ROLE OF MULTIPLE RESOURCES IN PREDICTING TIME-SHARING EFFICIENCY - EVALUATION OF 3 WORKLOAD MODELS IN A MULTIPLE-TASK SETTING

The goal of our study was to assess the validity of the assumptions un derlying three prominent workload models: the Time-Line Analysis and P rediction workload model (Parks & Boucek, 1989), the VACP workload mod el (Aldrich, Szabo, & Bierbaum, 1989), and the W/INDEX model (North & Riley, 1989). Sixteen subjects flew a low-fidelity flight simulation. Subjects were required to perform a two-axis tracking task, a concurre nt visual-monitoring task, and a discrete decision task. The decision task had 16 variations defined by two levels on each of the following dimensions: input modality (visual vs. auditory), processing code (spa tial vs. verbal), difficulty (easy vs. hard), and response modality (m anual vs. voice). Dual-task costs were found only for the tracking tas k. The tracking data were then analyzed using two approaches: a tradit ional analysis of variance (ANOVA) and a correlational analysis of tra cking performance versus model predictions. The ANOVA revealed that pe rformance on the tracking task was better when the concurrent decision task was responded to vocally and was easy. Input modality and proces sing code of the concurrent decision task had no significant effect on tracking performance. The correlational analysis was used to evaluate each of the three models, to determine what features were responsible for improving the models' fit, and to compare their performance with a pure time-line model that makes no multiple-resource assumptions. Al l three models did a good job of predicting variance between experimen tal conditions, accounting for between 56% and 84% of the variance in our data and between 10% and 40% of an earlier data set. Different fea tures of each model that affect the fit are then discussed. We conclud e that it is important for models to retain a multiple-resource coding , although the best features of that coding remain to be determined. C oding tasks by their demand level appears to be less critical.