Effects of stimulus meaningfulness on the acquisition of conditional relations and the emergence of symmetrical relations in adult humans

The goal of the present study was to investigate the effects of stimulus meaningfulness of sample and comparison stimuli on the acquisition of conditional relations and the emergence of symmetrical relations. Eight college students were trained on two types of baseline conditional discrimination tasks involving meaningful (English words) and non-meaningful (Swahili words) stimuli. One task involved English samples and Swahili comparisons (English–Swahili), whereas the other task involved Swahili samples and English comparisons (Swahili–English). Test trials, without programmed consequences, presented the symmetry probe of the baseline relations trained. That is, the English–Swahili baseline relations presented on the training trials were presented as the Swahili–English symmetrical relations on the test trials. Similarly, the Swahili–English baseline relations on the training trials were presented as the English–Swahili symmetrical relations on the test trials. The results show that the English–Swahili baseline relations were acquired faster than the Swahili–English baseline relations. The results also show that, relative to the acquisition of the baseline relations, the emergence of symmetrical relations was facilitated and delayed, respectively, on the English–Swahili and Swahili–English test trials. The present results suggest that stimulus meaningfulness of untrained successive discrimination of samples and simultaneous discrimination of comparisons on test trials affects the emergence of symmetrical relations, with the former playing a more important role than the latter.