Depth adjacency and the rod-and-frame illusion

The effects of psychological set on perception of first and second pain were determined for 20 subjects. Percutaneous electrical shock intensities (6–8 mA, 3 msec) sufficient to evoke double pain responses were used in all subjects. Psychological sets included PAST (“Place yourself in a previous experience that was free of any significant emotional tone”), PRESENT (“Feel your foot that will be shocked”), and FUTURE (“Think to yourself that you are about to be shocked”). Perception of second pain was never perceived in PAST and FUTURE sets but was always perceived in the PRESENT set. Furthermore, at minimal rates of stimulation ( > 1/3 sec), summation of second pain occurred in the PRESENT set but not in the FUTURE set. All subjects startled in the FUTURE set and did not startle in PAST or PRESENT sets. Each subject reported that the aversiveness of the shock related to painful sensations in PAST and PRESENT sets and to ones own body responses in the FUTURE set.