Studies in the Peripheral Retina: II. The Purkinje After-Image on the Near Foveal Area of the Retina

Although true second-order conditioning has, apparently, not previously been demonstrated in any American laboratory, it was found that by using electrodes implanted in the occipital sensory areas of hens, second-order limb responses could be readily established in approximately 33% of a group of 51 subjects developing first-order conditioned responses. In a number of subjects, the second-order responses remained stable for hundreds of trials and were highly resistant to extinction. Electrolytic damage at the sites of the cerebral reinforcing electrodes had no discernible effect on the stability of the second-order conditioned responses. They could also be evoked when direct current which temporally overlapped the cerebral conditioned stimuli was passed between or adjacent to the signal electrodes.