Sota Watanabe

Despite their impressive cognitive abilities, avian species have shown less evidence for metacognition than mammals. We suspect that commonly used tasks such as matching to sample might be too demanding to allow metacognitive processing within birds’ working memory. Here, we examined whether pigeons could control their behavior as a function of knowledge levels on a three-item sequence learning task, a reference memory task supposedly requiring fewer working memory resources. The experiment used two types of lists differing in familiarity. One was familiar to the pigeons through repeated exposure, whereas the other was novel in every new session. In test sessions, pigeons could choose between a trial with a hint specifying the next item to peck and one with no hint. However, successful responses in trials with a hint resulted in lowered rates of primary reinforcement:.60 in the first test and.75 in the second. Results showed that two of four pigeons chose the trial with a hint significantly more often before receiving a novel list than the familiar list in the four sessions of the first test, and three did so in the second test. Impressively, one bird showed robust evidence in the very first sessions in both tests. These results suggest that pigeons may monitor their long-term knowledge states and thereby control their environment before starting to solve a task.

The present study investigated how budgerigars and humans perceive a version of the Delboeuf illusion. In Experiment 1, we trained 4 budgerigars to discriminate between the sizes of two square targets, one of which was embedded in a concentric square frame. The birds accurately differentiated between the sizes of the targets when the target size disparity was large; however, when this disparity was small, they tended to choose the target embedded in the frame. Experiment 2 used the same stimuli and task as Experiment 1 but the participants were humans; the results suggested that the human participants perceived a normal Delboeuf illusion. Thus, these results indicate the adequacy of our stimuli and the inadequacy of tasks with two choices in comparative studies of the Delboeuf illusion as the simultaneous presentation of the two illusory figure(s) may cause unexpected choice bias.

Retinotopic encoding is preserved in primate visual cortex. However, several physiological and psychophysical studies have revealed that visual processes can be disengaged from retinotopic coordinates. We examined whether this non-retinotopic processing is common to humans and pigeons, two visually dominant vertebrate species with similar retinotopic organizations in their brains. We used a variant of Ternus-Pikler stimulus as a litmus test for non-retinotopic processing. Six humans and four pigeons were required to discriminate the rotational direction of a target disk placed among linearly arranged non-rotating disks. When all disks flickered in synchrony (a blank screen was inserted between the stimulus presentations) and moved in tandem back and forth, target localization was hampered in humans but not pigeons (Experiment 1). The duration of the blank screen (Experiment 2) and the connection between the disks (Experiment 3) did not affect the pigeons' performance. These results suggest that non-retinotopic processing in human vision is not a feature of pigeon vision, which is instead strictly retinotopic in case of motion. This may reflect the different mechanisms for stimulus selection in both species, in which local motion signals were pooled at later stages of visual processing in humans, but the signals were selected at early stages in pigeons. (C) 2014 Elsevier Ltd. All rights reserved.

A disk surrounded by smaller disks looks larger, and one surrounded by larger disks looks smaller than reality. This visual illusion, called the Ebbinghaus-Titchener illusion, remains one of the strongest and most robust illusions induced by contrast with the surrounding stimuli in humans. In the present study, we asked whether bantams would perceive this illusion. We trained three bantams to classify six diameters of target disks surrounded by inducer disks of a constant diameter into "small" or "large". In the test that followed, the diameters of the inducer disks were systematically changed. The results showed that the Ebbinghaus-Titchener figures also induce a strong illusion in bantams, but in the other direction, that is, bantams perceive a target disk surrounded by smaller disks to be smaller than it really is and vice versa. Possible confounding factors, such as the gap between target disk and inducer disks and the weighted sum of surface of these figural elements, could not account for the subjects' biased responses. Taken together with the pigeon study by Nakamura et al. (J Exp Psychol Anim Behav Process 34:375-387 2008), these results show that bantams as well as pigeons perceive an illusion induced by assimilation effects, not by contrast ones, for the Ebbinghaus-Titchener types of illusory figures. Perhaps perceptual processes underlying such illusory perception (i.e., lack of contrast effects) shown in bantams and pigeons may be partly shared among other avian species.

Seeking information in uncertain situations has been interpreted as evidence of metacognitive abilities. We examined whether pigeons could monitor their own knowledge states and seek new information when in need. In Experiment 1, we required the pigeons to learn novel sequences of responses for various trios of illustrations. On half of the trials, subjects were given the opportunity to ask for "hints" as to the next correct response in a sequence. If the subjects completed a trial correctly without any hints, they were rewarded with food and light. If the subjects sought one or more hints during the course of completing a trial correctly, they were rewarded either with food and light, or with light only. Incorrect responses resulted in a time-out. We analyzed when the pigeons sought hints. Two of four pigeons sought hints in early sessions more often than in the final sessions of learning novel sequences, and the frequency of hint-seeking was inversely correlated with accuracy on those trials in which hints were unavailable. In Experiment 2, however, the pigeons failed to generalize their "hint-seeking" behavior in a novel situation involving visual search as the primary task. In sum, the results suggest that this species might have an ability to differentiate between their own cognitive states of knowing and not knowing, although the evidence is inconclusive.

Although pigeons have been shown to be susceptible to several size and length illusions, other avian species have not been tested intensively for illusory perception. Here we report how bantams perceive the Zollner figure, in which parallel lines look nonparallel due to short crosshatches superimposed on the lines. Watanabe et al. (Cognition 119:137-141, 2011) showed that pigeons, like humans, perceived parallel lines as nonparallel but that the orientation of subjective convergence was opposite to that of humans. We trained three bantams to peck at the narrower (or wider) of the two gaps at the end of a pair of nonparallel lines. After adapting them to target lines with randomly oriented crosshatches (which result in no apparent illusion to humans), we tested the bantams' responses on randomly inserted probe trials, in which crosshatches that should induce the standard Zollner-like illusion for humans replaced the randomly oriented ones. The results suggested bantams, like pigeons, perceive a reversed Zollner illusion.

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 G(0), G(4), and G(8) respectively). Both of the two successfully trained bantams showed an illusion for G(0), but the direction of illusion was reversed; that is, they judged the line in G(0) to be "shorter" than that in G(4) and G(8). 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.

Pigeons are susceptible to several size and length illusions, but in some cases the bias has been shown to be opposite to that seen in humans. To further investigate how their perceptual system works, we asked how pigeons perceive orientation illusions. We used the Zollner illusion, in which parallel lines look non-parallel due to series of short crosshatches superimposed on the lines. First, we trained six birds to peck at the narrower (or wider) of the two gaps at the end of a pair of non-parallel target lines. After adapting the subjects to target lines with randomly oriented crosshatches (which result in no illusion at least to humans), we tested the pigeons' responses on randomly inserted probe trials, in which crosshatches that should induce the standard Zollner-like illusion for humans replaced the random-oriented ones. The results suggested that pigeons do perceive an illusion from Zollner figures, but in the direction opposite to that of humans. We propose that pigeons, contrary to humans, may assimilate the two lines of different orientations (each main line and crosshatch), which results in underestimation of acute angles, and this in turn may lead to a reversed Miner illusion. Such assimilation dominance appears consistent with previous reports obtained for line length and size illusions in this species. (C) 2010 Elsevier B.V. All rights reserved.

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.

Nakamura, Fujita, Ushitani, & Miyata (2006) have shown that pigeons perceive the standard Muller-Lyer illusion. In this report, the authors examined effects of bracket sizes on perception of this illusion in pigeons (Columba livia) and humans (Homo sapiens). In Experiment 1, three pigeons were retrained to classify six lengths of target lines into "long" and "short" by pecking two keys on the monitor, ignoring the two brackets oriented toward the same direction. In the tests that followed, the standard Muller-Lyer figures of different bracket sizes were presented. All birds chose "long" more frequently for the figures having inward-pointing brackets (><) than for those having outward-pointing brackets (<>), regardless of bracket sizes. The overestimation of the target lines of inward-pointing figures continued to increase in pigeons, whereas it decreased as the bracket size became longer in humans (Experiment 2). The results suggest that these two species perceive the standard Muller-Lyer illusion with long brackets in different ways. Perhaps pigeons might not perceive illusions induced by contrast with the surrounding stimuli.

Nakamura, et al. recently showed that pigeons experience the standard Muller-Lyer illusion but not the reversed illusion induced by detaching the arrowheads from the target line. This study re-examined pigeons' pereception of this reversed figure by using the stimuli known to induce the maximal contrast effect in humans (Fellows, 1967). Pigeons were retrained to classify six lengths of target lines into "long" and "short" categories by pecking two keys on the monitor, ignoring the two brackets so placed that these would not induce an illusion. In the test that followed, two birds' responses were not affected by directions of arrowheads, as shown in the previous study. The third pigeon significantly chose "long" for inward-pointing brackets figures (> <) more frequently than for outward-pointing (< >), that is, the direction of illusion was reversed from what is expected in humans. These results suggest that pigeons may not experience illusions induced by contrast with the surrounding stimuli.

A target circle surrounded by larger "inducer" circles looks smaller, and one surrounded by smaller circles looks larger than they really are. This is the Ebbinghaus-Titchener illusion, which remains one of the strongest and most robust of contrast illusions. Although there have been many studies on this illusion in humans, virtually none have addressed how nonhuman animals perceive the same figures. Here the authors show that the Ebbinghaus-Titchener figures also induce a strong illusion in pigeons but, surprisingly, in the other direction; that is, all five successfully trained pigeons judged the target circle surrounded by larger circles to be larger than it really is and vice versa. Further analyses proved that neither the gaps between target and inducer circles nor the cumulative weighted surface of these figural elements could account for the birds' responses. Pigeons are known to show similarities to humans on various cognitive and perceptual tasks including concept formation, short-term memory, and some visual illusions. Our results, taken together with pigeons' previously demonstrated failure at visual completion, provide strong evidence that pigeons may actually experience a visual world too different for us to imagine.