Punishment in the form of electric shock was delivered through implanted electrodes
following every response during a variable-interval schedule of food reinforcement. The
initial addition of punishment was found to produce a disproportionately large suppression
of responding with subsequent recovery, often complete, while the punishment was being
maintained. This recovery from punishment occurred within each daily period as well as
from day to day over periods as long as 60 days. At very intense punishment intensities,
this recovery process was usually reduced or absent. The same cycle of immediate suppression
and gradual recovery is produced by abrupt increases of an existing level of punishment.
Conversely, when an existing level of punishment is decreased, responding adjusted
gradually to a new and higher level. When the punishment is reduced to zero, however, the
previously punished responses briefly "overshoot," reaching a higher rate than is usual
for the unpunished level. No increase in the variability of the local response rate results
from the punishment of responses under variable-interval food reinforcement. Under this
simultaneous food and punishment schedule, responding continues to occur at a fairly
uniform rate, which is directly related to the degree of food deprivation and inversely
related to the punishment intensity. Interruption of the punishment process, either by a
period of no punishment, or by a complete time-out period, produces renewed suppression
upon the reinstatement of the punishment.
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