Transposition of line-length discrimination in African penguins (Spheniscus demersus)1

Four penguins (Spheniscus demersus) were trained to discriminate line length in a simultaneous discrimination task. After the birds' performances reached a discrimination criterion, the reinforcement ratio was decreased to .33. After the ratio of correct trials reached .90 in three successive sessions with a partial reinforcement procedure, probe-test sessions were introduced. In the probe-test trials, untrained lines were presented paired with the trained lines. The four probe-test trials were mixed into 45 discrimination trials. In the probe-test trials, the penguins that had been trained to peck shorter lines pecked the untrained shorter line rather than the longer line that was reinforced in the discrimination trials. In contrast, those birds that had been trained to peck the longer line pecked the untrained longer line, rather than the shorter line which was reinforced in the discrimination trials. All four birds demonstrated transposition in the line-length discrimination task.