The workload and stress associated with a 40-min vigilance task were examined under conditions wherein observers monitored an auditory or a visual display for changes in signal duration. Global workload scores fell in the midrange of the NASA Task Load Index, with scores on the Frustration subscale increasing linearly over time. These effects were unrelated to the sensory modality of signals. However, sensory modality was a significant moderator variable for stress. Observers became more stressed over time as indexed by responses to the Dundee Stress State Questionnaire, with evidence of recovery in the auditory but not the visual condition toward the end of the watch. This result and the finding that signal detection accuracy - although equated for difficulty under alerted conditions - favored the auditory mode, indicate that display modality and time on task should be considered carefully in the design of operations requiring sustained attention in order to enhance performance and reduce stress. Actual or potential applications of this research include domains in which monitoring is a crucial part, such as baggage screening, security operations, medical monitoring, and power plant operations.

Research performed during the last decade on estimation of mental workload has resulted in a subset of techniques exhibiting global sensitivity. Other techniques have also been demonstrated to have sensitivity in particular applications and can be used for diagnostic purposes. This paper reviews techniques that have shown sufficient sensitivity and robustness to be used in test and evaluation. Topics such as time scale considerations, available documentation, and appropriate procedures are also discussed. Recommendations are then made for workload estimation in test and evaluation situations.

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W r i g h t -P a t t e r s o n A i r Force Base, Ohio ABSTRACT A i r Force Aerospace Medical Research L a b o r a t o r y P r a c t i c a l c o n s i d e r a t i o n s make s u b j e c t i v e o p i n i o n one o f t h e most w i d e l y used methods t o assess mental workload. However, t h e v a l u e o f t h e d a t a o b t a i n e d by s u b j e c t i v e methods i s o f t e n l i m i t e d because s c a l e s a r e n o t s t a n d a r d i z e d and a r e n o t based on modern psychometric p r i n c i p l e s . T h i s paper d e s c r i b e s t h e development and v a l i d a t i o n o f a S u b j e c t i v e Workload Assessment Technique (SWAT) w h i c h uses c o n j o i n t measurement t o c o n s t r u c t i n t e r v a l l e v e l workload s c a l e s f r o m o r d i n a l r a n k i n g s o f combinations o f l e v e l s on t h r e e c o n t r i b u t o r y dimensions. An exDeriment was conducted t o i n v e s t i a a t e t h e c o n s t r u c t v a l i d i t v and c o n c u r r e n t v a l i d i t y ' o f t h e e c t o r group o f s u b j e c t s completes a s c a l e development phase and an e v e n t s c o r i n g phase. D u r i n g t h e s c a l e development phase, d a t a necessary t o develop a workload s c a l e a r e o b t a i n e d f r o m a group o f s u b j e c t s . D u r i n g t h e e v e n t s c o r i n g phase, s u b j e c t s r a t e t h e workload a s s o c i a t e d w i t h a p a r t i c u l a r t a s k and/or m i s s i o n segment. These a r e two d i s t i n c t e v e n t s and o c c u r a t d i f f e r e n t t i m e s . The e n t i r e SWAT procedure i s base upon an a p p l i c a t i o n o f a psychometric t e c h n i q u e known as c o n j o i n t measurement (Coombs e t a l , 1970, K r a n t z and Tversky, 1971). In c o n j o i n t measurement t h e j o i n t e f f e c t s o f s e v e r a l f a c t o r s Recommendations f o r f u r t h e r developme& a r e a r e i n v e s t i g a t e d and t h e r u l e o r c o m p o s i t i o n p r i n c i p l e t h a t r e l a t e s t h e f a c t o r s t o one another i s e x t r a c t e d f r o m t h e d a t a . One major advantage o f c o n j o i n t measurement and r e l a t e d s c a l i n g procedures i s t h a t o n l y t h e o r d i n a l aspects o f t h e d a t a a r e r e q u i r e d f o r t h e p r o d u c t i o n o f an i n t e r v a l l e v e l s c a l e which r e p r e s e n t s t h e j o i n t e f f e c t o f t h e f a c t o r s . The c a p a b i l i t y t o d e r i v e i n t e r v a l l e v e l d a t a f r o m s u b j e c t i v e judgements r e p r e s e n t s obvious advantages o v e r o r d i n a l l e v e l d a t a which t y p i c a l l y r e s u l t f r o m s u b j e c t i v e r a t i n g s . Because o n l y o r d i n a l p r o p e r t i e s o f t h e d a t a a r e needed t o generate a scale, t h e f i r s t s t e p i n t h e procedure i s t o o r d e r t h e dependent v a r i a b l e as a f u n c t i o n o f t h e j o i n t e f f e c t o f t h e f a c t o r s b e i n g i n v e s t i g a t e d . For example, degree o f workloa...

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