Andy Wills

• University of Plymouth

The inverse base-rate effect (IBRE) is an irrational phenomenon in predictive learning. It occurswhen people try to generalize what they have experienced to novel and ambiguous events. Thisirrational generalization manifests as a preference for rare, unlikely outcomes in the face ofambiguity. At least two formal mathematical models of this irration...

Previous work has shown that deferring feedback significantly impairs two-dimensional information-integration category learning, often thought to recruit an implicit learning system, but leaves intact unidimensional rule-based learning, commonly assumed to engage an explicit system. These results were taken to support the influential COmpetition be...

Models are often evaluated when their behavior is at its closest to a single, sometimes averaged, set of empirical results, but this evaluation neglects the fact that both model and human behavior can be heterogeneous. Here, we develop a measure, g-distance, which considers model adequacy as the extent to which models exhibit a similar range of beh...

The inverse base-rate effect (IBRE) is an irrational phenomenon in predictive learning. It occurs when people try to generalize what they have experienced to novel and ambiguous events. This irrational generalization manifests as a preference for rare, unlikely outcomes in the face of ambiguity. At least two formal mathematical models of this irrat...

Models are often evaluated when their behavior is at its closest to a single, sometimes averaged, set of empirical results, but this evaluation neglects the fact that both model and human behavior can be heterogeneous. Here, we develop a measure, g-distance, which considers model adequacy as the extent to which models exhibit a similar range of beh...

Previous work has shown that deferring feedback significantly impairs two-dimensional information-integration category learning, often thought to recruit an implicit learning system, but leaves intact unidimensional rule-based learning, commonly assumed to engage an explicit system (Smith et al., 2014). These results were taken to support the influ...

Early diagnosis and intervention for Autism Spectrum Disorder (ASD) has been shown to significantly improve the quality of life of autistic individuals. However, diagnostics methods for ASD rely on assessments based on clinical presentation that are prone to bias and can be challenging to arrive at an early diagnosis. There is a need for objective...

Flexible, adaptive behaviour depends on the application of prior learning to novel contexts (transfer). Transfer can take many forms, but the focus of the present study was on ‘task schemas’ – learning strategies that guide the earliest stages of engaging in a novel task. The central aim was to examine the architecture of task schemas and determine...

The inverse base-rate effect (IBRE) is an irrational phenomenon in predictive learning. It occurswhen people try to generalize what they have experienced to novel and ambiguous events. Thisirrational generalization manifests as a preference for rare, unlikely outcomes in the face ofambiguity. At least two formal mathematical models of this irration...

The inverse base-rate effect is a robust irrational bias that arises when people face ambiguity. The most prominent theories of this irrational bias depend on prediction error. In this study, we gradually removed elements of a predictive learning design to test the extent to which error-driven processes underlie this bias. In our first experiment,...

Models are often evaluated when their behavior is at its closest to a single, sometimes averaged, set of empirical results, but this evaluation neglects the fact that both model and human behavior can be heterogeneous. Here, we develop a measure, g-distance, which considers model adequacy as the extent to which models exhibit a similar range of beh...

Models are often evaluated when their behavior is at its closest to a single, sometimes averaged, set of empirical results, but this evaluation neglects the fact that both model and human behavior can be heterogeneous. Here, we develop a measure, g-distance, which considers model adequacy as the extent to which models exhibit a similar range of beh...

In order to create a basis for consensus on which of the many empirical findings working memory (WM) research has produced, Oberauer et al. (2018) have collaborated on identifying and classifying benchmark findings that every theory of WM should strive to explain. We introduce the 'BenchmarksWM' R data package that includes datasets demonstrating t...

Guessing an answer to an unfamiliar question prior to seeing the answer leads to better memory than studying alone (the pre-testing effect), which some theories attribute to increased curiosity. A similar effect occurs in general knowledge learning: people are more likely to recall information that they were initially curious to learn. Gruber and R...

The Inverse Base Rate Effect (IBRE) is a non-rational behavioural phenomenon in predictive learning. In the IBRE, participants learn that a stimulus compound AB leads to one outcome and that another compound AC leads to a different outcome. Importantly, AB and its outcome are presented three times as often as AC (and its outcome). On test, when ask...

Theories of associative learning often propose that learning is proportional to prediction error, or the difference between expected events and those that occur. Spicer et al. (2020) suggested an alternative, that humans might instead selectively attribute surprising outcomes to cues that they are not confident about, to maintain cue-outcome associ...

The inverse base rate effect (IBRE) is a nonrational behavioral phenomenon in predictive learning. Canonically, participants learn that the AB stimulus compound leads to one outcome and that AC leads to another outcome, with AB being presented three times as often as AC. When subsequently presented with BC, the outcome associated with AC is prefere...

We introduce the CAL model (Category Abstraction Learning), a cognitive framework formally describing category learning built on similarity-based generalization, dissimilarity-based abstraction, two attention learning mechanisms, error-driven knowledge structuring, and stimulus memorization. Our hypotheses draw on an array of empirical and theoreti...

Relative to studying alone, guessing the meanings of unknown words can improve later recognition of their meanings, even if those guesses were incorrect - the pretesting effect (PTE). The error-correction hypothesis suggests that incorrect guesses produce error signals that promote memory for the meanings when they are revealed. The current researc...

Spicer et al. (2020) reported a series of causal learning experiments in which participants appeared to learn most readily about cues when they were not certain of their causal status and proposed that their results were a consequence of participants’ use of theory protection. In the present issue, Chan et al. (2021) present an alternative view, us...

It is generally assumed that the Rescorla and Wagner (1972) model adequately accommodates the full results of simple cue competition experiments in humans (e.g. Dickinson et al., 1984), while the Bush and Mosteller (1951) model cannot. We present simulations that demonstrate this assumption is wrong in at least some circumstances. The Rescorla-Wagn...

It is generally assumed that the Rescorla and Wagner (1972) model adequately accommodates the full results of simple cue competition experiments in humans (e.g. Dickinson et al., 1984), while the Bush and Mosteller (1951) model cannot. We present simulations that demonstrate this assumption is wrong in at least some circumstances. The Rescorla-Wagn...

Integral stimuli (e.g. colours varying in saturation and brightness) are classically considered to be processed holistically (i.e. as undifferentiated stimulus wholes); people analyze such stimuli into their consistent dimensions only with substantial time, effort, training, or instruction (Foard & Kemler Nelson, 1984). In contrast, Combination The...

Analogical transfer has been previously reported to occur between rule-based, but not information-integration, perceptual category structures (Casale, Roeder, & Ashby, 2012). The current study investigated whether a similar pattern of results would be observed in cross-modality transfer. Participants were trained on either a rule-based structure, o...

Polymorphous concepts are hard to learn, and this is perhaps surprising because they, like many natural concepts, have an overall similarity structure. However, the dimensional summation hypothesis (Milton and Wills Journal of Experimental Psychology: Learning, Memory and Cognition, 30, 407–415 2004) predicts this difficulty. It also makes a number...

Attempting to retrieve the answer to a question on an initial test can improve memory for that answer on a subsequent test, relative to an equivalent study period. Such retrieval attempts can be beneficial even when they are unsuccessful, although this benefit is usually only seen with related word pairs. Three experiments examined the effects of p...

Polymorphous concepts are hard to learn, and this is perhaps surprising because they, like many natural concepts, have an overall similarity structure. However, the dimensional summation hypothesis (Milton & Wills, 2004) predicts this difficulty. It also makes a number of other predictions about polymorphous concept formation, which are tested here...

Research investigating transfer of strategies between unique tasks with a similar structure has tended to focus on the entire strategy rather than strategic task components. We investigated how different kinds of training affected performance at test where participants classified dot patterns according to their similarity to category templates by e...

Three experiments were conducted to investigate a possible role for certainty in human causal learning. In these experiments, human participants were initially trained with a set of cues, each of which was followed by the presence or absence of an outcome. In a subsequent training stage, 2 of these cues were trained in a causal compound, and the ch...

This article examines the effect that prior exposure to perceptual stimuli has on the prevalence of overall similarity (family resemblance) categorization. Experiment 1 demonstrated that participants who had previously encountered stimuli produced more overall similarity sorting when asked to free classify them than participants who were preexposed...

The Inverse Base Rate Effect (IBRE; Medin and Edelson (1988)) is a non-rational behavioural phenomenon in predictive learning. In the IBRE, participants learn that a stimulus compound AB leads to one outcome and that another compound AC leads to a different outcome. Importantly, AB and its outcome are presented three times as often as AC (and its o...

The current research examined the effects of errorful generation on memory, focusing particularly on the roles of motivation and surprise. In two experiments, participants were first presented with photographs of faces and were asked to associate four facts with each photograph. On Generate trials, the participants guessed two of the facts (Guess t...

Smith and Church (2018) present a “testimonial” review of dissociable learning processes in comparative and cognitive psychology, by which we mean they include only the portion of the available evidence that is consistent with their conclusions. For example, they conclude that learning the information-integration category-learning task with immedia...

The Inverse Base Rate effect (IBRE; Medin & Edelson, 1988) is a non-rational behavioral phenomenon in predictive learning. Canonically, participants learn that the AB stimulus compound leads to one outcome and that AC leads to another outcome, with AB being presented three times as often as AC. When subsequently presented with BC, the outcome assoc...

Analogical transfer occurs when someone transfers insights about shared structure from one task to another. Here, we explore this ability in categorization tasks. Previous work found that people could transfer knowledge between two unidimensional rule-based tasks, but could not for two information-integration tasks. In four experiments, we extended...

Potts and Shanks (2014) recently reported that making mistakes improved the encoding of novel information compared with simply studying. This benefit of generating errors is counterintuitive, since it resulted in less study time and more opportunity for proactive interference. Five experiments examined the effect of generating errors versus studyin...

The extent to which human outcome-response (O-R) priming effects are automatic or under cognitive control is currently unclear. Two experiments tested the effect of cognitive load on O-R priming to shed further light on the debate. In Experiment 1, two instrumental responses earned beer and chocolate points in an instrumental training phase. Instru...

In this paper, we introduce CALM, a process model that is designed to abstract solutions in simple and complex category learning tasks. The model includes strong assumptions about the interaction of processes driving learning behavior, typically addressed in terms of feature attention, stimulus generalization , rule abstraction and knowledge partit...

Learning theorists posit two reinforcement learning systems: model-free and model-based. Model-based learning incorporates knowledge about structure and contingencies in the world to assign candidate actions with an expected value. Model-free learning is ignorant of the world's structure; instead, actions hold a value based on prior reinforcement,...

Two experiments investigated what makes it more likely that pigeons’ behavior will come under the control of multiple relevant visual stimulus dimensions. Experiment 1 investigated the effect of stimulus set structure, using a conditional discrimination between circles that differed in both hue and diameter. Two training conditions differed in whet...

Behavioral evidence for the COVIS dual‐process model of category learning has been widely reported in over a hundred publications (Ashby & Valentin, 2016). It is generally accepted that the validity of such evidence depends on the accurate identification of individual participants' categorization strategies, a task that usually falls to Decision Bo...

In the phenomenon of transfer along a continuum (TAC), initial training on easy items facilitates later learning of a harder discrimination. TAC is a widely replicated cross-species phenomenon that is well predicted by certain kinds of associative theory (e.g., Sutherland & Mackintosh, 1971). A recent report of an approximately-opposite phenomenon...

Although instructions often emphasize categories (e.g., odd number → left hand response) rather than specific stimuli (e.g., 3 → left hand response), learning is often interpreted in terms of stimulus-response (S-R) bindings or, less frequently, stimulus-classification (S-C) bindings with little attention being paid to the importance of category-re...

publisher: Elsevier articletitle: In Defence of Effect-Centric Research journaltitle: Journal of Applied Research in Memory and Cognition articlelink: http://dx.doi.org/10.1016/j.jarmac.2016.10.005 content_type: simple-article copyright: © 2016 Society for Applied Research in Memory and Cognition. Published by Elsevier Inc. All rights reserved.

Traditionally it has been thought that the overall organisation of categories in the brain is taxonomic. To examine this assumption, we had adults sort 140–150 diverse, familiar objects from different basic-level categories. Almost all the participants (80/81) sorted the objects more thematically than taxonomically. Sorting was only weakly modulate...

Formal modeling in psychology is failing to live up to its potential due to a lack of effective collaboration. As a first step towards solving this problem, we have produced a set of freely available tools for distributed collaboration. This article describes those tools and the conceptual framework behind them. We also provide concrete examples of...

The idea that there are multiple learning systems has become increasingly influential in recent years, with many studies providing evidence that there is both a quick, similarity-based or feature-based system and a more effortful rule-based system. A smaller number of imaging studies have also examined whether neurally dissociable learning systems...

This article presents a comprehensive survey of research concerning interactions between associative learning and attention in humans. Four main findings are described. First, attention is biased toward stimuli that predict their consequences reliably (learned predictiveness). This finding is consistent with the approach taken by Mackintosh (1975)...

Objective: Generalization is the application of existing knowledge to novel situations. Questions remain about the precise role of the hippocampus in this facet of learning, but a connectionist model by Gluck and Myers (1993) predicts that generalization should be enhanced following hippocampal damage. Method: In a two-category learning task, a...

The influential competition between verbal and implicit systems (COVIS) model proposes that category learning is driven by two competing neural systems-an explicit, verbal, system, and a procedural-based, implicit, system. In the current fMRI study, participants learned either a conjunctive, rule-based (RB), category structure that is believed to e...

Inhibitory processes have been implicated in depressive rumination. Inhibitory deficits may cause difficulties in disengaging from ruminative content (e.g., Joormann, 2005), or rumination may constitute a working memory load, causing deficits in inhibitory control (e.g., Hertel, 2004). These hypotheses have different implications for the treatment...

Some argue that category learning is mediated by two competing learning systems: one explicit, one implicit (Ashby et al., 1998). These systems are hypothesised to be responsible for learning rule-based and information-integration category structures respectively. However, little experimental work has directly investigated whether people are consci...

This paper examines the ability of a dual-system, formal model of categorization COVIS (Ashby, Paul & Maddox, 2011) to predict the learning performance of participants on the six category structures described in Shepard, Hovland and Jenkin's (1961) seminal study. COVIS assumes that category learning is mediated by two dissociable neural systems tha...

Does cognition begin with an undifferentiated stimulus whole, which can be divided into distinct attributes if time and cognitive resources allow (Differentiation Theory)? Or does it begin with the attributes, which are combined if time and cognitive resources allow (Combination Theory)? Across psychology, use of the terms analytic and non-analytic...

Humans can spontaneously create rules that allow them to efficiently generalize what they have learned to novel situations. An enduring question is whether rule-based generalization is uniquely human or whether other animals can also abstract rules and apply them to novel situations. In recent years, there have been a number of high-profile claims...

Two theories explain how negative mood primes smoking behaviour. The stimulus-response (S-R) account argues that in the negative mood state, smoking is experienced as more reinforcing, establishing a direct (automatic) association between the negative mood state and smoking behaviour. By contrast, the incentive learning account argues that in the n...

The effects of two different types of training on rule-based and information-integration category learning were investigated in two experiments. In observational training, a category label is presented, followed by an example of that category and the participant's response. In feedback training, the stimulus is presented, the participant assigns it...

Some argue the common practice of inferring multiple processes or systems from a dissociation is flawed (Dunn, 2003). One proposed solution is state-trace analysis (Bamber, 1979), which involves plotting, across two or more conditions of interest, performance measured by either two dependent variables, or two conditions of the same dependent measur...

We report the first electrophysiological investigation of the inverse base-rate effect (IBRE), a robust non-rational bias in predictive learning. In the IBRE, participants learn that one pair of symptoms (AB) predicts a frequently occurring disease, whilst an overlapping pair of symptoms (AC) predicts a rarely occurring disease. Participants subseq...

Yeates, Jones, Wills, Aitken, McLaren and McLaren (2012) devised a serial reaction time (SRT) task that provided evidence for human learning without awareness. Adapting the SRT paradigm usually employed to investigate implicit learning, participants responded to two simple white circle fills on either side of a screen. Instead of these following a...

This research explored the role that associative learning may play in human sequence learning. Two-choice serial reaction time tasks were performed under incidental conditions using 2 different sequences. In both cases, an experimental group was trained on 4 subsequences: LLL, LRL, RLR, and RRR for Group "Same" and LLR, LRR, RLL, and RRL for Group...

Vanpaemel and Lee (2012) argued, and we agree, that the comparison of formal models can be facilitated by Bayesian methods. However, Bayesian methods neither precede nor supplant our proposals (Wills & Pothos, 2012), as Bayesian methods can be applied both to our proposals and to their polar opposites. Furthermore, the use of Bayesian methods to co...

It is sometimes argued that the implementation of an overall similarity classification is less effortful than the implementation of a single-dimension classification. In the current article, we argue that the evidence securely in support of this view is limited, and report additional evidence in support of the opposite proposition-overall similarit...

This study investigated the use of state-trace analysis (Bamber, 1979) when applied to computational models of human learning. We aimed to investigate the performance of simple recurrent networks (SRNs) on a sequence learning task. Elman’s (1990) SRN and Cleeremans & McClelland’s (1991) Augmented SRN are both benchmark models of human sequence lear...

Evidence for human learning without awareness of what is learned has been sought in serial reaction time (SRT) tasks in which, unknown to participants, the locations of stimuli follow a particular rule or sequence (Willingham, Nissen & Bullemer, 1989). A number of criticisms have been levelled at such tasks, including a lack of adequate control for...

Categorization is one of the fundamental building blocks of cognition, and the study of categorization is notable for the extent to which formal modeling has been a central and influential component of research. However, the field has seen a proliferation of noncomplementary models with little consensus on the relative adequacy of these accounts. P...

Unitization, the creation of new stimulus features by the fusion of preexisting features, is one of the hypothesized processes of perceptual learning (Goldstone Annual Review of Psychology, 49:585-612, 1998). Some argue that unitization occurs to the extent that it is required for successful task performance (e.g., Shiffrin & Lightfoot, 1997), whil...

We argue for an example of "core cognition" based on Diamond and Carey's (1986) work on expertise and recognition, which is not made use of in The Origin of Concepts. This mechanism for perceptual learning seems to have all the necessary characteristics in that it is innate, domain-specific (requires stimulus sets possessing a certain structure), a...

The effect of concurrent load on generalization performance in human contingency learning was examined in 2 experiments that employed the combined positive and negative patterning procedure of Shanks and Darby (1998). In Experiment 1, we tested 32 undergraduates and found that participants who were trained and tested under full attention showed gen...

Demonstrations of retrospective revaluation suggest that remembered stimuli undergo a reduction in association with the unconditioned stimulus (US) present during learning. Conversely, demonstrations of mediated conditioning in flavor-conditioning experiments with rats suggest that remembered stimuli undergo an increase in association with the US p...

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell...

A free classification study is presented in which the effect of time pressure and the spatial integration of the stimulus dimensions on overall similarity sorting is investigated. A 2 x 2 between-subjects factorial design was employed with the factors being the level of time pressure (high/low) and the spatial integration of the stimulus dimensions...

1. Introduction Emmanuel M. Pothos and Andy J. Wills 2. The generalized context model: an exemplar model of classification Robert M. Nosofsky 3. Prototype models of categorization: basic formulation, predictions, and limitations John Paul Minda and J. David Smith 4. COVIS F. Gregory Ashby, Erick J. Paul and W. Todd Maddox 5. Semantics without categ...

In an artificial grammar learning (AGL) experiment, participants were trained with instances of one grammatical structure before completing a test phase in which they were required to discriminate grammatical from randomly created strings. Importantly, the underlying structure used to generate test strings was different from that used to generate t...

Pigeons (Columba livia), gray squirrels (Sciurus carolinensis), and undergraduates (Homo sapiens) learned discrimination tasks involving multiple mutually redundant dimensions. First, pigeons and undergraduates learned conditional discriminations between stimuli composed of three spatially separated dimensions, after first learning to discriminate...

Pigeons and undergraduates learned conditional discriminations involving multiple spatially separated stimulus dimensions. Under some conditions, the dimensions were made available sequentially. In 3 experiments, the dimensions were all perfectly valid predictors of the response that would be reinforced and mutually redundant; in 2 others, they var...

Previous laboratory studies on social learning suggest that some animals can learn more readily if they first observe a conspecific demonstrator perform the task unsuccessfully and so fail to obtain a food reward than if they observe a successful demonstrator that obtains the food. This effect may indicate a difference in how easily animals are abl...

Contemporary theories of learning typically assume that learning is driven by prediction errors—in other words, that we learn more when our predictions turn out to be incorrect than we do when our predictions are correct. Results from the recording of electrical brain activity suggest one mechanism by which this might happen; we seem to direct visu...

The ability to group stimuli into meaningful categories is fundamental to natural behavior. Raw perceptions would be useless without an ability to classify items as, for example, threat or food. Previous work suggests that people have a tendency to group stimuli either on the basis of a single dimension or by overall similarity (e.g., Milton, F.N.,...

Two free classification experiments that investigate the persistence of sort strategy are reported. Participants tend to persist with their initial categorization type (family resemblance or unidimensional) for the remaining sorts, overriding the effects of otherwise influential stimulus properties. Sort type was found to persist even after a one-w...

The processes of overall similarity sorting were investigated in 5 free classification experiments. Experiments 1 and 2 demonstrated that increasing time pressure can reduce the likelihood of overall similarity categorization. Experiment 3 showed that a concurrent load also reduced overall similarity sorting. These findings suggest that overall sim...

Many naturally occurring categories vary across multiple stimulus dimensions (e.g. size, color, texture). When humans cat- egorize multidimensional stimuli on the basis of a single dimension this has been taken to indicate use of a rule that could be verbalized. Sorting on the basis of all the stimulus dimensions ('overall similarity' or 'family re...

Recent neuropsychological evidence, supporting a strong version of Whorfian principles of linguistic relativity, has reinvigorated debate about the role of language in colour categorisation. This paper questions the methodology used in this research and uses a novel approach to examine the unique contribution of language to categorisation behaviour...