Effects of Shifts in Delay of Reward in Rats as a Function of Reward Magnitude

Abstract
Four groups of rats first received either small or large reward following either zero or 30-second delay in a 2 × 2 design. Then each main group was divided into two equal groups, one subgroup continuing on the original delay interval (resulting in a 2 × 2 × 2 design). No shift in magnitude of reward was made throughout the experiment. The results showed no positive contrast effect (PCE) or negative contrast effect (NCE) under either small or large reward conditions. The absence of an NCE was discussed in terms of a possible “floor effect” associated with long delay.