Mass Distribution Of Objects Research Articles

Pseudo-Haptic Display of Mass and Mass Distribution During Object Rotation in Virtual Reality.

We propose and evaluate novel pseudo-haptic techniques to display mass and mass distribution for proxy-based object manipulation in virtual reality. These techniques are specifically designed to generate haptic effects during the object's rotation. They rely on manipulating the mapping between visual cues of motion and kinesthetic cues of force to generate a sense of heaviness, which alters the perception of the object's mass-related properties without changing the physical proxy. First we present a technique to display an object's mass by scaling its rotational motion relative to its mass. A psycho-physical experiment demonstrates that this technique effectively generates correct perceptions of relative mass between two virtual objects. We then present two pseudo-haptic techniques designed to display an object's mass distribution. One of them relies on manipulating the pivot point of rotation, while the other adjusts rotational motion based on the real-time dynamics of the moving object. An empirical study shows that both techniques can influence perception of mass distribution, with the second technique being significantly more effective.

Anticipatory grasping control modulates somatosensory perception.

Somatosensory perception is hampered on the moving limb during a goal-directed movement. This somatosensory suppression is mostly attributed to a forward model that predicts future states of the system based on the established motor command. Here, we examined whether and how this suppression is modulated by the predictability of object features important for controlling a grasping movement. Participants reached to grasp an object between thumb and index finger and then lifted it as straight as possible. Objects with symmetric or asymmetric mass distributions were presented either in a blocked or random manner, so that the object's mass distribution could be anticipated or not. At the moment of object contact, a brief vibrotactile stimulus of varying intensities was presented on the dorsal part of the moving index finger. Participants had to report whether they detected the stimulus. When the object's mass distribution was predictable, contact points with the object were modulated to the object's centre of mass. This modulation contributed to a minimized resultant object roll during lifting. When the object's mass distribution was unpredictable, participants chose a default grasping configuration, resulting in greater object roll for asymmetric mass distributions. Somatosensory perception was hampered when grasping both types of objects compared to baseline (no-movement). Importantly, somatosensory suppression was stronger when participants could predict the object's mass distribution. We suggest that the strength of somatosensory suppression depends on the predictability of movement-relevant object features.

Automatic crop detection under field conditions using the HSV colour space and morphological operations

Developing an automatic weeding system requires robust detection of the exact location of the crop to be protected from damage. Computer vision techniques can be an effective means of determining plant location. In this paper, a novel algorithm based on colour features and morphological erosion and dilation is proposed. This process segments cauliflower crop regions in the image from weeds and soil under natural illumination (cloudy, partially cloudy, and sunny). The proposed algorithm uses the HSV colour space for discriminating crop, weeds and soil. The region of interest (ROI) is defined by filtering each of the HSV channels between certain values (minimum and maximum threshold values). The region is then further refined by using a morphological erosion and dilation process. The moment method is applied to determine the position and mass distribution of objects in video sequences, as well as to track crops. The performance of the algorithm was assessed by comparing the obtained results with those of ground truth methods (manual annotation). A sensitivity of 98.91% and precision of 99.04% was achieved.

Digit Position and Forces Covary during Anticipatory Control of Whole-Hand Manipulation.

Theoretical perspectives on anticipatory planning of object manipulation have traditionally been informed by studies that have investigated kinematics (hand shaping and digit position) and kinetics (forces) in isolation. This poses limitations on our understanding of the integration of such domains, which have recently been shown to be strongly interdependent. Specifically, recent studies revealed strong covariation of digit position and load force during the loading phase of two-digit grasping. Here, we determined whether such digit force-position covariation is a general feature of grasping. We investigated the coordination of digit position and forces during five-digit whole-hand manipulation of an object with a variable mass distribution. Subjects were instructed to prevent object roll during the lift. As found in precision grasping, there was strong trial-to-trial covariation of digit position and force. This suggests that the natural variation of digit position that is compensated for by trial-to-trial variation in digit forces is a fundamental feature of grasp control, and not only specific to precision grasp. However, a main difference with precision grasping was that modulation of digit position to the object’s mass distribution was driven predominantly by the thumb, with little to no modulation of finger position. Modulation of thumb position rather than fingers is likely due to its greater range of motion and therefore adaptability to object properties. Our results underscore the flexibility of the central nervous system in implementing a range of solutions along the digit force-to-position continuum for dexterous manipulation.

Effects of Carpal Tunnel Syndrome on adaptation of multi-digit forces to object mass distribution for whole-hand manipulation

BackgroundCarpal tunnel syndrome (CTS) is a compression neuropathy of the median nerve that results in sensorimotor deficits in the hand. Until recently, the effects of CTS on hand function have been studied using mostly two-digit grip tasks. The purpose of this study was to investigate the coordination of multi-digit forces as a function of object center of mass (CM) during whole-hand grasping.MethodsFourteen CTS patients and age- and gender-matched controls were instructed to grasp, lift, hold, and release a grip device with five digits for seven consecutive lifts while maintaining its vertical orientation. The object CM was changed by adding a mass at different locations at the base of the object. We measured forces and torques exerted by each digit and object kinematics and analyzed modulation of these variables to object CM at object lift onset and during object hold. Our task requires a modulation of digit forces at and after object lift onset to generate a compensatory moment to counteract the external moment caused by the added mass and to minimize object tilt.ResultsWe found that CTS patients learned to generate a compensatory moment and minimized object roll to the same extent as controls. However, controls fully exploited the available degrees of freedom (DoF) in coordinating their multi-digit forces to generate a compensatory moment, i.e., digit normal forces, tangential forces, and the net center of pressure on the finger side of the device at object lift onset and during object hold. In contrast, patients modulated only one of these DoFs (the net center of pressure) to object CM by modulating individual normal forces at object lift onset. During object hold, however, CTS patients were able to modulate digit tangential force distribution to object CM.ConclusionsOur findings suggest that, although CTS did not affect patients’ ability to perform our manipulation task, it interfered with the modulation of specific grasp control variables. This phenomenon might be indicative of a lower degree of flexibility of the sensorimotor system in CTS to adapt to grasp task conditions.

Obtaining information by dynamic (effortful) touching.

Dynamic touching is effortful touching. It entails deformation of muscles and fascia and activation of the embedded mechanoreceptors, as when an object is supported and moved by the body. It is realized as exploratory activities that can vary widely in spatial and temporal extents (a momentary heft, an extended walk). Research has revealed the potential of dynamic touching for obtaining non-visual information about the body (e.g. limb orientation), attachments to the body (e.g. an object's height and width) and the relation of the body both to attachments (e.g. hand's location on a grasped object) and surrounding surfaces (e.g. places and their distances). Invariants over the exploratory activity (e.g. moments of a wielded object's mass distribution) seem to ground this 'information about'. The conception of a haptic medium as a nested tensegrity structure has been proposed to express the obtained information realized by myofascia deformation, by its invariants and transformations. The tensegrity proposal rationalizes the relative indifference of dynamic touch to the site of mechanical contact (hand, foot, torso or probe) and the overtness of exploratory activity. It also provides a framework for dynamic touching's fractal nature, and the finding that its degree of fractality may matter to its accomplishments.

Non-power law behavior in fragmentation cascades

Collisions resulting in fragmentation are important in shaping the mass spectrum of minor bodies in the asteroid belt, the Kuiper Belt, and debris disks. Models of fragmentation cascades typically find that in steady-state, the solution for the particle mass distribution is a power law in the mass. However, previous studies have typically assumed that the mass of the largest fragment produced in a collision with just enough energy to shatter the target and disperse half its mass to infinity is directly proportional to the target mass. We show that if this assumption is not satisfied, then the power law solution for the steady-state particle mass distribution is modified by a multiplicative factor, which is a slowly varying function of the mass. We derive analytic solutions for this correction factor and confirm our results numerically. We find that this correction factor proves important when extrapolating over many orders of magnitude in mass, such as when inferring the number of large objects in a system based on infrared observations. In the course of our work, we have also discovered an unrelated type of non-power law behavior: waves can persist in the mass distribution of objects even in the absence of upper or lower cutoffs to the mass distribution or breaks in the strength law.

Haptic selective attention by foot and by hand

Nonvisual perceptions of a wielded object's spatial properties are based on the quantities expressing the object's mass distribution, quantities that are invariant during the wielding. The mechanoreceptors underlying the kind of haptic perception involved in wielding – referred to as effortful, kinesthetic, or dynamic touch – are those embedded in the muscles, tendons, and ligaments. The present experiment's focus was the selectivity of this muscle-based form of haptic perception. For an occluded rod grasped by the hand at some intermediate position along its length, participants can attend to and report selectively the rod's full length, its partial lengths (fore or aft of the hand), and the position of the grip. The present experiment evaluated whether participants could similarly attend selectively when wielding by foot. For a given rod attached to and wielded by foot or attached to (i.e. grasped) and wielded by hand, participants reported (by magnitude production) the rod's whole length or fractional length leftward of the point of attachment. On measures of mean perceived length, accuracy, and reliability, the degree of differentiation of partial from full extent achieved by means of the foot matched that achieved by means of the hand. Despite their neural, anatomical, and experiential differences, the lower and upper limbs seem to abide by the same principles of selective muscle-based perception and seem to express this perceptual function with equal facility.

Haptic Perception of Affordances of a Sport Implement: Choosing Hockey Sticks for Power versus Precision Actions on the Basis of “Feel”

The present study investigated how changing the mass distribution of a hockey stick influenced the perceived affordances of a stick's utility for performing either a precision or power action. Top-weighted sticks were preferred for executing precisely controlled movements, both before and after using the stick to complete an interception action task. Initially, participants in the power condition preferred the bottom -weighted stick. However, once participants performed the power condition action task, they preferred a stick with a mass concentration closer to their point of grasp. These results indicate that a held object's perceived affordances are influenced both by its mass distribution, and the perceiver's level of experience using the tool for a given action. Human factors consideration include designing hand-held sporting equipment that capitalizes on people's sensitivity to an object's mass distribution.

Formation of a mass distribution of objects. ii. mergings in a two-component set of particles

The random quantity ξ, the number of pairwise mergings for a two-component sample N = N1 + N2, N2≤ N1, is found under the assumption that mergings only between particles of different types are possible. Let T0,T1,T2,..., Tm, ... be a sequence of times. We then have a discrete approximation of the process of mergings by a uniform Markov chain.

Formation of a mass distribution of objects in an initially uniform field. I. Mergings in a one-component set of particles

A random quantity ξ, the number of pairwise mergings in a finite set of particles, is constructed in a sequential scheme of complex trials. Let T0, T1,T2,…, Tm,…be a sequence of times. We then have a discrete approximation of the process of mergings by a uniform Markov chain.

Attentionally splitting the mass distribution of hand-held rods

Two experiments on the length-perception capabilities of effortful or dynamic touch differed only in terms of what the subject intended to perceive, while experimental conditions and apparatus were held constant. In each trial, a visually occluded rod was held as still as possible by the subject at an intermediate position. For two thirds of the trials, a weight was attached to the rod above or below the hand. In Experiment 1, in which the subject's task was to perceive the distance reachable with the portion of the rod forward of the hand, perceived extent was a function of the first moment of the mass distribution associated with the forward portion of the rod, and indifferent to the first moment of the entire rod. In Experiment 2, in which the task was to perceive the distance reachable with the entire rod if it was held at an end, the pattern of results was reversed. These results indicate the capability of selective sensitivity to different aspects of a hand-held object's mass distribution, without the possibility of differential exploration specific to these two tasks. Results are discussed in relation to possible roles of differential information, intention, and self-organization in the explanations of selective perceptual abilities.