Rhesus monkeys are known to recognize confidence about their immediate perceptual and cognitive decisions by using a betting procedure (Son and Kornell in The missing link in cognition: origins of self-reflective consciousness. Oxford University Press, New York, pp 296-320, 2005; Kornell et al. in Psychol Sci 18:64-71, 2007). In this report, we examined whether this ability is shared in two avian species (pigeons and bantams) in order to know how widespread this metacognitive ability is among animals. We trained pigeons and bantams to search for a differently colored disk (target) among others (distracters) displayed on a touch-sensitive monitor. In test, the subjects were required to choose one of two confidence icons, "risk" and "safe", after the visual search. A peck at the "risk" icon after a correct response in the visual search (i.e., a peck at the target) was reinforced by food and light, while that after an incorrect response (i.e., a peck at a distracter) resulted in a timeout. A peck at the "safe" icon was always reinforced by food and light, or by light only, regardless of the visual search result. The percentages of "safe" choices after incorrect responses were higher than after correct responses in all six pigeons and two of three bantams. This behavior generalized to novel stimuli in some subjects, and even to a novel line-classification task in a pigeon. These results suggest that these two distantly related avian species have in common a metacognitive ability that allows them to recognize confidence about their immediate perceptual decisions.

Whereas many mammals (some primates and mice) experience amodal completion, previous data split for avian species. However, experimental procedures have been quite different among the species, and thus a direct comparison of various avian species in the same experimental situation is needed. We tested whether bantams (Gallus gallus domesticus) would complete partly occluded figures using a visual search task on the touch monitor, which was successfully used in our previous study with pigeons. First, we trained 3 participants to search for a notched red diamond (a target) among complete diamonds (distracters). Next, white squares accompanied each figure with a small gap of a fixed size. In test, the location of the accompanying white squares sometimes changed. In some trials, the white squares exactly covered, or "occluded," the notched portion of the target. Humans are known to have great difficulty in finding such targets due to "automatic" completion of the notched part. However, bantams met no such difficulty at all. This result and the demonstration by Forkman (1998) of hens' amodal completion of figures placed on a perspective background, suggest that the perspective cue may have an important role in amodal completion in this species.

Humans perceive a line touching an edge of a large rectangle longer than the reality. Kanizsa (1979) has suggested that this illusion occurs because we perceive that the line is partly "hidden" behind the rectangle and automatically completes it. We tested whether bantams (Gallus gallus domesticus) would experience this perceptual phenomenon using a line classification task on the touch monitor, which was used in our previous study with rhesus monkeys and pigeons (Fujita, 2001). We trained three bantams to classify six lengths of black target lines into two categories, "short" or "long," ignoring a gray rectangle (Experiment 1) or a gray area (i.e., a left or a right half of the monitor was filled with gray; Experiment 2) located at the same distance (8 pixels) from the target line. In the test, the gap between the line and the gray rectangle (or area) sometimes changed (0, 4, or 8 pixels; we labeled these stimuli as G0, G4, and G8 respectively). Both of the two successfully trained bantams showed an illusion for G0, but the direction of illusion was reversed; that is, they judged the line in G0 to be "shorter" than that in G4 and G8. Further analyses proved that neither the gaps between the target line and the gray rectangle nor the total widths of the stimuli could account for the bantams' responses. These results suggest that bantams do not complete the "occluded" portion even when identification of its shape is not required.

To examine if a feature of episodic-like memory reported in rats is shared with other species, we investigated whether degus would form an integrated memory of object (what), place (where), and context (which). We used two E-shaped mazes with different contexts regarding the wall and the floor. Degus were entered into the middle arm and first explored the maze with two trial-unique objects placed at each end of the backbone of the E, with their location reversed between contexts. After being habituated to one of the objects in the holding cage, the degus re-explored the maze. Subjects explored the non-habituated object in these baseline trials. In the critical test, the objects were located at the end of the outer arms of the maze. Degus went into the arm where they expected the non-habituated object significantly more often than the other. This result suggests recollection of an integrated What-WhereWhich memory.

We investigated if and how Syrian hamsters (Mesocricetus auratus) show flexibility in their use of multiple sources of information in a spatial learning task. In Experiment 1, hamsters were trained to exit an arena through one of three doors. The goal, marked by a beacon, was fixed during the training phase. When the beacon was placed nearer to another door, the hamsters predominantly chose the original door rather than those with the relocated beacon (Tests A and C). The removal of the beacon had little effect on their performance (Test B). In Experiment 2, when we changed the shape of the apparatus to make the positional information of the goals other than the beacon invalid, a few individual subjects used the beacon (Test B'). However, after experiencing the invalidity of such positional information, the original door was less frequently chosen in a rerun of the beacon relocation test (Test C). Finally, in Experiment 3, we confirmed that hamsters could easily learn to use the beacon when it was the sole cue for navigation. These results suggest that, despite hamsters' limited tendency to use a beacon for navigation, they can flexibly use multiple strategies depending on their experience or environmental context.