Figure 2.

Task logic. (A) In an example of biconditional discrimination (Sanderson et al., 2006), two of four possible stimuli (A, B, C, and D) are presented simultaneously to a subject. If either both A and B are present or neither is present, the subject should make one response (such as release a lever). If either A or B but not both are present, the subject should make an alternative response (such as hold the lever until the end of the trial). Neurons must generate responses to specific stimulus-pairs (e.g., A + B) to perform this task successfully. A response to a single stimulus (e.g., A) is not sufficient to drive the correct response in one pairing without activating the incorrect response for the opposite pairing of that stimulus. (B) In the simplified task of single stimulus-response matching, network input is more specific, with just one input activated at a time.