In 1937 Muenzinger, Dove and Bernstone (5) reported a study with albino rats which presented evidence that the goal gradient is bi-directional. They considered this double winged gradient as a special case of the Thorndike effect (8), i.e., that the goal response 'spreads its effects' both forward and backward. Hull would state this effect in terms of learning being reinforced when the reinforcing state of affairs precedes the S -R conjunction as well as when it follows it.These results have been confirmed by Hill (2) and Jenkins (4). However, the hypothesis offered by Muenzinger, Dove and Bernstone to account for the bi-directional gradient has not found favor among Hull and his students. Hull (3, p. 162) recognizes the gradient (bi-directional) but dismisses it from theoretical consideration with the following statement: "However, since the reduction in a need necessarily follows rather than precedes the act which brings this about, it would seem that the forward gradient could hardly play much role in selective learning." 2
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