Central Executive and Phonological Loop Deficits

The following four studies either focus on working memory deficits in children with learning deficiencies or focus on the overall indicator of working memory on math performance. The common result of each study indicates that deficits in central executive function impact math and reading comprehension in all children, especially those with disabilities, disorders, or difficulties. Deficits in the phonological loop also greatly impact math and reading performance. And deficits in the visual-spatial sketchpad are often a result of a developmental disorder and only impact children in control groups if they receive an overload of concurrent visual-spatial tasks.

Swanson and Kim (2007) examined three hundred and fifty-three early elementary children from Southern California public and private schools. They used simple math calculations to complex algebraic equations to test the mathematical skills of each child. Their focus was to determine if there is a relation between working memory and arithmetic and “to test the hypothesis that controlled attention underlies mathematical development” (Swanson and Kim, 2007). The results of their study determine that the central executive function of the WM is most influential in determining mathematical performance and that the phonological loop makes an impact with its storage capacity of numbers. The study also notes that children with a large WM capacity have the ability to store larger amounts of information without depleting the WM and would, therefore, have more resources available to complete the problem. The opposite is true for children with a smaller WM capacity. If the capacity to store information is smaller then, the amount of resources available to solve the problem will be less.

Similar to Swanson and Kim’s (2007) findings, Andersson and Lyxell (2007) discovered that deficits in the central executive and phonological loop play a major role in children with mathematical difficulties. Their study focused on which working memory functions affect mathematical skills in 31 10 year-olds with mathematical difficulties (MD), 37 10 year-olds with mathematical and reading difficulties (comorbid math and reading difficulties) and 47 age-matched and 50 younger controls. The results of their study propose that children with MDs have a deficit in the functioning of the central executive. These children have trouble with processing and storing numerical and verbal information. Children with comorbid math and reading difficulties have a central executive deficit that is even more extensive and extends into problems with the phonological loop: “simultaneous processing and storage of information, shifting, controlled retrieval of information from long-term memory, and general processing speed” (Andersson & Lyxell, 2007). All children tested relied on visual-spatial processing and numerous executive functions, whereas the older children and those with only MDs also used strategies that involved the phonological loop to solve problems. The study suggests that children with comorbid math and reading difficulties may be experiencing developmental delays in the fractionation of the working memory, which is a process I will discuss in another section of this review.

Packiam-Alloway (2007) focused her investigation of the working memory on the reading and mathematical skills of children suffering from developmental coordination disorder (DCD). These children experience more problems with visual-spatial functions than they do with phonological functions. According to Packiam-Alloway (2007), children with DCD display a noticeable lack in motor skills and visual tasks such as clumsiness, poor posture, confusion about which hand to use, difficulties throwing or catching a ball, reading and writing difficulties, an inability to hold a pen or pencil correctly, inaccuracies in estimating object size, and difficulties in locating an object’s position in space. Packiam-Alloway (2007) hypothesizes that since there is evidence that children with DCD have trouble with literacy, there may be a correlation between verbal and visuospatial memory impairments. 55 primary grade children from England participated in this study. They were tested in a variety of verbal and visuospatial areas, as well as in their literacy and numeracy. The results of the study conclude that deficits in visual-spatial working memory are worse than deficits in the phonological loop in children with DCD. Because the visual-spatial sketchpad impacts one’s ability to mentally rotate objects or follow the movement of objects, children with DCD performed extremely poorly on all visual-spatial tasks. In the meantime, these children also did not do well on the verbal tasks, either. Therefore, the combination of processing and storing information during either task, verbal or visual-spatial, negatively affects the outcome. Packiam-Alloway (2007) suggests an intervention program for children with DCD that involves teachers reducing excessive working memory loads in classroom activities and developing children’s own strategies for coping with memory failures.

Van der Molen, et al. (2007) provided another study dealing with children with a type of learning disability. However, this time the focus is on mild intellectual disabilities (MID). Van der Molen’s et al. (2007) study tested 100 children, 50 with MIDs ages 13-17, 25 typically developing children ages 13-16, and 25 typically developing children ages 8-12. They used a digit span and a non-word test to assess the function of the phonological loop. The results of these tests indicate that the children with MIDs performed significantly worse on both tests than the children in the control groups. They also used four tests to assess the function of the central executive. The results on these tests provide different conclusions. The children with MIDs performed significantly worse on all tests when compared to the control group of the same age. However, there was not much difference in performance between the children with MIDs and the control group ages 8-12. Van der Molen, et al. (2007) explained the results of both investigations to suggest that children with MIDs have trouble with storage in the phonological loop and have a developmental-delay in regards to the functioning of the central executive. Van der Molen, et al. (2007) suggested that the results of this study may indicate a need to increase visual information and reduce verbal information when teaching children with MIDs.