Perception of coherent motion in random dot displays by pigeons and humans

Pigeons and humans were required to discriminate coherent from random motion in dynamic random dot displays. Coherence and velocity thresholds were determined for both species, and both thresholds were found to be substantially higher for pigeons than for humans. The results are discussed with reference to differences in motion processing in mammals and birds. It is suggested that the inferior motion sensitivity of pigeons can be attributed to poorer spatiotemporal motion integration.     

Detection of glass patterns by pigeons and humans: implications for differences in higher-level processing

Glass patterns have been used to examine mechanisms underlying form perception. The current investigation compared detection of Glass patterns by pigeons and humans and provides evidence for substantial species differences in global form perception. Subjects were required to discriminate, on a simultaneous display, a random dot pattern from a Glass pattern. Four different randomly presented Glass patterns were used (concentric, radial, parallel-vertical, and parallel-horizontal). Detection thresholds were measured by degrading the Glass patterns through the addition of random noise. For both humans and pigeons, discrimination decreased systematically with the addition of noise. Humans showed detection differences among the four patterns, with lowest thresholds to radial and concentric patterns and highest thresholds to the parallel-horizontal pattern. Pigeons did not show a detection difference across the four patterns. Implications for differences in neural processing of complex forms are discussed.     

Tracking and capture of constant and varying velocity stimuli: a cross-species comparison of pigeons and humans

The mechanisms underlying tracking and capture of moving objects in non-human animals are poorly understood. This set of experiments sought to further explore aspects of anticipatory tracking in pigeons and to conduct comparisons with human participants. In Experiment 1a, pigeons were presented with two types of varying velocities (fast-slow-fast or slow-fast-slow) in separate phases. They were readily able to track and anticipate both of these motion types. To examine the effects of predictability on anticipatory tracking, Experiment 1b presented the pigeons with the same two varying velocities randomly intermixed within a session. This resulted in reduced capture success, later capture, and errors that no longer anticipated ahead of the motion, suggesting that the anticipatory mechanism had been disrupted. This implies that the mechanisms involved in pigeon tracking are different from the predictive extrapolation mechanism proposed in humans. Experiment 2 tested this by presenting adult humans with a tracking task that was similar to tasks previously received by the pigeons. The capture behavior of humans was similar to the pigeons, but the errors revealed different processes underlying their tracking behavior.     

Effects of noise on pure-tone thresholds in blackbirds (Agelaius phoeniceus and Molothrus ater) and pigeons (Columba livia)

Blackbirds and pigeons were trained to detect tones in quiet and in broadband noise by using positive-reinforcement techniques. In Experiment 1, thresholds in noise were obtained in blackbirds as a function of both tone frequency and noise intensity for a pulsed noise masker (noise gated on and off with tone). For blackbirds, critical ratios (the ratio of the power of the just-detectable tone in noise to the power of the noise masker) obtained in pulsed noise showed no consistent relation to tone frequency. For pigeons, on the other hand, critical ratios obtained in continuous noise increased by about 3 dB/octave across their range of hearing, being similar to known critical ratio functions for cats and humans. In Experiment 2, critical ratios in blackbirds obtained with both continuous noise and pulsed noise were compared. Blackbird critical ratios were more stable in continuous noise and averaged 4 dB lower than critical ratios in pulsed noise. The blackbird critical ratio function obtained with continuous noise was similar to the known critical ratio function of another avian species, the parakeet. Thus, small birds appear to have atypical critical ratio functions, compared with pigeons and other vertebrates.     

Discrimination of intentional and random motion paths by pigeons

Twelve pigeons (Columba livia) were trained on a go/no-go schedule to discriminate between two kinds of movement patterns of dots, which to human observers appear to be "intentional" and "non-intentional" movements. In experiment 1, the intentional motion stimulus contained one dot (a "wolf") that moved systematically towards another dot as though stalking it, and three distractors ("sheep"). The non-intentional motion stimulus consisted of four distractors but no stalker. Birds showed some improvement of discrimination as the sessions progressed, but high levels of discrimination were not reached. In experiment 2, the same birds were tested with different stimuli. The same parameters were used but the number of intentionally moving dots in the intentional motion stimulus was altered, so that three wolves stalked one sheep. Despite the enhanced difference of movement patterns, the birds did not show any further improvement in discrimination. However, birds for which the non-intentional stimulus was associated with reward showed a decline in discrimination. These results indicated that pigeons can discriminate between stimuli that do and do not contain an element that human observer see as moving intentionally. However, as no feature-positive effect was found in experiment 1, it is assumed that pigeons did not perceive or discriminate these stimuli on the basis that the intentional stimuli contained a feature that the non-intentional stimuli lacked, though the convergence seen in experiment 2 may have been an effective feature for the pigeons. Pigeons seem to be able to recognise some form of multiple simultaneously goal-directed motions, compared to random motions, as a distinctive feature, but do not seem to use simple "intentional" motion paths of two geometrical figures, embedded in random motions, as a feature whose presence or absence differentiates motion displays. Electronic Publication     

The pigeon's discrimination of movement patterns (Lissajous figures) and contour-dependent rotational invariance

The ability of pigeons to discriminate complex motion patterns was investigated with the aid of moving Lissajous figures. The pigeons successfully learned to differentiate two successively presented cyclic trajectories of a single moving dot. This suggests that they can recognize a movement Gestalt when information about shape is minimal. They also quickly learned a new discrimination between moving-outline stimuli with repetitively changing contour patterns. Contrasting results were obtained when the dot or outline stimuli were axis-rotated through 90 degrees. Rotational invariance of pattern discrimination was clearly demonstrated only when moving contours were visible. Nevertheless, pigeons could discriminate the axis-orientation of a moving-dot or moving-outline pattern when trained to do so. Discrimination did not seem to depend on single parameters of motion but rather on the recognition of a temporally integrated movement Gestalt. The visual system of pigeons, as well as that of humans, may be well adapted to recognize the types of oscillatory movements that represent components of the motor behaviour shown by many living organisms.     

The effect of experience and of dots’ density and duration on the detection of coherent motion in dogs

Knowledge about the mechanisms underlying canine vision is far from being exhaustive, especially that concerning post-retinal elaboration. One aspect that has received little attention is motion perception, and in spite of the common belief that dogs are extremely apt at detecting moving stimuli, there is no scientific support for such an assumption. In fact, we recently showed that dogs have higher thresholds than humans for coherent motion detection (Kanizsar et al. in Sci Rep UK 7:11259, 2017). This term refers to the ability of the visual system to perceive several units moving in the same direction, as one coherently moving global unit. Coherent motion perception is commonly investigated using random dot displays, containing variable proportions of coherently moving dots. Here, we investigated the relative contribution of local and global integration mechanisms for coherent motion perception, and changes in detection thresholds as a result of repeated exposure to the experimental stimuli. Dogs who had been involved in the previous study were given a conditioned discrimination task, in which we systematically manipulated dot density and duration and, eventually, re-assessed our subjects’ threshold after extensive exposure to the stimuli. Decreasing dot duration impacted on dogs’ accuracy in detecting coherent motion only at very low duration values, revealing the efficacy of local integration mechanisms. Density impacted on dogs’ accuracy in a linear fashion, indicating less efficient global integration. There was limited evidence of improvement in the re-assessment but, with an average threshold at re-assessment of 29%, dogs’ ability to detect coherent motion remains much poorer than that of humans.     

Reorientation in diamond-shaped environments: encoding of features and angles in enclosures versus arrays by adult humans and pigeons (Columbia livia)

Although geometric reorientation has been extensively studied in numerous species, most research has been conducted in enclosed environments and has focused on use of the geometric property of relative wall length. The current studies investigated how angular information is used by adult humans and pigeons to orient and find a goal in enclosures or arrays that did not provide relative wall length information. In enclosed conditions, the angles formed a diamond shape connected by walls, whereas in array conditions, free-standing angles defined the diamond shape. Adult humans and pigeons were trained to locate two geometrically equivalent corners, either the 60° or 120° angles. Blue feature panels were located in the goal corners so that participants could use either the features or the local angular information to orient. Subsequent tests in manipulated environments isolated the individual cues from training or placed them in conflict with one another. In both enclosed and array environments, humans and pigeons were able to orient when either the angles or the features from training were removed. On conflict tests, female, but not male, adult humans weighted features more heavily than angular geometry. For pigeons, angles were weighted more heavily than features for birds that were trained to go to acute corners, but no difference in weighting was seen for birds trained to go to obtuse corners. These conflict test results were not affected by environment type. A subsequent test with pigeons ruled out an interpretation based on exclusive use of a principal axis rather than angle. Overall, the results indicate that, for both adult humans and pigeons, angular amplitude is a salient orientation cue in both enclosures and arrays of free-standing angles.     

Motion perception and aging.

The authors used a correlated motion paradigm to investigate the effects of aging and gender on motion sensitivity. In 2 experiments with a total of 50 elderly and 50 young subjects, motion thresholds were significantly higher for elderly women. The correlated motion signal, which was embedded in random motion, may have been coherent to subjects in much the same way a form is in Witkin's Embedded Figures Test (EFT). In Experiment 2, EFT scores were obtained. A significant positive relationship between motion thresholds and EFT performance was found within each age group. Although gender-related perceptual style differences may contribute to motion perception effects, the authors argue that a common neural factor contributes to performance on both the EFT and the correlated motion task.     

Recognition by humans and pigeons of novel views of 3-D objects and their photographs

Humans and pigeons were trained to discriminate between 2 views of actual 3-D objects or their photographs. They were tested on novel views that were either within the closest rotational distance between the training views (interpolated) or outside of that range (extrapolated). When training views were 60 degrees apart, pigeons, but not humans, recognized novel views of actual objects better than their pictures. Further, both species recognized interpolated views of both stimulus types better than extrapolated views, but a single distinctive geon enhanced recognition of novel views only for humans. When training views were 90 degrees apart, pigeons recognized interpolated views better than extrapolated views with actual objects but not with photographs. Thus, pigeons may represent actual objects differently than their pictures.     

DISCOUNTING OF DELAYED FOOD REWARDS IN PIGEONS AND RATS: IS THERE A MAGNITUDE EFFECT?

Temporal discounting refers to the decrease in the present, subjective value of a reward as the time to its receipt increases. Results from humans have shown that a hyperbola-like function describes the form of the discounting function when choices involve hypothetical monetary rewards. In addition, magnitude effects have been reported in which smaller reward amounts are discounted more steeply than larger amounts. The present research examines the cross-species generality of these findings using real rewards, namely food pellets, with both pigeons and rats. As with humans, an adjusting amount procedure was used to estimate the amount of immediate reward judged equal in value to a delayed reward. Different amounts of delayed food rewards (ranging from 5 to 32 pellets in pigeons and from 5 to 20 pellets in rats) were studied at delays varying from 1 s to 32 s. A simple hyperbola, similar to the hyperbola-like mathematical function that describes the discounting of hypothetical monetary rewards in humans, described the discounting of food rewards in both pigeons and rats. These results extend the generality of the mathematical model of discounting. Rates of discounting delayed food rewards were higher for pigeons than for rats. Unlike humans, however, neither pigeons nor rats showed a reliable magnitude effect: Rate of discounting did not vary systematically as a function of the amount of the delayed reward.     

Black-capped chickadee (Poecile atricapillus) and human (Homo sapiens) chord discrimination

Human music perception is related both to musical experience and the physical properties of sound. Examining the processing of music by nonhuman animals has been generally neglected. We tested both black-capped chickadees and humans in a chord discrimination task that replicates and extends prior research with pigeons. We found that chickadees and humans, in common with pigeons, showed similar patterns of discrimination across manipulations of the 3rd and 5th notes of the triadic chords. For all species (chickadee and humans here, pigeons previously), chords with half-step alterations in the 5th note were easier to discriminate than half-step manipulations of the 3rd note, which is likely due to the sensory consonance of these chords. There were differences among species in terms of the fine discrimination of the chords within this larger pattern of results. Further, the ability to relearn the chords when transposed to a new root differed across species. Our results provide new comparative data suggesting some similarities in chord perception that span a wide range of species, from pigeons (nonvocal learners) to songbirds and humans (vocal learners).     

Pigeons can discriminate “good” and “bad” paintings by children

Humans have the unique ability to create art, but non-human animals may be able to discriminate “good” art from “bad” art. In this study, I investigated whether pigeons could be trained to discriminate between paintings that had been judged by humans as either “bad” or “good”. To do this, adult human observers first classified several children’s paintings as either “good” (beautiful) or “bad” (ugly). Using operant conditioning procedures, pigeons were then reinforced for pecking at “good” paintings. After the pigeons learned the discrimination task, they were presented with novel pictures of both “good” and “bad” children’s paintings to test whether they had successfully learned to discriminate between these two stimulus categories. The results showed that pigeons could discriminate novel “good” and “bad” paintings. Then, to determine which cues the subjects used for the discrimination, I conducted tests of the stimuli when the paintings were of reduced size or grayscale. In addition, I tested their ability to discriminate when the painting stimuli were mosaic and partial occluded. The pigeons maintained discrimination performance when the paintings were reduced in size. However, discrimination performance decreased when stimuli were presented as grayscale images or when a mosaic effect was applied to the original stimuli in order to disrupt spatial frequency. Thus, the pigeons used both color and pattern cues for their discrimination. The partial occlusion did not disrupt the discriminative behavior suggesting that the pigeons did not attend to particular parts, namely upper, lower, left or right half, of the paintings. These results suggest that the pigeons are capable of learning the concept of a stimulus class that humans name “good” pictures. The second experiment showed that pigeons learned to discriminate watercolor paintings from pastel paintings. The subjects showed generalization to novel paintings. Then, as the first experiment, size reduction test, grayscale test, mosaic processing test and partial occlusion test were carried out. The results suggest that the pigeons used both color and pattern cues for the discrimination and show that non-human animals, such as pigeons, can be trained to discriminate abstract visual stimuli, such as pictures and may also have the ability to learn the concept of “beauty” as defined by humans.     

Purely chromatic perception of motion in depth: two eyes as sensitive as one

Motion hyperacuity (phase) thresholds were measured for both lateral and stereoscopic oscillatory motion in both luminance and equiluminant red/green gratings of 2 cycles per degree. Thresholds for lateral chromatic motion did not exhibit the inhibitory fall-off at low temporal frequencies that was found for luminance motion. Phase thresholds for purely chromatic motion were substantially higher than those for luminance gratings, in proportion to the ratio of cone signal modulation, but they could be predicted from the corresponding contrast sensitivities for both types of stimulus. Stereomovement thresholds in luminance gratings showed the stereomovement suppression effect relative to monocular motion sensitivity previously reported for line stimuli, but purely chromatic gratings did not. Together with the lack of an inhibitory fall-off, these results imply that chromatic and luminance motion are processed by different neural pathways, and that the chrominance pathway is capable of supporting a strong percept of stereoscopic motion from purely chromatic gratings.     

Symmetry and stimulus class formation in humans: Control by temporal location in a successive matching task

Symmetry refers to the observation that subjects will derive B‐A (e.g., in the presence of B, select A) after being trained on A‐B (e.g., in the presence of A, select B). Whereas symmetry is readily shown in humans, it has been difficult to demonstrate in nonhuman animals. This difficulty, at least in pigeons, may result from responding to specific stimulus properties that change when sample and comparison stimuli switch roles between training and testing. In three experiments with humans, we investigated to what extent human responding is influenced by the temporal location of stimuli using a successive matching‐to‐sample procedure. Our results indicate that temporal location does not spontaneously control responding in humans, although it does in pigeons. Therefore, the number of functional stimuli that humans respond to in this procedure may be half of the number of functional stimuli that the pigeons respond to. In a fourth experiment, we tested this assumption by doubling the number of functional stimuli controlling responding in human participants in an attempt to make the test more comparable to symmetry tests with pigeons. Here, we found that humans responded according to indirect class formation in the same manner as pigeons do. In sum, our results indicate that functional symmetry is readily observed in humans, even in cases where the temporal features of the stimuli prevent functional symmetry in pigeons. We argue that this difference in behavior between the two species does not necessarily reflect a difference in capacity to show functional symmetry between both species, but could also reflect a difference in the functional stimuli each species responds to.     

Qualitative similarities in the visual short-term memory of pigeons and people

Visual short-term memory plays a key role in guiding behavior, and individual differences in visual short-term memory capacity are strongly predictive of higher cognitive abilities. To provide a broader evolutionary context for understanding this memory system, we directly compared the behavior of pigeons and humans on a change detection task. Although pigeons had a lower storage capacity and a higher lapse rate than humans, both species stored multiple items in short-term memory and conformed to the same basic performance model. Thus, despite their very different evolutionary histories and neural architectures, pigeons and humans have functionally similar visual short-term memory systems, suggesting that the functional properties of visual short-term memory are subject to similar selective pressures across these distant species.     

整体运动知觉老化的方向不同步性及其总效应

采用随机点阵范式和实验内元分析技术,首次分离水平、垂直、旋转和径向运动形式下两两对立方向的运动一致性阈值,探究整体运动知觉(GMP)老化的方向不同步性及总效应。结果发现:四种运动形式下,老年组阈值均显著高于青年组,且元分析显示两组阈值之差的效应量大于0,表明相对于青年人,老年人的GMP存在显著下降。同时,老年组向右、向下、顺时针和外扩方向的阈值显著高于其对立方向及青年组,表明老年人这些方向的GMP衰退更加严重,提示GMP的老化存在方向不同步性。     

Dynamic object perception by pigeons: discrimination of action in video presentations

Two experiments examined the discrimination by pigeons of relative motion using computer-generated video stimuli. Using a go/no-go procedure, pigeons were tested with video stimuli in which the camera's perspective went either "around" or "through" an approaching object in a semi-realistic context. Experiment 1 found that pigeons could learn this discrimination and transfer it to videos composed from novel objects. Experiment 2 found that the order of the video's frames was critical to the discrimination of the videos. We hypothesize that the pigeons perceived a three-dimensional representation of the objects and the camera's relative motion and used this as the primary basis for discrimination. It is proposed that the pigeons might be able to form generalized natural categories for the different kinds of motions portrayed in the videos. Accepted after revision: 23 March 2001 Electronic Publication     

RISKY CHOICE IN PIGEONS AND HUMANS: A CROSS‐SPECIES COMPARISON

Pigeon and human subjects were given repeated choices between variable and adjusting delays to token reinforcement that titrated in relation to a subject's recent choice patterns. Indifference curves were generated under two different procedures: immediate exchange, in which a token earned during each trial was exchanged immediately for access to the terminal reinforcer (food for pigeons, video clips for humans), and delayed exchange, in which tokens accumulated and were exchanged after 11 trials. The former was designed as an analogue of procedures typically used with nonhuman subjects, the latter as an analogue to procedures typically used with human participants. Under both procedure types, different variable‐delay schedules were manipulated systematically across conditions in ways that altered the reinforcer immediacy of the risky option. Under immediate‐exchange conditions, both humans and pigeons consistently preferred the variable delay, and indifference points were generally ordered in relation to relative reinforcer immediacies. Such risk sensitivity was greatly reduced under delayed‐exchange conditions. Choice and trial‐initiation response latencies varied directly with indifference points, suggesting that local analyses may provide useful ancillary measures of reinforcer value. On the whole, the results indicate that modifying procedural features brings choices of pigeons and humans into better accord, and that human—nonhuman differences on risky choice procedures reported in the literature may be at least partly a product of procedural differences.     

Environmental enrichment affects suboptimal, risky, gambling-like choice by pigeons

Pigeons prefer a risky option with a low probability of a high payoff over a less risky option that results in more food. This finding is analogous to suboptimal human monetary gambling because in both cases there appears to be an overemphasis of the occurrence of the winning event and an underemphasis of the losing event. In the present research, we found that pigeons that were exposed to an enriched environment (a large cage with three other pigeons for 4 h a day) were less likely to show this suboptimal choice behavior compared with typically housed laboratory pigeons in a control group. These results have implications for the mechanisms underlying suboptimal choice by humans (e.g., problem gamblers), and they suggest that a enriched environment may allow for enhanced self-control.