Time-dependent changes in conditioned suppression.
Fear conditioning in pigeons peaks at middle delays, not right away or after long gaps.
01Research in Context
What this study did
The team worked with pigeons in a small lab chamber.
Each bird first learned to peck a red key for grain.
Next, a tone played for one minute. During the last five seconds the birds got a quick shock.
The birds were split into two groups. For one group the tone came before the shock. For the other group the tone came after the shock.
The twist: the researchers waited different lengths of time between training and testing. Some birds were tested right away. Others waited minutes or hours.
What they found
Birds trained with tone-before-shock showed a clear U-shaped curve.
Suppression was weak right after training, grew stronger at middle delays, then weakened again after long delays.
Birds trained with tone-after-shock showed almost no suppression at any delay.
In short, fear peaks in the middle, not at the start or end.
How this fits with other research
HEARST (1962) saw the same U-shape in a delayed-alternation task. Pigeons were worst at the shortest and longest waits, just like the fear curve here.
LYOSLOANE (1964) showed that timing inside one FR run changes suppression. If the scary cue comes early, the bird stops. If it comes late, the bird keeps pecking to get the food. The new study adds a second time layer: how long after training you test.
Locurto et al. (1980) found mixed effects when they switched reinforcement rules. Suppression lasted longer than acceleration. Together these papers say timing matters at three scales: inside a trial, across the session, and between sessions.
Why it matters
If you run fear-reduction programs, do not test right after training and think "no effect." The biggest change may show up later.
Also, check the order of events. CS-before-US gives a time curve; CS-after-US gives almost nothing.
When you write protocols, plan follow-up probes at middle delays. That is when you will see the clearest data and can adjust your treatment faster.
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02At a glance
03Original abstract
Time-dependent changes in a response following aversive conditioning were investigated using a conditioned suppression procedure in a within-subjects design. Four groups of pigeons received Pavlovian conditioning "off the baseline", immediately followed by an operant task. During the Pavlovian phase, two groups received a forward pairing of a tone with shock, one group received a backward pairing, and one group received a truly random pairing. One of the forward pairing groups also received a delay between the Pavlovian and operant phases. For all groups, key pecking was reinforced on a variable-interval schedule during the operant phase. Testing sessions were identical to training sessions, except that the tone used during Pavlovian conditioning was presented either 0, 15, 30, 45, of 60 minutes after the operant phase began. Testing sessions in which the Pavlovian phase was omitted were also included. The results showed suppression to change as a function of the retention interval, with maximum suppression occurring at intermediate intervals. This U-shaped function was obtained for 11 of the 12 pigeons in the forward-pairing groups and for three of the five in the truly random group. Pigeons in the background pairing group did not show changes in suppression as a function of the retention interval.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.29-199