Stable individual differences in number discrimination in infancy

Previous studies have shown that as a group 6-month-old infants successfully discriminate numerical changes when the values differ by at least a 1:2 ratio but fail at a 2:3 ratio (e.g. 8 vs. 16 but not 8 vs. 12). However, no studies have yet examined individual differences in number discrimination in infancy. Using a novel numerical change detection paradigm, we present more direct evidence that infants' numerical perception is ratio-dependent even within the range of discriminable ratios and thus adheres to Weber's Law. Furthermore, we show that infants' numerical discrimination at 6 months reliably predicts their numerical discrimination abilities but not visual short-term memory at 9 months. Thus, individual differences in numerical discrimination acuity may be stable within the first year of life and provide important avenues for future longitudinal research exploring the relationship between infant numerical discrimination and later developing math achievement.     

Stable individual differences across images in human saccadic eye movements.

Individual differences in eye movements during picture viewing were examined across image format, content, and foveal quality in 3 experiments. Experiment 1 demonstrated that an individual's fixation durations were strongly related across 3 types of scene formats and that saccade amplitudes followed the same pattern. In Experiment 2, a similar relationship was observed for fixation durations across faces and scenes, although the amplitude relationship did not hold as strongly. In Experiment 3, the duration and amplitude relationships were observed when foveal information was degraded and even removed. Eye movement characteristics differ across individuals, but there is a great deal of consistency within individuals when viewing different types of images.     

Examination of relationships among trait-like individual differences, state-like individual differences, and learning performance

Several authors (e.g., J.T. Austin & H.J. Klein, 1996; R. Kanfer, 1990b, 1992) have urged researchers to examine comprehensive models of distal individual differences as predictors of proximal motivational processes and performance. Two field studies in an academic setting tested a model of relationships among trait-like individual differences (cognitive ability, general self-efficacy, and goal orientation), state-like individual differences (state anxiety, task-specific self-efficacy, and goals), and learning performance. Most hypothesized relationships among these constructs received support when tested on 2 samples, when examining different performance episodes, and when using different goal orientation and state-anxiety measures. In general, state-like individual differences were found to mediate the relationships between trait-like individual differences and learning performance. Implications of these results are discussed and suggestions for future research are provided.     

Omission bias, individual differences, and normality

Omission bias is the preference for harm caused by omissions over equal or lesser harm caused by acts. Recent articles (Connolly & Reb, 2003; Patt & Zeckhauser, 2000; Tanner & Medin, in press) have raised questions about the generality of this phenomenon and have suggested that the opposite bias (action bias) sometimes exists. Prentice and Koehler (2003) have suggested that omission bias is sometimes confounded with a bias toward what is normal, a bias they find. We review this literature and report new data showing omission bias with appropriate methods, as well as a small normality bias that cannot explain the omission bias. The data suggest that the bias is largely based on the distinction between direct and indirect causation, rather than that between action and inaction as such. We report substantial individual differences: some subjects show action bias. We argue, though, that concern about omission bias is justified if only a substantial minority of people show it.     

Parsing the relations between SES and stress reactivity: examining individual differences in neonatal stress response

In an effort to further delineate the reported relations between socioeconomic status (SES) and stress reactivity in children, associations between three domains of perinatal risk: socio-demographic, obstetrical complications, and maternal psychological factors during the perinatal period, and cortisol and behavioral reactivity were examined in 100 healthy African American neonates whose families resided in low-income environments. Behavioral and cortisol response to a heel stick and the Neonatal Behavioral Assessment Scale (NBAS) was measured within the first 2 days of life. Significant associations were found between socio-demographic risk, obstetrical complications, and maternal psychological factors and neonatal behavior and cortisol in the context of the NBAS; few significant associations were found in the context of the heel stick. Greater magnitude of perinatal risk was associated with both higher and lower than average neonatal stress reactivity. The results provide preliminary data on the types of perinatal experiences that may have significant effects on stress reactivity in humans, especially in the context of families living in poverty. Application of these data to the hypothesis that prenatal stress results in programming of the fetal/neonatal stress response system is discussed.     

Extraversion,neuroticism and individual differences in event-related potentials

Event-related potentials (ERPs) in response to task-irrelevant tone pips were elicited during meaningful and meaningless speech passages for two groups of subjects selected on the basis of their scores on the extraversion-introversion scale of the Eysenck Personality Questionnaire, ERPs were recorded from two temporal (T3 and T4) and Wernicke (W1 and W2) scalp locations. Peak latencies and amplitudes of N1, P2 and N2 components were obtained for each subject during each meaningful and meaningless condition. The extraverts exhibited higher levels of subjective engagement in the meaningful-speech condition than in meaningless condition; the opposite trend was found for introverts. The extraverts showed greater N2 amplitude in the meaningful-speech condition than in the meaningless condition; the reverse trend across conditions was found for introverts.     

Age, gender, and individual differences in memory failure appraisal

Young adults (22 men and 24 women) and older adults (24 men and 24 women) rated 12 gender-neutral vignettes describing short-term, long-term, and very-long-term memory failures. Vignette target persons were young (21-32) or older (65-75) men or women. Subjects of both age and gender groups used a double standard: Failures of older targets of both genders were rated as signifying greater mental difficulty than failures of young targets; failures of young targets were attributed to lack of effort and attention. Young subjects judged very-long-term failures more harshly than did older subjects. Subjects' objective memory performance, self-rated memory failure frequency, memory failure discomfort, and depression made little difference in their target person ratings.     

Process differences and individual differences in some cognitive tasks

This study is based on three distinct elementary cognitive tasks (ECTs) using chronometric techniques: (a) the S. Sternberg memory scan task, (b) a visual scan task which is perfectly analogous to the memory scan, except that the target digit is presented first and the subject must then scan a set of digits and indicate the presence or absence of the target digit in the set, and (c) the Hick paradigm, which involves responding to a visual stimulus (a light going “on”) when the stimulus is one among sets of either 1, 2, 4, or 8 equally probable alternatives. Certain parameters of all three tasks, such as intercept and slope of RT as a function of set size, from which different cognitive processes are inferred, are compared experimentally and correlationally. Subjects were 48 university students, tested and retested on the three tasks in a counterbalanced design on two separate days to obtain the retest reliabilities needed to correct all correlations for attenuation. Subjects were also given Raven's Advanced Progressive Matrices as a measure of psychometric g. Parameters of the ECTs are significantly and, in some cases, quite substantially correlated with g. Virtually all of this correlation is due to the general factor of the various ECTs, rather than to specific processing components (independent of the general factor). The results also indicate that different ECT paradigms (e.g., visual search and memory search tasks) may yield markedly different values in terms of the group means of analogous parameters, indicating different processes, and yet not show independence of the parameters in terms of individual differences; that is, measurements of the different parameters in individuals are perfectly correlated (i.e., disattenuated correlations do not differ significantly from r = 1). This is found for the intercept parameter of visual and memory search. The reverse condition is also found for the other parameters (e.g., slope); that is, their mean values are nearly identical, suggesting the same processes, yet disattenuated correlations between individual differences are relatively low, or even negative, indicating different processes. Although the general factor clearly predominates, it does not completely overwhelm individual differences in various component processes that are distinct from the general factor.     

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.     

Trade-offs, individual differences, and misunderstandings about evolutionary psychology

Replies to comments on Evolutionary psychology: Controversies, questions, prospects, and limitations (see record 2010-02208-001) by Confer et al. The purpose of which was to clarify the logic of evolutionary psychology and clear up some of the more common misunderstandings about it. In this response, we address the key points raised by the commentators.     

Solitude experiences: varieties, settings, and individual differences

Solitude may be positive or negative, depending on situational and personal factors. From prior research, nine types of solitude were identified. Based on data from a questionnaire study of undergraduate participants, factor analysis suggests that these nine types can be reduced to three dimensions, two positive and one negative. These are, respectively, Inner-Directed Solitude (characterized by self-discovery and inner peace), Outer-Directed Solitude (characterized by intimacy and spirituality), and Loneliness. Personality and value correlates, as well as situational correlates, of the various types of solitude also were explored.     

Confusing developmental and individual differences

T. Globerson (1985, Developmental Review, 5, 261–273) compared the relative effects of an individual difference variable field dependency (FD/I) with a developmental variable (age) on a measure of M-capacity, in an analysis of variance (ANOVA) design. Age is a highly significant effect and the sum of squares associated with this factor accounts for 66% of the variance in M-capacity. FD/I is not significant and accounts for less than 1% of the variance in M-capacity. This is interpreted as indicating that M-capacity is a purely developmental phenomenon showing negligible individual differences. This paper argues that this result is an inevitable artifact of the experimental design. Further, the design is a common one in developmental psychology, and its dangers are largely unrecognized. The main problems concern (1) dichotomizing a continuous variable and treating the dichotomy as two levels of a factorial variable, (2) drawing inferences about the size of relationship between the continuous variable and the dependent variable on the basis of the variance accounted for by the factorial variable in the ANOVA, (3) differential reliability of measures of the independent variables, and (4) selective control of the sampling of the independent variables. These issues are explored in a simulation of Globerson's data and in an analogous analysis of data relating age and height, as independent variables, with weight as a dependent variable.     

Modeling individual differences in cognition

Many evaluations of cognitive models rely on data that have been averaged or aggregated across all experimental subjects, and so fail to consider the possibility of important individual differences between subjects. Other evaluations are done at the single-subject level, and so fail to benefit from the reduction of noise that data averaging or aggregation potentially provides. To overcome these weaknesses, we have developed a general approach to modeling individual differences using families of cognitive models in which different groups of subjects are identified as having different psychological behavior. Separate models with separate parameterizations are applied to each group of subjects, and Bayesian model selection is used to determine the appropriate number of groups. We evaluate this individual differences approach in a simulation study and show that it is superior in terms of the key modeling goals of prediction and understanding. We also provide two practical demonstrations of the approach, one using the ALCOVE model of category learning with data from four previously analyzed category learning experiments, the other using multidimensional scaling representational models with previously analyzed similarity data for colors. In both demonstrations, meaningful individual differences are found and the psychological models are able to account for this variation through interpretable differences in parameterization. The results highlight the potential of extending cognitive models to consider individual differences.     

Emotions,individual differences and time course: Reflections

I discuss the merits and demerits of the contributions to the present issue as I see them, and their implications for emotions research.