Role of acetylcholine in negative patterning in turtles (Chrysemys picta).

Turtles were run on a negative patterning task involving 2 positive elements, a key with white stripes on a black background, and a solid red key, and a compound stimulus combining the 2 elements, white stripes on a red background. Injections of scopolamine, methylscopolamine, or saline were started at the same time that the compound stimulus was introduced, after the animals had been autoshaped to press the key for each of the elements. Scopolamine disrupted the learning of negative patterning, but methylscopolamine had no effect.