Latently inhibited stimuli are weakened in their ability to serve as blockers and second-order reinforcers in Pavlovian fear conditioning

The ability of a preexposed (latently inhibited) conditioned stimulus (CS) to serve as (a) a blocker or (b) a second-order reinforcer in Pavlovian fear conditioning was tested in albino rats. Experiment 1 found that a preexposed CS was weakened in its ability to serve as a blocker. Experiment 2 found that a preexposed CS was weakened in its ability to serve as a reinforcer for second-order conditioning (SOC). Experiment 3 found that a 28-day retention interval between the last trial of element conditioning and the first trial of the SOC test did not enhance the ability of the preexposed CS to serve as a reinforcer for SOC, even though it did enhance the ability of that preexposed CS to evoke a first-order conditioned response. Experiment 4 was undertaken in an effort to show a contextually dependent attenuation of LI by employing a context shift between preexposure and element training. However, no attenuation of LI was found. Experiment 5 successfully demonstrated an attenuation of LI by reducing familiarity with the preexposure context prior to CS preexposure, reducing the amount of CS preexposure, and by using 100% reinforcement of the target CS during the first two days of the element training phase. Experiment 6 found that conducting stimulus preexposure and the test for blocking in different contexts did not enhance the ability of a preexposed CS to block conditioning to a neutral CS. Results are interpreted as supporting a learning-deficit view of latent inhibition