Threshold for conditioned suppression using x-rays as the pre-aversive stimulus.
A faint X-ray beam can function like a red-flag stimulus, quickly shutting down operant behavior in rats.
01Research in Context
What this study did
DeArmond (1966) worked with lab rats pressing a lever for food. The team paired a tiny X-ray dose with later foot-shock to see if the rats would stop pressing when the X-ray came on.
The X-ray ran at only 0.004 R/sec, far below medical levels. Researchers then tracked how much the radiation alone cut lever presses.
What they found
Even at that low dose, the X-ray acted like a warning signal. Lever pressing dropped sharply, showing the radiation had become a conditioned aversive stimulus.
The suppression happened fast and lasted while the beam was on, proving X-rays can enter a fear-learning chain at very weak intensities.
How this fits with other research
Farmer et al. (1966) showed rats will press a lever just to lower how often shocks arrive, no warning light needed. DeArmond (1966) adds that once any cue—here, X-rays—predicts shock, that cue alone can shut down behavior.
Lambert et al. (1973) found rats still learn avoidance even if the escape response gives one immediate shock, because it prevents five later. Together with DeArmond (1966), the pair tells us both warning cues and shock-rate math guide avoidance.
Navarick et al. (1972) noticed post-shock bursts that look like lever presses may actually be shock-triggered biting. D’s suppression measure avoids this confusion by counting only drops, not topographies, during the warning period.
Why it matters
If you run conditioning protocols, remember that any reliable precursor—sound, light, or even imperceptible radiation—can gain aversive control. Check your lab for unintended cues that might suppress desired responses. When data dip, ask: did a new background stimulus just become a ‘mini-X-ray’ for my subject?
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02At a glance
03Original abstract
Four male, 12-week-old Sprague-Dawley rats were used to determine the threshold for behavioral response to X-irradiation using the conditioned suppression technique. They were maintained at 80 per cent body weight and initially trained to stable performance on a VI 1 min schedule with 16 per cent sucrose solution as reinforcement. After a stable baseline was obtained, animals were placed in the instrumental conditioning box beneath the X-ray machine for a half-hour session each day. While subjects were actively pressing the lever for reinforcement, 15-sec X-ray exposures of 0.5 R/sec were administered, followed immediately by electric shock. After all animals had exhibited conditioned suppression, the dose-rate was decreased in subsequent sessions in an effort to establish threshold. The results indicate that X-rays at a dose-rate as low as 0.004 R/sec can be an effective pre-aversive stimulus for the rat.
Journal of the experimental analysis of behavior, 1966 · doi:10.1901/jeab.1966.9-29