Borrower: USD Call#: BF311 .H3345 1986 Lending String: NOS,*GZV,WIS,MZF,EM2 Location: Oversize (3rd Floor) Patron: Schieber. Frank iiiiiiii !!!!!!! iiiiiiii !!!!!!! Journal Title: Handbook of perception and human ODYSSEY ENABLED performance I ~ ~ - Charge iiiiiiii Volume: 2 Issue: Maxcost: 0.00 -(!) === Month/Year: 1986Pages: 1-49 +titlepage/verso - Shipping Address: - !!!!!!! -> -iiiiiiii Article Author: ·-(!) UNIVERSITY OF SOUTH DAKOTA ......... - USD LIBRARIES ILL ~ Article Title: Gopher, D. & Donchin, E; Chapter -iiiiiiii 414 E. CLARK STREET 0-. !!!!!!! 41. Workload-An examination of the concept. VERMILLION, SD 57069-2390 -I ...... ~ N co Fax: :::J N Imprint: New York ; Wiley, c1986. Ariel: 192.236.50.50 Mco Email: [email protected] ~ ILL Number: 85467209 z 1- llllllllllllllllllllllllllllllllllllllllllllllllll '0cu :J ....I --~ --- --· NOTICE: WARNING I CONCERNING COPYRiGHT RESTRiCTIONS • The copyright law of the United States (Title 17. C nited States Cod~) govems the making ofphotocopiL's or other reproductions of copyrighted matenaL • Under certain conditions speci lied in the law, libraries and archivt:s are authorized to fum ish a pholm.:opy or other reproductiorl. One of these speci fie "fair use" condition~ is that the photocopy or reproduction is nol to be "u:scJ for any purpose other than private study, scholarship, or research." [f u user makes a request tor, or tater uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. I HANDBOOK OF PERCEPTION AND HUMAN PERFORMANCE VOLUME II Cognitive Processes and Performance Editors: N/\51\ KENNETH R. BOFF Armstrong Aerospace Medical Research Laboratory LLOYD KAUFMAN New York University JAMES P. THOMAS University of California at Los Angeles jl .. A Wiley-lnterscience Publication ~ JOHN WILEY AND SONS New York • Chichester • Brisbane • Toronto • Singapore CHAPTER 41 WORKLOAD-AN EXAMINATION OF THE CONCEPT DANIEL GOPHER Faculty of Industrial Engineering and Management, Israel Institute of Technology, The Technion, Haifa, Israel EMANUEL DONCHIN Department of Psychology, University of Illinois, Champaign, Illinois CONTENTS 2.4.3. The Breakdown ofthe Single Channel, 41-12 2.5. The Architecture of the Central Processor, 41-13 1. Introduction 41-2 2.6. Energy Constraints on Processing Capabilities, I 1.1. Task Difficulty and Workload, 41-2 41-14 1.2. Workload and the Limitations on Performance, 2.6.1. The Single-Resource Model, 41-14 41-3 2.6,.2. Multiple-Resource Models, 41-16 1.3. The Logical Status of Workload, 41-3 2.7. Controlled and Automatic Processes, 41-18 1.3.1. A Definition of Workload, 41-3 2.8. The Nature of Capacity Limitations, 41-19 1.3.2. Workload as an Intervening Variable, 41-4 2.8.1. Dimensions of a Load Profile, 41-19 1.3.3. Workload as a Hypothetical Construct, 41-4 2.8.2. Conscious Control and Allocation Policy, 1.4. Workload and Attention, 41-4 41-20 2. The Limitations of the Central Processor: Historical Background 41-5 3. Techniques for the Measurement of Workload 41-21 2.1. Origins of the Notion of a Central Limited 3.1. Criteria for the Evaluation of Workload Processor, 41-5 Measures, 41-21 2.1.1. The Human as an Information Channel, 3.2. Workload as a Property ofthe~perator-Task 41-5 Loop, 41-21 2.1.2. The Putative Advantages of Information 3.2.1. Normative and Descriptive Approaches, Theory, 41-6 41-21 2.2. Channel Capacity as a Measure of Limits on the 3.2.2. Overview of Section, 41-22 Central Processor, 41-6 3.3. Subjective Measures, 41-22 2.2.1. Absolute Judgment, 41-6 3.3.1. Consistency of Subjective Estimates, 41-23 2.2.2. The Span of Short-Term Memory, 41•7 3.3.2. Theoretical·Considerations in the 2.3. Summary, 41-8 Interpretation and Use of Subjective 2.4. Bottleneck Models of Human Limitations, 41-8 Measures of Workload, 41-23 2.4.1. Single-Bottleneck Models, 41-9 3.3.3. Methodological Considerations, 41-24 2.4.2. Welford's Single-Channel Model, 41-10 3.4. Performance Measures, Primary Task, 41-24 41-1 41-2 HUMAN PERFORMANCE 3.5. Arousal Measures, 41-25 difficulty is, ofcourse, obvious. It is easier to read Agatha Christie 3.6. Specific Measures, 41-25 than James Joyce; it is more difficult to fly an airplane than to 3.6.1. Selection of a Secondary Task, 41-26 operate a washing machine. It is also clear that the same task 3.6.2. Types of Interference and Lack of will prove more difficult to some individuals than to others. Interference, 41-26 Furthermore, the ease with which the same individual performs 3.6.3. The Problems of Concurrency, 41-27 a given task on different occasions may vary. Yet, despite the 3.6.4. Allocation Policy, 41-28 apparent simplicity of the concept and the fairly easy judgments 3.7. Performance Operating Characteristics (POC), observers can make regarding the difficulty of tasks, the mea­ 41-28 surement of task difficulty is in itself a rather difficult task. 3.8. Basic Assumptions of the POC Methodology, 41-31 The problem exists because the difficulty of any task can 3.9. Psychophysiological Measures of Workload, 41-32 be inferred not directly from its physical (or "structural") de­ 3.9.1. Introductory Comments on the P300 scription, but rather from the interaction between task and Component, 41-32 operator. Hence, system designers need to be able to discriminate 3.9.2. The Latency of the P300 Component, 41-33 among alternate design options in favor of those that will ease 3.9.3. P300 and Perceptual/Central Processing the operator's task. On occasion, system managers must be able Resources, 41-35 to monitor variations in the difficulty a task presents to an 3.9.4. P300 and Resource Reciprocity, 41-40 operator actively using a system. It is on such occasions that 3.9.5. Summary and Conclusions, 41-41 the need to measure ''task difficulty" arises. And it is on such 4. Epilogue 41-42 occasions that the apparent simplicity of the measurement task is revealed as horrendously complex. Acknowledgment 41-43 Superficially the measurement task appears quite straight­ Reference Note 41-43 forward. One simply asks an operator whether the task is difficult and uses the subjective response as an index of difficulty. As References 41-44 discussed in Section 3.3 (and as O'Donnell and Eggemeier note in Chapter 42), such subjective reports have serious limitations. An operator is often an unreliable and invalid measuring in­ strument. Neither can it be assumed that the quality of per­ formance is a good measure of the difficulty of a task. People 1. INTRODUCTION often cope with an increase in task difficulty by increasing mental l and physical effort devoted to the task so that performance may ·~t 1.1. Task Difficulty and Workload remain stable despite a great increase in difficulty. The mea­ ·w"' surement of difficulty must capture the interaction between l The study and measurement of mental workload absorb sub­ these relevant variables. Workload is the label assigned to this stantial energy, resources, and effort. Major conferences devoted interactive feature. to the analysis and measurement of workload (Moray, 1979; An analogy might clarify the matter. Consider a simple Frazier & Crombie, 1982) follow a fairly uniform course. The resistive circuit in which a voltage source, say, a batter, is concept of workload is examined, attempts at a definition are imposing a voltage across some resistor. Both the voltage sup­ made, and the usual conclusion is that workload is a multidi­ plied by the battery and the resistance that characterizes the mensional, multifaceted concept that is difficult to define. It is resistor depend on the properties of these devices regardless, generally agreed that attempts to measure workload relying to a first approximation, ofthe circuit in which they are embedded on a single representative measure are unlikely to be of use. (though both voltage and resistance depend on such circum­ The conferees generally proceed to examine many different stances as the ambient temperature). However, specifying the procedures to measure and analyze workload. Practitioners tend voltage or the resistance alone will tell us very little about the to imply that the measure or class of measures they advocate circuit. There is, however, another variable that actually cap­ is uniquely preferable to many of the other proposed measures. tures the properties of the circuit, reflecting the interaction Persuasive arguments are presented for the unique suitability between the voltage and the resistance. The current flowing in of (1) subjective measures of workload (Sheridan, 1980), (b) the circuit is determined jointly by the properties of the battery secondary-task procedures (Jex, ~976; Pew, 1979), and (3) phys­ and those of the resistor and it is therefore a parameter of the iological measures (Donchin, 1979; Mulder, 1979). These writers circuit rather than of its individual elements. Variations in the are actually quite correct in holding to their particular views, current, given fixed voltage and resistance, can also be used as since the measures described often yield an interesting set of a means for assessing the degree to which the ambient conditions relations and in some circumstances seem to meet the practical affect the properties of circuit elements. needs of design engineers. We suggest that workload is analogous to current. Of course, O'Donnell and Eggemeier (Chapter 42) provide a survey, unlike the case with current, we cannot derive the workload written from the perspective of the design engineer, organizing associated with the interaction between a specific operator and the many techniques proposed for measuring workload. As they a specific task from an equation that combines measurable at­ indicate in the opening paragraphs of their chapter, the interest tributes of the operator with measurable attributes of the task in workload arises in evaluating "task difficulty." The assessment to yield workload.