Physiological and behavioral evaluation of mental load in shared attention tasks

Hand-held phone use is prohibited by French law to prevent any motor interference with driving. If freehand´s kit remains tolerated, its true impact (cognitive interference) is not already clearly determined. This experiment was aimed to study the effect of three communication tasks on driver´s behavior: listening to the radio, discussing with a passenger and holding a hands-free phone conversation. Performance was assessed through reaction time (RT) to visual stimuli when driving on a private closed circuit. Drivers were requested to leave their foot from the accelerator pedal when orange lights, placed on the dashboard, switched on. This stimulus was triggered while subjects performed both driving and one of the three additional tasks. Skin resistance level (SRL) and instantaneous heart rate (IHR) were continuously recorded as indices of arousal. Rest and driving were taken as reference. Phoning while driving elicited the highest RT. SRL showed 3 levels of arousal, from the lowest to the highest: rest, driving and the dual task condition (driving + communication). Thus, arousal remained constant whatever the additional task although IHR showed that arousal was higher when phoning than when listening to the radio. Thus, managing two tasks simultaneously elicited an increase in subjects´ arousal whereas RT increased selectively as a function of the secondary task requirements