“…Muenzinger demonstrated such effects in a series of investigations stretching back to the early thirties. The initial finding (Muenzinger, 1934), that a shock which was twice the threshold value for young rats (Muenzinger & Mize, 1933) would actually facilitate the learning of a light-dark discrimination beyond the influence of reward alone, was confirmed in a number of subsequent investigations (Muenzinger & Baxter, 1957;Muenzinger, Bernstone, & Richards, 1938;Muenzinger, Brown, Crow, & Powloski, 1952;Muenzinger & Powlowski, 1951;Muenzinger & Wood, 1935). Likewise, Drew (1938) and Freeburne and Taylor (1952) found that shock enhanced discrimination learning in rats beyond the effects of reward alone.…”