Individual differences in perceived pinch force and bite force

Six subjects made cross-modalmatches of pinch force and bite force to an electrocutaneous st4niulus. The electrocutaneous stimulus consisted ofbursts ofpulses, and the intensity ofthe stimulus was varied by changing the number of pulses per burst. All of the individual matching functions were fit well by powerfunctions. The scaling constants and exponents ofthe power functions covaried systematically with the maximum pinch force for 5 of the 6 subjects. The relationship was consistent with the hypothesis that subjects perceive their physical maxima equally, in agreement with Borg’s theory of relative perceived exertion. For both pinch force and bite force functions, the scale factors could be described by a single linear function ofthe exponents, suggesting that all of the matching functions converged at a single point with extreme values.     

Changes in the structure of children's isometric force variability with practice

This study examined the effect of age and practice on the structure of children's force variability to test the information processing hypothesis that a reduction of sensorimotor system noise accounts in large part for age-related reductions in perceptual-motor performance variability. In the study, 6-year-olds, 10-year-olds, and young adults practiced on 5 consecutive days (15 trials/day), maintaining for 15-s trials a constant level of force (5 or 25% of maximum voluntary contraction) against an object using a pinch grip (thumb and index finger). With increasing age, the amount of force error and variability decreased, but the sequential structure of variability increased in irregularity. With practice, children reduced the amount of variability by changing the structure of the force output so as to be more similar to that of their older counterparts. The findings provide further evidence that practice-driven changes in the structure of force output, rather than a decline in the amount of white noise, largely account for age-related reductions in the amount of force variability.     

Grip and load force control and coordination in individuals with diabetes in different manipulation tasks

The study aimed to investigate the control and coordination of grip force (normal component) and load force (tangential component) in three different manipulation tasks in individuals with diabetes with and with no diagnosis of diabetic peripheral neuropathy (DPN) and healthy controls. Twenty-four individuals with type 2 diabetes mellitus, 12 with no (nDPN) and 12 with DPN (wDPN), and 12 healthy controls performed three manipulation tasks (static holding, lifting and holding, and oscillation) with the dominant hand, using an instrumented handle. Relative safety margin (% of GF exerted above the minimum GF needed to hold the object) was measured in all tasks. Individuals with diabetes from the nDPN and wDPN groups set lower relative safety margin than controls only in the static holding task. No other group effect was revealed, except a lower coefficient of friction between skin and object surface in individuals with DPN. The coordination between grip and load force and grip force control was not affected by the diabetes during dynamic manipulation tasks (lifting and holding and oscillation). However, when individuals with diabetes without and with DPN performed a manipulation task in which the inflow of cutaneous information was small and stable (static holding), grip force control was affected by the disease. This finding indicates that individuals with type 2 diabetes mellitus not diagnosed with DPN, already show mild impairments in the nervous system that could affect grip force control and that could be one of the first signs of neuropathy caused by the diabetes.     

Changes in muscle and joint coordination in learning to direct forces

While it has been suggested that bi-articular muscles have a specialized role in directing external reaction forces, it is unclear how humans learn to coordinate mono- and bi-articular muscles to perform force-directing tasks. Participants were asked to direct pedal forces in a specified target direction during one-legged cycling. We expected that with practice, performance improvement would be associated with specific changes in joint torque patterns and mono- and bi-articular muscular coordination. Nine male participants practiced pedaling an ergometer with only their left leg, and were instructed to always direct their applied pedal force perpendicular to the crank arm (target direction) and to maintain a constant pedaling speed. After a single practice session, the mean error between the applied and target pedal force directions decreased significantly. This improved performance was accompanied by a significant decrease in the amount of ankle angular motion and a smaller increase in knee and hip angular motion. This coincided with a re-organization of lower extremity joint torques, with a decrease in ankle plantarflexor torque and an increase in knee and hip flexor torques. Changes were seen in both mono- and bi-articular muscle activity patterns. The mono-articular muscles exhibited greater alterations, and appeared to contribute to both mechanical work and force-directing. With practice, a loosening of the coupling between bi-articular thigh muscle activation and joint torque co-regulation was observed. The results demonstrated that participants were able to learn a complex and dynamic force-directing task by changing the direction of their applied pedal forces through re-organization of joint torque patterns and mono- and bi-articular muscle coordination.     

Sex differences and properties of the decreasing force during sustained static grip at various target forces

The purpose of this study was to examine properties and sex differences of the decreasing force during sustained isometric grip using various target forces, 50%, 75%, and 100% of maximal voluntary contraction (MVC), for 6 min. Participants were healthy, 15 men (height = 172.9 +/- 4.6 cm, body mass = 67.7 +/- 5.36 kg) and 15 women (height = 160.9 +/- 5.4 cm, body mass = 55.9 +/- 5.36 kg). The force decrease for target forces of 75% and 100% MVC was marked until 60 sec. from the onset of grip and then decreased gradually. On the other hand, the target force of 50% MVC was maintained for about 60 sec. and then decreased markedly until 100 sec. Differences in the decreasing force among target force levels was observed until 60 sec., and there were no significant differences of the time to decay to 20%, 30%, and 40% MVC. Namely, the time and force exertion reaching an almost steady state were considered to be almost the same at any target force. A sex difference on a parameter was found after 60 sec. or a decreasing force after 40% MVC, and women held it longer or higher than the men. However, the tendency was smaller in the latter phase of the steady state.     

High perceptual load makes everybody equal: eliminating individual differences in distractibility with load

Perceptual load has been found to be a powerful determinant of distractibility in laboratory tasks. The present study assessed how the effects of perceptual load on distractibility in the laboratory relate to individual differences in the likelihood of distractibility in daily life. Sixty-one subjects performed a response-competition task in which perceptual load was varied. As expected, individuals reporting high levels of distractibility (on the Cognitive Failures Questionnaire, an established measure of distractibility in daily life) experienced greater distractor interference than did individuals reporting low levels. The critical finding, however, was that this relationship was confined to task conditions of low perceptual load: High perceptual load reduced distractor interference for all subjects, eliminating any individual differences. These findings suggest that the level of perceptual load in a task can predict whether individual differences in distractibility will be found and that high-load modifications of daily tasks may prove useful in preventing unwanted consequences of high distractibility.     

Changes of lumbosacral joint compression force profile when walking caused by backpack loads

Walking with backpack loads induces additional mechanical stress on the spine and has been identified as a risk factor of lower-back pain. This study evaluated the effects of walking with backpack loads on the lumbosacral joint compression force profile in both the magnitude and time domains. Ten male adults geared with anatomical markers and trunk surface electromyographic sensors walked along a walkway embedded with three force plates with no load and various backpack loads (5%, 10%, 15%, and 20% body weight). Lower-body movements, ground reaction forces, and trunk muscle activations were measured using a synchronized motion analysis, force plate, and surface electromyography system. The force profiles of identified gait cycles were predicted using an integrated inverse dynamic and electromyography-assisted optimization model and evaluated statistically. The results showed that as backpack load increased, the 10th, 50th, and 90th percentiles of force profiles escalated disproportionately. However, no significant changes were observed in the timing of the two peak force incidences. Such changes in the compression force might be an indication of the combined effects of the increase in both gravitational and mass moment of inertia of the system (body plus pack loads) when walking with a backpack. Pearson correlation coefficients of the force profiles between the five loading conditions were greater than 0.94. Strong associations between the force profiles at different backpack loads were confirmed.     

Cuing interacts with perceptual load in visual search

We tested the strong form of the perceptual-load hypothesis, which posits that the amount of perceptual load is the only factor determining whether attention can be effectively focused. Participants performed a visual search task under conditions of low and high load and with either a 100% valid spatial cue or no spatial cue. With no cue, participants showed evidence of processing to-be-ignored stimuli when perceptual load was low but not when it was high, consistent with the perceptual-load hypothesis. However, with a 100% valid spatial cue, participants showed little evidence of processing to-be-ignored stimuli, even when perceptual load was low. These results suggest that although perceptual load may be an important factor in attentional selectivity, load alone is not sufficient to explain how and when selective attention is effective.     

Accountability forces in performance appraisal

This experiment investigated the effects of two factors felt to influence the quality of ratings: anticipated feedback sharing and knowledge of subordinates' self-assessment. One hundred and eighty subjects receiving either favorable, unfavorable, or no subordinate self-assessment information were led to anticipate either face-to-face, written, or no feedback sharing with a subordinate. Main effects were found both for type of feedback sharing and level of subordinate self-assessment. Partial support was also found for the interaction of feedback sharing and partial self-assessment effects. Supervisors anticipating sharing face-to-face feedback with a subordinate rated the latter's performance significantly more positively than did supervisors who received no self-assessment data; while supervisors receiving knowledge of an unfavorable self-assessment rated their subordinates significantly more negatively than those receiving no self-assessment information. Ancillary analyses support the contention that the impact of knowledge of self-assessment information is largely motivational, as opposed to informational, in nature. Despite their potential to influence ratings, it is suggested that face-to-face feedback sharing requirements and the use of subordinate self-assessment data are not necessarily detrimental, but rather that care should be taken to minimize their potential to reduce rating quality.     

Retention of relative force in the scaling of a serial force pattern with an attenuated-force tap

The present study was designed to examine the retention of relative force in the scaling of a serial force pattern in a finger-tapping sequence using an attenuated tap. On practice trials, 12 undergraduate students tapped a force plate connected to strain gauges that gave them feedback about the force. On test trials, participants recalled the force pattern (200 gm-200 gm-200 gm-100 gm) and the intertap interval (400 msec.) practiced during the practice period without the feedback (recalled task). Then, they adaptively produced a halved (halved task) or doubled force profile (doubled task) at the fixed intertap interval. Analyses showed that mean peak forces at the first three tap positions of the tapping sequence undershot the expected forces across all tasks. Hence, the ratios of the forces in Serial Positions 1:4, 2:4, and 3:4 were considerably lower than 2.0. This is a contextual effect suggesting that the last attenuated tap affected the first three taps of the tapping sequence. Thus, because the relative force of movements appears to be a weaker invariant feature than sequencing and relative timing for generalized motor program theory of Schmidt and Lee, this finding does not support the relative force for a generalized motor program.     

May the force be with you

This paper is a critical assessment of argumentum ad baculum, or appeal to force. Its principal contention is that, contrary to common opinion, there is no general fallacy of ad baculum. Most real-life ad baculums are, in fact, fairly strong. A basic logical form for reconstructed ad baculums is proposed, and a number of heterodoxical conclusions are also advanced and argued for. They include that ad baculum is not necessarily a prudential argument, that ad baculum need not involve force, violence, or threats, and that one can argue ad baculum to oneself. The starting point of the paper, however, is a critical evaluation of three ad baculums from the exercise sets of Irving Copi's well-known Introduction to Logic.     

Attentional set interacts with perceptual load in visual search

In the present study, we examined the hypothesis that perceptual load is the primary factor that determines the efficiency of attentional selection. Participants performed a visual search task under conditions of high- and low-load. In line with the perceptual load hypothesis, presenting conditions of highand low-load in separate blocks of trials resulted in processing of to-be-ignored stimuli only in the lowload condition (Experiment 1). However when high- and low-load conditions were randomly mixed in blocks of trials, the participants showed processing of to-be-ignored stimuli in both conditions, suggesting that high perceptual load is not necessarily sufficient to obtain perceptual selectivity (Experiment 2). An analysis of intertrial transition effects showed that on high-load trials, processing of to-be-ignored stimuli occurred only when the previous trial was a low-load trial. The results suggest that low perceptual load can engender broad attentional processing. On the other hand, when a high-load trial was preceded by another high-load trial, little processing of task-irrelevant stimuli was observed. The present results are discussed in terms of the interaction between expectancies and bottom-up factors in the efficiency of attentional selection.     

A pinch or a lesion: a reconceptualization of biting consequences in mice

Intruder and resident male colony mice exhibit an array of distinct defensive and offensive behaviors. Intruders typically show more boxing, flight, defensive sideways position, on the back position and general locomotion, while residents exhibit higher levels of attack, olfactory investigation, aggressive grooming, and biting, with a preference for dorsal bite locations. Here, analysis of bite locations on the body of the intruder mice showed that the majority of bites produced few lesions (i.e. actual puncturing of the skin) when compared to scrapes or no markings. Most bites were directed to the back of the opponent animal with very few bites directed towards the opponents' vulnerable ventrum. In particular, bites directed at the relatively hairless ventrum produced no lesions. These findings, along with previous work on mice and rats, suggest that intraspecific offense with preferred target sites for biting, facilitates an effective but largely nonwounding interaction between resident and intruder mice. Furthermore, bruise and wound analyses suggest an association between bite targets and tissue damage. The preference for specific bite locations may be complimented by a differential intensity of attack, with the back attracting the strongest bites and the ventrum the weakest. This apparent nonwounding fighting pattern contradicts the current evaluation of rodent wounding severity in this paradigm and can therefore refine the usage of this model and of the protocols associated with it.