Factors influencing inhibitory stimulus control: discrimination training and prior non-differential reinforcement.

In Exp. I, shallow U-shaped gradients of inhibition in the line-orientation dimension were obtained from birds that had a vertical (0 degrees ) line on a green surround correlated with extinction and a blank green surround correlated with reinforcement. Birds that had massed extinction in the presence of the 0 degrees line showed flat gradients. Thus, discrimination training, but not massed extinction, appears to generate inhibitory control. In Exp. II, as in studies of control by a stimulus correlated with punishment, non-differential training across the line-orientation dimension preceded further sessions. Steep inverted gradients about the 0 degrees line were obtained after discrimination training with the 0 degrees line correlated with extinction. Gradients obtained after massed extinction tended to be flat. Again, discrimination training was critical in obtaining negative gradients of stimulus control.