The effect of task difficulty and threat of aversive electric shock upon tonic physiological changes.

Thirteen subjects volunteered in an experiment which tested the relative effect of task difficulty and threat of aversive electric shock upon tonic changes in skeletal muscle (somatic) tension, respiration, heart rate (HR), and skin conductance level (SCL). They all performed two versions of a continuous perceptual-motor task (which is different from the reaction time task paradigm currently being preferred in related research), one difficult and one easy, under conditions of threat and no-threat. Electromyographic activity increased over the course of a task and, thus, showed clear physiological gradients which were steeper with the difficult task and threat. Initial HR activation was marked for the threat condition, and task difficulty added to this activation. SCL revealed a marked initial peak-response for all treatments, but was unresponsive to experimental manipulations. It was argued that a respiratory-somatic parallelism occurred during performance of both tasks for the no-threat (low effort) condition, and that threat (high effort) acted to dissolve this coupling in favour of a respiratory-cardiac parallelism.