Visual discrimination of species in dogs (Canis familiaris)

In most social interactions, an animal has to determine whether the other animal belongs to its own species. This perception may be visual and may involve several cognitive processes such as discrimination and categorization. Perceptual categorization is likely to be involved in species characterized by a great phenotypic diversity. As a consequence of intensive artificial selection, domestic dogs, Canis familiaris, present the largest phenotypic diversity among domestic mammals. The goal of our study was to determine whether dogs can discriminate any type of dog from other species and can group all dogs whatever their phenotypes within the same category. Nine pet dogs were successfully trained through instrumental conditioning using a clicker and food rewards to choose a rewarded image, S+, out of two images displayed on computer screens. The generalization step consisted in the presentation of a large sample of paired images of heads of dogs from different breeds and cross-breeds with those of other mammal species, included humans. A reversal phase followed the generalization step. Each of the nine subjects was able to group all the images of dogs within the same category. Thus, the dogs have the capacity of species discrimination despite their great phenotypic variability, based only on visual images of heads.     

Discrimination of human and dog faces and inversion responses in domestic dogs (Canis familiaris)

Although domestic dogs can respond to many facial cues displayed by other dogs and humans, it remains unclear whether they can differentiate individual dogs or humans based on facial cues alone and, if so, whether they would demonstrate the face inversion effect, a behavioural hallmark commonly used in primates to differentiate face processing from object processing. In this study, we first established the applicability of the visual paired comparison (VPC or preferential looking) procedure for dogs using a simple object discrimination task with 2D pictures. The animals demonstrated a clear looking preference for novel objects when simultaneously presented with prior-exposed familiar objects. We then adopted this VPC procedure to assess their face discrimination and inversion responses. Dogs showed a deviation from random behaviour, indicating discrimination capability when inspecting upright dog faces, human faces and object images; but the pattern of viewing preference was dependent upon image category. They directed longer viewing time at novel (vs. familiar) human faces and objects, but not at dog faces, instead, a longer viewing time at familiar (vs. novel) dog faces was observed. No significant looking preference was detected for inverted images regardless of image category. Our results indicate that domestic dogs can use facial cues alone to differentiate individual dogs and humans and that they exhibit a non-specific inversion response. In addition, the discrimination response by dogs of human and dog faces appears to differ with the type of face involved.     

Sex categorization of conspecific pictures in Japanese monkeys (Macaca fuscata)

We investigated whether monkeys discriminate the sex of individuals from their pictures. Whole-body pictures of adult and nonadult monkeys were used as stimuli. Two male Japanese monkeys were trained for a two-choice sex categorization task in which each of two choice pictures were assigned to male and female, respectively. Following the training, the monkeys were presented with novel monkey pictures, and whether they had acquired the categorization task was tested. The results suggested that while monkeys discriminate between the pictures of adult males and females, discrimination of nonadult pictures was difficult. Partial presentations of the pictures showed that conspicuous and sexually characteristic parts (i.e., underbellies including male scrotums or breasts including female nipples) played an important role in the sex categorization.     

Dogs can discriminate human smiling faces from blank expressions

Dogs have a unique ability to understand visual cues from humans. We investigated whether dogs can discriminate between human facial expressions. Photographs of human faces were used to test nine pet dogs in two-choice discrimination tasks. The training phases involved each dog learning to discriminate between a set of photographs of their owner’s smiling and blank face. Of the nine dogs, five fulfilled these criteria and were selected for test sessions. In the test phase, 10 sets of photographs of the owner’s smiling and blank face, which had previously not been seen by the dog, were presented. The dogs selected the owner’s smiling face significantly more often than expected by chance. In subsequent tests, 10 sets of smiling and blank face photographs of 20 persons unfamiliar to the dogs were presented (10 males and 10 females). There was no statistical difference between the accuracy in the case of the owners and that in the case of unfamiliar persons with the same gender as the owner. However, the accuracy was significantly lower in the case of unfamiliar persons of the opposite gender to that of the owner, than with the owners themselves. These results suggest that dogs can learn to discriminate human smiling faces from blank faces by looking at photographs. Although it remains unclear whether dogs have human-like systems for visual processing of human facial expressions, the ability to learn to discriminate human facial expressions may have helped dogs adapt to human society.     

Beyond the distributional input? A developmental investigation of asymmetry in infants’ categorization of cats and dogs

Two experiments are reported using a visual familiarization categorization procedure. In both experiments, infants were familiarized with sets of stimuli previously shown to contain asymmetric feature distributions that support an asymmetry in young infants' categorization of cats and dogs (i.e. infants' cat category excludes dogs but their dog category includes cats). In Experiment 1, the asymmetry was replicated in 4-month-old infants. In contrast, 10-month-old infants demonstrated exclusive category representations for both cats and dogs. In Experiment 2, an additional group of 10-month-olds demonstrated exclusive representations for both cats and dogs under conditions of very limited within-task category familiarization. Potential mechanisms underlying the shift from an asymmetric to a symmetric pattern of categorization in the first year are discussed.     

Long-term memory for categories and concepts in horses (Equus caballus)

Three horses (Equus caballus) with a history of performing cognitive tasks including discrimination learning, categorization, and concept use were tested to evaluate their long-term memory (LTM) in three experiments. In addition, use of LCD multi-displays for stimulus presentation was incorporated into cognition testing protocol for the first time with horses. Experiment 1 tested LTM for discrimination learning that originally occurred 6 years earlier. Five sets of stimuli were used and the two horses tested showed no decrement in performance on four of the sets; however, both horses did score below chance on one set. Experiment 2 examined long-term categorization recall 10 years after horses had demonstrated the ability to make stimulus selections based on shared characteristics within a given category. The horse tested for LTM after the decade-long interval immediately and consistently applied the previously learned categorization rule to not only familiar but also novel sets of stimuli. Experiment 3 tested another horse for LTM for a relative size concept. This horse had originally demonstrated concept rule use in order to select stimuli based on their relative size to one another. More than 7 years later and without further training, this horse reliably applied the previously established size concept to both familiar and novel sets of stimuli. These findings are the first reports of long-term categorical and conceptual memory in horses and are consistent with observations of domestic and wild horses, which indicate that behavioral and ecological events may be remembered for long periods of time. These studies also demonstrate the adaptive nature of horses with regard to their ability to generalize over several different testing conditions.     

物体分类任务中线索效应的ERP研究

本实验采用ERP技术,对图片分类任务中的线索效应进行研究。实验任务为:图形形状判断、动物/非动物判断。靶刺激图片前呈现线索。线索分为有效线索、无效线索和中性线索。结果发现:(1)有效线索条件下对靶刺激的早期知觉再认得到易化——知觉加工成分波幅下降;(2)有效线索条件下,靶刺激中与任务相关的信息得到加工——任务相关的特异性成分增强。有效线索易化对靶刺激的知觉辨认,提取与线索提供背景相关的信息,促进行为反应。     

Dogs do look at images: eye tracking in canine cognition research

Despite intense research on the visual communication of domestic dogs, their cognitive capacities have not yet been explored by eye tracking. The aim of the current study was to expand knowledge on the visual cognition of dogs using contact-free eye movement tracking under conditions where social cueing and associative learning were ruled out. We examined whether dogs spontaneously look at actual objects within pictures and can differentiate between pictures according to their novelty or categorical information content. Eye movements of six domestic dogs were tracked during presentation of digital color images of human faces, dog faces, toys, and alphabetic characters. We found that dogs focused their attention on the informative regions of the images without any task-specific pre-training and their gazing behavior depended on the image category. Dogs preferred the facial images of conspecifics over other categories and fixated on a familiar image longer than on novel stimuli regardless of the category. Dogs’ attraction to conspecifics over human faces and inanimate objects might reflect their natural interest, but further studies are needed to establish whether dogs possess picture object recognition. Contact-free eye movement tracking is a promising method for the broader exploration of processes underlying special socio-cognitive skills in dogs previously found in behavioral studies.     

A computer touch-screen apparatus for training visual discriminations in rats.

We describe an operant conditioning apparatus that uses computerized touch-screen technology and is designed for the versatile and highly controlled testing of rats in a potentially wide variety of behavioral paradigms. Although computer-controlled touch-screen systems have been developed for use with pigeons, monkeys, and humans, analogous technologies and methods have not yet been developed for rats. The development of a touch-screen system for rats could enhance the efficiency of behavioral research with rats, and may offer a unique tool for studying animal learning. In the first test of the utility of the apparatus, 3 Sprague-Dawley rats learned to activate the touch screen only after the touch-screen panel was made slightly movable. These animals then learned to discriminate visual stimuli presented on the computer monitor, but only after the food magazine and pellet dispenser were moved to the rear of the chamber opposite the stimulus display and response window. In a test of the utility of the modified apparatus, 6 Long-Evans rats learned to activate the touch screen and learned one of three different simple discriminations using computer-generated, visually presented stimuli. A basic method for training rats to activate the computer touch screen and for visual discrimination training is described. Results show that rats learned to activate the touch screen and discriminate visual stimuli presented on a computer monitor. Potential applications and advantages of the touch-screen-equipped rat operant conditioning chamber are discussed.     

The "style scheme" grounds perception of paintings

We studied the formation of style scheme (identification of the style that characterizes an artist) presenting 100 participants aesthetic visual stimuli. Participants were Spanish university students who volunteered: 72 women, 28 men of mean age 22.8 yr. Among those 50 were enrolled in History of Art and 50 students in Psychology. Stimuli belonged to different categories--High Art (pictures of well-known artists, like Van Gogh)/Popular Art (decorative pictures like Christmas postcards) and Representational (pictures with explicit meaning content, like a landscape)/Abstract (pictures without explicit meaning content, like Pollock's colored stains). Analysis using Signal Detection Theory techniques focused on how participants discriminate representational and abstract pictures. With High Art stimuli, participants can better discriminate representational paintings than abstract ones. However, the difference in discrimination between representational and abstract pictures diminishes among participants studying History of Art. It seems that prior education in art favors forming style schemes and to some extent enables the participant to detect the "meaning" in High Art abstract paintings.     

Gender Related Naming Practices: Similarities and Differences Between People and their Dogs

We compared final written letters and spoken phonemes and syllable length in the names of male (N = 250) and female (N = 197) Golden Retrievers to determine if the same gender-stereotyping trends occurring in humans also appeared in dog names. Names were taken from a website of the most popular Golden Retriever names in English speaking countries. Both male and female dogs had names ending in letters and phonemes characteristic of their respective human male and female counterparts. Female dogs had more syllables in their names than male dogs and a higher percentage of male dogs had one syllable names. We conclude that the similarities between human and dog naming practices reflect a pervasive gendered naming phonology.     

Naming and categorizing objects: Task differences modulate the polarity of semantic effects in the picture–word interference paradigm

The picture-word interference paradigm is a prominent tool for studying lexical retrieval during speech production. When participants name the pictures, interference from semantically related distractor words has regularly been shown. By contrast, when participants categorize the pictures, facilitation from semantically related distractors has typically been found. In the extant studies, however, differences in the task instructions (naming vs. categorizing) were confounded with the response level: While responses in naming were typically located at the basic level (e.g., "dog"), responses were located at the superordinate level in categorization (e.g., "animal"). The present study avoided this confound by having participants respond at the basic level in both naming and categorization, using the same pictures, distractors, and verbal responses. Our findings confirm the polarity reversal of the semantic effects--that is, semantic interference in naming, and semantic facilitation in categorization. These findings show that the polarity reversal of the semantic effect is indeed due to the different tasks and is not an artifact of the different response levels used in previous studies. Implications for current models of language production are discussed.     

A dog at the keyboard: using arbitrary signs to communicate requests

As a consequence of domestication, dogs have a special readiness for communication with humans. We here investigate whether a dog might be able to acquire and consistently produce a set of arbitrary signs in her communication with humans, as was demonstrated in “linguistic” individuals of several species. A female mongrel dog was submitted to a training schedule in which, after basic command training and after acquiring the verbal labels of rewarding objects or activities, she learned to ask for such objects or activities by selecting lexigrams and pressing keys on a keyboard. Systematic records taken during spontaneous interaction with one of the experimenters showed that lexigrams were used in an appropriate, intentional way, in accordance with the immediate motivational context. The dog only utilized the keyboard in the experimenter’s presence and gazed to him more frequently after key pressing than before, an indication that lexigram use did have communicative content. Results suggest that dogs may be able to learn a conventional system of signs associated to specific objects and activities, functionally analogous to spontaneous soliciting behaviors and point to the potential fruitfulness of the keyboard/lexigram procedure for studying dog communication and cognition. This is the first report to systematically analyze the learning of arbitrary sign production in dogs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quantity discrimination in Tenebrio molitor: evidence of numerosity discrimination in an invertebrate?

Numerosity discrimination, the ability to distinguish between sets with more and less items, is recognised as the foundation for higher numerical abilities. Understanding numerosity discrimination from a comparative perspective is hence pivotal in tracing the evolution of numerical representation systems. However, numerosity discrimination has been well studied only in vertebrates, where two innate systems of number representation have been described: an ‘analog magnitude system’ used to discriminate among numerosities by representing them as cardinal magnitudes and a ‘parallel individualisation system’ that allows precise discrimination among small arrays of items (≤4) by representing objects individually. We investigated the existence of quantity discrimination in an insect species (Tenebrio molitor) by using a spontaneous two-choice procedure in which males were exposed to substrates bearing odours from different numbers of females (≤4) in increasing numerosity ratios (1:4, 1:3 and 1:2). We show that males can discriminate sources of odours reflecting 1 versus 4 and 1 versus 3 females, but not 2 versus 4 or 1 versus 2, indicating that T. molitor males exhibit a marked preference for sources reflecting more female donors only when numerosity ratios are below 1:2. We discuss the functional significance of this finding and whether our pattern of results could be best explained by summation of a non-numerical continuous variable or by the existence of a numerosity discrimination mechanism with an operational signature ratio of 1:2.     

The legitimizing role of accent on discrimination against immigrants

This article analyses the influence of accent on discrimination against immigrants by examining the hypothesis that accent leads to discrimination only in more prejudiced individuals, merely because people speaking with a native accent are perceived to be better qualified than those whose accent is non‐standard. In Study 1 (N = 71), we found that only prejudiced individuals use accent to discriminate against immigrants. In Study 2 (N = 124), we replicated this effect and found that the influence of accent on discrimination is mediated by the perceived quality of the accent. Study 3 (N = 105) replicated the previous results even after controlling for the effect of stereotyping. These results are the first experimental illustration of the hypothesis that accent triggers intergroup discrimination only among prejudiced individuals because they evaluate native accents as being qualitatively better than accents of immigrants, thereby legitimizing ingroup bias.     

Object categorization: reversals and explanations of the basic-level advantage

People are generally faster and more accurate to name or categorize objects at the basic level (e.g., dog) relative to more general (animal) or specific (collie) levels, an effect replicated in Experiment 1 for categorization of object pictures. To some, this pattern suggests a dual-process mechanism, in which objects first activate basic-level categories directly and later engage more general or specific categories through the spread of activation in a processing hierarchy. This account is, however, challenged by data from Experiment 2 showing that neuropsychological patients with impairments of conceptual knowledge categorize more accurately at superordinate levels than at the basic level--suggesting that knowledge about an object's general nature does not depend on prior basic-level categorization. The authors consider how a parallel distributed processing theory of conceptual knowledge can reconcile the apparent discrepancy. This theory predicts that if healthy individuals are encouraged to make rapid categorization responses, the usual basic > general advantage should also reverse, a prediction tested and confirmed in Experiment 3. Implications for theories of visual object recognition are discussed.     

The discrimination of natural movement by budgerigars (Melopsittacus undulates) and pigeons (Columba livia)

Three experiments examined the ability of birds to discriminate between the actions of walking forwards and backwards as demonstrated by video clips of a human walking a dog. Experiment 1 revealed that budgerigars (Melopsittacus undulates) could discriminate between these actions when the demonstrators moved consistently from left to right. Test trials then revealed that the discrimination transferred, without additional training, to clips of the demonstrators moving from right to left. Experiment 2 replicated the findings from Experiment 1 except that the demonstrators walked as if on a treadmill in the center of the display screen. The results from the first 2 experiments were replicated with pigeons in Experiment 3. The results cannot be explained if it is assumed that animals rely on static cues, such as those derived from individual postures, in order to discriminate between the actions of another animal. Instead, this type of discrimination appears to be controlled by dynamic cues derived from changes in the posture of the demonstrators.     

Differential outcomes facilitate same/different concept learning

Commonly recognized, the training procedure one employs often affects the results they obtain. Here, we demonstrate for the first time that abstract-concept learning is affected by employing a differential-outcomes procedure. The differential-outcome effect has been shown to occur for item-specific strategies but has not been established for relational strategies. To test whether different-outcome expectancies can facilitate a relational strategy, eight pigeons were trained and tested in a two-item same/different task with pictures. After pecking an upper picture, they pecked a lower picture if the pictures were the same or a white rectangle if the pictures were different. Two groups of pigeons were rewarded with either different outcomes (sounds and food amounts) or same outcomes. Both groups were trained to criterion with successively larger picture sets (8–1,024 items) and were transfer tested with novel pictures following each acquisition. With the smallest training sets, neither group showed any novel-stimulus transfer. But after acquiring the task with 32 pictures, the different-outcomes group responded more accurately to novel pictures than the same-outcome group. As the training set-size increased, both groups’ transfer performance converged and became equivalent to training performance. These results show for the first time that training with different outcomes facilitates abstract-concept learning.     

Categorization of two-dimensional and three-dimensional stimuli by 18-month-old infants

In two experiments, 18-month-old infants’ categorization of 3D replicas and 2D photographs of the same animals and vehicles were compared to explore infants’ flexibility in categorization across different object representations. Using a sequential touching procedure, infants completed one superordinate and two basic-level categorization tasks with 3D replicas, 2D cut out photographs, or 2D images on photo cubes (“2D cubes”). For superordinate sets, 3D replicas elicited longer mean run lengths than 2D cut outs, and 3D replicas elicited equivalent mean run lengths as 2D cubes. For basic-level sets, infants categorized high-contrast animal sets when presented with 3D replicas, but they failed to categorize any of the 2D photograph sets. Categorization processes appear to differ for 3D and 2D stimuli, and infants’ discovery of object properties over time while manipulating objects may facilitate categorization, as least at the superordinate level. These findings are discussed in the context of infants’ representation abilities and the integration of perception and action.