Different Occupations Associated with Amyotrophic Lateral Sclerosis: Is Diesel Exhaust the Link?

The cause of sporadic amyotrophic lateral sclerosis (SALS) remains unknown. We attempted to find out if occupational exposure to toxicants plays a part in the pathogenesis of this disease. In an Australia-wide case-control study we compared the lifetime occupations of 611 SALS and 775 control individuals. Occupations were coded using country-specific as well as international classifications. The risk of SALS for each occupation was calculated with odds ratios using logistic regression. In addition, the literature was searched for possible toxicant links between our findings and previously-reported occupational associations with SALS. Male occupations in our study that required lower skills and tasks tended to have increased risks of SALS, and conversely, those occupations that required higher skills and tasks had decreased risks of SALS. Of all the occupations, only truck drivers, where exposure to diesel exhaust is common, maintained an increased risk of SALS throughout all occupational groups. Another large case-control study has also found truck drivers to be at risk of SALS, and almost two-thirds of occupations, as well as military duties, that have previously been associated with SALS have potential exposure to diesel exhaust. In conclusion, two of the largest case-control studies of SALS have now found that truck drivers have an increased risk of SALS. Since exposure to diesel exhaust is common in truck drivers, as well as in other occupations that have been linked to SALS, exposure to this toxicant may underlie some of the occupations that are associated with SALS.     

Generalization of Auditory Sensory and Cognitive Learning in Typically Developing Children

Despite the well-established involvement of both sensory (“bottom-up”) and cognitive (“top-down”) processes in literacy, the extent to which auditory or cognitive (memory or attention) learning transfers to phonological and reading skills remains unclear. Most research has demonstrated learning of the trained task or even learning transfer to a closely related task. However, few studies have reported “far-transfer” to a different domain, such as the improvement of phonological and reading skills following auditory or cognitive training. This study assessed the effectiveness of auditory, memory or attention training on far-transfer measures involving phonological and reading skills in typically developing children. Mid-transfer was also assessed through untrained auditory, attention and memory tasks. Sixty 5- to 8-year-old children with normal hearing were quasi-randomly assigned to one of five training groups: attention group (AG), memory group (MG), auditory sensory group (SG), placebo group (PG; drawing, painting), and a control, untrained group (CG). Compliance, mid-transfer and far-transfer measures were evaluated before and after training. All trained groups received 12 x 45-min training sessions over 12 weeks. The CG did not receive any intervention. All trained groups, especially older children, exhibited significant learning of the trained task. On pre- to post-training measures (test-retest), most groups exhibited improvements on most tasks. There was significant mid-transfer for a visual digit span task, with highest span in the MG, relative to other groups. These results show that both sensory and cognitive (memory or attention) training can lead to learning in the trained task and to mid-transfer learning on a task (visual digit span) within the same domain as the trained tasks. However, learning did not transfer to measures of language (reading and phonological awareness), as the PG and CG improved as much as the other trained groups. Further research is required to investigate the effects of various stimuli and lengths of training on the generalization of sensory and cognitive learning to literacy skills.     

Brain Deactivation in the Outperformance in Bimodal Tasks: An fMRI Study

While it is known that some individuals can effectively perform two tasks simultaneously, other individuals cannot. How the brain deals with performing simultaneous tasks remains unclear. In the present study, we aimed to assess which brain areas corresponded to various phenomena in task performance. Nineteen subjects were requested to sequentially perform three blocks of tasks, including two unimodal tasks and one bimodal task. The unimodal tasks measured either visual feature binding or auditory pitch comparison, while the bimodal task required performance of the two tasks simultaneously. The functional magnetic resonance imaging (fMRI) results are compatible with previous studies showing that distinct brain areas, such as the visual cortices, frontal eye field (FEF), lateral parietal lobe (BA7), and medial and inferior frontal lobe, are involved in processing of visual unimodal tasks. In addition, the temporal lobes and Brodmann area 43 (BA43) were involved in processing of auditory unimodal tasks. These results lend support to concepts of modality-specific attention. Compared to the unimodal tasks, bimodal tasks required activation of additional brain areas. Furthermore, while deactivated brain areas were related to good performance in the bimodal task, these areas were not deactivated where the subject performed well in only one of the two simultaneous tasks. These results indicate that efficient information processing does not require some brain areas to be overly active; rather, the specific brain areas need to be relatively deactivated to remain alert and perform well on two tasks simultaneously. Meanwhile, it can also offer a neural basis for biofeedback in training courses, such as courses in how to perform multiple tasks simultaneously.     

Health and safety among film technicians working extended shifts

This paper presents selected results from a pilot research. The study of film technicians' work schedules and occupational hazards was based on a questionnaire administered to all 2200 film technicians (650 valid replies; response rate = 30%), interviews with producers and technicians on film-shooting organization and scheduling, courses in film technique, individual interviews with workers in trade at high risk, and review of the literature on freelancers, on the effects of intermittent work, and on risk factors for musculoskeletal injuries. Work schedules showed a tendency to extremely long work shifts (14 hours per day on average, and up to 19 hours in some trades). Occupational constraints and work schedules were found to relate to an increased risk of work-related injuries. Technicians identified fatigue associated with work schedules as the principal risk of accidents and one of the factors responsible for causing or aggravating their many musculoskeletal injuries. Work schedules were not the only cause of these injuries: stress--due to time constraints, work responsibilities and job insecurity--was also an important risk factor, consistent with the literature on musculoskeletal disorders. Physical workload was also problematic, particularly when demanding tasks had to be performed under severe time constraints.     

Detour behaviour in horses (<Emphasis Type="Italic">Equus caballus</Emphasis>)

The objective of this study was to investigate the ability of horses (Equus caballus) to detour around symmetric and asymmetric obstacles. Ten female Italian saddle horses were each used in three detour tasks. In the first task, the ability to detour around a symmetrical obstacle was evaluated; in the second and third tasks subjects were required to perform a detour around an asymmetrical obstacle with two different degrees of asymmetry. The direction chosen to move around the obstacle and time required to make the detour were recorded. The results suggest that horses have the spatial abilities required to perform detour tasks with both symmetric and asymmetric obstacles. The strategy used to perform the task varied between subjects. For five horses, lateralized behaviour was observed when detouring the obstacle; this was consistently in one direction (three on the left and two on the right). For these horses, no evidence of spatial learning or reasoning was found. The other five horses did not solve this task in a lateralized manner, and a trend towards decreasing lateralization was observed as asymmetry, and hence task difficulty, increased. These non-lateralized horses may have higher spatial reasoning abilities.     

The formation of class fractions in the Gilded Age

Data available from employment records of manual labour occupations in larger northeastern American cities in the years 1890 and 1900 are used to support an argument in contrast to human capital theory that economic discrimination can be explained as the rational behaviour of identifiable groups in particular market positions. Craft unionists from 1900 on, particularly in the building trades, satisfied at least minimal criteria to be regarded as a distinctive stratum or class fraction. Craft union workers utilized organizational capacities based on ethnic solidarity and barriers to entry in order to develop a distinctive stratum of skilled labourers, wage differentials reflecting at least partly craft unions' capacity to control access to training and employment.     

Occupational mortality of California women, 1979-1981.

A review of California''s mortality data for 1979 through 1981, encompassing 61,561 female and 111,877 male deaths, shows differential female mortality risk by labor force status and by occupation. High patterns of risk were found for women in a number of occupations, including waitresses, licensed vocational nurses and health aides, cosmetologists, telephone operators, housekeepers and janitors, and launderers and dry cleaners. Patterns of mortality risk were similar for each race within these occupational groups. The mortality risks for women were generally higher than those for men. The association of mortality with certain occupational does not necessarily imply a causal relationship but is certainly a signal that further research is required and that physicians need to consider work-related factors in evaluating the health of women.     

Functional Anatomy of Writing with the Dominant Hand

While writing performed by any body part is similar in style, indicating a common program, writing with the dominant hand is particularly skilled. We hypothesized that this skill utilizes a special motor network supplementing the motor equivalence areas. Using functional magnetic resonance imaging in 13 normal subjects, we studied nine conditions: writing, zigzagging and tapping, each with the right hand, left hand and right foot. We identified brain regions activated with the right (dominant) hand writing task, exceeding the activation common to right-hand use and the writing program, both identified without right-hand writing itself. Right-hand writing significantly differed from the other tasks. First, we observed stronger activations in the left dorsal prefrontal cortex, left intraparietal sulcus and right cerebellum. Second, the left anterior putamen was required to initiate all the tested tasks, but only showed sustained activation during the right-hand writing condition. Lastly, an exploratory analysis showed clusters in the left ventral premotor cortex and inferior and superior parietal cortices were only significantly active for right-hand writing. The increased activation with right-hand writing cannot be ascribed to increased effort, since this is a well-practiced task much easier to perform than some of the other tasks studied. Because parietal-premotor connections code for particular skills, it would seem that the parietal and premotor regions, together with basal ganglia-sustained activation likely underlie the special skill of handwriting with the dominant hand.     

The geometry of the Pareto front in biological phenotype space

When organisms perform a single task, selection leads to phenotypes that maximize performance at that task. When organisms need to perform multiple tasks, a trade‐off arises because no phenotype can optimize all tasks. Recent work addressed this question, and assumed that the performance at each task decays with distance in trait space from the best phenotype at that task. Under this assumption, the best‐fitness solutions (termed the Pareto front) lie on simple low‐dimensional shapes in trait space: line segments, triangles and other polygons. The vertices of these polygons are specialists at a single task. Here, we generalize this finding, by considering performance functions of general form, not necessarily functions that decay monotonically with distance from their peak. We find that, except for performance functions with highly eccentric contours, simple shapes in phenotype space are still found, but with mildly curving edges instead of straight ones. In a wide range of systems, complex data on multiple quantitative traits, which might be expected to fill a high‐dimensional phenotype space, is predicted instead to collapse onto low‐dimensional shapes; phenotypes near the vertices of these shapes are predicted to be specialists, and can thus suggest which tasks may be at play.     

News & Analyses

ABSTRACT

The purpose of this study was to examine preschoolers' (n = 11) ability to follow instructions in the presence or absence of a real dog while executing a variety of motor skills tasks. These tasks were divided into one of three general classifications: 1) Modeling Tasks: the children were asked to emulate the behavior of a model, 2) Competition Tasks: the children were asked to do the task faster than a competitor, and 3) Tandem Tasks: the children were asked to do the tasks at the same time as a co-performer. Typical and Identified (language impaired) preschool children were randomly assigned to perform five tasks of each general classification alone, with a human, with a real dog, and with a stuffed dog that was similar in size and appearance to the live dog. Two independent raters rated each child's adherence to instructions (interrater reliability = 0.99) on a 7-point scale. A significant interaction between task classification and type of co-performer revealed that in the Modeling Tasks the preschoolers adhered better to the instructions when the real dog was present relative to the other conditions. In the Tandem Tasks the children adhered to instructions best when they performed the task with a human, followed by the stuffed dog (as manipulated by a human), the real dog, and worst when they were asked to perform the tasks alone. The type of co-performer made no significant difference in the Competition Tasks. These results indicate the presence of a real dog tends to be beneficial for promoting preschoolers' compliance with instructions in motor skills tasks that require modeling behavior, but not in those tasks that stress competition or those performed in tandem.     

How similar are nut-cracking and stone-flaking? A functional approach to percussive technology

Various authors have suggested similarities between tool use in early hominins and chimpanzees. This has been particularly evident in studies of nut-cracking which is considered to be the most complex skill exhibited by wild apes, and has also been interpreted as a precursor of more complex stone-flaking abilities. It has been argued that there is no major qualitative difference between what the chimpanzee does when he cracks a nut and what early hominins did when they detached a flake from a core. In this paper, similarities and differences between skills involved in stone-flaking and nut-cracking are explored through an experimental protocol with human subjects performing both tasks. We suggest that a ‘functional’ approach to percussive action, based on the distinction between functional parameters that characterize each task and parameters that characterize the agent''s actions and movements, is a fruitful method for understanding those constraints which need to be mastered to perform each task successfully, and subsequently, the nature of skill involved in both tasks.     

The effects of task and saliency on latencies for colour and motion processing

In human visual perception, there is evidence that different visual attributes, such as colour, form and motion, have different neural-processing latencies. Specifically, recent studies have suggested that colour changes are processed faster than motion changes. We propose that the processing latencies should not be considered as fixed quantities for different attributes, but instead depend upon attribute salience and the observer's task. We asked observers to respond to high- and low-salience colour and motion changes in three different tasks. The tasks varied from having a strong motor component to having a strong perceptual component. Increasing salience led to shorter processing times in all three tasks. We also found an interaction between task and attribute: motion was processed more quickly in reaction-time tasks, whereas colour was processed more quickly in more perceptual tasks. Our results caution against making direct comparisons between latencies for processing different visual attributes without equating salience or considering task effects. More-salient attributes are processed faster than less-salient ones, and attributes that are critical for the task are also processed more quickly.     

What Do Eye Gaze Metrics Tell Us about Motor Imagery?

Many of the brain structures involved in performing real movements also have increased activity during imagined movements or during motor observation, and this could be the neural substrate underlying the effects of motor imagery in motor learning or motor rehabilitation. In the absence of any objective physiological method of measurement, it is currently impossible to be sure that the patient is indeed performing the task as instructed. Eye gaze recording during a motor imagery task could be a possible way to “spy” on the activity an individual is really engaged in. The aim of the present study was to compare the pattern of eye movement metrics during motor observation, visual and kinesthetic motor imagery (VI, KI), target fixation, and mental calculation. Twenty-two healthy subjects (16 females and 6 males), were required to perform tests in five conditions using imagery in the Box and Block Test tasks following the procedure described by Liepert et al. Eye movements were analysed by a non-invasive oculometric measure (SMI RED250 system). Two parameters describing gaze pattern were calculated: the index of ocular mobility (saccade duration over saccade + fixation duration) and the number of midline crossings (i.e. the number of times the subjects gaze crossed the midline of the screen when performing the different tasks). Both parameters were significantly different between visual imagery and kinesthesic imagery, visual imagery and mental calculation, and visual imagery and target fixation. For the first time we were able to show that eye movement patterns are different during VI and KI tasks. Our results suggest gaze metric parameters could be used as an objective unobtrusive approach to assess engagement in a motor imagery task. Further studies should define how oculomotor parameters could be used as an indicator of the rehabilitation task a patient is engaged in.     

A Within-Animal Comparison of Skilled Forelimb Assessments in Rats

A variety of skilled reaching tasks have been developed to evaluate forelimb function in rodent models. The single pellet skilled reaching task and pasta matrix task have provided valuable insight into recovery of forelimb function in models of neurological injury and disease. Recently, several automated measures have been developed to reduce the cost and time burden of forelimb assessment in rodents. Here, we provide a within-subject comparison of three common forelimb assessments to allow direct evaluation of sensitivity and efficiency across tasks. Rats were trained to perform the single pellet skilled reaching task, the pasta matrix task, and the isometric pull task. Once proficient on all three tasks, rats received an ischemic lesion of motor cortex and striatum to impair use of the trained limb. On the second week post-lesion, all three tasks measured a significant deficit in forelimb function. Performance was well-correlated across tasks. By the sixth week post-lesion, only the isometric pull task measured a significant deficit in forelimb function, suggesting that this task is more sensitive to chronic impairments. The number of training days required to reach asymptotic performance was longer for the isometric pull task, but the total experimenter time required to collect and analyze data was substantially lower. These findings suggest that the isometric pull task represents an efficient, sensitive measure of forelimb function to facilitate preclinical evaluation in models of neurological injury and disease.     

Transferring learning from external to internal weights in echo-state networks with sparse connectivity

Modifying weights within a recurrent network to improve performance on a task has proven to be difficult. Echo-state networks in which modification is restricted to the weights of connections onto network outputs provide an easier alternative, but at the expense of modifying the typically sparse architecture of the network by including feedback from the output back into the network. We derive methods for using the values of the output weights from a trained echo-state network to set recurrent weights within the network. The result of this "transfer of learning" is a recurrent network that performs the task without requiring the output feedback present in the original network. We also discuss a hybrid version in which online learning is applied to both output and recurrent weights. Both approaches provide efficient ways of training recurrent networks to perform complex tasks. Through an analysis of the conditions required to make transfer of learning work, we define the concept of a "self-sensing" network state, and we compare and contrast this with compressed sensing.     

Task failure during fatiguing contractions performed by humans.

By comparing the physiological adjustments that occur when two similar fatiguing contractions are performed to failure, it is possible to identify mechanisms that limit the duration of the more difficult task. This approach has been used to study two fatiguing contractions, referred to as the force and position tasks, which differed in the type of feedback given to the subject and the amount of support provided by the surroundings. Even though the two tasks required a similar net muscle torque during submaximal isometric contractions, the duration that the position task could be sustained was consistently much briefer than that for the force task. The position task involved a greater rate of increase in EMG activity and more marked changes in motor unit recruitment and rate coding compared with the force task. These observations are consistent with the hypothesis that the motor unit pool was recruited more rapidly during the position task. The difference in motor unit behavior appeared to be caused by variation in synaptic input, likely involving heightened sensitivity of the stretch reflex during the position task. Upon repeat performances of the two fatiguing contractions, some subjects were able to increase the time to failure for the force task but not the position task. Furthermore, the time to failure for the position task could be influenced by the postural demands associated with maintaining the position of the limb, and the difference in the two durations was enhanced when the postural activity evoked a pressor response. These observations indicate that the difference in the duration of the two fatiguing contractions was attributable to differences in the control strategy used to sustain the tasks and the magnitude of the associated postural activity.     

Work-Related Fatal-Injury Risk of Construction Workers by Occupation and Cause of Death

To assess cause- and occupation-specific risks of work related fatal injuries among U.S. construction workers, the National Traumatic Occupational Fatalities (NTOF) surveillance system and Current Population Survey were used to obtain injury and employment data for the years 1990 through 1994. Risks were assessed by both rate and working lifetime risk. The occupation found to have the highest fatal-injury rate in construction was electrical-power installers and repairers (96.6 deaths/100,000 workers), followed by structural-metal workers (86.4) and operating engineers (41.0). The occupation found to have the largest numbers of fatalities was construction laborers (1133 deaths), followed by carpenters (408), and construction supervisors (392). The leading causes of death varied by occupation. Construction in general has experienced a decline in fatal-injury rates over the years; however, this decline did not occur equally across occupations and causes of death. The presentation of working lifetime injury risks provides a measure of risk for occupational injuries that can be compared with occupational illness risk assessments. This study is the first to provide a comprehensive national profile of work-related fatal-injury risks among United States construction workers by occupation and cause of death. The results will be useful in focusing research and prevention efforts on specific hazards in high-risk construction occupations.     

A psychophysiological assessment battery

This research project was the first step in the development of a psychophysiological assessment battery. The battery consisted of eight tasks that have a history of use within the field of psychophysiology. These tasks were examined on a nonpathological, physically healthy sample. This sample was administered the assessment battery three times over the course of 16 weeks. The response systems of HR, SC, RR, TPA, and FPA were examined. Two major research questions were then examined. The first question was whether a subject would display a stable physiological profile on the assessment battery across the three administrations. The second question was whether there would be individual differences in physiological profiles on the assessment battery. These differences were examined in terms of individual response stereotypy (IRS) and stimulus response specificity (SRS). Depending on the task, from 30 to 100% of the subjects displayed stable physiological profiles across administrations. Twenty-five subjects displayed a high degree of SRS. Five subjects displayed a high degree of IRS.