Lecturer's Précis - Van der Linden, Coyette, and Seron (1992)
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First published online 14:30 GMT 30th January 2003, Copyright Derek J. Smith (Chartered Engineer). This version [HT.1 - transfer of copyright] dated 18:00 14th January 2010
Van der Linden, Coyette, and Seron (1992) Lecturer's Précis
This is a recent case study relevant to the topic of central executive function. Patient AM - a head-injured 29 year old right-handed male geometrician - sustained a head injury in August 1987 in a road-traffic accident. When tested in 1988, the authors record that:
"AM showed no sign of intellectual deterioration, no frontal dysfunction, and no attentional deficits. [MRI] showed restricted left low-intensity fronto-basal lesions, a left hyper-intensity white matter lesion in the left frontal periventricular area, a cerebellar and a moderate bilateral frontal atrophy. [He] was alert and well oriented in time and space. Oral language was fluent, without lexical or syntactical deficits, and comprehension was essentially normal. Reading and writing evidenced no difficulties. Mental and written simple calculation were normal and there were no signs of apraxia or agnosia." (Op cit, p304)
AM was found to perform normally in the following areas:
There were slight deficits in the following areas:
And yet AM reported severe problems arising in the course of his professional activities. For example, he complained of being unable to assimilate new scientific information. When reading scientific papers, he would repeatedly forget what had already been read, and have to go back and start again. Further test batteries were then administered:
Daneman and Carpenter Technique: AM was firstly tested using the Daneman and Carpenter (1983) sentence span technique. This technique involves presenting sequences of 2 to 6 sentences, each of 13 to 16 words. The subject has to read the sentences out loud, and attempt to remember the last word of each. He is then asked to recall as many last words as possible (in any order). The sentence span is the mean number of sentences which can be coped with at 60% accuracy or better. A range of subtests allows for different types of stimulus material (eg. meaningful vs meaningless) and different types of test (eg. recall vs recognition). Overall, these tasks are believed to tax two different aspects of working memory function, namely a processing function and a storage function. AM achieved an all-subtest score of 0 against a norm of 3.1 (sd=0.8). All subtests were below average except:
Phonological Similarity Technique: AM showed normal similarity and word-length effects, and it was concluded that "as these components of working memory did not seem to be involved in AM's verbal span deficit, it remained to explore central executive functioning." (Op cit, p311; emphasis added.)
Brown-Peterson Technique: The exploration of central executive functioning was carried out using the Brown-Peterson technique, namely that of retaining verbal or nonverbal information over different short delays filled by distractor tasks of variable nature, complexity, and likelihood to interfere. The results for verbal and nonverbal tasks are given below:
On the basis of which, the authors continue:
"We must conclude that maintenance rehearsal was intact. The fact that AM's deficit increased with the complexity of the interferent task and with delay supports the hypothesis that his working memory deficit was caused by a reduction in the capacity of the central executive system. More specifically, the resources of the patient were insufficient to meet the demands of the distractor tasks and maintenance rehearsal simultaneously." (Op cit, p315, emphasis added.)
Daneman and Tardiff Technique: Finally, a technique derived from Daneman and Tardiff (1987) was used, with the intention of separately assessing the processing and storage aspects of the central executive. In this paradigm, 4 words are presented which can be combined to make longer words. Thus (for example) MUSE, AU, VENT, and BERGE, can be combined to make MUSEAU, AUVENT, and AUBERGE. These combinations can be at, or not at, one of the syllable boundaries of the derived word. The task is for the patient to find the new word which does not contain one of these syllable boundaries, and the necessary trials are carried out with or without a memory load (ie. the patient does not always have to recall the individual words as well use them to select one of the target derived word.) The number of correct selections is therefore held to be a measure of processing, while the number of correct recalls is a measure of memory. AM performed normally on the process measures regardless of whether there was a memory load or not (26 out of a possible 27 when loaded, and 23 when not loaded, against control norms of 25 and 24.6 respectively). The memory performance, however, was deficient (17 out of 27, against a norm of 22.1). The authors interpret this as follows:
"In conclusion, the evidence from this verbal span task suggests that the central executive dysfunction observed in AM was strictly a storage capacity deficit: AM disposed of fewer total resources, and on a task that required both the processing and storage of the processing products, these resources were allocated to processing to the detriment of storage." (Op cit, p317.)
This thus reproduces experimentally the type of deficit of which AM had originally complained (above).
Daneman, M. & Carpenter, P.A. (1983). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behaviour, 19:450-466.
Daneman, M. & Tardiff, T. (1987). Working memory and reading skill re-examined. In Coltheart, M. (Ed.). Attention and Performance VII. Hillsdale, NJ: Erlbaum.
Van der Linden, M., Coyette, F., & Seron, X. (1992). Selective impairment of the 'central executive' component of working memory: A single case study. Cognitive Neuropsychology, 9:301-326.