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 reactio n time task was analyzed to provide data that can be compared with noise-co mpatibility paradigms previously obtained in humans. Rats were first traine d in an auditory pitch discrimination task involving a Go/Nogo response cho ice. In a subsequent phase, the two tones used in the previous phase were s imultaneously presented in different combinations from two locations. Only the presence of the correct tone from the correct location was predictive o f the reward. The observed behavioral strategies suggest a competition betw een two processes: one involving stimulus evaluation, response preparation and execution, the other involving recognition of the stimulus features ass ociated with inhibition of the Go-response. The reaction times in the most adopted strategies towards the end of the experiment suggest an effect of s timulus 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 subsequen t motor action may depend on whether stimulus identification processes can pass information to the response activation system prior to completion of s ensory processing. The data are discussed in the framework of processing st ages theory and dimensional overlap model. (C) 1999 Elsevier Science B.V. A ll rights reserved.