Health psychology (option) classic study: Brady (1958)

Aim and procedure

Aim: to test whether high stress and the hormones it produces are related to the development of ulcers, prompted by interest in the stress of business executives.

Sample: 8 rhesus monkeys, tested in 4 pairs.

Procedure: monkeys sat in restraining chairs and were trained to press a lever. A tone came before a half-second electric shock to the feet every 20 seconds unless the lever was pressed in time.

• The executive monkey in each pair could press the lever to avoid the shock for both monkeys.
• The yoked control received exactly the same shocks but had no control.
• Shock sessions followed a schedule of 6 hours on and 6 hours off. The study ran for several months.

Results and conclusions

• All 4 executive monkeys died of ulcers (between 9 and 48 days, as reported in Pearson's summary). None of the yoked monkeys died.
• The shocks alone were not the main stressor, since yoked monkeys showed little ulceration. The critical factor was the stress of trying to avoid the shocks (responsibility and vigilance).
• Stomach acid was highest during the rest periods, when sympathetic arousal stopped and the stomach was flooded with digestive secretions.
• Conclusion: high, prolonged stress can cause serious physical illness, especially of the gastrointestinal system.

Evaluation

• Strengths: standardised, controlled procedure with a yoked control receiving identical shocks, so the psychological factor (control and vigilance) could be isolated; physiological outcomes are objective; supports a link between stress and illness, as in Selye's GAS.
• Weaknesses: the executives were not randomly allocated: in each pair the monkey that responded faster in early training became the executive (a flaw pointed out by Weiss, 1972), and faster responders may have been more emotional to begin with, so they may already have been more stress-prone; only 8 monkeys; monkeys are not human executives (generalisability); Weiss (1972) found the opposite in rats: rats that could control shocks developed fewer ulcers than yoked rats with no control; ulcers are now known to be mainly caused by bacterial infection, with stress a contributing factor.
• Ethics: severe, prolonged suffering and death; restraint for long periods. It would not be permitted under the Animals (Scientific Procedures) Act 1986 and the 3Rs today.

Worked example

Explain why Brady used yoked control monkeys.

1. Each yoked monkey received exactly the same shocks as its executive partner.
2. The only difference was that it had no control and no responsibility for avoiding shocks.
3. So any difference in ulcers could be put down to the psychological stress of control, not the shocks themselves.

Answer: To hold the physical stressor constant and isolate the effect of control.

Check yourself

1. How many monkeys were in Brady's study?
   Show answer

   8. 8 rhesus monkeys in 4 pairs.

2. How often did shocks occur unless the lever was pressed? Give the number of seconds.
   Show answer

   20 seconds. Every 20 seconds.

3. What was the role of the yoked control monkey?
   • It received the same shocks but had no control over them
   • It pressed the lever to protect itself and its partner
   • It received no shocks at all
   • It was given drugs to prevent ulcers
   Show answer

   It received the same shocks but had no control over them. Same shocks, no control.

4. What happened to the monkeys?
   • All yoked monkeys died; executives survived
   • No monkeys developed ulcers
   • Half of each group died
   • All four executive monkeys died of ulcers; no yoked monkeys died
   Show answer

   All four executive monkeys died of ulcers; no yoked monkeys died. Only the executives died.

5. When was stomach acidity highest in the executive monkeys?
   • During the shock periods
   • During the rest periods
   • Before training
   • Only on the first day
   Show answer

   During the rest periods. After arousal stopped, digestive secretions flooded the stomach.

6. Which methodological flaw undermines Brady's conclusion?
   • There was a control group
   • The shocks were standardised
   • The study lasted several months
   • The executives were chosen because they learned fastest, not by random allocation
   Show answer

   The executives were chosen because they learned fastest, not by random allocation. Pre-existing differences may explain the ulcers.

7. Explain why Brady's (1958) study would be considered unethical today.
   Show answer

   The monkeys were restrained for long periods and given repeated electric shocks that caused severe suffering and death from ulcers, which breaches the Animals (Scientific Procedures) Act 1986 and the 3Rs, especially refinement.. Harm plus the rule it breaks.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification, Issue 6 (November 2024, first assessment January 2026)
• Pearson IAL Psychology summary of studies: WPS03
• Brady, Porter, Conrad and Mason (1958), Avoidance behavior and the development of gastroduodenal ulcers, Journal of the Experimental Analysis of Behavior 1
• Weiss (1972), Psychological factors in stress and disease, Scientific American 226(6)
• GOV.UK: Research and testing using animals, licences and compliance

Last updated 8 November 2026. Spotted a mistake? Tell us.