Recent studies suggest that a decision-tree rating scale called the Modified Cooper-Harper (MCH) rating scale is a globally sensitive indicator of change in mental loading (Wienville and Casali 1983a). The present study was directed at developing refinements in the scale and at obtaining additional background information. The MCH scale and five design variations of the scale were studied in two independent aircraft-simulator experiments. Aspects studied were the decisiontree structure, the number of categories, the d&ision.:sequence and the effects of computer implementation. Results using the rating scales indicate that the MCH scale and its computerized version are generally more consistent than the others. Attendant questionnaire results indicate that pilots base their ratings on the same factors that researchers believe are the important elements of the multidimensional construct of workload.

V e h i c l e S i m u l a t i o n L a b o r a t o r y V i r g i n i a P o l y t e c h n i c I n s t i t u t e and S t a t e U n i v e r s i t y Rlacksburg, V i r g i n i a 24061The M o d i f i e d Cooper-Harper (1ICI.I) s c a l e h a s been shown t o b e a s e n s i t i v e i n d i c a t o r of workload i n s e v e r a l d i f f e r e n t t y p e s of a i r c r e w t a s k s ( W i e r w i l l e and C a s a l i , 1983). The s t u d y t o be d e s c r i b e d i n t h i s paper was u n d e r t a k e n t o d e t e r m i n e i f c e r t a i n v a r i a t i o n s of t h e s c a l e might p r o v i d e even g r e a t e r s e n s i t i v i t y and t o d e t e r m i n e t h e r e a s o n s f o r t h e s e n s i t i v i t y of t h e s c a l e .The MCH s c a l e , which i s a 1 0 p o i n t s c a l e , and f i v e newly d e v i s e d s c a l e s were examined i n two d i f f e r e n t a i r c r a f t s i m u l a t o r experiments i n which p i l o t l o a d i n g was t r e a t e d as a n independent v a r i a b l e . The f i v e s c a l e s i n c l u d e d a 1 5 p o i n t s c a l e , computerized v e r s i o n s of t h e IICH and 15 p o i n t s c a l e s , a s c a l e i n which t h e d e c i s i o n t r e e was removed, and one i n which a 1 5 p o i n t l e f t -t o -r i g h t format was used. The r e s u l t s of t h e s t u d y i n d i c a t e t h a t w h i l e one of t h e new s c a l e s may be more s e n s i t i v e i n a g i v e n experiment, t a s k dependency i s a problem. The MCH s c a l e on t h e o t h e r hand e x h i b i t s c o n s i s t e n t s e n s i t i v i t y and r e n a i n s t h e s c a l e recommended f o r g e n e r a l use.The MCH s c a l e r e s u l t s a r e c o n s i s t e n t w i t h e a r l i e r e x p e r i m e n t s a l s o . T h i s paper p r e s e n t s t h e r e s u l t s of t h e r a t i n g s c a l e experiments and a l s o d e s c r i b e s t h e q u e s t i o n n a i r e r e s u l t s whic;l were d i r e c t e d a t o b t a i n i n g a b e t t e r u n d e r s t a n d i n g of t h e r e a s o n s f o r t h e r e l a t i v e s e n s i t i v i t y of t h e MCH s c a l e and i t s v a r i a t i o n s . INTRODUCTIONI t h a s g r a d u a l l y become recognized t h a t r a t i n g s c a l e s , pi?operly designed and t e s t e d , r e p r e s e n t a s e n s i t i v e and economical means f o r e s t i m a t i n g mental workload.They can be used i n a s y s t e m a t i c manner t o o b t a i n a s i n g l e numerical r e s p o n s e , which e s t i m a t e s t h e magnitude of t h e nlultidimensional c o n s t r u c t of m e n t a l workload.One of t h e most p o p u l a r and widely a c c e p t e d s c a l e s i t h e s o -c a l l e d Cooper-Harper s c a l e (Cooper and Harper, 1 9 6 9 ) . T h i s s c a l e 1.11corporates a n u n u s u a l d e c i s i o n t r e e and d e s c r i p t o r s d i r e c t e d a t handl.ing q u a l i t i e s , s t a b i l i t y , and workload.The s c a l e i s w e l l s u i t e d f o r e s t i m a t i o n of workload i n manual c o n t r o l systems.For example...

The present study investigated dialogue-based human-computer task allocation. Five levels of allocation mode, four command strategies and a control condition, were examined in a high-task-load situation using a Latin square design. Five male participants acted as controllers in a simplified representation of an air traffic control system, sharing their task with a computer controller. Performance measures were metered on-line, and subjective ratings were recorded between trials. There were significant differences among the groups in the percentage of planes landed by the human-computer system, the total number of commands executed, and the number of allocation commands used. Other variables suggested for further study include comparisons of input mode, dialogue-initiation style, and degraded performance levels of the computer controller.