Most perceptual tasks require sequential steps to be carried out. 
This must be the case, for example, when subjects discriminate the 
difference in frequency between two mechanical vibrations applied 
sequentially to their fingertips. This perceptual task can be 
understood as a chain of neural operations: encoding the two 
consecutive stimulus frequencies, maintaining the first stimulus 
in working memory, comparing the second stimulus to the memory 
trace left by the first stimulus, and communicating the result of 
the comparison to the motor apparatus. The divisions between these 
steps may be artificial, but breaking the problem into pieces is 
helpful. Here I discuss several such pieces, although, in the long 
run, I aim for an integrated understanding of the perceptual 
processes, at least to the extent possible within the minimalist 
environment of a laboratory task.

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