In addiction a set of perceptual representation (drugs and related paraphernalia) is tagged as salient and repeatedly selected for conscious processing. Understanding the neural systems by which perceptual representations are tagged as salient might allow better understanding of how these systems are disrupted in addiction. This proposal employs dense array ERPs and statistical, topographic, and dipole analyses to study the neural systems that attach salience to perceptual representations. Detecting task-relevant stimuli may require interaction between an orbito-frontal salience evaluation system and perceptual representations in the posterior brain. There is a potential ERP index of this orbito-frontal/posterior interaction: an inferior prefrontal P2a and a coincident posterior N2b. If the P2a indexes salience evaluation it should be independent of the stimulus and response modalities. If the N2b indexes perceptual processing it should be dependent upon stimulus feature. We test this model by manipulating target-defining feature, response type, and target salience. The task manipulations present relevant and irrelevant stimuli in different tasks: Passive, Silent Count, Keypress, and Withhold Keypress. In the Passive task there is no target detection so there should be no P2a. In the Count and Withhold tasks there is detection but no motor response; in the Keypress task there is both detection and a motor response. Since the perceptual and salience processing demands are equivalent we predict an equal P2a and N2b across active tasks. In the stimulus manipulation experiments the target-defining feature is changed. In one task subjects respond to visual stimuli occurring at a specific location while in another they respond to specific objects regardless of location. In a third task subjects respond to tones. We predict equivalent P2a's across target modalities but different topographic distributions of the N2b depending upon the salient feature. The final experiments manipulate the salience value of the stimulus. One study presents objects with no, small, or large reward value. The P2a should be larger to the more valuable stimuli with a constant N2b. The other study presents stimuli in different locations in salient and non-salient blocks. Constricted attention in the salient blocks should produce a larger P2a and N2b to foveal stimuli.
