Considerations for linking seatpan and backrest angles

Modern ergonomic chairs typically have several dimensions that can be adjusted independently of one another. Finding a desirable setting for any one dimension can depend on how other dimensions are set, thereby confronting users with a significant control problem. One design strategy for dealing with this problem has been to link changes in seatpan and backrest angles in some ratio, such that a one‐degree change in seatpan angle is associated with a two‐ or three‐degree change in backrest angle. However, there is no evidence to justify the choice of a particular ratio. This article presents data that addresses this issue. Subjects, performing either an entry or verification task, could adjust the chair to any position. Backrest and seatpan angles were plotted over time and analyzed using both graphical and statistical methods. The resulting scatter plots do not support the industry standard, 1:2 or 1:3 ratio, of changes in seatpan to backrest angles. The possibility of a variable linkage is discussed; however, problems associated with such a solution raise the possibility that control issues might be best addressed through training and exploration.     

Occupational stress factors in visual display terminal (VDT) operation: a review of empirical research

A review of the literature involving empirical research (experimental and field investigations) on stressful aspects of visual display terminal (VDT) operation is presented. Studies reviewed included assessment of visual fatigue and/or performance, musculoskeletal symptoms and operator attitudes towards job demands and quality of working life. In addition, some investigation included discussions and evaluations of the physical attributes of VDT workplaces; including ergonomic factors (task lighting, glare conditions, anthropometric configuration of VDT and accompanying furniture), environmental factors (temperature, humidity, radiation) and psychosocial factors (job demand, work content, work-rest schedules).

The literature reveals that levels of visual and musculoskeletal complaints among VDT operators are high. Moreover, ergonomic field assessment of VDT workplaces indicate that the majority of those examined were suboptimal with respect to existing recommendations regarding lighting, glare control and anthropometric dimensions of screen, keyboard, desk and chair. Nevertheless, evidence of causal linkages between specific ergonomic attributes of the workplace and specific patterns of symptomatology are lacking.

Finally, work demand and task structure attributes to the VDT operation were demonstrated to have strong effects on incidences of reports of visual and postural symptoms as well as on psychosocial attitudinal indicators. Hence, it is argued that approaches toward stress reduction must include job content as well as ergonomic factors.     

Postural dynamics and the preferred critical boundary for visually guided reaching

How do people choose an action to satisfy a goal from among the actions that are afforded by the environment? In 3 experiments the action modes used by actors to reach for a block placed at various distances from them were observed. In each experiment, when actors were not restricted in how they could reach for the object, the transition from their reaching using only arm extension to a mode of reaching in which they used the upper torso to lean forward occurred at closer distances than each actor's absolute critical boundary, beyond which the former action was no longer afforded. In Experiments 2 and 3 actors' seated posture was varied so that the effect of postural dynamics on the distance at which actors actually chose to make the transition between action modes, the preferred critical boundary, could be examined. The results are consistent with the proposal that the preferred critical boundary reflects the relative comfort of available modes of reaching.     

Predicting the frequency of dream recall.

Tested the hypothesis that dream recallers would have better memory for visual stimuli than dream nonrecallers. 50 recaller and 50 nonrecaller undergraduates were given tests of short- and long-term memory, incidental memory, and a personality battery consisting of measures of anxiety, repression-sensitization, and internal-external control. Results indicate that the memory variables and the Ss' self-reported number of awakenings distinguished between recallers and nonrecallers, whereas personality measures did not. It is concluded that the most important variable in dream recall may be individual differences in memory ability rather than differences in personality per se. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Normative,descriptive and formative approaches to describing normal work area

This paper examines normative and formative approaches toward describing normal work area. Squires’ model of normal work area is an example of a normative approach, which prescribes the shape of normal work area. Squires’ model has been taken as the starting point for more recent attempts to delineate reach boundaries in the workplace. However, his original paper does not present the derivation for his model or his claim that the distal boundary of his normal work area can be described by a prolate epicycloid. This paper presents the derivation for Squires’ model and shows that the resulting curve is not a prolate epicycloid, but a related form, a hypotrochoid. It then identifies shortcomings of normative models, like Squires’, notably the viability of the reach assumptions on which such normative models are based and their inability to deal with context-conditioned variability in the workplace. Finally, it examines the application of formative models, which attempt to identify constraints on the types of reach actions that people use. Data on how people actually reach may constitute a more appropriate foundation for constructing work area models needed to develop workplace standards.     

Effect of acoustic confusability on levels of information processing.

Employed a modification of M. I. Posner and R. F. Mitchell's choice RT design in which 10 experimentally naive undergraduates were required to respond "same" or "different" to simultaneous pairs of letters. Response was always on the basis of name identity (e.g., AA and Aa are "same," AB is "different"). Letter pairs were selected from populations of acoustically confusable or nonconfusable letters. Each pair of letters was either physically identical, had identical names, or had different names. The RTs to physically identical pairs were fastest, and did not differ between confusable and nonconfusable pairs. For all other comparisons, RT to acoustically confusable pairs took longer than to nonconfusable pairs. Results appear to support the hypothesis of an auditory encoding stage at which comparisons between items are made on the basis of acoustic components of their memory representations. (French summary) (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)