something like a single channel transmission line (see Welford ..

Study of the single channel hypothesis and input regulation within a continuous
Photo provided by Flickr

Chapter 29 - Ergonomics OVERVIEW

The taxonomy of complex systems described by Rasmussen, Pejtersen and Schmidts (1990) represents one of the most ambitious attempts to cover at the same time the context and its influence on the operator. Its main idea is to integrate, in a systematic fashion, the different elements of which it is composed and to bring out the degrees of freedom and the constraints within which individual strategies can be developed. Its exhaustive aim makes it difficult to manipulate, but the use of multiple modes of representation, including graphs, to illustrate the constraints has a heuristic value that is bound to be attractive to many readers. Other approaches are more targeted. What the authors seek is the selection of factors that can influence a precise activity. Hence, with an interest in the control of processes in a changing environment, Brehmer (1990) proposes a series of temporal characteristics of the context which affect the control and anticipation of the operator (see ). This author’s typology has been developed from “micro-worlds”, computerized simulations of dynamic situations, but the author himself, along with many others since, used it for the continuous-process industry (Van Daele 1992). For certain activities, the influence of the environment is well known, and the selection of factors is not too difficult. Thus, if we are interested in heart rate in the work environment, we often limit ourselves to describing the air temperatures, the physical constraints of the task or the age and training of the subject—even though we know that by doing so we perhaps leave out relevant elements. For others, the choice is more difficult. Studies on human error, for example, show that the factors capable of producing them are numerous (Reason 1989). Sometimes, when theoretical knowledge is insufficient, only statistical processing, combining context and activity analysis, allows us to bring out the relevant contextual factors (Fadier 1990).

On the division of attention: a disproof of the single channel hypothesis
Photo provided by Pexels

Wolfgang Laurig and Joachim Vedder

Features are separable when they can be changed without affecting the perception of other features of an object. Line lengths of histograms are a case in point. On the other hand, integral features refer to features which, when changed, change the total appearance of the object. For instance, one cannot change features of the mouth in a schematic drawing of a face without altering the total appearance of the picture. Again, colour and brightness are integral in the sense that one cannot change a colour without altering the brightness impression at the same time. The principles of separable and integral features, and of emergent properties evolving from changes of single features of an object, are applied in so-called integrated or diagnostic displays. The rationale of these displays is that, rather than displaying individual parameters, different parameters are integrated into a single display, the total composition of which indicates what may be actually wrong with a system.

06/09/2013 · This is also known as the SINGLE CHANNEL HYPOTHESIS - until one stimulus has had a decision made about it, ..
Photo provided by Flickr

An activity is defined as the set of behaviours and resources used by the operator so that work occurs—that is to say, the transformation or production of goods or the rendering of a service. This activity can be understood through observation in different ways. Faverge (1972) has described four forms of analysis. The first is an analysis in terms of gestures and postures, where the observer locates, within the visible activity of the operator, classes of behaviour that are recognizable and repeated during work. These activities are often coupled with a precise response: for example, the heart rate, which allows us to assess the physical load associated with each activity. The second form of analysis is in terms of information uptake. What is discovered, through direct observation—or with the aid of cameras or recorders of eye movements—is the set of signals picked up by the operator in the information field surrounding him or her. This analysis is particularly useful in cognitive ergonomics in trying to better understand the information processing carried out by the operator. The third type of analysis is in terms of regulation. The idea is to identify the adjustments of activity carried out by the operator in order to deal with either fluctuations in the environment or changes in his own condition. There we find the direct intervention of context within the analysis. One of the most frequently cited research projects in this area is that of Sperandio (1972). This author studied the activity of air traffic controllers and identified important strategy changes during an increase in air traffic. He interpreted them as an attempt to simplify the activity by aiming to maintain an acceptable load level, while at the same time continuing to meet the requirements of the task. The fourth is an analysis in terms of thought processes. This type of analysis has been widely used in the ergonomics of highly automated posts. Indeed, the design of computerized aids, and notably intelligent aids for the operator, requires a thorough understanding of the way in which the operator reasons in order to solve certain problems. The reasoning involved in scheduling, anticipation and diagnosis has been the subject of analyses, an example of which can be found in . However, the evidence of mental activity can only be inferred. Apart from certain observable aspects of behaviour, such as eye movements and problem-solving time, most of these analyses resort to verbal response. Particular emphasis has been placed, in recent years, on the knowledge necessary to accomplish certain activities, with researchers trying not to postulate them at the outset but to make them apparent through the analysis itself.

Single‐channel hypothesis in the brain. WELFORD, WELFORD. You’re reading a free preview. Subscribe to read the entire article. Try 2 weeks free now . DeepDyve is your
Photo provided by Pexels


Porter - Faculty & Research - Harvard …

It was clear from assessment using the cube model () that high time demands could not be accepted if there were concurrent high or moderate demands in terms of force and postural strain. In order to reduce these demands, mechanized object handling and tool suspension was deemed a necessity. There was consensus developed around this conclusion. Using a simple computer-aided design (CAD) program (ROOMER), an equipment library was created. Various workplace station layouts could be developed very easily and modified in close interaction with the users. This design approach has significant advantages compared with merely looking at plans. It gives the user an immediate vision of what the intended workplace may look like.

Effect of Complexity of the Second Response on …

The formal procedure of producing standards is still the same today. But since the emphasis has shifted more and more to the international or the European level, more and more activities are being transferred to these committees. Drafts are now usually worked out directly in these committees and are no longer based on existing national standards. After the decision has been made that a standard should be developed, work directly starts at one of these supranational levels, based on whatever input there may be available, sometimes starting from zero. This changes the role of the national ergonomics committees quite dramatically. While heretofore they formally developed their own national standards according to their national rules, they now have the task of observing and influencing standardization on the supranational levels—via the experts who work out the standards or via comments made at the different steps of voting (within the CEN, a national standardization project will be halted if a comparable project is being simultaneously worked on at the CEN level). This makes the task still more complicated, since this influence can only be exerted indirectly and since the preparation of ergonomics standards is not just a matter of pure science but a matter of bargaining, consensus and agreement (not least due to the political implications which the standard might have). This, of course, is one of the reasons why the process of producing an international or European ergonomics standard usually takes several years and why ergonomics standards cannot reflect the latest state of the art in ergonomics. International ergonomics standards thus have to be examined every five years, and, if necessary, undergo revision.