Number-of-responses matching in pigeons (Columba livia): Choice biases following delay and no-sample tests

In a symbolic matching-to-sample task, pigeons learned to discriminate between 5 and 15 key pecks (samples): different choices were correct following the smaller and the larger response requirements. Subsequently, accuracy was tested in delayed matching, with the delay spent in darkness, contrarily to previous studies, that used illuminated delays. On average, delayed choices reflected indifference between the choices, but individual analyses showed different biases, replicating previous findings. It has been suggested that the end result of a delay may be similar to presenting no sample to begin with, so we compared preferences following a delay and following trials where no pecks were required. Performance in the two situations differed and, on zero-peck trials, a bias towards the “small” choice was found. Finally, to assess if the “small” bias was due to stimulus generalization, we compared zero-peck trials and trials with small response requirements (ranging from one to four) and found a discontinuity between zero and non-zero samples that may seem to be at odds with a generalization account.The present work was conducted at the Psychology Research Centre (PSI/01662), University of Minho, and was supported by the Portuguese Foundation for Science and Technology and the Portuguese Ministry of Science, Technology and Higher Education through national funds. It was also co-financed by FEDER – through COMPETE2020 – under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007653)