Avoidance-Trained Rats Do Not “Anticipate” Periodically Scheduled Free Shock
Four rats, trained under a free-operant avoidance schedule, received a response-independent shock (US) every 6 min. Signalled and unsignalled US conditions were given in separate blocks of sessions. Response rate was elevated temporarily following the delivery of the US but was relatively stable over the remainder of the 6-min. period, i.e., unchanged between USs. Only when a signal (CS) preceded US did avoidance change during the US cycle. For two subjects initially given CS-US, impaired avoidance developed during the CS. For the two subjects initially given unsignalled US, inserting the CS led to enhanced avoidance during the CS periods.