Univariate and multivariate skewness and kurtosis for measuring nonnormality: Prevalence,influence and estimation

Nonnormality of univariate data has been extensively examined previously (Blanca et al., Methodology: European Journal of Research Methods for the Behavioral and Social Sciences, 9(2), 78–84, 2013; Miceeri, Psychological Bulletin, 105(1), 156, 1989). However, less is known of the potential nonnormality of multivariate data although multivariate analysis is commonly used in psychological and educational research. Using univariate and multivariate skewness and kurtosis as measures of nonnormality, this study examined 1,567 univariate distriubtions and 254 multivariate distributions collected from authors of articles published in Psychological Science and the American Education Research Journal. We found that 74 % of univariate distributions and 68 % multivariate distributions deviated from normal distributions. In a simulation study using typical values of skewness and kurtosis that we collected, we found that the resulting type I error rates were 17 % in a t-test and 30 % in a factor analysis under some conditions. Hence, we argue that it is time to routinely report skewness and kurtosis along with other summary statistics such as means and variances. To facilitate future report of skewness and kurtosis, we provide a tutorial on how to compute univariate and multivariate skewness and kurtosis by SAS, SPSS, R and a newly developed Web application.     

Distractor filtering in media multitaskers

A growing amount of modern media is consumed simultaneously, a phenomenon known as 'media multitasking'. Individuals who regularly engage in this activity, heavy media multitaskers (HMMs), are more affected by irrelevant information that can intrude into a primary task than are light media multitaskers (LMMs--Ophir et al, 2009 Proceedings of the National Academy of Sciences of the USA 106 15583). However, the locus of this deficit is unknown, as previous research is consistent with both memory and attentional explanations. Here, we isolated attentional processes by employing a singleton distractor task with low working-memory demands. In this task, LMMs used top-down information to improve their performance, yet HMMs did not. This difference in performance in an established attentional capture task argues for the presence of attentional differences in HMMs and is consistent with the idea that HMMs maintain a wider attentional scope than LMMs, even when instructed otherwise.     

Limits of generalization between categories and implications for theories of category specificity

Both domain-specific and expertise accounts of category specialization assume that generalization occurs within a domain but not between domains. Yet it is often difficult to define the boundaries and critical features of object domains. Differences in how categories are defined make it difficult to adjudicate between accounts of category specificity and may lead to contradictory results. For example, evidence for whether car experts recruit the fusiform face area is mixed, and this inconsistency may be due to the inclusion of antique cars in one of those previous studies (e.g., Grill-Spector, Knouf, & Kanwisher, 2004). The present study tested the generalization of expertise from modern to antique cars and found that modern-car experts showed expert discrimination and holistic processing of modern cars but not of antique cars. These findings suggest that the neural specialization underlying perceptual expertise is highly specific and may not generalize to distinct subclasses, even when they share some degree of perceptual and conceptual features.     

Should we reject the expertise hypothesis?

On the basis of a review of the literature and the results of three experiments with dog experts, Robbins and McKone [Robbins, R. A., & McKone, E. (2006). No face-like processing for objects-of-expertise in three behavioural tasks, Cognition] argue that there is little or no evidence supporting an expertise account of the differences in configural processing that are typically observed between faces and non-face objects. In the spirit of a debate that has become overly polarized, we believe that R&M often emphasized relatively unimportant controversial issues at the expense of bigger, more important questions. We also feel that some of R&M's arguments are rooted in methodological confusions that should be clarified because they have implications beyond this specific debate. In this commentary, we first clarify issues surrounding the proper statistical analysis of the composite paradigm, a methodology that is commonly used to assess configural and holistic effects in both face and non-face objects. We then discuss several theoretical issues that we feel are central to the debate regarding accounts of face-specificity. We also briefly review positive evidence for the correlation between measures of behavioral expertise and neural markers of face-selectivity. Unlike R&M, we believe the positive evidence for expertise effects, both behavioral and neural, greatly outweighs evidence stemming from null results and that it clearly motivates the importance of future work on the role of experience in the specialization of visual cortex.     

Comprehension skill, inference-making ability, and their relation to knowledge

In this study we investigated the relation between young children's comprehension skill and inference-making ability using a procedure that controlled individual differences in general knowledge (Barnes & Dennis, 1998; Barnes, Dennis, & Haefele-Kalvaitis, 1996). A multiepisode story was read to the children, and their ability to make two types of inference was assessed: coherence inferences, which were essential for adequate comprehension of the text, and elaborative inferences, which enhanced the text representation but which were not crucial to understanding. There was a strong relation between comprehension skill and inference-making ability even when knowledge was equally available to all participants. Subsidiary analyses of the source of inference failures revealed different underlying sources of difficulty for good and poor comprehenders.     

Odor recognition: familiarity, identifiability, and encoding consistency

The investigation examined the association between the perceived identity of odorous stimuli and the ability to recognize the previous occurrence of them. The stimuli comprised 20 relatively familiar odorous objects such as chocolate, leather, popcorn, and soy sauce. Participants rated the familiarity of the odors and sought to identify them. At various intervals up to 7 days after initial inspection, the participants sought to recognize the odors among sets of distractor odors that included such items as soap, cloves, pipe tobacco, and so on. The recognition response entailed a confidence rating as to whether or not an item had appeared in the original set. At the time of testing, the participants also sought to identify the stimuli again. The results upheld previous findings of excellent initial recognition memory for environmentally relevant odors and slow forgetting. The results also uncovered, for the first time, a strong association between recognition memory and identifiability, rated familiarity, and the ability to use an odor label consistently at inspection and subsequent testing. Encodability seems to enhance rather than to permit recognizability. Even items identified incorrectly or inconsistently were recognized at levels above chance.