Segregation of task-relevant conditioned stimuli from background stimuli by associative learning

In the real world, task-relevant, conditioned stimuli are often embedded in a varying background, from which they have to be segregated. Besides sensory mechanisms, associative learning assumingly plays an important role for the segregation of the conditioned from the background stimuli, especially if conditioned and background stimuli are spectro-temporally structured, and psychophysically similar. We therefore investigated the influence of spectro-temporally structured background tones on associative learning of conditioned tones depending on the complexity of the behavioral task and the psychophysical similarity between conditioned and background tones. Frequency-modulated tone sweeps were used as conditioned stimuli, and persisting frequency-modulated tones as background. In a shuttle-box, Mongolian gerbils were subjected to a simple detection task, or to a more complex discrimination task. In contrast to detection learning, introduction or change of background tones affected discrimination performance both during learning and at the stage of retrieval, especially when conditioned and background tones were spectro-temporally similar. The change from a familiar to a new background tone at the stage of retrieval caused a prefrontal dopamine increase and lead to relearning of task-relevant associations. We conclude that conditioned stimuli and background stimuli are processed concomitantly, which might provide contextual information, but requires additional cognitive processing. (c) 2009 Elsevier B.V. All rights reserved.