Latent inhibition and overshadowing in conditioned emotional response conditioning with rats.

Abstract

In order to test whether unreinforced preexposure to one element of a compound conditioned stimulus (CS) would prevent that element from overshadowing the other element, groups of rats were given 20 preexposure trials to a light prior to conditioned emotional response (CER) conditioning or were given no preexposure. In CER conditioning, subjects received either a noise + light or a noise followed by shock. In animals given no preexposure, the presence of the light significantly attenuated conditioned suppression to the noise CS. However, in the preexposed compound-cue group no reduction in suppression to the noise CS was observed after 4 CER trials. After 8 CER trials, suppression to the noise CS was significantly attenuated. Latent inhibition temporarily reduced the extent to which the light CS overshadowed the noise CS. Overshadowing of the noise in the preexposed compound-cue group after 8 CER trials was not accompanied by any increase in suppression to the light CS.

The effects of stimulus preexposure on taste-mediated environmental conditioning: Potentiation and overshadowing

“…Otherwise, they would likely have served as effective overshadowing stimuli, as they did in the group for which the environmental stimuli were novel at the time of conditioning (Group No Pre). For example, it has been demonstrated in other preparations that familiarity with one of the stimuli subsequently used in a compound overshadowing procedure reduces the amount of overshadowing this stimulus exerts on a reinforced trial (e.g., Carr, 1974). In Group Box of the present experiment, a familiar environmental stimulus significantly reduced the amount of environment-mediated taste overshadowing.…”

Overshadowing by fixed- and variable-duration stimuli

“…Such nonreinforced preexposure can also influence the ability of a CS to overshadow another: by slowing the speed with which the preexposed CS conditions, the degree to which the overshadowed cue can acquire associative strength is increased (e.g. Carr, 1974). It is thus possible that fixed and variable cues differ not in their ability to reach asymptote, but in their associability, and that this produced the effects we observed; although it is not immediately obvious how any current theories could explain how associability could be influenced by the temporal properties of the stimulus in this way, this must remain a logical possibility.…”

Determinants of cue interactions

“…In terms of theory, a counteraction between latent inhibition and overshadowing is generally more likely to occur if both individual effects are strong. There are other studies of CS preexposure and overshadowing in the literature that are difficult to interpret for similar reasons (e.g., Carr, 1974;Schnur, 1975).…”