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At least 217 records · Page 12Linked to original sources
PubMed2000

Perceptual independence of whole length, partial length, and hand position in wielding a rod.

Previous investigations of dynamic touch have shown that, in wielding an occluded rod, the nonvisible perceptions of total rod length, hand position, and fractional rod length above or below the hand are different functions of the eigenvalues and eigenvectors of the inertia tensor. The implication that the 3 perceptions are independent covariants of the inertia tensor of a wielded object was tested with the complete identification experimental procedure using the statistical prescriptions of F. G. Ashby and J. T. Townsend (1986). The confirmed independence is discussed in the context of the generalized psychological or perception-information hypothesis.

Adult↗
PubMed2002

Perceptual behavior: recurrence analysis of a haptic exploratory procedure.

Various object properties are perceptible by wielding. We asked whether the dynamics of wielding differed as a function of the to-be-perceived property. Wielding motions were analyzed to determine if they differed under the intention to perceive or not perceive rod length (experiment 1), to perceive object height versus object width (experiment 2), and to perceive the length forward of where the rod was grasped versus the position of the grasp (experiment 3). Perceiving these different properties is known to depend on different components of the object's inertia tensor. Analyses of the subtle recurrent patterns in the phase space of the hand motions revealed differences in wielding across the different perceptual intentions. Haptic exploratory procedures may exhibit distinct exploratory dynamics.

Adult↗
PubMedDate not supplied

Discriminability of load heaviness: implications for the psychophysical approach to manual lifting.

The main objective of this study was to investigate human ability to discriminate between different levels of load heaviness in manual lifting. Twelve male college students participated in the laboratory experiment. Twenty-eight sequences of five boxes that weighed from 5 to 64 lbs (2.27-29.1 kg) were used. The subjects were asked to arrange boxes in each sequence in order of the perceived (increasing or decreasing) heaviness, i.e., from lightest to the heaviest box, or from heaviest to the lightest box. The subjects were also asked to assign linguistic descriptors of perceived load heaviness to each box in the sequence, and to indicate the confidence levels regarding correctness of the assigned box order and assignment of linguistic values. The independent variables included magnitude of weight and load differential between the successive weights in a sequence. The number of sequential ordering errors, assignment of linguistic variables, and estimated confidence levels were highly dependent on the load differential and weight range. It was concluded that in order to assure reliable results of the psychophysical approach to determining the values of maximum acceptable weight of lift, the adjustment process for male subjects should require using small weights of at least 4 lbs (1.8 kg) to be added or removed from the lifted box. The results of this study also suggest that the error rate in load discriminability can be controlled below the 10% level, if the relative difference in weight between successive boxes lifted is at least 12%. Given the above findings, it is suggested that usefulness of some of the recommendations for setting safe limits for manual lifting tasks, which were reached based on the psychophysical approach and broadly reported in the past, may need to be carefully re-examined. Finally, this study showed that the Weber fraction for load heaviness over the range of lifted weights from 8.6 to 29.1 kg is between 0.03 and 0.04.

Biomechanical Phenomena↗
PubMedDate not supplied

Psychophysical capacity of industrial workers for lifting symmetrical and asymmetrical loads symmetrically and asymmetrically for 8 h work shifts.

This paper presents comprehensive maximum acceptable weight of lift (psychophysical lifting capacity) database for male and female industrial workers for lifting symmetrical and asymmetrical loads symmetrically and asymmetrically for 8 h work shifts. The experimental data collected in previous studies on experienced (industrial) and inexperienced (non-industrial) materials handlers (Mital 1984a, Mital and Fard 1986) and the patterns of responses between the two populations (Mital 1985, 1987) were used to generate this database. Since previous work (Mital 1985, 1987) showed that responses of both experienced and inexperienced materials handlers to task variables are similar and also provided multipliers relating the psychophysical lifting capacities of the two populations, it was possible: (1) to convert psychophysical capacity data for asymmetrical lifting of symmetrical and asymmetrical loads, collected on inexperienced workers to reflect psychophysical lifting capacity of experienced workers for asymmetrical lifting; and (2) to take psychophysical lifting capacity data of experienced industrial workers for symmetrical lifting of symmetrical loads and generate from it their psychophysical lifting capacity for symmetrical and asymmetrical lifting of symmetrical and asymmetrical loads by using the response patterns of inexperienced workers to lifting symmetrical and asymmetrical loads symmetrically and asymmetrically. Both approaches were used and, as expected, provided almost identical values for the psychophysical lifting capacity of industrial workers for symmetrical and asymmetrical lifting of symmetrical and asymmetrical loads. Therefore, the final database tables provided in this paper used combined values generated by the two methods.

Databases, Bibliographic↗
PubMed1996

Effects of asymmetric dynamic and isometric liftings on strength/force and rating of perceived exertion.

A laboratory study was undertaken to determine the postural and physical characteristics and subjective stress during dynamic lifting of a usual load (10 kg) compared with during isometric lifting. The authors also aimed to clarify the effects of asymmetric lifting on these parameters. The subjects were thirteen male college students. They were asked to lift a box weighing 10 kg. They performed sixteen different lifting tasks from the floor to a height of 71 cm, involving a combination of three independent factors: two lifting modes (isometric lifting and dynamic lifting), four lifting angles in relation to the sagittal plane (sagittal plane, right 45 degree, right 90 degree and left 90 degree planes) and two lifting postures (squat and stoop). For each lifting task, strengths or forces and ground reaction forces were measured. At the end of each task, the authors asked the subjects to rate their perceived exertion (RPE) during lifting at ten sites of the body. Angle factor had a significant effect on isometric strengths and dynamic peak forces. Isometric strengths during the maximum 3 s were highest in lifting in the right 45 degree plane, followed by that in the sagittal plane, while those in the right 90 degree and left 90 degree planes were the lowest. However, peak forces in dynamic lifting were the highest in the lifting in the sagittal plane, followed by that in the right 45 degree plane, while those in the right 90 degree and left 90 degree planes were the lowest. Postural factor had a significant effect on height at peak force, which is higher in squat lifting than in stoop lifting. RPEs for the left arm, the backs and the right whole body in isometric lifting were significantly higher than in dynamic lifting of 10 kg. There were remarkably high RPEs for the ipsilateral thigh to the box in right 90 degree and left 90 degree planes during both isometric and dynamic liftings. Locations of the resultant force consisting of three component forces on the force plate were closer to the foot on the same side as the box in asymmetric lifting. Thus, some similarities and differences were found between isometric lifting and dynamic liftings regarding the indexes of strength used in this experiment. The authors consider that the subjects used the foot nearer to the box as a fulcrum during asymmetric lifting. Dynamic measurement using the 10 kg weight is less stressful than the conventional isometric measurement. It was possible to obtain the height data at peak force and time-based changes in the force and the box location during lifting only through dynamic lifting measurement. The results provide new knowledge about the biomechanical features of dynamic lifting tasks.

Adolescent↗
PubMed1997

Subjective perceptual methods for comparing backpacks.

Subjective perceptual methods may provide useful information about small differences in backpack design when physiological and biomechanical comparisons are ineffective. This study used two subjective perceptual methods, category ratio scale (CRS) ratings of perceived discomfort and written questionnaires for comparing two types of leisure backpack. CRS ratings of perceived discomfort for each of 24 body regions after 30 min of uphill (15% grade) treadmill walking at 3 km h-1 in 10 males, failed to distinguish between a New Zealand designed backpack (Pack A) and a British designed backpack (Pack B), each weighted to 20 kg. A simple pre- and post-walking written questionnaire using either a visual analogue linear scale or free-format responses indicated that more subjects found Pack A easier to adjust but that it had less comfortable shoulder and waist straps. It was considered to be more comfortable with regard to balance and posture and for shoulder, back and leg muscular tension. Pack B was initially more comfortable but required more lumbar support. Pack B was considered more comfortable for waist and shoulder pressure only. Overall preference was for Pack A (seven subjects) rather than Pack B (three subjects). In conclusion, in this study a questionnaire approach was found to be more useful than CRS ratings of perceived discomfort and the New Zealand designed backpack was preferred.

Adult↗
PubMed1997

Matching object size by controlling finger span and hand shape.

The ability of human subjects to accurately control finger span (distance between thumb and one finger) was studied. The experiments were performed without visual feedback of the hand and were designed to study the dependence of accuracy on object size, shape, distance, orientation and finger configuration. The effects of finger combination and sensory modality used to perceive object size (vision and haptics) were also studied. Subjects were quite proficient at this task; the small errors tended to be predominantly negative, i.e., finger span < object size. The thumb-little finger combination was less accurate than the other finger combinations, irrespective of the sensory modality used. Subjects made larger under-estimating errors when matching the size of cylinders than when matching cubes and parallelepipeds. No effect of viewing distance, object orientation and finger configuration was found. Accuracy in matching object size was not dependent on the sensory modality used. The question of how the individual degrees of freedom of the fingers and thumb contributed to the control of finger span was also addressed. Principal components analysis showed that two components could characterize the hand postures used, irrespective of object size. The amplitude of the first principal component was constant, and the amplitude of the second scaled linearly with object size. This finding suggests that all of the degrees of freedom of the hand are controlled as a unit. This result is discussed in relation to the 'virtual finger' hypothesis for grasping.

Adult↗
PubMed2004

How accurate is partial weightbearing?

The accuracy of partial weightbearing was assessed in six healthy volunteers and 23 patients who had sustained either a fracture of a lower limb or surgery. They were trained to weightbear partially using the conventional bathroom scale method and were assessed in a gait laboratory using force platforms. The amount of weight exerted on the involved limb during three-point crutch walking was determined. Four of six volunteers exerted a mean of 27% of body weight more than required. The remaining two volunteers exerted a mean of 8.5% of body weight less than required. Of the 23 patients, 21 exerted a mean of 35.3% of body weight more than that prescribed and two patients exerted a mean of 11.97% of body weight less than that prescribed. In both groups there was little relationship between the weightbearing prescribed and actual weightbearing. None of the patients or volunteers was able to reproduce the extent of partial weightbearing for which they were trained using the bathroom scale method, confirming that this technique of instructing patients in partial weightbearing is inaccurate.

Adolescent↗
PubMed2006

Changes in posture and perceived exertion in adolescents wearing backpacks with and without abdominal supports.

OBJECTIVE: The goal was to examine whether backpacks with an abdominal support device improve posture and decrease exertion while walking among adolescents. DESIGN: Double-blinded trial, with 20 subjects, performed at a University Spine Center. On day 1, adolescents walked on a treadmill for 5 mins with photographic measurement of posture and responded to the Borg scale of perceived exertion before and after ambulation. On day 2, they repeated the trial four more times wearing a backpack randomly loaded with either 10% or 20% of body weight and with or without the Back Balancer abdominal support. Postural measures were recorded by a blinded observer. RESULTS: Postural changes (forward lean) wearing a backpack with abdominal support were significantly lower while carrying both 10% and 20% of body weight (P = 0.024 and P = 0.008, respectively) vs. no abdominal support. In addition, perceived exertion at 10% and 20% of body weight was significantly greater without abdominal support (P = 0.042 and P = 0.018, respectively). CONCLUSIONS: Forward lean and perceived exertion while wearing backpacks in adolescents can be significantly decreased with abdominal support. This may increase comfort and decrease complications, such as back pain, that may arise from backpack use.

Abdomen↗
PubMed2005

Disturbances of grip force behaviour in focal hand dystonia: evidence for a generalised impairment of sensory-motor integration?

BACKGROUND: Focal task specific dystonia occurs preferentially during performance of a specific task. There may be an inefficiently high grip force when doing manipulative tasks other than the trigger task, possibly reflecting a generalised impairment of sensory-motor integration. OBJECTIVE: To examine how well subjects with writer's cramp (n = 4) or musician's cramp (n = 5) adapted their grip force when lifting a new object or catching a weight. METHODS: Nine patients with focal hand dystonia and 10 controls were studied. Experiments addressed different motor behaviours: (A) lifting and holding an object; (B) adjusting grip force in anticipation of or in reaction to a change in load force by catching a small weight dropped expectedly or unexpectedly into a hand held receptacle. RESULTS: In (A), patients produced a grip force overshoot during the initial lifts; force overflow was most pronounced in those with writer's cramp. Patients and controls adjusted their grip force to object weight within one or two lifts, though patients settled to a steady force level above normal. In (B), patients with focal hand dystonia and normal controls showed similar predictive grip force adjustments to expected changes in object load, suggesting that this aspect of sensory-motor integration was normal. Patients had a shorter latency of grip force response than controls after an unexpected load increase, reflecting either a greater level of preparatory motor activity or a disinhibited spinal reflex response. CONCLUSIONS: The overall increased grip force in patients with focal hand dystonia is likely to be a prelearned phenomenon rather than a primary disorder of sensory-motor integration.

Adult↗
PubMed2003

Abnormal sequencing of motor actions in patients with schizophrenia: evidence from grip force adjustments during object manipulation.

OBJECTIVE: During object manipulation, grip force must be adjusted in anticipation of destabilizing load forces to prevent the object from slipping. This study used three gripping tasks to assess whether schizophrenia affects the predictive mechanisms required for the scaling, timing, and/or sequencing of motor actions. METHOD: Sixteen patients with schizophrenia and 16 comparison subjects matched for age, sex, and educational level 1) lifted objects of various mass and texture (lift task) and 2) used a manipulandum to hit (hit task) or resist (resist task) impacts produced by a collision with a pendulum. For an optimized performance, all tasks demanded a predictive increase in grip force and the timing of external events. The fluid sequencing of finger and hand submovements was required for the lift and the hit tasks but not for the resist task. RESULTS: Patients were impaired in the smooth execution of both the lift and the hit tasks but not in the performance of the resist task. In all three tasks, the scaling of grip force was similar for patients and comparison subjects. CONCLUSIONS: Schizophrenia is associated with a specific deficit in the sequencing of motor actions rather than with an overall problem in the predictive control of movement.

Adolescent↗
PubMed1993

Further studies of psychophysically determined maximum acceptable weights and forces.

The effects of lifting boxes without handles, pulling long distances, carrying different size boxes, combining three handling tasks, and lifting with extended horizontal reach were studied using a psychophysical methodology. Six male industrial workers performed 42 variations of lifting, lowering, pushing, pulling, and carrying tasks. Lifting boxes without handles produced consistent decreases (median, 16%) in maximum acceptable weights when compared with lifting boxes with handles. Lifting with extended horizontal reach (approximately 48 cm) produced consistent decreases (median, 48%) in maximum acceptable weights when compared with lifting close to the body (approximately 17 cm). No significant heart rate or oxygen consumption differences occurred in either of these variables. No significant differences in maximum acceptable weight of carry were observed among box sizes; however, the maximum acceptable force of pulling was lower for longer (15.2 m) pulling tasks. The maximum acceptable weight for combination tasks was similar to that of the limiting component.

Adult↗
PubMed2004

Maximum isometric lifting strengths of men in teamwork.

This study reexamined the additivity of maximum isometric teamwork lifting strength using experienced and height-matched young male participants. The maximum isometric lifting strength was measured for four exertion heights (45, 75, 105, and 140 cm) and four lifting styles (one-, two, three-, and four-person exertions). The results showed that actual teamwork strength could be greater or lower than the sum of individual strengths. If it was greater, the difference between the two could be either significant or nonsignificant, but if it was lower, there was no significant difference between the two. Actual teamwork strength ranged from 90.0% to 134.8% of the sum of individual strengths, indicating that experienced and height-matched participants could overcome the problem of lack of coordination in isometric teamwork lifting. The results also showed that some teamwork members, especially weaker members, might be forced to exert strengths higher than their maximum individual voluntary strengths in teamwork lifting. To avoid such overexertion in teamwork, it is recommended that the weight of the handled load be controlled and lower than the sum of all members' strengths. Additionally, members with significantly different strength abilities should not be assigned to the same team. Actual or potential applications of this research include designing member assignments in teamwork lifting tasks.

Adult↗
PubMed2004

The effects of global grouping laws on surface lightness perception.

Previous studies of lightness perception have shown that local surface grouping laws such as proximity and T junction were powerful determinants of target surface lightness. Recent lightness theories also emphasize the importance of local grouping of surfaces. In this study, we further examined the effects of three global grouping laws--symmetry, repetition, and alternation--on lightness perception. Local surface grouping laws such as proximity and good continuation were controlled across all of our stimulus displays. Participants' lightness perception consistently depended on a given surface's belongingness as determined by these laws--that is, global grouping laws affected a target surface's lightness perception. Our results indicate that global grouping laws determine a target surface's lightness when local surface grouping does not produce any distinct surface belongingness. Implications of our basic results are discussed in terms of a recent lightness theory.

Form Perception↗
PubMed2001

Estimating the minimum grip force required when grasping objects under impulsive loading conditions.

As an aid to studying the efficiency of grip force scaling in the context of collisions, we present a simple cost-effective approach to estimating the slip ratio--that is, the minimum grip-to-load-force ratio needed to prevent object slippage. The grip apparatus comprises a sturdy load cell to measure grip force and two linear potentiometers to provide detailed description of finger movements. The slip ratio was estimated by plotting the magnitude of finger movement against the grip-to-load-force ratio at the time of impact. The slip ratio was dependent on the direction of loading, which stresses the importance of estimating slip ratios in a context similar to that of the experiment in which the efficiency of subjects' behavior is to be assessed.

Adult↗