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PubMed1993

Developmental changes in understanding an illusion based on perceptual adaptation: effects of feedback.

Children and adults were exposed to an illusion created by perceptual adaptation, in which they perceived two identical bottles, held simultaneously in a different hand, as being different in weight. Prior research has shown that young children treat the perceived difference as real rather than illusory. In an initial study, feedback designed to signal the illusory nature of the weight difference led many third graders to acquire an erroneous rule. Older children and adults more often gave a correct response, although there was no clear evidence that they understood the illusion. In Study 2, confronting children with the discrepancy between the preillusion phase of the testing and the subsequent experience of an illusion helped them to infer an understanding of the illusion when the discrepancy was large. The results have implications for the development of the understanding of perceptual processes, the appearance-reality distinction, and the child's theory of mind.

Adolescent↗
PubMed1992

Development of human precision grip. II. Anticipatory control of isometric forces targeted for object's weight.

The development of anticipatory control during lifts with the precision grip was examined in 100 children aged 1 to 15 years and in 15 adults. The children were instructed to lift an instrumented test object by using the precision grip between the thumb and index finger. The employed grip force, load force (vertical lifting force), vertical position and their corresponding time derivatives (i.e., grip and load force rates and acceleration) were recorded. The weight of the object was varied between trials to access the influence of the object's weight in the previous trial on the isometric force output. Already by the second year, children began to use information pertaining to the object's weight in the previous lift, i.e., they began to use an anticipatory control strategy. This occurred concomitant to the development of mainly bell shaped force rate profiles (Forssberg et al. 1991). The succeeding development of a more mature anticipatory control was gradual and adult-like capacity was not reached until 8-11 years of age.

Adolescent↗
PubMed1992

Independent control of the digits: changes in perceived heaviness over a wide range of force.

Perceived heaviness of a weight lifted by flexion of the distal joint of one digit increases when an adjacent digit concurrently lifts a weight. The present study confirmed this finding for relatively low weights (representing 3-5% maximal voluntary force) and a method was adapted to show that this effect occurs for much larger weights (20-25% maximal force). Thus, the increase in perceived heaviness is likely to operate over a wide range of muscle force generated by the hand. As perceived heaviness is biased by the magnitude of the central motor commands, these findings may reflect a lack of complete independence of motor commands to the long flexor muscles acting on the digits.

Fingers↗
PubMed1986

Mass-discrimination in weightlessness and readaptation to earth's gravity.

Five members of the first Spacelab mission (STS-9) were tested on several occasions for weight-discrimination before and after the flight, and for mass-discrimination under microgravity in flight. Thresholds for mass-discrimination were higher than for preflight weight-discrimination by a factor of about 1.8, and there was no clear evidence of improvement throughout the ten day mission. Too few tests were conducted to monitor the improvement during the first two days of flight, when adaptation to weightlessness may have occurred. Subjects reported perceptual aftereffects of body heaviness for two or three days after the flight. Their weight-discrimination thresholds were raised during this period, when they were re-adapting to normal gravity. Incomplete adaptation to altered arm weight can only partly explain the raised threshold for mass-discrimination in microgravity. Differences in the sensory information available with and without gravity are discussed.

Adaptation, Physiological↗
PubMed1978

Further evidence of impaired tactile learning after removals of the second somatic sensory projection cortex (SII) in the monkey.

Four rhesus monkeys with bilateral removals of SII and five unoperated monkeys were trained on tests of tactile equivalence, weight discrimination and generalization, tactile discrimination learning (including concurrent learning and serial reversal) and inter-manual transfer of tactile learning. Lesioned animals were impaired on almost all tactile learning tasks and on inter-manual transfer but not on the test of tactile equivalence nor on the propioceptive tasks. The results are considered in the context of previous studies of somatosensory and parietal cortex.

Animals↗
PubMed1979

The physiological cost of carrying light and heavy loads.

Nine subjects walked on a treadmill with load weights equal to 10% and 40% of body weight carried on the back. Although the speed of the treadmill was selected so that the measured oxygen consumption (VO2) was the same for both load conditions, the heavier load placed an extra strain on the cardiopulmonary system and was perceived by all subjects as harder work than the lighter load. When the subjects worked at their own pace, walking on a level road or climbing stairs with load weights equal to 10% and 40% of body weight, they compensated for the heavier load by decreasing walking speed or climbing rate. Although the energy costs calculated from walking speed, body and load weight for self-paced walking and the external work of stair climbing were the same for both load conditions, the heavier load was again perceived as harder work. These findings are discussed as they relate to the definition of acceptable load weights.

Adult↗
PubMed1991

Body Mass Index and perceived weight status in young adults.

Body Mass Index (BMI) was calculated from self-reported height and weight for 1,123 university students who returned a questionnaire mailed to a 10 percent random sample of the entire undergraduate population of a large midwestern university. Seventeen percent of the females and 20 percent of the males were determined to be in excess of normal BMI standards. However, significantly more women (40%) considered themselves overweight in comparison to men (24%). Also, significantly more women (53%) than men (20%) reported experiencing discomfort due to excessive weight. Inaccurate perceptions of body image are common among individuals with eating disorders. There is a higher incidence of eating disorders among college-age women than among their male peers. A distorted body image as reflected by perceived overweight may serve as a marker for individuals at risk for eating disorders.

Body Image↗
PubMed2003

Perceptual constancy and the perceived magnitude of muscle forces.

The present study used a force-matching task to measure how accurately subjects could match a force using different muscle groups. Forces ranging in magnitude from 2 to 10 N were produced and matched by three muscle groups: the elbow flexors, the forearm and hand muscles involved in the palmar prehensile grasp, and the index finger flexors. The ability to match forces was considered in terms of precision, that is, how closely the matching forces approximated the reference force produced on the contralateral side, and accuracy, which is the reproducibility of the matching force estimates. The results indicated that the perceived magnitude of forces varied as a function of the muscle group generating the force. Forces produced by the index finger flexors were consistently overestimated in magnitude when matched by elbow flexion forces, and elbow forces were underestimated when matched by flexing the index finger. When evaluated in terms of constant and absolute errors, the index finger flexors were the most precise matching muscle group and the elbow flexors the least precise. These results suggest that forces are perceived relatively, and are scaled with reference to the operating range of the muscles. They also indicate that there is little perceptual constancy in the perceived magnitude of forces generated by different muscle groups.

Adult↗
PubMed2005

Information and force level interact in regulating force output during two and three digit grip configurations.

The experiment examined the force fluctuations during two and three digit grip configurations to investigate the relationship between task performance and inter-digit individuation as a function of force level and visual information intermittency rate over approximately 100-fold range (0.21-20 Hz). Subjects grasped an object with either the index finger (two digit grip) or the index and middle finger (three digit grip) opposing the thumb and produced isometric force to match a low and high total force level target. Force accuracy was lower at the large visual intermittency conditions and the higher force level. The force variability was lower in the three digit grip. Inter-digit individuation increased as a function of visual intermittency rate and was greater at the low force level. There was no improvement in performance or inter-digit individuation when visual feedback intermittency was greater than approximately 6 Hz (approximately 150 ms). Linear regression between the measures of task performance and inter-digit individuation yielded a significant negative relationship that was only present in the two digit grip when visual feedback rate was 1.67 Hz or lower and in the three digit grip when the feedback rate was 10 Hz or lower. The greater biomechanical degrees of freedom in the three digit grip configuration enable the subject to use, more effectively, visual information feedback at faster timescales in maximizing task performance by increasing digit independence. The shift from visual to nonvisual dominated motor control processes is dependent on the interaction of informational and biomechanical degrees of freedom.

Adult↗
PubMed1997

Coordination of fingertip forces during human manipulation can emerge from independent neural networks controlling each engaged digit.

We investigated the coordination of fingertip forces in subjects who lifted an object (i) using the index finger and thumb of their right hand, (ii) using their left and right index fingers, and (iii) cooperatively with another subject using the right index finger. The forces applied normal and tangential to the two parallel grip surfaces of the test object and the vertical movement of the object were recorded. The friction between the object and the digits was varied independently at each surface between blocks of trials by changing the materials covering the grip surfaces. The object's weight and surface materials were held constant across consecutive trials. The performance was remarkably similar whether the task was shared by two subjects or carried out unimanually or bimanually by a single subject. The local friction was the main factor determining the normal:tangential force ratio employed at each digit-object interface. Irrespective of grasp configuration, the subjects adapted the force ratios to the local frictional conditions such that they maintained adequate safety margins against slips at each of the engaged digits during the various phases of the lifting task. Importantly, the observed force adjustments were not obligatory mechanical consequences of the task. In all three grasp configurations an incidental slip at one of the digits elicited a normal force increase at both engaged digits such that the normal:tangential force ratio was restored at the non-slipping digit and increased at the slipping digit. The initial development of the fingertip forces prior to object lift-off revealed that the subjects employed digit-specific anticipatory mechanisms using weight and frictional experiences in the previous trial. Because grasp stability was accomplished in a similar manner whether the task was carried out by one subject or cooperatively by two subjects, it was concluded that anticipatory adjustments of the fingertip forces can emerge from the action of anatomically independent neural networks controlling each engaged digit. In contrast, important aspects of the temporal coordination of the digits was organized by a "higher level" sensory-based control that influenced both digits. In lifts by single subjects this control was mast probably based on tactile and visual input and on communication between neural control mechanisms associated with each digit. In the two-subject grasp configuration this synchronization information was based on auditory and visual cues.

Adolescent↗
PubMed1997

The influence of peripheral load on resetting voluntary movement by cortical stimulation: importance of the induced twitch.

We studied the effects of changes in loading torque on the effectiveness of magnetic cortical stimulation in evoking phase resetting of voluntary wrist movement. Nine normal subjects were studied (five on two occasions), while making rhythmical movements of the right wrist, at their preferred rate, against extension torque loads of 0.35 Nm, 0.26 Nm and 0.18 Nm, flexion torque loads of 0.09 Nm and 0.18 Nm and without external load. The position records of individual trials were used to measure the effectiveness of resetting (resetting index: the slope of the phase-response curve) and the "null phase", the phase to which the trials were being reset. The loading torque had a strong influence upon both the resetting index and the null phase, generated by a constant intensity of cortical stimulation such that the largest resetting indices were obtained for movements made against the largest extension torque load (mean resetting index 0.72). The degree of resetting and null phase were related to the mean amplitude and direction of the first poststimulus position peak, which in turn was largely determined by the twitch induced by the cortical shock. The timings of the averaged poststimulus position peaks following the first were simple multiples of the prestimulus movement period. Our results indicate that loading conditions profoundly influence the effectiveness of magnetic cortical stimulation in resetting a voluntary movement and that these effects appear to be largely explicable by the changes in the muscle twitch evoked by the stimulus with the different loads. We suggest that the magnetic shock is therefore unlikely to reset voluntary movement by an action directly upon the motor programme. We propose that the main method by which magnetic cortical stimulation resets repetitive wrist movement is indirect: normal generation of repetitive wrist flexion and extension is disrupted by the cortical shock, following which afferent information related to the twitch induced is able to reset the movement.

Adult↗
PubMed1997

Differential control of the digits of the human hand: evidence from digital anaesthesia and weight matching.

The present study assessed changes in perceived heaviness of weights lifted by the thumb, index, ring and little fingers during anaesthesia of the "lifting" digit. Subjects (n = 19) lifted weights solely by flexion of the distal joint of the digit, using a bilateral weight-matching paradigm. Changes in perceived heaviness during anaesthesia differed in both their sign and magnitude for the different digits. Anaesthesia of the thumb and index finger produced large increases in perceived heaviness (median, thumb: +41%; index finger: +13%), whereas anaesthesia of the ring finger decreases perceived heaviness (-14%). Anaesthesia of the little finger also reduced perceived heaviness (median, -21%; n = 6). Because perceived heaviness is biased by signals of motor commands, these findings suggest a net facilitatory reflex effect of the digital nerve inputs from the thumb and index fingers onto their respective flexor motoneurones with the corresponding effect for the ring and little fingers being inhibitory.

Adult↗
PubMed2006

Measuring and quantifying dynamic visual signals in jumping spiders.

Animals emit visual signals that involve simultaneous, sequential movements of appendages that unfold with varying dynamics in time and space. Algorithms have been recently reported (e.g. Peters et al. in Anim Behav 64:131-146, 2002) that enable quantitative characterization of movements as optical flow patterns. For decades, acoustical signals have been rendered by techniques that decompose sound into amplitude, time, and spectral components. Using an optic-flow algorithm we examined visual courtship behaviours of jumping spiders and depict their complex visual signals as "speed waveform", "speed surface", and "speed waterfall" plots analogous to acoustic waveforms, spectrograms, and waterfall plots, respectively. In addition, these "speed profiles" are compatible with analytical techniques developed for auditory analysis. Using examples from the jumping spider Habronattus pugillis we show that we can statistically differentiate displays of different "sky island" populations supporting previous work on diversification. We also examined visual displays from the jumping spider Habronattus dossenus and show that distinct seismic components of vibratory displays are produced concurrently with statistically distinct motion signals. Given that dynamic visual signals are common, from insects to birds to mammals, we propose that optical-flow algorithms and the analyses described here will be useful for many researchers.

Algorithms↗
PubMed2005

Submaximal force production during perceptually guided isometric exercise.

The aim of this study was to examine submaximal isometric force production guided by perceptual feelings of exertion. Thirty young adults performed isometric knee extensions on an isokinetic dynamometer. Subjects performed five different tests; the first test was the same for all subjects (standard naïve test). During the standard naïve test, subjects were asked to randomly produce force at perceived contraction intensities (25%, 50% and 75% of their maximum voluntary contraction (MVC)), with 100% MVC performed as the final intensity. All intensities, including the 100% MVC, were randomly performed in the other four tests (control tests 1 and 2, post 20% MVC and post 100% MVC tests). Post 20% MVC and post 100% MVC tests included fatiguing isometric exercise at 20% and 100% MVC respectively, which were performed prior to the test protocol. Results show that absolute peak force increased with increasing intensity (P<0.001) during all tests. During the standard naïve test, absolute peak force at 25% and 50% MVC was significantly lower (P=0.009) compared to control test 2, post 20% MVC and 100% MVC tests, and relative peak force was lower at all intensities compared to all other tests (P<0.001). Absolute and relative peak force was most accurate at 50% MVC (-12.06 N and -2.42%, respectively). Prior fatiguing isometric exercise did not affect the subsequent perceptual response range. In conclusion, isometric force was most accurate at 25% MVC but under-produced (perceptually overestimated) during higher contraction intensities preceding a maximal voluntary contraction (100% MVC). The ability to match absolute force with target contraction intensities was most accurate at 50% MVC during all five experimental conditions and poor at opposite ends of the force domain. Furthermore, prior fatiguing isometric exercise did not have an effect on the subsequent perceptual response range.

Adult↗
PubMed2004

Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment.

Exercise in the heat causes "central fatigue", associated with reduced skeletal muscle recruitment during sustained isometric contractions. A similar mechanism may cause fatigue during prolonged dynamic exercise in the heat. The aim of this study was to determine whether centrally regulated skeletal muscle recruitment was altered during dynamic exercise in hot (35 degrees C) compared with cool (15 degrees C) environments. Ten male subjects performed two self-paced, 20-km cycling time-trials, one at 35 degrees C (HOT condition) and one at 15 degrees C (COOL condition). Rectal temperature rose significantly in both conditions, reaching maximum values at 20 km of 39.2+/-0.2 degrees C in HOT and 38.8+/-0.1 degrees C in COOL (P<0.005 HOT vs. COOL). Core temperatures at all other distances were not different between conditions. Power output and integrated electromyographic activity (iEMG) of the quadriceps muscle began to decrease early in the HOT trial, when core temperatures, heart rates and ratings of perceived exertion (RPE) were similar in both conditions. iEMG was significantly lower in HOT than in COOL at 10 and 20 km, while power output was significantly reduced in the period from 80% to 100% of the trial duration in the HOT compared with COOL condition. Thus, reduced power output and iEMG activity during self-paced exercise in the heat occurs before there is any abnormal increase in rectal temperature, heart rate or perception of effort. This adaptation appears to form part of an anticipatory response which adjusts muscle recruitment and power output to reduce heat production, thereby ensuring that thermal homeostasis is maintained during exercise in the heat.

Adult↗
PubMed2005

Kinematic cues in perceptual weight judgement and their origins in box lifting.

When accepting a parcel from another person, we are able to use information about that person's movement to estimate in advance the weight of the parcel, that is, to judge its weight from observed action. Perceptual weight judgment provides a powerful method to study our interpretation of other people's actions, but it is not known what sources of information are used in judging weight. We have manipulated full form videos to obtain precise control of the perceived kinematics of a box lifting action, and use this technique to explore the kinematic cues that affect weight judgment. We find that observers rely most on the duration of the lifting movement to judge weight, and make less use of the durations of the grasp phase, when the box is first gripped, or the place phase, when the box is put down. These findings can be compared to the kinematics of natural box lifting behaviour, where we find that the duration of the grasp component is the best predictor of true box weight. The lack of accord between the optimal cues predicted by the natural behaviour and the cues actually used in the perceptual task has implications for our understanding of action observation in terms of a motor simulation. The differences between perceptual and motor behaviour are evidence against a strong version of the motor simulation hypothesis.

Adolescent↗