Conditioned inhibition of classical conditioning was investigated
with the startle reflex and the skin conductance response (SCR)
in humans using a serial presentation of the conditioned inhibitor
(X) and of the conditioned stimulus (CS). The unconditioned
stimulus (US) was a shock. During conditioning, participants
were presented with two different reinforced CS (A, B) and with
X preceding A (noted X → A). During X → A, A was not
reinforced with the US. During the summation test, B, X →
B, and Y → B were presented (Y was a new stimulus that
tested the specificity of the inhibitory properties of X). B
was not reinforced during the summation test. A, B, X, and Y
were lights of different colors. Participants were divided into
a low and a high anxious group based on the TPQ (C.R. Cloninger,
1987). In the low anxious group, conditioned startle potentiation
and SCR responses to A were inhibited when X preceded A (noted
AXA). This differential responding to A and
AXA emerged earlier with the SCR than with startle.
During the summation test, the inhibitory properties of X did
not transfer to B. In the high anxious group, there was only
a differential SCR to A and AXA. X did not inhibit
startle potentiation to A.