Conceptual influences on category-based induction

"Shape bias" goes social: Children categorize people by weight rather than race

Children tend to categorize novel objects according to their shape rather than their color, texture, or other salient properties-known as "shape bias." We investigated whether this bias also extends to the social domain, where it should lead children to categorize people according to their weight (their body shape) rather than their race (their skin color). In Study 1, participants (n = 50 US 4- and 5-year-olds) were asked to extend a novel label from a target object/person to either an object/person who shared the target's shape/weight, color/race, or neither. Children selected the shape-/weight-matched individual over the color-/race-matched individual (dobjects  = 1.58, dpeople  = 0.99) and their shape biases were correlated across the two domains. In Study 2, participants (n = 20 US 4- and 5-year-olds) were asked to extend a novel internal property from a target person to either a person who shared the target's weight, race, or neither. Again, children selected the weight-matched individual (d = 1.98), suggesting they view an individual's weight as more predictive of their internal properties than their race. Overall, results suggest that children's early shape bias extends into the social domain. Implications for weight bias and early social cognition are discussed. RESEARCH HIGHLIGHTS: Preschoolers extend novel labels based on people's weight rather than their race. Preschoolers infer internal features based on people's weight rather than their race. Shape biases are present, and correlated, across the social and object domains.

Relevance and the Role of Labels in Categorization

Language has been shown to influence the ability to form categories. Nevertheless, in most prior work, the effects of language could have been bolstered by the fact that linguistic labels were introduced by the experimenter prior to the categorization task in ways that could have highlighted their relevance for the task. Here, we compared the potency of labels to that of other non-linguistic cues on how people categorized novel, perceptually ambiguous natural kinds (e.g., flowers or birds). Importantly, we varied whether these cues were explicitly presented as relevant to the categorization task. In Experiment 1, we compared labels, numbers, and symbols: One group of participants was told to pay attention to these cues because they would be helpful (Relevant condition), a second group was told that the cues were irrelevant and should be ignored (Irrelevant condition), and a third group was told nothing about the cues (Neutral condition). Even though task relevance affected overall reliance on cues during categorization, participants were more likely to use labels to determine category boundaries, compared to numbers or symbols. In Experiments 2 and 3, we replicated and fine-tuned the advantage of labels in more stringent categorization tasks. These results offer novel evidence for the position that labels offer unique indications of category membership, compared to non-linguistic cues.

From features to categories: The development of inductive generalization

Young children can generalize from known to novel, but the underlying mechanism is still debated. Some argue that from an early age generalization is category-based and undergoes little development, while others believe that early generalization is similarity-based, and the use of categories emerges over time. The current research brings new evidence to the debate. In Experiment 1 (N = 118), we presented 3- to 5-year-olds and adults with a category learning task followed by an exemplar generation task. Then, in Experiment 2 (N = 126), we presented the same tasks but provided participants with additional conceptual information about the category members. Our results indicate that early reasoning undergoes dramatic development: whereas young children rely mostly on salient features, adults rely on category information. These results challenge category-based accounts of early generalization while supporting similarity-based accounts. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

"I am not a junkie": Social categorization and differentiation among people who use drugs

BACKGROUND

Substance use stigma is a form of group-based exclusion, and delineating pathways from stigma to poor health requires a deeper understanding of the social dynamics of people who use drugs (PWUD). Outside of recovery, scant research has examined the role of social identity in addiction. Framed by Social Identity Theory/Self-Categorization Theory, this qualitative study investigated strategies of within-group categorization and differentiation among PWUD and the roles these social categories may play in shaping intragroup attitudes, perceptions, and behaviors.

METHODS

Data come from the Rural Opioid Initiative, a multi-site study of the overdose epidemic in rural United States. We conducted in-depth interviews with people who reported using opioids or injecting any drug (n=355) living in 65 counties across 10 states. Interviews focused on participants' biographical histories, past and current drug use, risk behaviors, and experiences with healthcare providers and law enforcement. Social categories and dimensions along which categories were evaluated were inductively identified using reflexive thematic analysis.

RESULTS

We identified seven social categories that were commonly appraised by participants along eight evaluative dimensions. Categories included drug of choice, route of administration, method of attainment, gender, age, genesis of use, and recovery approach. Categories were evaluated by participants based on ascribed characteristics of morality, destructiveness, aversiveness, control, functionality, victimhood, recklessness, and determination. Participants performed nuanced identity work during interviews, including reifying social categories, defining 'addict' prototypicality, reflexively comparing self to other, and disidentifying from the PWUD supra-category.

CONCLUSION

We identify several facets of identity, both behavioral and demographic, along which people who use drugs perceive salient social boundaries. Beyond an addiction-recovery binary, identity is shaped by multiple aspects of the social self in substance use. Patterns of categorization and differentiation revealed negative intragroup attitudes, including stigma, that may hinder solidary-building and collective action in this marginalized group.

Children's knowledge of superordinate words predicts subsequent inductive reasoning

Children's early language knowledge-typically assessed using standardized word comprehension tests or through parental reports-has been positively linked to a variety of later outcomes, from reasoning tests to academic performance to income and health. To better understand the mechanisms behind these links, we examined whether knowledge of certain "seed words"-words with high inductive potential-is positively associated with inductive reasoning. This hypothesis stems from prior work on the effects of language on categorization suggesting that certain words may be important for helping people to deploy categorical hypotheses. Using a longitudinal design, we assessed 36 2- to 4-year-old children's knowledge of 333 words of varying levels of generality (e.g., toy vs. pinwheel, number vs. five). We predicted that adjusting for overall vocabulary, knowledge of more general words (e.g., toy, number) would predict children's performance on inductive reasoning tasks administered 6 months later (i.e., a subset of the Stanford-Binet Intelligence Scales for Early Childhood-Fifth Edition [SB-5] and Woodcock-Johnson Tests of Cognitive Abilities [WJ] concept formation tasks). This prediction was confirmed for one of the measures of inductive reasoning (i.e., the SB-5 but not the WJ) and notably for the task considered to be less reliant on language. Although our experimental design demonstrates only a correlational relationship between seed word knowledge and inductive reasoning ability, our results are consistent with the possibility that early knowledge of certain seed words facilitates performance on putatively nonverbal reasoning tasks.

Of Pandemics and Zombies: The Influence of Prior Concepts on COVID-19 Pandemic-Related Behaviors

We use a concepts and categories research perspective to explore how prior conceptual knowledge influences thinking about a novel disease, namely COVID-19. We collected measures of how similar people thought COVID-19 was to several existing concepts that may have served as other possible comparison points for the pandemic. We also collected participants' self-reported engagement in pandemic-related behaviors. We found that thinking the COVID-19 pandemic was similar to other serious disease outbreaks predicted greater social distancing and mask-wearing, whereas likening COVID-19 to the seasonal flu predicted engaging in significantly fewer of these behaviors. Thinking of COVID-19 as similar to zombie apocalypse scenarios or moments of major societal upheaval predicted stocking-up behaviors, but not disease mitigation behaviors. These early category comparisons influenced behaviors over a six-month span of longitudinal data collection. Our findings suggest that early conceptual comparisons track with emergent disease categories over time and influence the behaviors people engage in related to the disease. Our research illustrates how early concept formation influences behaviors over time, and suggests ways for public health experts to communicate with the public about emergent diseases.

Strength or Nausea? Children's Reasoning About the Health Consequences of Food Consumption

Children’s reasoning on food properties and health relationships can contribute to healthier food choices. Food properties can either be positive (“gives strength”) or negative (“gives nausea”). One of the main challenges in public health is to foster children’s dietary variety, which contributes to a normal and healthy development. To face this challenge, it is essential to investigate how children generalize these positive and negative properties to other foods, including familiar and unfamiliar ones. In the present experiment, we hypothesized that children might rely on cues of food processing (e.g., signs of human intervention such as slicing) to convey information about item edibility. Furthermore, capitalizing on previous results showing that food rejections (i.e., food neophobia and picky eating) are a significant source of inter-individual variability to children’s inferences in the food domain, we followed an individual approach. We expected that children would generalize the positive properties to familiar foods and, in contrast, that they would generalize more often the negative properties to unfamiliar foods. However, we expected that children would generalize more positive and less negative properties to unfamiliar sliced foods than to whole unfamiliar foods. Finally, we expected that children displaying higher levels of food rejections would generalize more negative properties than children displaying lower levels of food rejections. One-hundred and twenty-six children, aged 3–6 years, performed an induction task in which they had to generalize positive or negative health-related properties to familiar or unfamiliar foods, whole or sliced. We measured children’s probability of generalization for positive and negative properties. The children’s food rejection score was assessed on a standardized scale. Results indicated that children evaluated positively familiar foods (regardless of processing), whereas they tend to view unfamiliar food negatively. In contrast, children were at chance for processed unfamiliar foods. Furthermore, children displaying higher levels of food rejections were more likely to generalize the negative properties to all kinds of foods than children displaying lower levels of food rejections. These findings entitle us to hypothesize that knowledge-based food education programs should take into account the valence of the properties taught to children, as well as the state of processing of the food presented. Furthermore, one should take children’s interindividual differences into account because they influence how the knowledge gained through these programs may be generalized.

The Influence of Gender Categories and Gender Stereotypes on Young Children's Generalizations of Biological and Behavioral Characteristics

We examined the influence of categorization and stereotyping on young children's (N = 96; 39 to 71 months of age) use of gender to make generalizations regarding novel biological and behavioral characteristics. Participants were asked to sort pictures of children according to either gender, common gender stereotypes, or shirt color. Then participants performed a triad inductive reasoning task. Children in the Stereotype condition consistently generalized on the basis of gender, but performance was inconsistent in the absence of stereotyping. Results are discussed in relation to variability in early gender cognition.

Children's beliefs about causes of human characteristics: Genes, environment, or choice?

To what extent do our genes make us nice, smart, or athletic? The explanatory frameworks we employ have broad consequences for how we evaluate and interact with others. Yet to date, little is known regarding when and how young children appeal to genetic explanations to understand human difference. The current study examined children's (aged 7-13 years) and adults' explanations for a set of human characteristics, contrasting genetic attributions with environmental and choice-based attributions. Whereas most adults and older children offered an unprompted genetic explanation at least once on an open-ended task, such explanations were not seen from younger children. However, even younger children, once trained on the mechanism of genes, endorsed genetic explanations for a range of characteristics-often in combination with environment and choice. Moreover, only adults favored genetic explanations for intelligence and athleticism; children, in contrast, favored environment and choice explanations for these characteristics. These findings suggest that children can employ genetic explanations in principled ways as early as 7 years of age but also that such explanations are used to account for a wider range of features by adults. Our study provides some of the first evidence regarding the ways in which genetic attributions emerge and change starting in early childhood. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Learning Progressions: An Empirically Grounded, Learner-Centered Framework to Guide Biology Instruction

Vision and Change challenged biology instructors to develop evidence-based instructional approaches that were grounded in the core concepts and competencies of biology. This call for reform provides an opportunity for new educational tools to be incorporated into biology education. In this essay, we advocate for learning progressions as one such educational tool. First, we address what learning progressions are and how they leverage research from the cognitive and learning sciences to inform instructional practices. Next, we use a published learning progression about carbon cycling to illustrate how learning progressions describe the maturation of student thinking about a key topic. Then, we discuss how learning progressions can inform undergraduate biology instruction, citing three particular learning progressions that could guide instruction about a number of key topics taught in introductory biology courses. Finally, we describe some challenges associated with learning progressions in undergraduate biology and some recommendations for how to address these challenges.

The influence of theoretical knowledge on similarity judgment

The similarity of the features between two entities has been assumed to be the essential factor for distinguishing these two entities across a variety of cognitive acts; however, the mechanism underlying the similarity processing remains unclear. The perceptual-based account suggests that similarity judgment is based on perceptual features between entities, whereas other accounts assume that similarity judgment relies heavily on one's previous knowledge of the entities. In Experiment 1, we explored the influence of theoretical knowledge on similarity judgment when perceptual features conflict with conceptual information. In Experiment 2, we examined whether categorization tasks further influence the results of the similarity judgment. Our results showed that the theoretical knowledge contributed to the overall similarity of the stimuli. In addition, carrying out a categorization task or not did not contribute more to the processes of the similarity judgment. Overall, these findings suggest that the conceptual information is more important than perceptual features while judging the similarity of two entities; if sufficient theoretical knowledge is available, the criteria for carrying out the categorization task might be consistent with those for the similarity judgment in the present study.

Inductive Reasoning Differs Between Taxonomic and Thematic Contexts: Electrophysiological Evidence

Inductive reasoning can be performed in different contexts, but it is unclear whether the neural mechanism of reasoning performed in a thematic context (e.g., bee has x, so honey has x) is the same as that performed in a taxonomic context (e.g., bee has x, so butterfly has x). In the present study, participants were required to judge whether a conclusion was acceptable or not based on its premise, for which the taxonomic or thematic distances between premise and conclusion objects were either far or near. The Event related potential (ERP) results indicated that the effect of context (taxonomic vs. thematic) was initially observed in the P2 component; while the distance effect (far vs. near) was observed in N400 and late components. Moreover, the distance effect on thematic-based inductive reasoning was found in the anterior regions, while the distance effect on taxonomic-based inductive reasoning conditions was found in the posterior regions. These results support the view that inductive reasoning is performed differently under different semantic contexts.

Ontological Constraints in Children's Inductive Inferences: Evidence From a Comparison of Inferences Within Animals and Vehicles

There is a lively debate concerning the role of conceptual and perceptual information in young children's inductive inferences. While most studies focus on the role of basic level categories in induction the present research contributes to the debate by asking whether children's inductions are guided by ontological constraints. Two studies use a novel inductive paradigm to test whether young children have an expectation that all animals share internal commonalities that do not extend to perceptually similar inanimates. The results show that children make category-consistent responses when asked to project an internal feature from an animal to either a dissimilar animal or a similar toy replica. However, the children do not have a universal preference for category-consistent responses in an analogous task involving vehicles and vehicle toy replicas. The results also show the role of context and individual factors in inferences. Children's early reliance on ontological commitments in induction cannot be explained by perceptual similarity or by children's sensitivity to the authenticity of objects.

Inductive reasoning 2.0

Inductive reasoning entails using existing knowledge to make predictions about novel cases. The first part of this review summarizes key inductive phenomena and critically evaluates theories of induction. We highlight recent theoretical advances, with a special emphasis on the structured statistical approach, the importance of sampling assumptions in Bayesian models, and connectionist modeling. A number of new research directions in this field are identified including comparisons of inductive and deductive reasoning, the identification of common core processes in induction and memory tasks and induction involving category uncertainty. The implications of induction research for areas as diverse as complex decision-making and fear generalization are discussed. This article is categorized under: Psychology > Reasoning and Decision Making Psychology > Learning.

An associative account of the development of word learning

Word learning is a notoriously difficult induction problem because meaning is underdetermined by positive examples. How do children solve this problem? Some have argued that word learning is achieved by means of inference: young word learners rely on a number of assumptions that reduce the overall hypothesis space by favoring some meanings over others. However, these approaches have difficulty explaining how words are learned from conversations or text, without pointing or explicit instruction. In this research, we propose an associative mechanism that can account for such learning. In a series of experiments, 4-year-olds and adults were presented with sets of words that included a single nonsense word (e.g. dax). Some lists were taxonomic (i.,e., all items were members of a given category), some were associative (i.e., all items were associates of a given category, but not members), and some were mixed. Participants were asked to indicate whether the nonsense word was an animal or an artifact. Adults exhibited evidence of learning when lists consisted of either associatively or taxonomically related items. In contrast, children exhibited evidence of word learning only when lists consisted of associatively related items. These results present challenges to several extant models of word learning, and a new model based on the distinction between syntagmatic and paradigmatic associations is proposed.

How language shapes the cultural inheritance of categories

It is widely recognized that language plays a key role in the transmission of human culture, but relatively little is known about the mechanisms by which language simultaneously encourages both cultural stability and cultural innovation. This paper examines this issue by focusing on the use of language to transmit categories, focusing on two universal devices: labels (e.g., shark, woman) and generics (e.g., "sharks attack swimmers"; "women are nurturing"). We propose that labels and generics each assume two key principles: norms and essentialism. The normative assumption permits transmission of category information with great fidelity, whereas essentialism invites innovation by means of an open-ended, placeholder structure. Additionally, we sketch out how labels and generics aid in conceptual alignment and the progressive "looping" between categories and cultural practices. In this way, human language is a technology that enhances and expands the categorization capacities that we share with other animals.

The Origins of Social Categorization

Forming conceptually-rich social categories helps people to navigate the complex social world by allowing them to reason about the likely thoughts, beliefs, actions, and interactions of others, as guided by group membership. Nevertheless, social categorization often has nefarious consequences. We suggest that the foundation of the human ability to form useful social categories is in place in infancy: social categories guide the inferences infants make about the shared characteristics and social relationships of other people. We also suggest that the ability to form abstract social categories may be separable from the eventual negative downstream consequences of social categorization, including prejudice, discrimination, and stereotyping. Although a tendency to form inductively-rich social categories appears early in ontogeny, prejudice based on each particular category dimension may not be inevitable.

Changes in Beliefs About Category Homogeneity and Variability Across Childhood

Effective category-based induction requires understanding that categories include both fundamental similarities between members and important variation. This article explores 4- to 11-year-olds' (n = 207) and adults' (n = 49) intuitions about this balance between within-category homogeneity and variability using a novel induction task in which participants predict the distribution of a property among members of a novel category. Across childhood, children learned to recognize variability within categories-showing increasing sensitivity to the role of property type and domain in constraining inferences. Children below the age of 6 showed evidence for a domain-general assumption that categories are homogeneous-generalizing properties broadly to 100% of category members. These studies support important developmental changes in category representations that may influence category-based induction.

An Essentialist Account of Authenticity

The concept of authenticity is central to how people value many different types of objects and yet there is considerable disagreement about how individuals evaluate authenticity or how the concept itself should be defined. This paper attempts to reconcile previous approaches by proposing a novel view of authenticity. Specifically, I draw upon past research on psychological essentialism and propose that when people evaluate the authenticity of objects, they do so by evaluating the extent to which the object embodies or reflects a valued essence. I suggest that this explanation of authenticity provides an overarching framework that describes how people evaluate object authenticity across a variety of contexts and I report the results of three experiments that directly test the predictions made by this explanation.

Conceptual influences on induction: A case for a late onset

This research examines the mechanism of early induction, the development of induction, and the ways attentional and conceptual factors contribute to induction across development. Different theoretical views offer different answers to these questions. Six experiments with 4- and 5-year-olds, 7-year-olds and adults (N=208) test these competing theories by teaching categories for which category membership and perceptual similarity are in conflict, and varying orthogonally conceptual and attentional factors that may potentially affect inductive inference. The results suggest that early induction is similarity-based; conceptual information plays a negligible role in early induction, but its role increases gradually, with the 7-year-olds being a transitional group. And finally, there is substantial contribution of attention to the development of induction: only adults, but not children, could perform category-based induction without attentional support. Therefore, category-based induction exhibits protracted development, with attentional factors contributing early in development and conceptual factors contributing later in development. These results are discussed in relation to existing theories of development of inductive inference and broader theoretical views on cognitive development.

Inductive generalization with familiar categories: developmental changes in children's reliance on perceptual similarity and kind information

Inductive generalization is ubiquitous in human cognition; however, the factors underpinning this ability early in development remain contested. The present study was designed to (1) test the predictions of the naïve theory and a similarity-based account and (2) examine the mechanism by which labels promote induction. In Experiment 1, 3- to 5-year-old children made inferences about highly familiar categories. The results were not fully consistent with either theoretical account. In contrast to the predictions of the naïve theory approach, the youngest children in the study did not ignore perceptually compelling lures in favor of category-match items; in contrast to the predictions of the similarity-based account, no group of participants favored perceptually compelling lures in the presence of dissimilar-looking category-match items. In Experiment 2 we investigated the mechanisms by which labels promote induction by examining the influence of different label types, namely category labels (e.g., the target and category-match both labeled as bird) and descriptor labels (e.g., the target and the perceptual lure both labeled as brown) on induction performance. In contrast to the predictions of the naïve theory approach, descriptor labels but not category labels affected induction in 3-year-old children. Consistent with the predictions of the similarity-based account, descriptor labels affected the performance of children in all age groups included in the study. The implications of these findings for the developmental account of induction are discussed.

Opening the cuebox: the information children and young adults generate and rely on when making inferences from memory

We used a cue-generation and a cue-selection paradigm to investigate the cues children (9- to 12-year-olds) and young adults (17-year-olds) generate and select for a range of inferences from memory. We found that children generated more cues than young adults, who, when asked why they did not generate some particular cues, responded that they did not consider them relevant for the task at hand. On average, the cues generated by children were more perceptual but as informative as the cues generated by young adults. When asked to select the most informative of two cues, both children and young adults tended to choose a hidden (i.e., not perceptual) cue. Our results suggest a developmental change in the cuebox (i.e., the set of cues used to make inferences from memory): New cues are added to the cuebox as more cues are learned, and some old, perceptual cues, although informative, are replaced with hidden cues, which, by both children and young adults, are generally assumed to be more informative than perceptual cues.

The development of categorization: effects of classification and inference training on category representation

Does category representation change in the course of development? And if so, how and why? The current study attempted to answer these questions by examining category learning and category representation. In Experiment 1, 4-year-olds, 6-year-olds, and adults were trained with either a classification task or an inference task and their categorization performance and memory for items were tested. Adults and 6-year-olds exhibited an important asymmetry: they relied on a single deterministic feature during classification training, but not during inference training. In contrast, regardless of the training condition, 4-year-olds relied on multiple probabilistic features. In Experiment 2, 4-year-olds were presented with classification training and their attention was explicitly directed to the deterministic feature. Under this condition, their categorization performance was similar to that of older participants in Experiment 1, yet their memory performance pointed to a similarity-based representation, which was similar to that of 4-year-olds in Experiment 1. These results are discussed in relation to theories of categorization and the role of selective attention in the development of category learning.

Drift in children's categories: when experienced distributions conflict with prior learning

Psychological intuitions about natural category structure do not always correspond to the true structure of the world. The current study explores young children's responses to conflict between intuitive structure and authoritative feedback using a semi-supervised learning (Zhu et al., 2007) paradigm. In three experiments, 160 children between the ages of 4 and 8 learned a one-dimensional decision criterion for distinguishing yummy and yucky 'alien fruits'. They then categorized a large number of new fruits without corrective feedback. The distribution of the new fruits was manipulated such that the natural boundary in the stimuli did not always correspond to the learned boundary. Children changed their decision criteria to reflect the structure of the new stimuli, effectively unlearning the original boundary. Younger children were especially swayed by the distributional information, being relatively insensitive to feedback that the original non-natural boundary was, in fact, still correct. Results are discussed in terms of children's ability to selectively attend to specific information (i.e. feedback vs. distribution), and their interests in forming generally useful representations of experience.

Conceptually coherent categories support label-based inductive generalization in preschoolers

Why do words support inductive generalization in preschoolers? The current study provides evidence that they do so, at least in part, by working with conceptual knowledge to establish kind membership. A sample of 30 4-year-olds learned new labels for novel items, sometimes along with additional non-obvious information, and were then asked to generalize a novel object property to a target item based on either visual similarity or shared label. Children were more likely to generalize properties based on shared labels (over perceptual similarity) if they initially learned causally coherent properties of items referenced by those labels than if they initially learned non-causal properties of those items or learned no properties at all. This finding suggests that novel words best support inductive inference when they are known by children to reference conceptually coherent categories. Therefore, conceptual information permeates the process of inductive inference in young children. Results are discussed with respect to their implications for the "word-as-feature" and "knowledge-based" accounts of early inductive inference.

Building theory-based concepts: four-year-olds preferentially seek explanations for features of kinds

Is the structure of human concepts continuous across development, or does it undergo qualitative transformations? Extensive evidence with adults has demonstrated that they are motivated to understand why categories have the features they do. To investigate whether young children display a similar motivation-an issue that bears on the question of continuity vs. transformation in conceptual structure-we conducted three studies involving 4-year-olds (N=90) and adults (N=124). Experiments 1 and 2 suggested that 4-year-olds indeed display a strong motivation to explain why categories have the features they do. Specifically, when provided with the option of asking "why?" about features of novel categories vs. features of individuals from other novel categories, children preferred to ask "why?" about the category features. Moreover, children's explanatory preference was specific to facts about categories per se and did not extend to facts that were merely presented in the context of multiple category instances. Experiment 3 also ruled out the possibility that the category facts were preferred because these facts were more surprising. In sum, these three studies reveal an early-emerging motivation to make sense of the categories encountered in the world and, more generally, speak to the richness of children's conceptual representations.

Matching based on biological categories in Orangutans (Pongo abelii) and a Gorilla (Gorilla gorilla gorilla)

Following a series of experiments in which six orangutans and one gorilla discriminated photographs of different animal species in a two-choice touch screen procedure, Vonk & MacDonald (2002) and Vonk & MacDonald (2004) concluded that orangutans, but not the gorilla, seemed to learn intermediate level category discriminations, such as primates versus non-primates, more rapidly than they learned concrete level discriminations, such as orangutans versus humans. In the current experiments, four of the same orangutans and the gorilla were presented with delayed matching-to-sample tasks in which they were rewarded for matching photos of different members of the same primate species; golden lion tamarins, Japanese macaques, and proboscis monkeys, or family; gibbons, lemurs (Experiment 1), and subsequently for matching photos of different species within the following classes: birds, reptiles, insects, mammals, and fish (Experiment 2). Members of both Great Ape species were rapidly able to match the photos at levels above chance. Orangutans matched images from both category levels spontaneously whereas the gorilla showed effects of learning to match intermediate level categories. The results show that biological knowledge is not necessary to form natural categories at both concrete and intermediate levels.