Visual control of an action discrimination in pigeons

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.

Dogs fail to recognize a human pointing gesture in two-dimensional depictions of motion cues

Few studies have investigated biological motion perception in dogs and it remains unknown whether dogs recognise the biological identity of two-dimensional animations of human motion cues. To test this, we assessed the dogs' (N = 32) responses to point-light displays of a human performing a pointing gesture towards one of two pots. At the start of the experiment the demonstrator was a real-life person, but over the course of the test dogs were presented with two-dimensional figurative representations of pointing gestures in which visual information was progressively removed until only the isolated motion cues remained. Dogs' accuracy was above chance level only with real-life and black-and-white videos, but not with the silhouette or the point-light figure. Dogs' accuracy during these conditions was significantly lower than in the real-life condition. This result could not be explained by trial order since dogs' performance was still not higher than chance when only the point-light figure condition was presented after the initial demonstration. The results imply that dogs are unable to recognise humans in two-dimensional depictions of human motion cues only. In spite of extensive exposure to human movement, dogs need more perceptual cues to detect equivalence between human two-dimensional animations and the represented living entity.

Dynamic Corridor Illusion in Pigeons: Humanlike Pictorial Cue Precedence Over Motion Parallax Cue in Size Perception

Depth information is necessary for perceiving the real size of objects at varying visual distances. To investigate to what extent this size constancy present in another vertebrate class, we addressed the two questions using pigeons: (a) whether pigeons see a corridor illusion based on size constancy and (b) whether pigeons prioritize pictorial cues over motion parallax cues for size constancy, like humans. We trained pigeons to classify target sizes on a corridor. In addition, we presented a dynamic version of corridor illusion in which the target and corridor moved side by side. Target speed was changed to manipulate motion parallax. With the static corridor, pigeons overestimated the target size when it was located higher, indicating that pigeons see a corridor illusion like humans. With the dynamic corridor, the pigeons overestimated the target size depending on target position, as in the static condition, but target speed did not affect their responses, indicating that the pictorial precedence also applies to pigeons. In a follow-up experiment using the same stimulus, we confirmed that humans perceive object size based on pictorial cues. These results suggest that size constancy characteristics are highly similar between pigeons and humans, despite the differences in their phylogeny and neural systems.

Pigeons process actor-action configurations more readily than bystander-action configurations

Behavior requires an actor. Two experiments using complex conditional action discriminations examined whether pigeons privilege information related to the digital actor who is engaged in behavior. In Experiment 1, each of two video displays contained a digital model, one an actor engaged in one of two behaviors (Indian dance or martial arts) and one a neutrally posed bystander. To correctly classify the display, the pigeons needed to conditionally process the action in conjunction with distinctive physical features of the actor or the bystander. Four actor-conditional pigeons learned to correctly discriminate the actions based on the identity of the actors, whereas four bystander-conditional birds failed to learn. Experiment 2 established that this failure was not due to the latter group's inability to spatially integrate information across the distance between the two models. Potentially, the colocalization of the relevant model identity and the action was critical due to a fundamental configural or integral representation of these properties. These findings contribute to our understanding of the evolution of action recognition, the recognition of social behavior, and forms of observational learning by animals.

Pigeons integrate visual motion signals differently than humans

Perceiving motion is a fundamental ability for animals. Primates integrate local 1D motion across orientation and space to compute a rigid 2D motion. It is unknown whether the rule of 2D motion integration is universal within the vertebrate clade; comparative studies of animals with different ecological backgrounds from primates may help answer that question. Here we investigated 2D motion integration in pigeons, using hierarchically structured motion stimuli, namely a barber-pole illusion and plaid motion. The pigeons were trained to report the direction of motion of random dots. When a barber-pole or plaid stimulus was presented, they reported the direction perpendicular to the grating orientation for barber-pole and the vector average of two component gratings for plaid motion. These results demonstrate that pigeons perceive different directions than humans from the same motion stimuli, and suggest that the 2D integrating rules in the primate brain has been elaborated through phylogenetic or ecological factors specific to the clade.

Pigeons simultaneously attend to static and dynamic features of complex displays

The simultaneous processing and attention to temporally dynamic and static features remains an open and important question in theories of avian visual cognition. Here, four pigeons (Columba livia) learned to discriminate complex displays involving concurrently available static and dynamic features. These displays consisted of 20 elements built from combinations of two, binary-valued, static visual dimensions: red vs. green element color, large vs. small element size; and two binary-valued dynamic dimensions; fast vs slow element motion, right vs up motion direction. One combination of these four features was reinforced on a VI schedule. The remaining 15 combinations of element color, size, speed and direction were never reinforced. During acquisition, all four dimensions were simultaneously discriminated. Varying the number of elements revealed that a single element was sufficient to support discrimination of all four dimensions. The pigeons agreed on the relative discriminability of stimuli within and across the different dimensions, with the difference in motion direction being the hardest for all birds. Redundant facilitation suggested rapid, perhaps parallel, processing of both dynamic and static features. No attentional trade-offs between dynamic or static dimensions were observed. These results agree with theories of avian vision employing the notion of multiple independent channels for different types of information.

Complex conditional control by pigeons in a continuous virtual environment

We tested two pigeons in a continuously streaming digital environment. Using animation software that constantly presented a dynamic, three-dimensional (3D) environment, the animals were tested with a conditional object identification task. The correct object at a given time depended on the virtual context currently streaming in front of the pigeon. Pigeons were required to accurately peck correct target objects in the environment for food reward, while suppressing any pecks to intermixed distractor objects which delayed the next object's presentation. Experiment 1 established that the pigeons' discrimination of two objects could be controlled by the surface material of the digital terrain. Experiment 2 established that the pigeons' discrimination of four objects could be conjunctively controlled by both the surface material and topography of the streaming environment. These experiments indicate that pigeons can simultaneously process and use at least two context cues from a streaming environment to control their identification behavior of passing objects. These results add to the promise of testing interactive digital environments with animals to advance our understanding of cognition and behavior.

Experimental Divergences in the Visual Cognition of Birds and Mammals

The comparative analysis of visual cognition across classes of animals yields important information regarding underlying cognitive and neural mechanisms involved with this foundational aspect of behavior. Birds, and pigeons specifically, have been an important source and model for this comparison, especially in relation to mammals. During these investigations, an extensive number of experiments have found divergent results in how pigeons and humans process visual information. Four areas of these divergences are collected, reviewed, and analyzed. We examine the potential contribution and limitations of experimental, spatial, and attentional factors in the interpretation of these findings and their implications for mechanisms of visual cognition in birds and mammals. Recommendations are made to help advance these comparisons in service of understanding the general principles by which different classes and species generate representations of the visual world.

Discrimination of complex human behavior by pigeons (Columba livia) and humans

The cognitive and neural mechanisms for recognizing and categorizing behavior are not well understood in non-human animals. In the current experiments, pigeons and humans learned to categorize two non-repeating, complex human behaviors (“martial arts” vs. “Indian dance”). Using multiple video exemplars of a digital human model, pigeons discriminated these behaviors in a go/no-go task and humans in a choice task. Experiment 1 found that pigeons already experienced with discriminating the locomotive actions of digital animals acquired the discrimination more rapidly when action information was available than when only pose information was available. Experiments 2 and 3 found this same dynamic superiority effect with naïve pigeons and human participants. Both species used the same combination of immediately available static pose information and more slowly perceived dynamic action cues to discriminate the behavioral categories. Theories based on generalized visual mechanisms, as opposed to embodied, species-specific action networks, offer a parsimonious account of how these different animals recognize behavior across and within species.