“…It is significant that, for both of our voluntary groups, there is a trend toward an increasing number of conditioned responses with increased training. This is in marked contrast to the findings of Marquis and Porter, who found no increase in voluntary conditioned wink reactions, and to those of Yacorzynski and Guthrie (11), who, using voluntary hand withdrawal to a shock on the other hand, found an actual decrease in the number of voluntary conditioned responses. One possible explanation of this may lie in the fact that these experimenters used approximately only a third as many stimulations per sitting as was used in the present experiment.…”