Speech input output interfaces as a disruptive influence in transport control systems: a case against direct voice input/output interfaces in command and control

The present work follows on from experiments which have demonstrated that the presence of the speech task gives rise to deleterious effects on performance in the concurrent visual-manual task, contrary to the predictions that might be derived from the processing resources model proposed by Wickens (1984). In the current research a simulated driving task was used to investigate the effect of a concurrent auditory task on performance and it was concluded that similar interactions could occur with increasing memory load. Pilot research was conducted confirming this effect in 1998 and the present report adds new evidence to this original work. This recent experiment investigated the effect of increasing the complexity of a counting task using digits presented verbally to the participants. In the simple conditions the participants simply added or subtracted the verbal digits to an earlier count value or the value presented initially. To increase the memory load the subjects were asked to alternate regularly between addition and subtraction and it was observed that subjects counting and driving performance was significantly worse in this alternating condition when compared to the simple addition and subtraction conditions. This pattern of results was taken as further evidence that the concurrent execution of visual-manual and verbal-vocal tasks concurrently was likely to result in significant performance decrements, in either task, when the memory load was greater for the distinct tasks. It is proposed that these observations are significant with respect to the design of communication systems and the use of verbal feedback whilst training individuals to accomplish these tasks. This evidence supports the view that hands-free speech interfaces in cars may present a significant risk because of the diversion of attention from the primary driving task