Human multiple-task performance in cell-phone usage and driving. Dissertation University of Michigan.

For more than two decades, there has been much speculation and debate about the sources of dual-task performance decrements in driving and cell-phone usage. Some researchers argue that a single-channel cognitive processing system limits people's ability to drive and talk on a cell-phone simultaneously. Other researchers argue that cognitive processing is not limited, but that dual-task performance decrements stem from peripheral perceptual-motor conflicts. Despite arduous attempts, no viable theory has been proposed yet to account for the effects of response modality (vocal versus manual) on dual-task performance in the driving environment. The present dissertation serves to elucidate the effects of cell-phone usage on driving. Toward this objective, five experiments with the psychological refractory period (PRP) procedure were conducted. Interpretation of the results provides tests for the theoretical framework of the EPIC (Executive-Process Interactive Control) architecture (Meyers & Kieras, 1997a, 1997b) for modelling human dual-task performance. EPIC's architecture is precise, flexible, parsimonious, and assumes no limited cognitive processing capacity. Rather, it assumes people have flexible, strategic control over how tasks are scheduled. Furthermore, according to EPIC, peripheral (e.g., perceptual-motor) constraints and task instructions mediate dual-task performance decrements. Results from the five experiments reveal that these assumptions apply specifically to driving and cell-phone usage. Depending on instructions about the relative priority of cell-phone usage and on the response modality (vocal or manual) entailed by it, driving performance (e.g., steering) may suffer more or less because of the executive processes that are required to co-ordinate these tasks. Implications of these results suggest that recommendations may be made concerning cell-phone equipment design, change in government policies for cell-phone usage, prerequisites for licensing, and training to induce flexible, more efficient task scheduling. These recommendations as outlined in the dissertation, suggest that a decrement in driving caused by cell-phone usage is not obligatory. There are some individuals who will show no appreciable evidence of a dual-task decrement in performance and others who will. Understanding the nature of these decrements might ultimately improve driving performance on the road. (A)