Stimulus congruence affects perceptual processes in a novel Go/Nogo conflict paradigm in rats

The performance of freely moving rats (n=18) in a decision-making reaction time task was analyzed to provide data that can be compared with noise-compatibility paradigms previously obtained in humans. Rats were first trained in an auditory pitch discrimination task involving a Go/Nogo response choice. In a subsequent phase, the two tones used in the previous phase were simultaneously presented in different combinations from two locations. Only the presence of the correct tone from the correct location was predictive of the reward. The observed behavioral strategies suggest a competition between two processes: one involving stimulus evaluation, response preparation and execution, the other involving recognition of the stimulus features associated with inhibition of the Go-response. The reaction times in the most adopted strategies towards the end of the experiment suggest an effect of stimulus congruence. Perceptual processes are affected by the congruence of 'pitch' and 'location' stimulus dimensions and the duration of the response may, but need not, be affected by overlapping dimensions. The analysis of error and aborted trials also suggest that subject's reaction and subsequent motor action may depend on whether stimulus identification processes can pass information to the response activation system prior to completion of sensory processing. The data are discussed in the framework of processing stages theory and dimensional overlap model.