Nature benefits revisited: Differences in gait kinematics between nature and urban images disappear when image types are controlled for likeability.

Exposure to urban environments requires more cognitive processing than exposure to nature; an effect that can even be measured analysing gait kinematics whilst people walk towards photographic images. Here, we investigated whether differences in cognitive load between nature and urban scenes are still present when scenes are matched for their liking scores. Participants were exposed to images of nature and urban scenes that had been matched a priori for their liking scores by an independent participant sample (n = 300). Participants (N = 44) were either asked to memorise each image during walking or to rate each image for its visual discomfort after each walk. Irrespective of experimental task, liking score but not environment type predicted gait velocity. Moreover, subjective visual discomfort was predictive of gait velocity. The positive impact of nature described in the literature thus might, at least in part, be due to people's aesthetic preferences for nature images.

Fixation Prediction and Visual Priority Maps for Biped Locomotion.

This paper presents an analysis of the low-level features and key spatial points used by humans during locomotion over diverse types of terrain. Although, a number of methods for creating saliency maps and task-dependent approaches have been proposed to estimate the areas of an image that attract human attention, none of these can straightforwardly be applied to sequences captured during locomotion, which contain dynamic content derived from a moving viewpoint. We used a novel learning-based method for creating a visual priority map informed by human eye tracking data. Our proposed priority map is created based on two fixation types: first exploiting the observation that humans search for safe foot placement and second that they observe the edges of a path as a guide to safe traversal of the terrain. Texture features and the difference between them, observed at the region around an eye position, are employed within a support vector machine to create a visual priority map for biped locomotion. The results show that our proposed method outperforms the state-of-the-art, particularly for more complex terrains, where achieving smooth locomotion needs more attention on the traversing path.

How visual perceptual grouping influences foot placement.

Everybody would agree that vision guides locomotion; but how does vision influence choice when there are different solutions for possible foot placement? We addressed this question by investigating the impact of perceptual grouping on foot placement in humans. Participants performed a stepping stone task in which pathways consisted of target stones in a spatially regular path of foot falls and visual distractor stones in their proximity. Target and distractor stones differed in shape and colour so that each subset of stones could be easily grouped perceptually. In half of the trials, one target stone swapped shape and colour with a distractor in its close proximity. We show that in these 'swapped' conditions, participants chose the perceptually groupable, instead of the spatially regular, stepping location in over 40% of trials, even if the distance between perceptually groupable steps was substantially larger than normal step width/length. This reveals that the existence of a pathway that could be traversed without spatial disruption to periodic stepping is not sufficient to guarantee participants will select it and suggests competition between different types of visual input when choosing foot placement. We propose that a bias in foot placement choice in favour of visual grouping exists as, in nature, sudden changes in visual characteristics of the ground increase the uncertainty for stability.

Experimental identification of the behaviour of and lateral forces from freely-walking pedestrians on laterally oscillating structures in a virtual reality environment.

Modelling pedestrian loading on lively structures such as bridges remains a challenge. This is because pedestrians have the capacity to interact with vibrating structures which can lead to amplification of the structural response. Current design guidelines are often inaccurate and limiting as they do not sufficiently acknowledge this effect. This originates in scarcity of data on pedestrian behaviour on vibrating ground and uncertainty as to the accuracy of results from previous experimental campaigns aiming to quantify pedestrian behaviour in this case. To this end, this paper presents a novel experimental setup developed to evaluate pedestrian actions on laterally oscillating ground in the laboratory environment while avoiding the implications of artificiality and allowing for unconstrained gait. A biologically-inspired approach was adopted in its development, relying on appreciation of operational complexities of biological systems, in particular their adaptability and control requirements. In determination of pedestrian forces to the structure consideration was given to signal processing issues which have been neglected in past studies. The results from tests conducted on the setup are related to results from previous experimental investigations and outputs of the inverted pendulum pedestrian model for walking on laterally oscillating ground, which is capable of generating self-excited forces.

Episodic memory and appetite regulation in humans.

Psychological and neurobiological evidence implicates hippocampal-dependent memory processes in the control of hunger and food intake. In humans, these have been revealed in the hyperphagia that is associated with amnesia. However, it remains unclear whether 'memory for recent eating' plays a significant role in neurologically intact humans. In this study we isolated the extent to which memory for a recently consumed meal influences hunger and fullness over a three-hour period. Before lunch, half of our volunteers were shown 300 ml of soup and half were shown 500 ml. Orthogonal to this, half consumed 300 ml and half consumed 500 ml. This process yielded four separate groups (25 volunteers in each). Independent manipulation of the 'actual' and 'perceived' soup portion was achieved using a computer-controlled peristaltic pump. This was designed to either refill or draw soup from a soup bowl in a covert manner. Immediately after lunch, self-reported hunger was influenced by the actual and not the perceived amount of soup consumed. However, two and three hours after meal termination this pattern was reversed - hunger was predicted by the perceived amount and not the actual amount. Participants who thought they had consumed the larger 500-ml portion reported significantly less hunger. This was also associated with an increase in the 'expected satiation' of the soup 24-hours later. For the first time, this manipulation exposes the independent and important contribution of memory processes to satiety. Opportunities exist to capitalise on this finding to reduce energy intake in humans.

Ability of the planar spring-mass model to predict mechanical parameters in running humans.

The planar spring-mass model is a simple mathematical model of bouncing gaits, such as running, trotting and hopping. Although this model has been widely used in the study of locomotion, its accuracy in predicting locomotor mechanics has not been systematically quantified. We determined the percent error of the model in predicting 10 locomotor parameters in running humans by comparing the model predictions to experimental data from humans running in normal gravity and simulated reduced gravity. We tested the hypotheses that the model would overestimate horizontal impulse and the change in mechanical energy of the centre of mass (COM) during stance. The model provided good predictions of stance time, vertical impulse, contact length, duty factor, relative stride length and relative peak force. All predictions of these parameters were within 20% of measured values and at least 90% of predictions of each parameter were within 10% of measured values (median absolute errors: <7%). This suggests that the model incorporates all features of running humans that have a significant influence upon these six parameters. As simulated gravity level decreased, the magnitude of the errors in predicting each of these parameters either decreased or stayed constant, indicating that this is a good model of running in simulated reduced gravity. As hypothesised, horizontal impulse and change in mechanical energy of the COM during stance were overestimated (median absolute errors: 43.6% and 26.2%, respectively). Aerial time and peak vertical COM displacement during stance were also systematically overestimated (median absolute errors: 17.7% and 22.9%, respectively). Care should be taken to ensure that the model is used only to investigate parameters which it can predict accurately. It would be useful to extend this analysis to other species and gaits.

The effect of speed and gradient on hyperextension of the equine carpus.

The equine carpus has a well-defined limit to joint extension at approximately 180 degrees . During locomotion however, the carpus hyperextends during stance phase. Hyperextension is resisted by the carpal bones and ligaments, and it has been proposed that large increased hyperextension might relate to potentially damaging stress levels in the carpus. The aim of this study was to investigate the relationship between peak hyperextension of the carpus (PCE) and speed during locomotion on the level and on an incline. Five Thoroughbred horses were exercised on a treadmill at speeds between 1.8 and 10 m/s at 0% and +7.5% gradients. PCE was obtained using optical motion capture and linear regression used to describe the relationship between PCE and speed on each gradient. PCE increased linearly with speed during locomotion. The rate of increase was greater on a +7.5% gradient. The fit of the regression equations was increased considerably by subtracting standing carpal angle from PCE during locomotion.

Dynamically similar locomotion in horses.

It is possible for animals of very different sizes to use the same patterns of locomotion, i.e. to move in a ;dynamically similar fashion'. This will only occur, however, if relevant biomechanical parameters scale with size in such a way that they compensate for the effects of size differences. Here we apply this principle to understanding the effects of size on locomotion within a species: the domestic horse. We predict that, without any factor to compensate for size differences, detectable deviations from dynamically similar locomotion would occur over the size range present in adult horses. We measured relative stride length (RSL) and duty factor (DF) in 21 trotting horses (body mass: 86-714 kg), and interpolated the data to predict RSL and DF at equivalent speeds (Froude numbers: 0.5, 0.75, 1.0). RSL and DF at equal Froude number were not significantly related to body mass. This is consistent with the hypothesis that horses trot in a dynamically similar fashion at equal Froude number. We show that the nonlinear stress-strain relationship of tendon can contribute to reducing deviations from dynamic similarity, ;buffering' the effects of variation in body mass, but conclude that this effect is unlikely to explain fully our results. This suggests that a ;compensatory distortion' may occur in horses, counteracting the effects of size differences. The approach used here is also applicable to understanding the consequences of size changes within an individual during growth.

Consequences of forward translation of the point of force application for the mechanics of running.

In running humans, the point of force application between the foot and the ground moves forwards during the stance phase. Our aim was to determine the mechanical consequences of this 'point of force translation' (POFT). We modified the planar spring-mass model of locomotion to incorporate POFT, and then compared spring-mass simulations with and without POFT. We found that, if leg stiffness is adjusted appropriately, it is possible to maintain very similar values of peak vertical ground reaction force (GRF), stance time, contact length and vertical centre of mass displacement, whether or not POFT occurs. The leg stiffness required to achieve this increased as the distance of POFT increased. Peak horizontal GRF and mechanical work per step were lower when POFT occurred. The results indicate that the lack of POFT in the traditional spring-mass model should not prevent it from providing good predictions of peak vertical GRF, stance time, contact length and vertical centre of mass displacement in running humans, if an appropriate spring stiffness is used. However, the model can be expected to overestimate peak horizontal GRF and mechanical work per step. When POFT occurs, the spring stiffness in the traditional spring-mass model is not equivalent to leg stiffness. Therefore, caution should be exercised when using spring stiffness to understand how the musculoskeletal system adapts to different running conditions. This can explain the contradictory results in the literature regarding the effect of running speed on leg stiffness.

Scaling of elastic energy storage in mammalian limb tendons: do small mammals really lose out?

It is widely believed that elastic energy storage is more important in the locomotion of larger mammals. This is based on: (a) comparison of kangaroos with the smaller kangaroo rat; and (b) calculations that predict that the capacity for elastic energy storage relative to body mass increases with size. Here we argue that: (i) data from kangaroos and kangaroo rats cannot be generalized to other mammals; (ii) the elastic energy storage capacity relative to body mass is not indicative of the importance of elastic energy to an animal; and (iii) the contribution of elastic energy to the mechanical work of locomotion will not increase as rapidly with size as the mass-specific energy storage capacity, because larger mammals must do relatively more mechanical work per stride. We predict how the ratio of elastic energy storage to mechanical work will change with size in quadrupedal mammals by combining empirical scaling relationships from the literature. The results suggest that the percentage contribution of elastic energy to the mechanical work of locomotion decreases with size, so that elastic energy is more important in the locomotion of smaller mammals. This now needs to be tested experimentally.

Distorting limb design for dynamically similar locomotion.

Terrestrial mammals of different sizes tend to move in a dynamically similar manner when travelling at speeds corresponding to equal values of the Froude number. This means that certain dimensionless locomotor parameters, including peak vertical ground reaction force relative to body weight, stride length relative to leg length and duty factor, are independent of animal size. The Froude number is consequently used to define equivalent speeds for mammals of different sizes. However, most musculoskeletal-tissue properties, including tendon elastic modulus, do not scale in a dynamically similar manner. Therefore, mammals could not be completely dynamically similar, even if perfectly geometrically similar. We argue that, for mammals to move in a dynamically similar manner, they must exhibit systematic 'distortions' of limb structure with size that compensate for the size independence of the tendon elastic modulus. An implication of this is that comparing mammals at equal Froude numbers cannot remove all size-dependent effects. We show that the previously published allometry of limb moment arms is sufficient to compensate for size-independent tendon properties. This suggests that it is an important factor in allowing mammals of different sizes to move in a dynamically similar manner.