Ten women with specific chronic animal phobias were treated by graded exposure in vivo in two to four two-hour treatment sessions. Sessions were divided into four balanced half-hour epochs, half with visual feedback of true heart rate plus instructions to lower heart rate during approach to the phobic stimulus.
All patients improved significantly from the start to end of sessions on heart rate and on subjective anxiety. Feedback of heart rate plus instructions to lower it substantially reduced heart rate during epochs of feedback, compared to non-feedback epochs without instructions, but this effect did not generalize to skin conductance or to subjective anxiety in our short-term experiment.
Nunes JS, Marks IM. Feedback of True Heart Rate During Exposure in Vivo. Arch Gen Psychiatry. 1975;32(7):933–936. doi:10.1001/archpsyc.1975.01760250125014