PROCESSING OF HIERARCHICAL STIMULUS STRUCTURES HAS ADVANTAGES IN HUMANS AND ANIMALS

Carmesin and Schwegler (1994) have determined theoretically that a lin ear hierarchical stimulus structure can be encoded by a parallel netwo rk of minimal complexity. The experiments reported here compare the ef ficiency with which humans and pigeons process sets of stimulus pairs embodying different inequality structures. Groups of subjects of each species were taught to discriminate all 10 pairwise combinations of 5 stimuli with an operant conditioning method. For one group, the reward /punishment allocations within the pairs agreed with a linear hierarch y. For a second and third group, the reinforcement allocations of one or three, respectively, of the stimulus pairs deviated from such order ing. The time it took the subjects to learn the tasks as well as the f inal choice latencies and/or error rates increased with the number of deviating inequalities. The results agree with the assumption that bot h humans and pigeons encode stimulus inequality structures with parall el processing neural networks rather than with a sequentially processi ng algorithm.