Two procedures for studying partial reinforcement effects in classical conditioning of the planarian

Abstract

The effects of partial reinforcement in classical conditioning of the planarian were studied. Three groups of six planaria each were given 50 lights (CS) and 50 shocks (UCS) on each of five consecutive days. For one group all of the lights and shocks were paired (100 per cent reinforcement). For the second group 50 per cent of the lights and shocks were paired, with the remaining stimuli delivered unpaired. The third group received all of the stimuli unpaired (0 per cent reinforcement). A fourth group was given 25 CS-UCS trials interspersed with 25 CS-only trials. All groups received 50 CS-only extinction trials on day 6 and again on day 7. During acquisition all conditioning groups made significantly more responses to the CS than the 0 per cent control. During extinction responding was greatest in the two partial reinforcement groups, while responding in the 100 per cent group dropped below the level of the control group. The results were related to other investigations of the phyletic generality of the partial reinforcement effect (PRE), and to theoretical accounts of the PRE. It was concluded that, at the phyletic level of the planarian, cognitive conceptualizations are less applicable than are non-cognitive, S-R accounts of the PRE.