Sex and hand-preference effects in the simultaneous and consecutive discrimination of lifted weight

Determination of maximum acceptable and comfortable height during one-handed lifting

BACKGROUND

One-handed lifting commonly occurs in the industry. Specific guidelines of proper heights during one-handed lifting could be valuable information to design or to assess the risk of work environment.

OBJECTIVE

The objective of this study was to determine the maximum acceptable height and comfortable height during one-handed vertical lifting by gender, participant height, hand, and object weight.

METHODS

Based on the psychophysical method, 72 males and 50 females, divided into four different height groups, determined their maximum acceptable and comfortable heights by each hand (left and right) and various object weights (1 kg, 3 kg, 5 kg, and 8 kg).

RESULTS

Males revealed significantly greater maximum acceptable heights (males: 157 cm; females: 135 cm) and higher comfortable heights (males: 104 cm; females: 96 cm) compared to females. The participants' heights, which hand was used to lift, and the object weight were significant factors in determining the maximum acceptable height for both males and females. The multiple linear regression model of the maximum acceptable height showed more robust predictive power (R2 = 0.55) compared to the comfortable height (R2 = 0.20) as a function of gender, participant height, hand, and object weight.

CONCLUSIONS

Results suggest that gender, participant height, hand, and object weight are important variables to consider when determining the proper surface height of one-handed vertical lifting. Using the robust predictive model, an appropriate maximum acceptable height could be suggested based on the material handler's anthropometric information and object weight.

Hemispheric Asymmetries in Price Estimation: Do Brain Hemispheres Attribute Different Monetary Values?

The Spatial Numerical Association of Response Codes (SNARC) effect has been associated with a wide range of magnitude processing. This effect is due to an implicit relationship between numbers and horizontal space, according to which weaker magnitudes and smaller numbers are represented on the left, whereas stronger magnitudes and larger numbers are represented on the right. However, for some particular type of magnitudes such as price, judgments may be also influenced by perceived quality and thus involving valence attribution biases driven by brain asymmetries. In the present study, a lateralized tachistoscopic presentation was used in a price estimation task, using a weight estimation task as a control, to assess differences in asymmetries between these two attributes. Results show a side bias in the former condition but not in the latter, thus indicating that other non-numerical mechanisms are involved in price estimation. Specifically, prices were estimated lower in the left visual field than in the right visual field. The proposed explanation is that price appraisal might involve a valence attribution mechanism leading to a better perceived quality (related to higher prices) when objects are processed primarily in the left hemisphere, and to a lower perceived quality (related to lower prices) when objects are processed primarily in the right hemisphere.

Properties of the size-weight illusion as shown by lines of subjective equality

We studied the size-weight illusion through comparative judgments. The experiment had two direct aims: to verify whether the relative contribution of size to apparent heaviness can differ for different stimulus sets, and to verify whether that contribution can differ for different methods of comparing two objects (consecutive vs. simultaneous weighing). Thirty university students participated. Results show that the relative contribution of size depends on stimulus set, but is independent of the method used for comparing objects. The first finding implies that a linear model cannot describe the integration of size and weight information in the illusion; the second finding is evidence for the low-level character of the integration process.

Discrimination of grip force for preschool children aged 5 to 6 years

The ability to discriminate grip force was investigated in 30 preschool children aged 5 to 6 years in an experiment controlling for motivation and muscle fatigue. The subjects were required to maintain a relatively high force during the discrimination with forces of the standard stimulus being 1.0, 2.0, and 3.0 kgf. Comparison stimuli changed at an interval of 0.1 kgf. Discrimination was measured in terms of the lower threshold, upper threshold, and interval of uncertainty. Since the statistical analyses indicated that there were no significant gender differences, data for boys and girls were combined. Although the upper and lower thresholds and the interval of uncertainty increased with the force required by the standard stimuli, Weber fractions did not remain constant when the stimulus intensity changed, unlike the findings in previous studies for adults.

Spatial field advantages for tactile line bisection as a function of hemispheric specialisation inferred from dichotic listening

Thirty left-ear advantaged (LEA) and 30 right-ear advantaged (REA) right-handed subjects performed tactile line bisection (TLB) in left and right spatial fields, and at midline. REA subjects were found to perform significantly better in the right spatial field than in the left and LEA subjects significantly better in the left than in the right. Significant directional deviations were found only at midline with the left hand deviating to the right and the right hand to the left. These findings suggest that TLB is primarily a spatial task subserved by feedforward motor processes and that directional deviations are due to the differential scaling of egocentric space.

Factor analysis and the cerebral hemispheres: pilot study and parietal functions

Although research on lateral differences has proliferated, attempts to specify fundamental dichotomies of hemispheric processing have yielded less than satisfactory results. The factor analysis of behavioral asymmetries can provide a different approach by helping to identify common functions underlying disparate tasks. It can also provide information on individual differences and interrelationships among functions. Here, the viability of the approach is demonstrated with a small pilot study (N = 29), and with two larger experiments (N = 70 and N = 60) that stress parietal lobe function. Seven lateralized functions were identified: auditory lexical, spatial attentive, spatial positional, spatial quantitative, tactile figural, visual emotional and visual lexical. A range of positive, negative and null correlations was found between functions, contrary to lateralization strength, hemisphericity, and independence models of individual differences in lateralization. However, a pattern of intercorrelations was observed among functions believed to be localized to the perisylvian region (Brodmann areas 22 and 39), which is consistent with the neurodevelopment theory of Geschwind and Galaburda (Cerebral Lateralization Biological Mechanisms, Associations and Pathology, The MIT Press, Cambridge, MA, 1987).

Different pattern of hemisphere specialization between identical kinesthetic spatial and weight discrimination tasks

Thumb position discrimination and weight discrimination tasks were examined in female students. Task procedures were identical for the position and weight tasks. Different weights were loaded for each positioning and the thumb was abducted to discriminate the weight. The Weber ratio was obtained by the method of constant stimuli and was compared between right and left. The results of position discrimination indicated left thumb (right hemisphere) superiority, while the results of weight discrimination indicated no laterality despite identical tasks. Directed attention is suggested to play an important role in the appearance of hemisphere lateralization.

Can shape be perceived by dynamic touch?

The possibility that some aspects of the shapes of solid objects can be perceived through dynamic touch, even when the objects are not touched, but simply wielded with a handle, was investigated in four experiments. Wooden solids were constructed of three sizes and five shapes: hemisphere, cylinder, parallelepiped, cone, and pyramid. Experiments 1 and 2 involved comparisons (judgments of same or different) between and among wielded objects of the same mass. In Experiments 3 and 4, subjects were required to wield an object and to select a match from a visible arrangement of objects of the five shapes; the wielded objects were of two sizes, each different from that of the visible objects. The success of subjects at these tasks, and the patternings of errors, are seen to involve the characteristic moment of inertia profiles of each shape, and a ratio of the object's resistances to rotation around orthogonal axes is shown to be a strong predictor of performance in the identification experiments. The results are discussed with reference to dynamic touch and to the notion of shape invariants that do not reduce to aspects of object surface.

Matching forces: constant errors and differential thresholds

A contralateral limb-matching procedure was used to study the perception of forces generated by the elbow flexor muscles. Subjects were required to generate forces ranging from 15 to 85% of their maximum voluntary contraction (MVC range: 169-482 N), and after achieving the target force to produce a force of the same perceived intensity with their contralateral arm. Under these conditions, subjects consistently overestimated the amplitude of the two lowest forces, and the most accurate matching of forces occurred in the middle of the response range (around 50% MVC). This pattern of constant errors could be explained in terms of an artifact of the starting position, which has been shown to influence the accuracy of judgements of stimulus magnitude. The Weber fraction for force calculated from the matching data was 0.07, which is within the range reported previously for weight. These thresholds are, however, considerably lower than those described for friction and the moment of inertia, the perception of which also involves the proprioceptive system.

Manual asymmetry in weight discrimination: hand preference or hemispheric specialization?

One-handed weight discrimination was investigated as a function of hand, hand preference and hemispheric specialization. Differential thresholds (DLs) were measured for the left and right hands and left- and right-handed male and female subjects. DLs were found to be lower for the hand contralateral to the ear that proved superior in a verbal dichotic listening task. These results establish the existence of a manual asymmetry for the discrimination of lifted weight with the advantage accruing for the hand contralateral to the non-language cerebral hemisphere.

Manual asymmetry in weight discrimination: hand or spatial-field advantage?

Sixty subjects who were either left-handed or right-handed performed one-handed weight discrimination using their left and right hands in the left and right spatial fields. Differential thresholds, for the left and right hands of both left-handed and right-handed subjects, were found to be lower in the spatial field contralateral to the ear which proved superior in a dichotic listening test. It is concluded that manual asymmetry for weight discrimination results primarily from the mapping of sensorimotor events in the spatial fields onto contralateral cerebral cortex, with an advantage in the spatial field contralateral to the nonlanguage cerebral hemisphere.