Object representation in the bottlenose dolphin (Tursiops truncatus): integration of visual and echoic information.

A dolphin performed a 3-alternative matching-to-sample task in different modality conditions (visual/echoic, both vision and echolocation: visual, vision only; echoic, echolocation only). In Experiment 1, training occurred in the dual-modality (visual/echoic) condition. Choice accuracy in tests of all conditions was above chance without further training. In Experiment 2, unfamiliar objects with complementary similarity relations in vision and echolocation were presented in single-modality conditions until accuracy was about 70%. When tested in the visual/echoic condition, accuracy immediately rose (95%), suggesting integration across modalities. In Experiment 3, conditions varied between presentation of sample and alternatives. The dolphin successfully matched familiar objects in the cross-modal conditions. These data suggest that the dolphin has an object-based representational system.

On-line choice and the representation of serially structured stimuli.

Three groups of pigeons were trained to discriminate between a target temporal sequence, consisting of red, green, and blue, and distractor sequences consisting of all other combinations of these three colors presented on a pecking key. Response alternatives were provided during the course of the trial (on-line decisions) as well as the end of the trial (postsequence decisions). Different temporal phrasing patterns emphasized the first stimulus in the sequence, the final stimulus, or all stimuli equally. The phrasing pattern did not affect the speed of acquisition, but groups receiving emphasized stimuli relied more heavily on those stimuli than on the other stimuli for their discriminations. The patterns of both on-line choices during the sequence and terminal choices following the sequence were consistent with the use of hierarchical representations and inconsistent with a simple item-by-item prospective discrimination scheme.