Wednesday, June 18, 2014

Executive function profiles in children with and without Specific Language Impairment

Marton, K., Campanelli, L., Scheuer, J., Yoon, J., & Eichorn, N. (2012). Executive function profiles in children with and without Specific Language Impairment. Journal of Applied Psycholinguistics 12(3), 57–73.

Children with an unexpected delay in developing language known as specific language impairment (SLI) have been found to be less accurate on slower in performing a variety of cognitively demanding tasks. This paper investigates the hypothesis that these impairments result from deficits in executive functions, particularly working memory, inhibition, and sustained attention. Inhibition refers to the ability to ignore distracting information (“resistance to interference”), and to prevent previous tasks or routines from interfering with performance on new tasks (“inhibition of prepotent response”).

In this study, children with SLI and groups matched on age and language completed tests of visuospatial short term memory, resistance to interference, inhibition of prepotent response, and sustained attention. The SLI group performed more poorly than age-matched peers on the visuospatial short term memory and resistance to interference. Findings for the sustained attention task were mixed with no differences in the ability of the SLI group to identify correct sequences, but significantly poorer ability to reject incorrect sequences. No group differences were found in the task measuring inhibition of prepotent response.

These researchers provide a theoretically motivated evaluation of executive functions in SLI. One challenge in comparing the results to other studies with the same purpose is that these studies tend to adopt a variety of theoretical perspective and tasks. Further research is needed to examine the role of linguistic and cognitive factors across participant groups and tasks.


Blogger: Laura Pauls is a doctoral student in the LWM lab, and has completed her MClSc in speech language pathology.

Friday, May 23, 2014

The concurrent validity of the N-back task as a working memory measure

Jaeggi, S.M., Buschkuehl, M., Perrig, W. J., & Meier, B. (2010). The concurrent validity of the N-back task as a working memory measure. Memory, 18, 4, 394-412. doi: http://dx.doi.org/10.1080/09658211003702171.

This article presents psychometric properties—reliability and concurrent validity—of the n-back task to assess working memory (WM) and other aspects of cognition such as executive functions (EF) and fluid intelligence (Gf). In the n-back task, the participant views or hears items in a sequence with items occasionally repeating. The participant is asked whether a current item is the same as the one presented ‘n’ back. So, in a 1-back task, the person judges if the item is the same as the one before; in a 2-back task, the person judges if the item is the same as the one before the one that was just shown (i.e., 2-items ago), etc. You can try a n-back task at this website: http://cognitivefun.net/test/4.
The n-back task is frequently used in neuroimaging studies and sometimes is considered a “pure” WM measure. However, not all of the previous evidence show strong links between n-back performance and scores on other measures commonly used to assess working memory such as simple or complex span tasks. In a simple span task, a person recalls the list of items presented such as repeating a list of digits. In a complex span, the person must manipulate the items in the list in some way (i.e., make a judgment about the item), and then recall items. Stronger associations have been found between the n-back and measures of executive functions and fluid intelligence.
In this paper, three experiments were conducted to further examine the reliability of  the n-back task by measuring performance in 1-, 2-, and 3-back tasks, simple and complex span tasks, and EF and Gf. Overall, the n-task was moderately reliable based on split-half correlations comparing odd and even items (correlation range: 0.11 to 0.94). Reaction time (RT) was more reliable than accuracy, and the 2-back was more reliable than 1- and 3-back. The empirical results also confirmed previous findings of poor association between n-back and complex span tasks, but moderate correlation with simple span tasks. The test correlated poorly with EF, however it presented moderate-to-high correlations with Gf.
Although n-back and complex span tasks are considered to measure working memory, the tasks demands differ with n-back tasks requiring more continuous performance and attentional control and complex span tasks being more self-paced and self-ordered. It may be that the n-back and complex span tasks explain different parts of the variance in Gf. Caution is warranted in the use and interpretation of the n-back task.


Blogger: Alberto Filgueiras is a visiting doctoral student to the LWM lab from the Pontifical Catholic University of Rio de Janeiro, Brazil.

Monday, May 5, 2014

Executive functions: what they are, how they work, and why they evolved

Barkley, R. (2012). Executive functions: what they are, how they work, and why they evolved. New York: Guilford press.

The focus of this text is to provide an understanding of both the how and why of executive functions. Barkley suggests that executive functions evolved to solve social problems. According to this view, there is a daily need to look ahead and anticipate what others are likely to do in the context of pursuing one’s own self-interests. Executive functions are seen as comprising both ‘cold’ cognitive functions of ‘what, where, and when’, as well as ‘hot’ cognitive or motivational functions of ‘why’. One key to the development of executive functions is the ability to create internal representations of stimuli that are no longer present. With these internalized representations, we can create a conscious mental life capable of imagining a hypothetical future. As we become self-aware, we shift our motivations towards attaining a goal, that is, a hypothetical future of our imagining. Using self-directed private speech, we coach ourselves through the actions necessary to achieve that goal. Barkley argues that one of the most distinctive features characterizing executive function impairments is the social disability arising due to a failure to act insightfully in the social context while pursuing a future goal.

The ideas described in this text have important clinical implications. The emphasis on both the individual’s motivations as well as cognitive abilities in setting future goals and plans is important. It calls for a need to consider an individual’s reason to pursue a goal as well as their ability to select and pursue that goal.


Blogger: Lisa Archibald

Individual differences in working memory capacity and what they tell us about controlled attention, general fluid intelligence, and functions of the prefrontal cortex

Engle, R. W., Kane, M. J., & Tuholski, S. W. (1999). Individual differences in working memory capacity and what they tell us about controlled attention, general fluid intelligence, and functions of the prefrontal cortex. In: A. Miyake & P. Shah. Models of Working Memory: Mechanisms of Active Maintenance and Executive Control. Cambridge: Cambridge University Press. pp. 102-134. doi: http://dx.doi.org/10.1017/CBO9781139174909.007.

Engle, Kane and Tuholski describe a working memory model to explain individual differences in performance of WM tasks, and their relation to General Fluid Intelligence (gF) and controlled attention. Working Memory is defined as a system of procedures and skills used to activate and maintain long-term memory traces above threshold, as well as limited-capacity controlled attention. Thus, Working Memory capacity is not about memory limitations per se, but rather about the limits of sustained attention in the face of distraction and interference during tasks. Engle et al.’s model includes the short-term memory and central executive components described in other models. Importantly, the central executive is responsible for achieving activation through controlled processing, maintaining activation and blocking interference. Encoding, maintenance and grouping skills transform novel information into something familiar to be retained for longer periods in the focus of attention (for example, chunking numbers in a numerical span). This last component can be of many types (phonological, visual, spatial, auditory, etc.) and can vary according to attentional demands and individual differences.

According to Engle et al., controlled attention is the key feature of WM linking it to higher level processing. Evidence is reviewed showing that Working Memory tasks are uniquely associated with gF even when differences in short-term memory have been taken into account. Consistent with this view, working memory has been linked to learning in many studies, and has been the focus of specific interventions.

Blogger: Gabriela Hora is working as a volunteer research assistant in the LWM lab.


An Embedded-Processes Model of Working Memory

Cowan, N. (1999). An Embedded-Processes Model of Working Memory. In: A. Miyake & P. Shah. Models of Working Memory: Mechanisms of Active Maintenance and Executive Control. Cambridge: Cambridge University Press. pp. 62-101. doi: http://dx.doi.org/10.1017/CBO9781139174909.006.

This chapter presents Nelson Cowan’s model of Working Memory (WM). According to Cowan, WM is a functional system that retains both old and new information in a state suitable for manipulating and carrying out mental operations. Initially, a stimulus is stored for a brief moment (hundreds of milliseconds) in a sensory storage mechanism, which then activates representations in long-term memory (LTM). In this model, these activated representations constitute Short Term Storage (or Short Term Memory—STM). STM is responsible for holding information relevant to the task at hand. A subset of these activations (and novel stimuli) are held within our focus of attention. The Central Executive, then, gathers those mental representations for processing or manipulating.
According to this account, individual differences in WM tasks can be explained by limitations in both attention and LTM. Attention is limited by the amount of information that can be held in the focus of attention at a given time. LTM contributions, on the other hand, are limited by how long representations can remain activated in STM. If activations are lost (decay) over time, those representations will not be available in an easily accessible state for processing by the central executive. Cowan reviews considerable evidence that activated LTM indeed decays through time—in 10 to 20 seconds, and that without chunking or rehearsal participants tend to retain about 4±1 items in working memory tasks.
            Cowan’s model provides an excellent rationale for the use of warm up activities to activate related knowledge prior to the teaching of new skills. By activating LTM for familiar and related concepts, these concepts will be easier for children to access and connect to new information.


Blogger: Alberto Filgueiras is a visiting doctoral student at the LWM lab from the Pontifical Catholic University of Rio de Janeiro, Brazil.