SELECTIVE ATTENTION AFFECTS AUTOMATIC RESPONSES: THE EFFECTS OF ATTENTION ON THE ACHILLES TENDON REFLEX (MOTOR PREPARATION, ORIENTING, DIVIDED, FOCUSED, MOTOR CONTROL)

Cognitive psychologists agree that manipulations of selective attention affect voluntary responses. But, they do not agree on the locus of the effects or the mechanisms involved. A new approach to these questions seems advantageous.;Two dual-task experiments were performed. Primary task conditions were shadow, memorize, or memorize while shadowing a repeated series of auditory digits. They were randomly probed with t-reflexes or foot-key presses to taps on the knee. Reaction time results were ordered as follows: control < shadow < memorize < memorize while shadowing. Reflex amplitude results were ordered similarly. Only the difference between control and dual-task reflex amplitude was reliable. The ordering of tasks suggests a direct relationship between changes in reflex amplitude and voluntary reaction time: low amplitude goes with fast reaction time.;Three cost-benefit experiments were performed. Conditions with .8 and .5 cue validity were compared. T-reflexes were elicited concurrently with the voluntary response signal. Pairings of response signal and voluntary response modalities were varied across experiments. The response signal activated visual or proprioceptive pathways. The response was vocal or pedal.;When attention was directed toward sensorimotor pathways, reflex amplitude was at or below control level. Valid and invalid trials were not different. When attention was directed away from sensorimotor pathways, reflex amplitude was above control level. With high validity cues, reflex amplitude was lower for valid than for invalid trials. With the same cues, reaction time was always faster for valid than for invalid trials.;Recent work in neuromotor control shows that reflexes are highly modifiable. A comparison of Achilles tendon reflex (t-reflex) and voluntary responses in the same tasks might provide evidence that manipulations of attention affect reflex amplitudes and that there is a systematic relationship between changes in reflex amplitude and reaction time. Such findings should clarify some issues in the attention literature.;When attention was directed away from sensorimotor pathways, a direct relationship between reaction time and reflex amplitudes was found with both divided and focused attention manipulations. Conditions which increase reaction time also increase reflex amplitudes. Implications of these results for both attention and motor preparation theory were discussed.