Asymmetrical sample training and asymmetrical retention functions in one-to-one and many-to-one matching in pigeons

Pigeons were trained in a matching task with either color (group color-first) or line (group line-first) samples. After asymmetrical training in which each group was initially trained with the same sample on all trials, marked retention asymmetries were obtained. In both groups, accuracy dropped precipitously on trials involving the initially trained sample and remained high on trials involving the sample introduced second in training, suggesting that asymmetrical training encouraged a single-code/default strategy in which only the sample trained initially was coded. Pigeons next received concurrent training with the alternate set of samples mapped to the same set of comparisons as were the first set of samples (many-to-one, MTO, procedure). Retention testing revealed no marked retention asymmetries in group line-first whereas marked retention asymmetries occurred with both sets of samples in group color-first. Hence, only birds in group color-first continued to use a single-code/default strategy after MTO training.