Modeling individual differences using Dirichlet processes

We introduce a Bayesian framework for modeling individual differences, in which subjects are assumed to belong to one of a potentially infinite number of groups. In this model, the groups observed in any particular data set are not viewed as a fixed set that fully explains the variation between individuals, but rather as representatives of a latent, arbitrarily rich structure. As more people are seen, and more details about the individual differences are revealed, the number of inferred groups is allowed to grow. We use the Dirichlet process—a distribution widely used in nonparametric Bayesian statistics—to define a prior for the model, allowing us to learn flexible parameter distributions without overfitting the data, or requiring the complex computations typically required for determining the dimensionality of a model. As an initial demonstration of the approach, we present three applications that analyze the individual differences in category learning, choice of publication outlets, and web-browsing behavior.     

Factors contributing to individual differences in facial expression categorisation

Individuals vary in perceptual accuracy when categorising facial expressions, yet it is unclear how these individual differences in non-clinical population are related to cognitive processing stages at facial information acquisition and interpretation. We tested 104 healthy adults in a facial expression categorisation task, and correlated their categorisation accuracy with face-viewing gaze allocation and personal traits assessed with Autism Quotient, anxiety inventory and Self-Monitoring Scale. The gaze allocation had limited but emotion-specific impact on categorising expressions. Specifically, longer gaze at the eyes and nose regions were coupled with more accurate categorisation of disgust and sad expressions, respectively. Regarding trait measurements, higher autistic score was coupled with better recognition of sad but worse recognition of anger expressions, and contributed to categorisation bias towards sad expressions; whereas higher anxiety level was associated with greater categorisation accuracy across all expressions and with increased tendency of gazing at the nose region. It seems that both anxiety and autistic-like traits were associated with individual variation in expression categorisation, but this association is not necessarily mediated by variation in gaze allocation at expression-specific local facial regions. The results suggest that both facial information acquisition and interpretation capabilities contribute to individual differences in expression categorisation within non-clinical populations.     

Domain-specificity and individual differences in worry

Worrying is generally perceived to be an undesirable mental state. An evolutionary approach suggests, however, despite the potential distress, worry may function to focus individuals’ attention on evolutionarily-relevant tasks. In the current study (N = 193), we demonstrated that participants’ primary worries were focused within domains central to reproductive success and mate-value. Furthermore, mating strategy predicted worries in the domains of social status and mating. Neuroticism, as an individual difference reflecting vigilance to threats, was correlated with worry about fitness-relevant but not fitness-irrelevant domains. The current study documents the first domain-specific assessment of worries and complements this analysis with intriguing individual difference predictors of worry.     

Impact of individual differences upon emotion-induced memory trade-offs

After seeing a scene containing an emotional component (e.g., a snake in a forest) people often demonstrate a “trade-off” in memory, where memory for the emotional component (e.g., the snake) is good, but memory for the non-emotional elements (e.g., the forest) is poor. The result is an incomplete memory retaining central emotional information at the expense of neutral background information. Though almost everyone demonstrates the trade-off, there may be individual differences in the magnitude of the effect. We investigated whether differences in the strength of the trade-off would correlate with anxiety levels, working memory capacity, and executive functioning abilities. Sixty-four participants studied scenes comprised of a negative or neutral item placed on a neutral background, and memory was later tested for items and backgrounds separately. The magnitude of the trade-off correlated positively with anxiety and negatively with visuospatial working memory and executive function. These results suggest that greater anxiety, poor visuospatial working memory, and poor executive function may inhibit formation of complete mental representations of these complex emotional scenes.     

The factorial structure of individual differences in visual perception

Although at first glance the way we perceive the world is similar for most individuals and resembles a veridical interpretation of the environment, the persistent individual differences found in many perceptual processes continue to inspire and confuse researchers. Despite numerous attempts to map out the reliable factors and correlates of individual variance in perception, the factorial structure of vision has remained elusive. The current article reviews recent developments in the study of individual differences in perception with a focus on work that has applied latent variable techniques for analysing performance across multiple visual paradigms. As this overview reveals, studies that have attempted to answer the question whether one general or several specific factors best describe vision tend to reject the monolithic view. Some general notes are also provided regarding pitfalls that should be taken into account when designing such research in the future.     

Self-organizing individual differences in brain development

Brain development is self-organizing in that the unique structure of each brain evolves in unpredictable ways through recursive modifications of synaptic networks. In this article, I review mechanisms of neural change in real time and over development, and I argue that change at each of these time scales embodies principles of self-organizing systems. I demonstrate how corticolimbic configurations that emerge within occasions lay down synaptic structure across occasions, giving rise to individual trajectories that become entrenched with age. Emotions have a powerful influence on this process.This is because the neural processes mediating emotion consolidate patterns of activation across the brain, through their enhancement of inter-regional coordination in real time and their contribution to synaptic shaping over development. The loss of corticolimbic plasticity with age is an unfortunate fact of development, but it is compensated in part by transitional phases and individual learning experiences through which habits are modified or replaced. I emphasize variations in inter-systemic coupling as a key mediator of developing individual differences, and I discuss the acquisition of anxious/depressive appraisals as an example.     

Handedness differences in information framing

Previous research has shown that strength of handedness predicts differences in sensory illusions, Stroop interference, episodic memory, and beliefs about body image. Recent evidence also suggests handedness differences in the susceptibility to common decision biases such as anchoring and sunk cost. The present paper extends this line of work to attribute framing effects. Sixty-three undergraduates were asked to advise a friend concerning the use of a safe allergy medication during pregnancy. A third of the participants received negatively-framed information concerning the fetal risk of the drug (1–3% chance of having a malformed child); another third received positively-framed information (97–99% chance of having a normal child); and the final third received no counseling information and served as the control. Results indicated that, as predicted, inconsistent (mixed)-handers were more responsive than consistent (strong)-handers to information changes and readily update their beliefs. Although not significant, the data also suggested that only inconsistent handers were affected by information framing. Theoretical implications as well as ongoing work in holistic versus analytic processing, contextual sensitivity, and brain asymmetry will be discussed.     

Sustained attention in language production: An individual differences investigation

Whereas it has long been assumed that most linguistic processes underlying language production happen automatically, accumulating evidence suggests that these processes do require some form of attention. Here we investigated the contribution of sustained attention: the ability to maintain alertness over time. In Experiment 1, participants’ sustained attention ability was measured using auditory and visual continuous performance tasks. Subsequently, employing a dual-task procedure, participants described pictures using simple noun phrases and performed an arrow-discrimination task while their vocal and manual response times (RTs) and the durations of their gazes to the pictures were measured. Earlier research has demonstrated that gaze duration reflects language planning processes up to and including phonological encoding. The speakers’ sustained attention ability correlated with the magnitude of the tail of the vocal RT distribution, reflecting the proportion of very slow responses, but not with individual differences in gaze duration. This suggests that sustained attention was most important after phonological encoding. Experiment 2 showed that the involvement of sustained attention was significantly stronger in a dual-task situation (picture naming and arrow discrimination) than in simple naming. Thus, individual differences in maintaining attention on the production processes become especially apparent when a simultaneous second task also requires attentional resources.     

Understanding causal conditionals: A study of individual differences

Previous studies have suggested that a minority of university students, of lower cognitive ability, are inclined to interpret abstract conditional statements, if p then q, as if they were conjunctions: p and q. In the present study we administered the conditional truth table task to a large sample of students (n = 160), but using realistic, everyday causal conditionals. We also measured their general intelligence. While individual differences were found, these were not consistent with some participants adopting a conjunctive interpretation of such statements. Rather, it appears that students of lower cognitive ability are rather likely to assume that a conditional implies its converse, so that it means also if q then p. The results are discussed with reference to the suppositional theory of conditionals and our more general account of hypothetical thinking.     

Developmental analyses of individual differences in intelligence: Comments on Demetriou et al. (2013)

In this commentary, I mention strengths of the work reported by Demetriou et al. (2013), including sophisticated methods, a powerful integrative theory, and provocative findings. I also suggest ways in which this line of work could be extended, including extending the developmental trajectory, moving beyond tests and tasks, and exploring the full richness of individual variations.     

Dissociative style and individual differences in verbal working memory span

Dissociative style is mostly studied as a risk factor for dissociative pathology, but it may also reflect a fundamental characteristic of healthy information processing. Due to the close link between attention and working memory and the previous finding of enhanced attentional abilities with a high dissociative style, a positive relationship was also expected between dissociative style and verbal working memory span. In a sample of 119 psychology students, it was found that the verbal span of the high-dissociative group was about half a word larger than of the medium and low-dissociative groups. It is suggested that dissociative style may be one of only very few individual differences that is directly relevant to consciousness research.     

An individual differences analysis of the self-teaching hypothesis

The self-teaching hypothesis suggests that children learn orthographic structure of words through the experience of phonologically recoding them. The current study is an individual differences analysis of the self-teaching hypothesis. A total of 40 children in Grades 2 and 3 (7-9 years of age) completed tests of phonological recoding, word identification, and orthographic knowledge. The relation of phonological recoding and word identification was significantly mediated by orthographic knowledge. Furthermore, two aspects of orthographic knowledge (perhaps word-specific and general orthographic knowledge) mediated different variance shared between phonological recoding and word identification. Results support an individual differences version of the self-teaching hypothesis and emphasize the importance of phonological recoding in the primary curriculum.     

When logic and belief collide: Individual differences in reasoning times support a selective processing model

When the validity of a deductive conclusion conflicts with its believability people often respond in a belief-biased manner. This study used response times to test the selective processing model, which views belief-bias effects as arising from the interplay between superficial heuristic processes and more rigorous analytic processes. Participants were split into three response groups according to their propensity to endorse logically normative conclusions. The low-logic, high belief-bias group demonstrated rapid responding, consistent with heuristic processing. The medium-logic, moderate belief-bias group showed slower responding, consistent with enhanced analytic processing, albeit selectively biased by conclusion believability. The high-logic, low belief-bias group's relatively unbiased responses came at the cost of increased processing times, especially with invalid-believable conclusions. These findings support selective processing claims that distinct heuristic and analytic processing systems underpin reasoning, and indicate that certain individuals differentially engage one system more than the other. A minor amendment is proposed to the current selective processing model to capture the full range of observed effects.     

Measuring individual differences in sensitivities to basic emotions in faces

The assessment of individual differences in facial expression recognition is normally required to address two major issues: (1) high agreement level (ceiling effect) and (2) differential difficulty levels across emotions. We propose a new assessment method designed to quantify individual differences in the recognition of the six basic emotions, 'sensitivities to basic emotions in faces.' We attempted to address the two major assessment issues by using morphing techniques and item response theory (IRT). We used morphing to create intermediate, mixed facial expression stimuli with various levels of recognition difficulty. Applying IRT enabled us to estimate the individual latent trait levels underlying the recognition of respective emotions (sensitivity scores), unbiased by stimulus properties that constitute difficulty. In a series of two experiments we demonstrated that the sensitivity scores successfully addressed the two major assessment issues and their concomitant individual variability. Intriguingly, correlational analyses of the sensitivity scores to different emotions produced orthogonality between happy and non-happy emotion recognition. To our knowledge, this is the first report of the independence of happiness recognition, unaffected by stimulus difficulty.     

The role of individual differences in emotion regulation efficacy

Emotion regulation (ER) helps to maintain mental health and achieve optimal functioning. Whether people benefit from various ER strategies may depend on individual difference variables. A sample of undergraduates (N = 378, M_age = 18.6) underwent a negative emotion induction and then were assigned to learn about and perform an ER strategy (cognitive reappraisal, acceptance, or distraction). We tested whether individual differences (cognitive restructuring skills, need for cognition, mindfulness, and experiential avoidance) moderated the efficacy of ER (i.e., decreased negative emotion from before to after applying the strategy). Experientially avoidant individuals had less efficacy in applying the acceptance strategy, compared to the cognitive reappraisal and distraction strategies. Motivation and perceived ability to use each strategy were examined as mediators.     

Executive functions in decision making: An individual differences approach

This individual differences study examined the relationships between three executive functions (updating, shifting, and inhibition), measured as latent variables, and performance on two cognitively demanding subtests of the Adult Decision Making Competence battery: Applying Decision Rules and Consistency in Risk Perception. Structural equation modelling showed that executive functions contribute differentially to performance in these two tasks, with Applying Decision Rules being mainly related to inhibition and Consistency in Risk Perception mainly associated to shifting. The results suggest that the successful application of decision rules requires the capacity to selectively focus attention and inhibit irrelevant (or no more relevant) stimuli. They also suggest that consistency in risk perception depends on the ability to shift between judgement contexts.     

Using the process dissociation procedure to estimate recollection and familiarity in working memory: An experimental and individual differences investigation

Numerous studies have found that working memory capacity and perceptual speed predict variation in fluid intelligence. Within the cognitive ageing literature, perceptual speed accounts for substantial ageing variance in working memory capacity and fluid intelligence. However, within young adults, the interrelationships among these three abilities are less clear. The current work investigated these relationships via confirmatory factor analyses and structural equation modelling using tasks with verbal, spatial, and numerical content. The results indicate that working memory capacity and perceptual speed were not related in a large, cognitively diverse sample of young adults. However, both working memory capacity and perceptual speed accounted for unique variance in fluid intelligence. The results are discussed in relation to previous research with young and older adults.     

Common and distinct factors in decision making under ambiguity and risk: A psychometric study of individual differences

The relation between decision making under ambiguity and risky decision making was examined. In Studies 1 and 2, choices under ambiguity were measured for a large sample receiving an Ellsberg-type Ambiguity-Probability Tradeoff Task. Participants with extreme scores were recruited for Part 2 of each study which consisted of a risky decision making task (Study 1) or a series of decisions under ambiguity in “real life” scenarios (Study 2). Despite a time gap of up to 2 months, individual differences in scores on Part 1 predicted scores on Part 2. In Study 3 participants received in a single session several risky decision making tasks, several measures of decision making under ambiguity, and several personality scales related to uncertainty and decision making style. Taken together, the findings support the existence of a stable dispositional trait to reduce uncertainty in decision making but also task-specific differences related to gains and losses.