In three experiments with rats, the temporal relationships under which
a conditioned inhibitor would transfer its inhibitory potential to an
independently trained exciter in a summation test were investigated.
Each experiment varied the temporal relationship between the inhibitor
and the transfer exciter at test (serial or simultaneous) and, in add
ition, manipulated either the inhibitor-training exciter (serial or si
multaneous), training excitor-unconditioned stimulus (US) (trace or de
lay), or the transfer excitor-US (trace or delay)temporal relationship
s. Conditioned inhibition was found only when the no-US expectation ev
oked by the conditioned inhibitor was temporally aligned with the US e
xpectation evoked by the transfer exciter, independent of whether the
inhibitor was trained as a serial or simultaneous signal for US omissi
on. Results are discussed in terms of the temporal coding hypothesis a
nd the comparator hypothesis.