Naomi P. Friedman

The relations among inhibition and interference control functions: a latent-variable analysis.

This study used data from 220 adults to examine the relations among 3 inhibition-related functions. Confirmatory factor analysis suggested that Prepotent Response Inhibition and Resistance to Distractor Interference were closely related, but both were unrelated to Resistance to Proactive Interference. Structural equation modeling, which combined Prepotent Response Inhibition and Resistance to Distractor Interference into a single latent variable, indicated that 1 aspect of random number generation performance, task-switching ability, and everyday cognitive failures were related to Response-Distractor Inhibition, whereas reading span recall and unwanted intrusive thoughts were related to Resistance to Proactive Interference. These results suggest that the term inhibition has been overextended and that researchers need to be more specific when discussing and measuring inhibition-related functions.

The Nature and Organization of Individual Differences in Executive Functions: Four General Conclusions

Executive functions (EFs)—a set of general-purpose control processes that regulate one’s thoughts and behaviors—have become a popular research topic lately and have been studied in many subdisciplines of psychological science. This article summarizes the EF research that our group has conducted to understand the nature of individual differences in EFs and their cognitive and biological underpinnings. In the context of a new theoretical framework that we have been developing (the unity/diversity framework), we describe four general conclusions that have emerged. Specifically, we argue that individual differences in EFs, as measured with simple laboratory tasks, (a) show both unity and diversity (different EFs are correlated yet separable), (b) reflect substantial genetic contributions, (c) are related to various clinically and societally important phenomena, and (d) show some developmental stability.

How are visuospatial working memory, executive functioning, and spatial abilities related? A latent-variable analysis.

This study examined the relationships among visuospatial working memory (WM) executive functioning, and spatial abilities. One hundred sixty-seven participants performed visuospatial short-term memory (STM) and WM span tasks, executive functioning tasks, and a set of paper-and-pencil tests of spatial abilities that load on 3 correlated but distinguishable factors (Spatial Visualization, Spatial Relations, and Perceptual Speed). Confirmatory factor analysis results indicated that, in the visuospatial domain, processing-and-storage WM tasks and storage-oriented STM tasks equally implicate executive functioning and are not clearly distinguishable. These results provide a contrast with existing evidence from the verbal domain and support the proposal that the visuospatial sketchpad may be closely tied to the central executive. Further, structural equation modeling results supported the prediction that, whereas they all implicate some degree of visuospatial storage, the 3 spatial ability factors differ in the degree of executive involvement (highest for Spatial Visualization and lowest for Perceptual Speed). Such results highlight the usefulness of a WM perspective in characterizing the nature of cognitive abilities and, more generally, human intelligence.

Individual Differences in Executive Functions Are Almost Entirely Genetic in Origin

Recent psychological and neuropsychological research suggests that executive functions--the cognitive control processes that regulate thought and action--are multifaceted and that different types of executive functions are correlated but separable. The present multivariate twin study of 3 executive functions (inhibiting dominant responses, updating working memory representations, and shifting between task sets), measured as latent variables, examined why people vary in these executive control abilities and why these abilities are correlated but separable from a behavioral genetic perspective. Results indicated that executive functions are correlated because they are influenced by a highly heritable (99%) common factor that goes beyond general intelligence or perceptual speed, and they are separable because of additional genetic influences unique to particular executive functions. This combination of general and specific genetic influences places executive functions among the most heritable psychological traits. These results highlight the potential of genetic approaches for uncovering the biological underpinnings of executive functions and suggest a need for examining multiple types of executive functions to distinguish different levels of genetic influences.

Not All Executive Functions Are Related to Intelligence

Accumulating evidence suggests that executive functions (EFs) are related to intelligence, despite neuropsychological results initially considered evidence of no such relation. However, findings that EFs are not unitary raise the issue of how intelligence relates to different EFs. This study examined the relations of fluid and crystallized intelligence and Wechsler Adult Intelligence Scale IQ to three separable EFs—inhibiting prepotent responses (inhibiting), shifting mental sets (shifting), and updating working memory (updating)—in young adults. Updating was highly correlated with the intelligence measures, but inhibiting and shifting were not. Furthermore, in structural equation models controlling for the inter-EF correlations, updating remained strongly related to intelligence, but the relations of inhibiting and shifting to intelligence were small and not significant. The results indicate that intelligence measures differentially relate to these three EFs, suggesting that current intelligence measures do not equally assess a wide range of executive control abilities likely required for many “intelligent” behaviors.

Behavioral disinhibition: liability for externalizing spectrum disorders and its genetic and environmental relation to response inhibition across adolescence.

Behavioral disinhibition has been characterized as a generalized vulnerability to externalizing disorders. Despite increasing evidence for its validity and heritability, the structural stability of behavioral disinhibition across adolescence and the strength and etiology of its relation to executive functions have not been studied. In this multivariate twin study, the authors assessed behavioral disinhibition using measures tapping substance use, conduct disorder, attention-deficit/hyperactivity disorder (ADHD), and novelty seeking at ages 12 and 17. Executive functions were assessed with laboratory-based cognitive tasks at age 17. Results indicated that, at age 12, behavioral disinhibition was dominated by ADHD and conduct problems and was highly heritable. At age 17, the contributions of the 4 components were more balanced, and the proportion of variance attributable to genetic factors was somewhat smaller, with additional variance due to shared environmental influences. At both ages, behavioral disinhibition was more closely related to response inhibition than other executive functions (working memory updating and task-set shifting), and this relationship was primarily genetic in origin. These results highlight the dynamic nature of behavioral disinhibition across adolescence and suggest that response inhibition may be an important mechanism underlying vulnerability to disinhibitory psychopathology.

Greater Attention Problems During Childhood Predict Poorer Executive Functioning in Late Adolescence

Attention problems (behavior problems including inattention, disorganization, impulsivity, and hyperactivity) are widely thought to reflect deficits in executive functions (EFs). However, it is unclear whether attention problems differentially relate to distinct EFs and how developmental stability and change predict levels of EFs in late adolescence. We investigated, in an unselected sample, how teacher-rated attention problems from ages 7 to 14 years related to three correlated but separable EFs, measured as latent variables at age 17. Attention problems at all ages significantly predicted later levels of response inhibition and working memory updating, and to some extent set shifting; the relation to inhibiting was stronger than the relations to the other EFs or IQ. Growth models indicated that attention problems were quite stable in this age range, and it was the initial levels of problems, rather than their changes across time, that predicted later EFs. These results support the hypothesis that attention problems primarily reflect difficulties with response inhibition.

Developmental Trajectories in Toddlers’ Self-restraint Predict Individual Differences in Executive Functions 14 Years Later: A Behavioral Genetic Analysis

We examined whether self-restraint in early childhood predicted individual differences in 3 executive functions (EFs; inhibiting prepotent responses, updating working memory, and shifting task sets) in late adolescence in a sample of approximately 950 twins. At ages 14, 20, 24, and 36 months, the children were shown an attractive toy and told not to touch it for 30 s. Latency to touch the toy increased with age, and latent class growth modeling distinguished 2 groups of children that differed in their latencies to touch the toy at all 4 time points. Using confirmatory factor analysis, we decomposed the 3 EFs (measured with latent variables at age 17 years) into a Common EF factor (isomorphic to response inhibition ability) and 2 factors specific to updating and shifting. Less-restrained children had significantly lower scores on the Common EF factor, equivalent scores on the Updating-Specific factor, and higher scores on the Shifting-Specific factor than did the more-restrained children. The less-restrained group also had lower IQ scores, but this effect was entirely mediated by the EF components. Twin models indicated that the associations were primarily genetic in origin for the Common EF variable but split between genetics and nonshared environment for the Shifting-Specific variable. These results suggest a biological relation between individual differences in self-restraint and EFs, one that begins early in life and persists into late adolescence.

Differential roles for visuospatial and verbal working memory in situation model construction.

Two experiments investigated the processing of the spatial and causal dimensions of situation models. In Experiment 1, participants read texts varying in spatial and causal demands while responding to on-line spatial and causal probes. Experiment 2 used the same design, but used texts that more tightly integrated spatial and causal information. In both experiments, spatially oriented dependent measures were generally influenced by spatial, but not causal, demands, whereas causally oriented measures were influenced by causal, but not spatial, demands. In addition, spatially oriented dependent measures were generally correlated with a measure of spatial working memory capacity, whereas causally oriented measures were correlated with a measure of verbal working memory capacity. These results indicate that spatial and causal dimensions of situation models are maintained and elaborated independently in different working memory subsystems.

Comparison of four scoring methods for the reading span test

This study compared four common methods for scoring a popular working memory span task, Daneman and Carpenter’s (1980) reading span test. More continuous measures, such as the total number of words recalled or the proportion of words per set averaged across all sets, were more normally distributed, had higher reliability, and had higher correlations with criterion measures (reading comprehension and Verbal SAT) than did traditional span scores that quantified the highest set size completed or the number of words in correct sets. Furthermore, creation of arbitrary groups (e.g., high-span and low-span groups) led to poor reliability and greatly reduced predictive power. It is recommended that researchers score span tasks with continuous measures and avoid post hoc dichotomization of working memory span groups.