Learning the specific quality of taste reinforcement in larval Drosophila

The only property of reinforcement insects are commonly thought to learn about is its value. We show that larval Drosophila not only remember the value of reinforcement (How much?), but also its quality (What?). This is demonstrated both within the appetitive domain by using sugar vs amino acid as different reward qualities, and within the aversive domain by using bitter vs high-concentration salt as different qualities of punishment. From the available literature, such nuanced memories for the quality of reinforcement are unexpected and pose a challenge to present models of how insect memory is organized. Given that animals as simple as larval Drosophila, endowed with but 10,000 neurons, operate with both reinforcement value and quality, we suggest that both are fundamental aspects of mnemonic processing—in any brain.

Pattern and Quality of Reinforcement in Extinction in Albino Rats

This experiment examined the effects of successive (3 or 1) nonrewards prior to a sucrose reward and the effects of successive (3 or 1) alfalfa rewards prior to a sucrose reward on resistance to extinction. Long runs of nonrewards or long runs of alfalfa rewards led to greater resistance to extinction than did short runs. Ss who experienced nonrewards and those who experienced alfalfa rewards were not substantially different from each other. The findings were discussed within Capaldi's sequential theory.

Effects of Quality and Quantity of Reinforcement Upon Response Rate in Acquisition and Extinction

This experiment investigated the effects of quality and quantity of reinforcement upon a lever-pressing response, within the context of repeated acquisition and extinction sessions. Eighteen Sprague-Dawley albino rats were subjected to a 2-by-3 experimental design which incorporated two levels of quality of reinforcement (8% and 32% sucrose pellets) and three levels of quantity of reinforcement (20, 40, or 80 pellets given in each acquisition session). Rate of responding during each acquisition session varied directly with sucrose content of the pellet, but was independent of number of reinforcements (pellets) received in each acquisition session. In extinction, total number of responses varied directly with both number of reinforcements and sucrose content of the pellet. Latency to the first lever-pressing response in both acquisition and extinction was found to be heterogeneous for all Ss and insensitive to variations in quantity and quality of reinforcement.