and semicircular canals in spatial orientation: Dynamics of the visually perceived eye level during gondola centrifugation

The visually perceived eye level (VPEL) was measured during gondola centrifugation. Subjects (N = 11) were seated upright, facing motion in a swing-out gondola The head was adjusted so that Reid's baseline was tilted 10 degrees anterior end up. The subjects were requested to adjust the position of a small luminous dot so that it was perceived as gravitationally at eye level. In the 1-g environment, the VPEL was a few degrees below the true gravitational eye level (M = -1.75 degrees, SD = 1.90 degrees). After rapid acceleration of the centrifuge to 2 G (vectorial sum of the earth gravity force and the centrifugal force), there was an exponentially increasing depression of the VPEL. The initial value was -6.4 degrees +/- 5.2 degrees. During 10 min at 2 G, the VPEL approached an asymptotic value of -24.8 degrees +/- 5.4 degrees. The time constant showed a large interindividual variability, ranging from 59 to 1,000 sec (M = 261 sec, median = 147 sec). The findings are discussed, taking into consideration otolith-semicircular-canal interaction, as well as memory functions of the vestibular system.     

The overestimation of vertical distance and slope and its role in the moon illusion

Six experiments were conducted to test the hypothesis that overestimation of vertical distance is a pervasive phenomenon. The experiments involved judgments of: (a) vertical distance looking upward; (b) vertical distance looking downward; (c) the slope of a real hill; (d) the recalled slopes of streets; (e) the magnitudes of angles drawn on paper; (f) the distances to afterimages projected into the sky. The results showed that a very strong illusion of overestimation of both vertical distance and slope occurred in all situations except for the judgments of drawn angles by males. Furthermore, in five of the six experiments females showed a greater amount of the illusion than males. The discussion pointed out the difficulty of explaining the moon illusion by the assumptions of a flattened sky surface and Emmert’s law in light of the data.     

Light and dark adaptation of visually perceived eye level controlled by visual pitch

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level averages approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30° topbackward or 20° topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.     

Visually perceived eye level: changes induced by a pitched-from-vertical 2-line visual field.

The physical elevation corresponding to visually perceived eye level (VPEL) changes linearly with the pitch of a visual field. Deviations from true eye level average more than 0.5 times the angle of pitch over a 65 degrees pitch range. A visual field consisting of 2 dim, isolated vertical lines in darkness is more than 4/5 as effective as that of a complexly structured visual field; 2 horizontal lines have a small and inconsistent effect. Differences in influence on VPEL between pitched-from-vertical and horizontal lines were predicted from an analysis that extracted differences in retinal perspective resulting from changes in pitch. The Great Circle Model (GCM), based on a spherical approximation to the erect, stationary eye, predicts the present results and results of 8 other sets of experiments. The model treats the influence of a single line on VPEL as systematically related to the elevation of the intersection between the great circle containing the image of the line and the central vertical retinal meridian; generalized GCM combines visual inputs with inputs from the body-referenced mechanism and maps onto the central nervous system.     

Differences in influence between pitched-from-vertical lines and slanted-from-frontal horizontal lines on egocentric localization

The visual field exerts powerful effects on egocentric spatial localization along both horizontal and vertical dimensions. Thus, (1) prism-produced visual pitch and visual slant generate similar mislocalizations of visually perceived eye level (VPEL) and visually perceived straight ahead (VPSA) and (2) in darkness curare-produced extraocular muscle paresis under eccentric gaze generates similar mislocalizations in VPEL and VPSA that are essentially eliminated by introducing a normal visual field. In the present experiments, however, a search for influences of real visual slant on VPSA to correspond to the influences of visual pitch on VPEL failed to find one. Although the elevation corresponding to VPEL changes linearly with the pitch of a visual field consisting of two isolated 66.5°-long pitched-from-vertical lines, the corresponding manipulation of change in the slant of either a horizontal two-line or a horizontal four-line visual field on VPSA did not occur. The average slope of the VPEL-versus-pitch function across 5 subjects was +0.40 over a ±30° pitch range, but was indistinguishable from 0.00 for the VPSA-versus-slant function over a ±30° slant range. Possible contributions to the difference between susceptibility of VPEL and VPSA to visual influence from extraretinal eye position information, gravity, and several retinal gradients are discussed.     

Uphill and Downhill in a Flat World: The Conceptual Topography of the Yupno House

Speakers of many languages around the world rely on body‐based contrasts (e.g., left/right ) for spatial communication and cognition. Speakers of Yupno, a language of Papua New Guinea's mountainous interior, rely instead on an environment‐based uphill/downhill contrast. Body‐based contrasts are as easy to use indoors as outdoors, but environment‐based contrasts may not be. Do Yupno speakers still use uphill/downhill contrasts indoors and, if so, how? We report three studies on spatial communication within the Yupno house. Even in this flat world, uphill/downhill contrasts are pervasive. However, the terms are not used according to the slopes beyond the house's walls, as reported in other groups. Instead, the house is treated as a microworld, with a “conceptual topography” that is strikingly reminiscent of the physical topography of the Yupno valley. The phenomenon illustrates some of the distinctive properties of environment‐based reference systems, as well as the universal power and plasticity of spatial contrasts.     

Invariance of the psychometric function for character recognition across the visual field.

The psychometric function for recognition of singly presented digits as a function of digit contrast was measured at 2 degrees steps across the horizontal meridian of the visual field, under monocular and binocular viewing conditions. A maximum-likelihood staircase procedure was used in a 10-alternative forced-choice recognition paradigm to gather the data Both the Weibull and the logistic psychometric functions provide excellent fits to the observed data. The slopes of these functions at their point of inflection ranged from 4.0 to 5.0 proportion-correct/log10-unit contrast, for both monocular and binocular viewing and for all loci in the visual field. These slope values correspond to short-term measurements (around 30 trials, or 1 min) and do not include performance variations of longer duration; the latter are estimated to increase slope by a factor of about 1.5. A single psychometric function shape, centered around a threshold value, therefore describes recognition performance at all retinal loci and binocularity. An empirical comparison of slope results across the literature shows that the function's slope is about twice that reported for a number of detection tasks. The comparison of recognition contrast thresholds, percentage correct values, and other performance measures across studies requires the knowledge of the psychometric function's slope, and our results thus provide a firm basis for the study of low-contrast character recognition.     

Perception of visual inclination in a real and simulated urban environment

The perceived inclination of slopes is generally overestimated. We claim that overestimation depends on the use of impoverished stimuli and on the distance between the observer and an inclined surface. In experiment 1, participants reported the perceived inclination of a set of urban roads from two different viewing distances. Observers did not overestimate the perceived inclination of slopes when they saw roads from the shorter viewing distances, whereas they slightly overestimated the perceived inclination of slopes from the farther distance. In experiment 2, participants reported the perceived inclination of a set of stereoscopic slides representing the same urban roads as in experiment 1. Here, observers did not overestimate the perceived inclination of slopes when the projected stereoscopic image contained horizontal disparity and simulated the shorter viewing distance; while they revealed a slight overestimation from the farther distance. We found always overestimation when the binocular image did not contain horizontal disparity, independently from the viewing distance. In conclusion, slopes are overestimated when (a) horizontal disparity is absent, and (b) the viewing distance is increased.     

Up by upwest: Is slope like north?

Terrain slope can be used to encode the location of a goal. However, this directional information may be encoded using a conceptual north (i.e., invariantly with respect to the environment), or in an observer-relative fashion (i.e., varying depending on the direction one faces when learning the goal). This study examines which representation is used, whether the sensory modality in which slope is encoded (visual, kinaesthetic, or both) influences representations, and whether use of slope varies for men and women. In a square room, with a sloped floor explicitly pointed out as the only useful cue, participants encoded the corner in which a goal was hidden. Without direct sensory access to slope cues, participants used a dial to point to the goal. For each trial, the goal was hidden uphill or downhill, and the participants were informed whether they faced uphill or downhill when pointing. In support of observer-relative representations, participants pointed more accurately and quickly when facing concordantly with the hiding position. There was no effect of sensory modality, providing support for functional equivalence. Sex did not interact with the findings on modality or reference frame, but spatial measures correlated with success on the slope task differently for each sex.     

Processing spatial layout by perception and sensorimotor interaction

Everyone has the feeling that perception is usually accurate - we apprehend the layout of the world without significant error, and therefore we can interact with it effectively. Several lines of experimentation, however, show that perceived layout is seldom accurate enough to account for the success of visually guided behaviour. A visual world that has more texture on one side, for example, induces a shift of the body's straight ahead to that side and a mislocalization of a small target to the opposite side. Motor interaction with the target remains accurate, however, as measured by a jab with the finger. Slopes of hills are overestimated, even while matching the slopes of the same hills with the forearm is more accurate. The discrepancy shrinks as the estimated range is reduced, until the two estimates are hardly discrepant for a segment of a slope within arm's reach. From an evolutionary standpoint, the function of perception is not to provide an accurate physical layout of the world, but to inform the planning of future behaviour. Illusions - inaccuracies in perception - are perceived as such only when they can be verified by objective means, such as measuring the slope of a hill, the range of a landmark, or the location of a target. Normally such illusions are not checked and are accepted as reality without contradiction.     

Use of slope and feature cues in pigeon (Columba livia) goal-searching behavior

Terrain slope provides a directional frame of reference for reorientation and navigation, similar to cardinal directions. Previous studies have shown that, in a goal location task, slope is a very salient cue and that pigeons tend to rely on it even if it is not the most informative cue. Such a strong dependence on one type of information, when there are more effective predictors of reward, is a key premise for a modular view of information processing. Here we tested the provocative hypothesis of a "slope module" for reorientation in slanted environments. Pigeons had to solve a goal location task using slope or another, theoretically salient cue: a beacon feature. Overall, searching behavior was controlled almost equally by the two cues. The fact that, for the first time, slope failed to capture most of the associative strength allows us to reject a strong modularity view and suggests instead that there is competition between cues based on salience. As an interesting additional finding, the reliance on slope and the feature was affected by training location (uphill vs. downhill), suggesting the possibility of a modulatory role of effort on the cue-weighting mechanism of reorientation.     

How long is your arm? Using multisensory illusions to modify body image from the third person perspective

Updating body representations from the 3rd person perspectives (3PP) seems to require viewing the real body, unlike when viewing from a 1st person perspective. Here, 3PP updating was investigated through induction of a physically impossible multisensory illusion in which participants viewed real-time 3PP video of themselves having their arm pulled until it stretched to twice its normal length. The illusion elicited the subjective experience that the participant's own arm had been stretched and caused an overestimation of reaching distance, although actual reaches were unaffected. Multisensory illusions from the 3PP can alter body image when applied to real bodies.     

The field dependence/independence cognitive style does not control the spatial perception of elevation

Earlier work described the presence of a significant connection between an individual's ability to disregard distracting aspects of a visual field in the classical rod-and-frame test (RFT), in which a subject is required to set a rod so that it will appear vertical in the presence of a square frame that is roll tilted from vertical, and in paper-and-pencil tests, in which the subject is required to find a hidden figure embedded in a more complex figure (the Embedded Figures Test [EFT]; see, e.g., Witkin, Dyk, Faterson, Goodenough, & Karp, 1962; Witkin et al., 1954; Witkin, Oltman, Raskin, & Karp, 1971). This has led to a belief in the existence of a bipolar dimension of cognitive style that is utilized in such disembedding tasks--namely, the extent to which an individual is dependent on or independent from the influence of a distracting visual field. The influence of an inducing visual field on the perception of elevation measured by the setting of a visual target to appear at eye level (the visually perceived eye level [VPEL] discrimination) has also been found to be correlated with the RFT. We have thus explored the possible involvement of the dependence/independence cognitive style on the VPEL discrimination. Measurements were made on each of 18 subjects (9 of them female, 9 male) setting a small target to the VPEL in the presence of a pitched visual field across a range of six pitches from -30 degrees (topbackward) to +20 degrees (topforward) and on each of three tests generally recognized as tests of cognitive spatial abilities: the EFT, the Gestalt Completion Test, and the Snowy Pictures Test (SPT). Although there were significant pairwise correlations relating performance on the three cognitive tests (+.73, +.48, and +.71), the correlation of each of these three with the slope of the VPEL-versus-pitch function was not significant, as it was with the slope of the perception of visual pitch of the field (PVP)-versus-pitch function. VPEL, PVP, and a cognitive factor separated into three essentially independent factors in a multiple-factor analysis, with the three cognitive tests clustering at the cognitive factor, and with no significant loading on either of the other two factors. From the above considerations and a multiple-factor analytic treatment including additional results from this and other laboratories, we conclude that the cognitive-processing style held to be involved in the performance on the EFT and the perception of vertical as measured by the RFT is not general for egocentric space perception; it does not involve the perception of elevation.     

Visually perceived eye level with reversible pitch stimuli: implications for the great circle and implicit surface models

Visually perceived eye level (VPEL) and perceived pitch were measured while subjects viewed two sets of stimuli that were either upright or pitched top-toward or top-away from them. The first set of stimuli, a pair of vertical lines viewed at various angles of pitch, caused systematic changes in perceived pitch and upward and downward VPEL shifts for the top-toward and top-away pitches, respectively. Neither the perceived pitch nor the VPEL measures with these stimuli differed between monocular and binocular viewing. The second set of stimuli was constructed so that, when viewed at the appropriate pitch angle, the projected orientations of the lines in the retinal image of each stimulus were similar to those generated by a pair of vertical lines pitched by a lesser amount in the opposite direction. When viewed monocularly, these stimuli appeared pitched in the direction opposite their physical pitch, yet produced VPEL shifts consistent with the direction of their physical pitch. These results clearly demonstrate a dissociation between perceived pitch and VPEL. The same stimuli, when viewed binocularly, appeared pitched in the direction of their physical pitch and caused VPEL shifts indistinguishable from those obtained monocularly. The retinal image orientations of these stimuli, however, corresponded to those of vertical line stimuli pitched in the opposite direction. This finding is therefore consistent with the hypothesis that VPEL and perceived pitch are processed independently, but inconsistent with the specific version of this hypothesis which states that differences in VPEL are determined solely on the basis of the orientation of lines in the retinal image.     

Perception: A HyperCard stack for demonstrating visual perceptual phenomena

Perception is a HyperCard stack that allows users to explore visual illusions and other perceptual phenomena on the Apple Macintosh. The stack contains over 20 demonstrations of intersecting line illusions, size and shape illusions, subjective contours, color assimilation, and so forth. As a presentation tool for classroom or laboratory demonstrations, Perception offers three unique features for displaying visual phenomena: (1) the capability to “dissolve” the inducing elements of an illusion in order to show the objective state of affairs, (2) the ability to quickly reverse the inducing elements of an illusion and therefore the effects of the distortion, and (3) animation of the various components of an illusion to produce continuous distortions in-real time. These features are illustrated with use of the Orbison, Titchener, Hering, and Wundt illusions. Use of the stack reveals two interesting and unanticipated findings: (1) an apparent size distortion in the central square of the Orbison illusion as it moves back and forth across the background of concentric rings, and (2) perceptual aftereffects that arise when the inducing elements of the Titchener, Hering, or Wundt illusion is dissolved.