Towards describing scenes by animals: Pigeons' ordinal discrimination of objects varying in depth.

The perception of a complex scene requires visual mechanisms that include identifying objects and their relative placement in depth. To examine apparent depth perception in birds, we tested four pigeons with a novel multiple-sequential-choice procedure. We created 3D-rendered scene stimuli containing three objects located at different apparent depths based on a variety of pictorial cues and placed small circular target response areas on them. The pigeons were trained to sequentially choose among the multiple response areas to report the object closest in apparent depth (ordinal position; front then middle object). After the pigeons learned this sequential depth discrimination, their use of three different monocular depth cues (occlusion, relative size, height in field) was tested, and their flexibility evaluated using three novel objects. In addition to the contribution to understanding apparent depth perception in birds, the use of more flexible open-ended choice discriminations, as employed here, has considerable promise for creating informative production-like tasks in nonverbal animals.

Dynamically occluded action recognition by pigeons.

Identifying the behaviors of organisms is essential for an animal's survival. This ability is particularly challenged when the "actors" are dynamically occluded by other objects and become fragmented as they move through an environment. Even when fragmented in time and across space, humans readily recognize the behavior of these dynamically occluded objects and actors. How animals process such fragmented information, especially when involving motion, remains uncertain. In three experiments, we investigated the ability of six pigeons to discriminate between the running and walking actions of digital animal models when dynamically occluded. The pigeons were tested in a go/no-go procedure using three models that transited behind multiple occluders in a semirealistic scene. Without ever seeing the entirety of the animal model at one time, all the pigeons learned to discriminate among these two behaviors. This discrimination transferred to an unfamiliar model, transit direction, transiting rates, camera perspectives, and occluders. Tests with different static and dynamic features indicated that the pigeons relied on motion features for the discrimination, especially articulated motion. These experiments demonstrate that pigeons, like humans, can discriminate actions even when their view of the actor is fragmented in time and space.

Use of different attentional strategies by pigeons and humans in multidimensional visual search.

To study comparative attentional allocation strategies, pigeons and humans were tested using simultaneously available discrimination tasks. Given visual search displays containing 32 items from two orthogonal dimensions, participants were reinforced for selecting the eight brightest (or darkest) of 16 brightness items and the eight most vertical (or horizontal) of 16 orientation items. Consistent with a sequential dimensional strategy, humans preferentially chose items from one dimension before switching to the other to complete the search. In contrast, the pigeons did not preferentially stay within one dimension over consecutive choices. Instead, they chose the items most likely to yield reward based on item discriminability. Computational models that incorporated a "dimensional staying" factor accounted best for the human data, while simulations using only discriminability reproduced the pigeons' data. These results suggest that humans are sensitive to the benefits of attentional staying and the costs of switching between dimensional tasks, while there was no evidence that these factors influenced the pigeons' choice behavior. These findings suggest fundamental differences in how pigeons and humans allocate attention in complex choice situations. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Initial evidence for probabilistic reasoning in a grey parrot (Psittacus erithacus).

Research has shown that some forms of inferential reasoning are likely widespread throughout the animal kingdom (e.g., exclusion, in which a subject infers the placement of a reward by eliminating potential alternative sites), but other types of inferential tasks have not been extensively tested. We examined whether a nonhuman might succeed in an experiment based on probabilistic reasoning, specifically, the ability to make inferences about a sample based on information about a population. A Grey parrot (Psittacus erithacus), previously trained to use English labels referentially to identify objects, observed a human researcher deposit 2 different types of items in a 3:1 ratio (e.g., 3 corks and 1 piece of paper) into an opaque bucket. One item was then randomly withdrawn while hidden from the parrot's view. When asked to identify the still-hidden object, the parrot's vocal responses tracked this 3:1 ratio over a large number of trials. Some levels of probabilistic reasoning therefore are not limited to humans, nonhuman primates, or even mammals. (PsycINFO Database Record

Piagetian liquid conservation in grey parrots (Psittacus erithacus).

An understanding of Piagetian liquid conservation was investigated in four Grey parrots (Psittacus erithacus), their ages ranging from initially less than 1 year old to 18 years old. They were tested in several conditions: on the ability to choose between (a) identical containers filled with a greater or lesser quantity of a desirable liquid to see if they would reliably take the larger amount and (b) equal quantities of liquid that were visibly or invisibly transferred from identical to different-sized containers to examine their abilities with respect to conservation. Invisible transfers examined the extent to which birds chose based on perceptual evaluations of quantity and the effects of task order on their decisions. Adult birds succeeded on all or most aspects of the tests. As a chick (∼6 months), 1 bird was unable or unwilling to choose between the smaller and larger quantities in the first stage of testing, but upon reaching juvenile status succeeded in all aspects of the tests. Grey parrots thus demonstrate some understanding of liquid conservation. (PsycINFO Database Record

Delayed gratification: A grey parrot (Psittacus erithacus) will wait for a better reward.

Delay of gratification, the ability to forgo an immediate reward to gain either better quality or quantity, has been used as a metric for temporal discounting, self-control, and the ability to plan for the future in both humans (particularly children) and nonhumans. The task involved can be parsed in several ways, such that the subjects can be required to wait, not only for a better or a larger reward, but also such that the rewards can either be in view or hidden during the delay interval. We have demonstrated that a Grey parrot (Psittacus erithacus) trained in the use of English speech could respond to the label "wait" for up to 15 min, in a task that has many similarities to those used with young children, to receive a better quality reward, whether or not the better quality reward or the experimenter was in view.