Responding in the squirrel monkey under second-order schedules of shock delivery.
A simple flash of light can maintain behavior when it reliably signals a future event, so choose your signals carefully.
01Research in Context
What this study did
Scientists watched squirrel monkeys press a lever. Every few minutes the monkey got a short flash of light. After several flashes the monkey also got a brief electric shock.
The flashes came on a fixed-interval schedule. The shocks came on a second-order schedule. The team wanted to know if the flashes alone could keep the lever pressing going.
What they found
The monkeys kept pressing even though the only immediate event was a tiny light. Longer flash periods made the pressing slow down. Shorter flashes kept the pace high.
The pattern looked like a typical fixed-interval scallop: pause, then quick burst. Shock was delayed, yet the light kept the chain alive.
How this fits with other research
Greene et al. (1978) ran almost the same setup but added a fixed-time arm. They proved the lever press really mattered; when shocks came no matter what, pressing dropped. That confirms the 1972 effect was true operant behavior, not just general activity.
Weisman et al. (1975) swapped monkeys for pigeons and mixed food with shock. Shock still cut response rate, showing the suppressive punch of aversive stimuli travels across species and reinforcers.
Appel (1968) had already shown that when shock is used as a punisher it stops bar pressing. Byrd (1972) flips the coin: the same stimulus can also reinforce and maintain pressing if the contingency is arranged that way. Together the papers map both sides of shock’s action.
Why it matters
You probably won’t use shock in clinic, but you will use brief, neutral stimuli such as tokens, clicks, or check marks. This study reminds us that even tiny signals can prop up behavior if they reliably point to a later consequence. When you build token boards or sticker charts, keep the gap short and the signal clear. If progress slows, tighten the schedule instead of adding bigger rewards.
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02At a glance
03Original abstract
Lever-pressing responses were maintained in the squirrel monkey when the only consequence of responding was the delivery of a response-produced electric shock, or alternatively, a brief visual stimulus that was occasionally followed by an electric shock. When shock was produced by the first response occurring after 8 min (8-min fixed-interval schedule), a period of no responding at the beginning of the interval was followed by a gradual increase in response rate during the interval. Similar rates and patterns of responding were maintained when a 1-sec visual stimulus was produced by the first response occurring after 8 min and shock delivery followed the brief stimulus. Subsequently, patterns of positively accelerated responding were engendered during individual fixed-interval components when the first response occurring after 4 min produced a 1-sec visual stimulus and shock delivery followed the second, and later the fourth, presentation of the 1-sec stimulus. When the duration of the brief stimulus was varied over a 100-fold range from 0.1 to 10.0 sec (1) mean response rates decreased monotonically as stimulus duration increased, and (2) patterns of positively accelerated responding were least variable and response rates during the initial part of each 4-min interval were lowest at a stimulus duration of 1 sec.
Journal of the experimental analysis of behavior, 1972 · doi:10.1901/jeab.1972.18-155