Visual discrimination of primate species based on faces in chimpanzees

Many primate studies have investigated discrimination of individual faces within the same species. However, few studies have looked at discrimination between primate species faces at the categorical level. This study systematically examined the factors important for visual discrimination between primate species faces in chimpanzees, including: colour, orientation, familiarity, and perceptual similarity. Five adult female chimpanzees were tested on their ability to discriminate identical and categorical (non-identical) images of different primate species faces in a series of touchscreen matching-to-sample experiments. Discrimination performance for chimpanzee, gorilla, and orangutan faces was better in colour than in greyscale. An inversion effect was also found, with higher accuracy for upright than inverted faces. Discrimination performance for unfamiliar (baboon and capuchin monkey) and highly familiar (chimpanzee and human) but perceptually different species was equally high. After excluding effects of colour and familiarity, difficulty in discriminating between different species faces can be best explained by their perceptual similarity to each other. Categorical discrimination performance for unfamiliar, perceptually similar faces (gorilla and orangutan) was significantly worse than unfamiliar, perceptually different faces (baboon and capuchin monkey). Moreover, multidimensional scaling analysis of the image similarity data based on local feature matching revealed greater similarity between chimpanzee, gorilla and orangutan faces than between human, baboon and capuchin monkey faces. We conclude our chimpanzees appear to perceive similarity in primate faces in a similar way to humans. Information about perceptual similarity is likely prioritized over the potential influence of previous experience or a conceptual representation of species for categorical discrimination between species faces.     

Pattern discrimination by the honeybee: disruption as a cue

The discrimination of pattern disruption in freely flying honeybees (Apis mellifera) was examined. Bees were trained to discriminate at a fixed distance between a regularly repeated black/white pattern and the same pattern at a different magnification in targets of the same angular size. The locations of areas of black were regularly shuffled to make them useless as cues. The results of the experiments indicate that the bees discriminate the disruption of the pattern as a whole, irrespective of the actual pattern. Bees trained to prefer a larger period transfer to an even larger period, when given a forced choice with a pair of patterns of differing disruption from those they were trained on, as if their spontaneous preference has not been overcome. Bees trained to prefer a smaller period, however, prefer the former negative pattern rather than transfer to an even smaller period. These results show that the bees do not rely solely on learning the absolute period of a pattern nor the relative disruption of two patterns, and they are confused when these two cues conflict in tests with unfamiliar targets. Bees can discriminate between fields of view that differ in average disruption as a generalized cue, irrespective of pattern. Accepted: 7 April 1997     

Neural representations of personally familiar and unfamiliar faces in the anterior inferior temporal cortex of monkeys

To investigate the neural representations of faces in primates, particularly in relation to their personal familiarity or unfamiliarity, neuronal activities were chronically recorded from the ventral portion of the anterior inferior temporal cortex (AITv) of macaque monkeys during the performance of a facial identification task using either personally familiar or unfamiliar faces as stimuli. By calculating the correlation coefficients between neuronal responses to the faces for all possible pairs of faces given in the task and then using the coefficients as neuronal population-based similarity measures between the faces in pairs, we analyzed the similarity/dissimilarity relationship between the faces, which were potentially represented by the activities of a population of the face-responsive neurons recorded in the area AITv. The results showed that, for personally familiar faces, different identities were represented by different patterns of activities of the population of AITv neurons irrespective of the view (e.g., front, 90° left, etc.), while different views were not represented independently of their facial identities, which was consistent with our previous report. In the case of personally unfamiliar faces, the faces possessing different identities but presented in the same frontal view were represented as similar, which contrasts with the results for personally familiar faces. These results, taken together, outline the neuronal representations of personally familiar and unfamiliar faces in the AITv neuronal population.     

Practicing coarse orientation discrimination improves orientation signals in macaque cortical area v4

Practice improves the performance in visual tasks, but mechanisms underlying this adult brain plasticity are unclear. Single-cell studies reported no [1], weak [2], or moderate [3, 4] perceptual learning-related changes in macaque visual areas V1 and V4, whereas none were found in middle temporal (MT) [5]. These conflicting results and modeling of human (e.g., [6, 7]) and monkey data [8] suggested that changes in the readout of visual cortical signals underlie perceptual learning, rather than changes in these signals. In the V4 learning studies, monkeys discriminated small differences in orientation, whereas in the MT study, the animals discriminated opponent motion directions. Analogous to the latter study, we trained monkeys to discriminate static orthogonal orientations masked by noise. V4 neurons showed robust increases in their capacity to discriminate the trained orientations during the course of the training. This effect was observed during discrimination and passive fixation but specifically for the trained orientations. The improvement in neural discrimination was due to decreased response variability and an increase of the difference between the mean responses for the two trained orientations. These findings demonstrate that perceptual learning in a coarse discrimination task indeed can change the response properties of a cortical sensory area.     

Orangutans (Pongo pygmaeus) Remember Old Acquaintances

Many social animals can discriminate between familiar and unfamiliar faces. Orangutans, however, lead a semi-solitary life and spend much of the day alone. As such, they may be less adept at recognizing conspecifics and are a good model for determining how social structure influences the evolution of social cognition such as facial recognition. The present study is the first report of whether orangutans can distinguish among individual faces. We adopted a preferential looking method and found that orangutans used facial discrimination to identify known conspecifics. This suggests that frequent and intense social interaction is not necessary for facial discrimination, although our findings were limited by the small number of stimuli and the unequal numbers of male and female orangutans depicted in the stimuli.     

Rival recognition in the territorial tawny dragon (Ctenophorus decresii)

The ability to discriminate between familiar and unfamiliar conspecifics is important in territorial animals as it allows animals to distinguish neighbours from non-neighbours. This prevents wasting time and energy in unnecessary aggressive interactions. I investigated the ability of adult males of a territorial lizard, the tawny dragon (Ctenophorus decresii), to distinguish familiar from unfamiliar rivals in a laboratory setting. Males significantly reduced their aggression levels in repeat interactions with familiar rivals and increased their aggression levels towards unfamiliar males. The time taken for interactions to be settled was also significantly lower towards familiar than unfamiliar males. The results of this study suggest that adult male tawny dragons can discriminate familiar from unfamiliar conspecifics. Furthermore, animals were presented with three new rivals in succession and showed a robust ability to discriminate between familiar and unfamiliar males.     

Shape discrimination in sheep and calves

Sheep and calves have been trained, using an operant conditioning method in which they pressed panels with their muzzles in order to obtain food, to discriminate between simultaneously presented shapes. In the discrimination task the animals faced two response panels upon which were projected the shapes to be discriminated. Only presses on the panel associated with the correct shape were reinforced, and after each reinforcement the position of the positive stimulus was randomly varied. The results obtained demonstrated that sheep and calves can discriminate between a variety of similar shapes.     

Changes in odor quality discrimination following recovery from olfactory nerve transection

Following recovery from olfactory nerve transection, animals regain their ability to discriminate between odors. Odor discrimination is restored after new neurons establish connections with the olfactory bulb. However, it is not known if the new connections alter odor quality perception. To address this question, 20 adult hamsters were first trained to discriminate between cinnamon and strawberry odors. After reaching criterion (> or = 90% correct response), half of the animals received a bilateral nerve transection (BTX) and half a surgical sham procedure. Animals were not tested again until day 40, a point in recovery when connections are re-established with the bulb. When BTX animals were tested without food reinforcement, they could not perform the odor discrimination task. Sham animals, however, could discriminate, demonstrating that the behavioral response had not been extinguished during the 40 day period. When reinforcement was resumed, BTX animals were able to discriminate between cinnamon and strawberry after four test sessions. In addition, their ability to discriminate between these two familiar odors was no different than that of BTX and sham animals tested with two novel odors, baby powder and coffee. These findings suggest that, after recovery from nerve transection, there are alterations in sensory perception and that restoration of odor quality discrimination requires that the animal must again learn to associate individual odor sensations with a behavioral response.      

Discrimination of consonance and dissonance in Java sparrows

Six adult Java sparrows were trained to discriminate between consonant and dissonant sounds consisting of three tones. In the consonance group, the perching response was reinforced when consonance was presented, but not when dissonance was presented. Both groups were given an inversion test, in which the first inversion of the chord was used as a stimulus. Four of six birds learned the discrimination and were given two tests. In the first test, novel consonances and novel dissonances were presented. All birds maintained the discrimination. When inverted consonances and dissonances were presented in the second test, the discriminative behavior was not well demonstrated. When novel dissonances consisting of tones with different intervals were presented in the third test, birds trained to perch for dissonance performed well, whereas those trained to perch for consonance did not. In summary, Java sparrows were able to discriminate between consonances and dissonances and demonstrated generalization to new combinations, they do not discriminate the same consonances and dissonances.     

Young female pigs can discriminate individual differences in odours from conspecific urine

The ability to discriminate odour cues from different conspecifics has been demonstrated in a variety of small mammalian species. We used a habituation-dishabituation procedure to investigate whether 10-week-old female pigs,Sus scrofa , are able to discriminate between urinary odours from similar-aged conspecifics that were unfamiliar (not encountered for at least 7 weeks). We also examined whether environmental factors can affect the ease with which urine from different individuals is discriminated. Subjects receiving urine samples from the same unfamiliar individual in two successive 2-min exposures separated by a 15-min interval showed habituation in their investigation response to the urine in the second exposure. This habituation was maintained in a third 2-min exposure, 15 min later, if the urine sample was again from the same individual. However, if the urine sample was from a different unfamiliar individual, there was a dishabituation of the investigation response. This was taken to indicate an ability to discriminate the two samples. These data indicate that young pigs could use urinary cues to discriminate other individuals. Effective individual discrimination should facilitate the formation and maintenance of stable social groupings but could be disrupted if, for example, animals from the same group share common odour cues that mask individually distinctive scents. However, urine samples from individuals living in the same group appeared to be no more difficult to discriminate than those from individuals living in different groups. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Social Interaction is Necessary for Discrimination between and Memory for Odours of Close Relatives in Golden Hamsters

The role of social experience in recognition of individuals and their odours is not well understood. In a previous study, hamsters discriminated between the odours of their familiar litter mates, but they did not discriminate between the odours of two males or two females from a different litter that were unfamiliar to them. In this paper the role of social experience in discrimination between odours of male litter mates is examined using habituation techniques. Males, tested 1.5–2 mo after separation from their litter mates, discriminated between the flank gland odours of their foster brothers, but they did not discriminate between flank odours from their unfamiliar brothers that had been reared by another mother (Expt. 1). In Expt. 2, adult males did not discriminate between the flank gland odours of two males from a different litter after a week of exposure across a barrier to their sights, sounds, and odours, but subjects did discriminate between the odours of these same males after five brief encounters with them. A month after the encounters, however, subjects no longer discriminated between these odours. In contrast, adult males discriminated between the flank odours of their brothers 9 mo after separation from them (Expt. 3). These results suggest that hamsters must have direct interactions with closely related individuals to discriminate between their odours because the odours of close kin are so similar. Experience with nest mates results in long-lasting memories for their odours.     

Orientation discrimination and categorization of photographs of natural objects by pigeons

In Experiment 1, pigeons trained to discriminate rightside-up and upside-down orientations of slides of natural scenes with humans successfully transferred to new slides of the same kind. Experiment 2 revealed that both the orientations of the human figures and of the background scenes controlled the discrimination. When they were oppositely oriented, the background orientation cue was dominant. In Experiment 3 slides showing objects on a white background were presented either rightside up or upside down, with each slide presented in one orientation only. One group of pigeons learned to classify the slides according to their orientations. The other group learned to classify the slides according to arbitrary groupings. When the slides were shown rotated by 180 degrees, the latter group continued to discriminate the individual slides (i.e., the pigeons showed orientation invariance). The former group classified the rotated slides according to their orientations (i.e., orientation discrimination). In Experiment 4, pigeons learned the orientation discrimination with separate sets of human and bird figures. Partial reversal training in one object class transferred to the rest of stimuli in this object class but did not to the other object class. These results suggest that pigeons can learn to discriminate photographs on the basis of orientation but that orientation-based equivalence relationship is not formed between object classes.     

Meadow voles,Microtus pennsylvanicus,can discriminate between scents of individual house cats,Felis catus

Individual discrimination provides animals the opportunity to adjust their exposure and behavior when interacting with other animals, both conspecifics and heterospecifics. Meadow voles, Microtus pennsylvanicus, were exposed to scents of house cats, Felis catus. Our first experiment tested whether meadow voles could discriminate between caudal, interdigital, and facial scents produced by a cat with a habituation–dishabituation paradigm. Upon exposure to the familiar scent and a novel one, meadow voles did not investigate either scent more than the other. Our second experiment tested whether meadow voles discriminate between the facial scents of different cats. When exposed to a familiar scent of one cat and the unfamiliar scent of another cat, the meadow voles did discriminate and investigated the unfamiliar scent more than the familiar scent. The results suggest that meadow voles will discriminate between cats using any scent that the cat may inadvertently leave within the environment, thereby reducing the vole's risk of predation by that individual.     

Comparison of visual and olfactory reversal learning in pigeons

Pigeons trained to discriminate between either two differentodors or two different colored lights acquired their discriminationsat the same rate. When the discrimination problems were reversedwithin a modality, however, the birds using visual cues acquirednew discriminations more rapidly than in original learning (positivetransfer), whereas the birds using olfactory cues acquired thediscrimination reversal less rapidly. On subsequent reversals,pigeons in the visual task condition developed a successivediscrimination reversal set with repeated reversals of the stimuli,while those in the olfactory condition did not. In a secondexperiment designed to assess the acquisition of redundant cues,birds received additional training with visual and olfactorycues in compound as discriminative stimuli, and were then testedwith only visual or olfactory cues. Birds previously trainedwith odor attended to visual cues in the compound, whereas birdspreviously trained to discriminate between lights did not attendto odor cues until they were presented alone. These resultsdemonstrate that the selection of stimuli may play a crucialrole in the performance of successive discrimination reversalsand suggest that, in contrast to rats, birds selectively attendto visual over olfactory cues in discrimination learning.     

Burying Beetle Larvae Discriminate Between Individual Parents and Between Some Classes of Adults

Offspring begging can be triggered by a variety of acoustic, visual or chemical cues from the parents. In many birds, nestlings use information derived from these cues to discriminate between individual parents or different classes of adults. Although begging occurs in some insects, we know very little about discrimination between adults by insect larvae. Here, we examine whether begging larvae in the burying beetle Nicrophorus vespilloides can discriminate between individual parents or different classes of adults. We found that larvae showed no discrimination between male and female beetles, but that they begged more towards breeding beetles than towards non‐breeding ones. These results were robust regardless of whether larvae had been reared in presence or absence of adult beetles, thus suggesting that larval discrimination is based on an innate template that requires no prior exposure to adult beetles. We also found that larvae begged more towards unfamiliar beetles than towards familiar ones, suggesting that they can learn to discriminate between individual parents based on cues about familiarity. We conclude that insect larvae may benefit from discriminating between different classes of adult beetles, as it allows them to lower the costs associated with begging in response to irrelevant environmental cues (costly in terms of wasted effort) and with not begging in response to the presence of caring parents (costly in terms of lost feeding opportunities).     

Facial Recognition in a Group-Living Cichlid Fish

The theoretical underpinnings of the mechanisms of sociality, e.g. territoriality, hierarchy, and reciprocity, are based on assumptions of individual recognition. While behavioural evidence suggests individual recognition is widespread, the cues that animals use to recognise individuals are established in only a handful of systems. Here, we use digital models to demonstrate that facial features are the visual cue used for individual recognition in the social fish Neolamprologus pulcher. Focal fish were exposed to digital images showing four different combinations of familiar and unfamiliar face and body colorations. Focal fish attended to digital models with unfamiliar faces longer and from a further distance to the model than to models with familiar faces. These results strongly suggest that fish can distinguish individuals accurately using facial colour patterns. Our observations also suggest that fish are able to rapidly (≤ 0.5 sec) discriminate between familiar and unfamiliar individuals, a speed of recognition comparable to primates including humans.     

Experience-dependent adult cortical plasticity requires cognitive association between sensation and reward

We tested the involvement of cognition in adult experience-dependent neuroplasticity using primate cortical implants. In a prior study, learning an operant sensory discrimination increased cortical excitability and target selectivity. Here, the prior task was separated into three behavioral phases. First, naive animals were exposed to stimulus-reward pairings from the prior study. These yoked animals did not have to discriminate to be rewarded and did not learn the discrimination. The plasticity observed in the prior study did not occur. Second, the animals were classically conditioned to discriminate the same stimuli in a simplified format. Learning was accompanied by increased sensory response strength and an increased range of sensory inputs eliciting responses. The third study recreated the original operant discrimination, and selectivity for task targets increased. These studies demonstrate that cognitive association between sensory stimuli and reinforcers accompanies adult experience-dependent cortical plasticity and suggest that selectivity in representation and action are linked.     

The role of the 'face-cell' area in the discrimination and recognition of faces by monkeys.

Cortical neurons that are selectively sensitive to faces, parts of faces and particular facial expressions are concentrated in the banks and floor of the superior temporal sulcus in macaque monkeys. Their existence has prompted suggestions that it is damage to such a region in the human brain that leads to prosopagnosia: the inability to recognize faces or to discriminate between faces. This was tested by removing the face-cell area in a group of monkeys. The animals learned to discriminate between pictures of faces or inanimate objects, to select the odd face from a group, to inspect a face then select the matching face from a pair of faces after a variable delay, to discriminate between novel and familiar faces, and to identify specific faces. Removing the face-cell area produced no or little impairment which in the latter case was not specific for faces. In contrast, several prosopagnosic patients were impaired at several of these tasks. The animals were less able than before to discern the angle of regard in pictures of faces, suggesting that this area of the brain may be concerned with the perception of facial expression and bearing, which are important social signals in primates.     

Categorical perception of orientation in monkeys

Structural and functional substrates of orientation processing in monkeys have been clarified. However, orientation perception in monkeys has not been fully studied. In this study, the cognitive mechanism that controls monkeys' perception of orientation was evaluated. After the monkeys were trained to discriminate between a cardinal and an oblique orientation (e.g., 0 degrees and 30 degrees), their perceptual mechanisms underlying orientation discrimination were tested by using six orientations, ranging from 0 degrees to 150 degrees, including ones used in the discrimination training. Generalization tests showed that the monkeys who were trained with cardinal orientations (e.g., 0 degrees) as positive stimuli generalized their responses to the other cardinal orientation (e.g., 90 degrees). Similarly, the monkeys who were trained with oblique orientations (e.g., 30 degrees) as positive stimuli generalized their responses to all other oblique orientations (e.g., 60 degrees, 120 degrees, and 150 degrees). These findings indicated that the monkeys abstracted the quality of the cardinal/oblique category from the physical features of orientation stimuli although they were not trained to do so. Such an abstraction also suggested a discrepancy between a continuously and orderly arranged cortical map and a discontinuously categorized perception of orientation. The present findings provide insight into the learning-correlated plasticity of cortical orientation preference.     

Symmetry perception by poultry chicks and its implications for three-dimensional object recognition

Bilateral symmetry is visually salient to diverse animals including birds, but whereas experimental studies typically use bilaterally symmetrical two-dimensional patterns that are viewed approximately fronto-parallel; in nature, animals observe three-dimensional objects from all angles. Many animals and plant structures have a plane of bilateral symmetry. Here, we first (experiment I) give evidence that young poultry chicks readily generalize bilateral symmetry as a feature of two-dimensional patterns in fronto-parallel view. We then test the ability of chicks to recognize symmetry in images that would be produced by the transformed view produced by a 40° horizontal combined with a 20° vertical rotation of a pattern on a spherical surface. Experiment II gives evidence that chicks trained to distinguish symmetrical from asymmetrical patterns treat rotated views of symmetrical 'objects' as symmetrical. Experiment III gives evidence that chicks trained to discriminate rotated views of symmetrical 'objects' from asymmetrical patterns generalize to novel symmetrical objects either in fronto-parallel or rotated view. These findings emphasize the importance of bilateral symmetry for three-dimensional object recognition and raise questions about the underlying mechanisms of symmetry perception.