Effect of number and location of negative trials on a feature positive discrimination

Abstract

<p>Pigeons were trained to discriminate between two displays differentiated only by a distinctive feature on the positive display. The development of a simultaneous discrimination was measured by the percent of key pecks on the positive display that were directed to the distinctive feature. The effect of a) the sequence of positive and negative trials, b) the number of negative trials, and c) the shape of the distinctive feature on the development of discrimination were examined.</p> <p>An alternating sequence of block of positive trials and a block of negative trials was interrupted by session breaks either between positive trials, or between positive and negative trials. The location of the session break preserved or prevented within session transitions from negative trials to positive. Sequences that preserved the within session transition from negative to positive trials were highly effective in producing control of key pecking by the distinctive feature. Sequences that prevented within session transitions from negative to positive trials were less effective, particularly when the shape of the distinctive feature was less preferred. The more trials in the negative block the more rapidly discrimination occurred. However, not even the longest block was capable of producing control of key pecking by the less preferred distinctive feature when the session break prevented a within session transition from negative to positive trials.</p> <p>The preparation employed in this experiment was particularly suitable for evaluating the effect of sequential variable on stimulus control. While differential responding between positive and negative displays can be controlled by the sequence of reinforcement and non-reinforcement itself, differential responding within the positive display cannot.</p>