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Talk; Other LD

Friday stream 1 Session 14.00 - 15.40 Length 25 minutes

Cognitive profiles of children with dyslexia, dyscalculia and hyperlexia: evidence from a study with 12-year-old students

Aryan van_der_Leij and Victor van_Daal

(1) University of Amsterdam (2) University of Wales, Bangor avdleij@educ.uva.nl

Abstract

The present study was designed to investigate whether categories of learning disabilities are related to differences in cognitive functioning. Categories of learning disabilities were defined by performances on the behavioral level, i.e. achievement in automatisation of word identification, automatisation of arithmetic, and in listening comprehension, and the performance profiles across the three skills. From a sample 12-year old students at the beginning of secondary education in the Netherlands students were selected with severe problems in one, two, or all three of these skills. In addition, a normal control group was selected. The findings indicate that 'pure' dyslexia at this age is associated with deficits in phonological recoding, English word recognition, and spelling skills, and in naming speed for letters and digits, but not with deficits in other areas. 'Pure' dyscalculia shows only a (weak) relation to a deficit in the executive control function of working memory, while 'pure' hyperlexia relates only to a lack of verbal knowledge. The idea that multiple learning disabilities are associated with a combination of deficits in specific areas is most strongly supported by the finding that a 'general skill deficit' is related to deficits in all these and some other areas (e.g. phonological awareness, auditory short-term memory, rate of articulation, and naming speed for colors and pictures). Although the differences are in the predicted direction, the position of a 'double automatisation deficit' in word recognition and arithmetic is less clear.

Method:

1. Selection of all LD students (89) and a group of normal age controls (38) from a school district.
2. Test them on classification variables:
   - word reading (Dutch) (One Minute Test)
   - arithmetic (speeded calculation)
   - listening comprehension.
3. Categorization of students on basis of scores
   - 1 s.d. < average of normal controls on classification variables: single, double or triple learning disabilities (Figure 1 and Table 1):
   - RD = reading disability ('dyslexia')
   - AD = arithmetic disability ('dyscalculia')
   - CD = comprehension disability ('hyperlexia')
   - RD+AD
   - RD+CD
   - AD+CD
   - RD+AD+CD = GD = general (triple) disability
4. Test the subjects on a variety of tasks, related to five neuropsychological levels (Figure 2).
5. Analyse differences between the subcategories on the five levels and underlying tasks: z-scores and effect-sizes (ES) (Tables 2-4).

Figure 1. Categories of learning disabilities.

Normal age controls: 38

Figure 2. Tasks related to five neuropsychological levels

Results

Single disabilities(Table 2):

As single disabilities, reading disability RD ('pure' dyslexia), arithmetic disability AD ('pure' dyscalculia) and comprehension CD ('pure' hyperlexia) are easy to distinguish from each other:

RD is associated with deficits at the
- verbal level (phonological recoding, naming speed for letters and digits)
- academic level (English word recognition, spelling).

AD shows a relation to a deficit at the
- memory level (executive control function of working memory)
- and (less outspoken) attention level (visual search)

CD does not relate to lower level processing at any level.

Multiple learning disabilities (Table 3, 4):

General learning disabilities GD (triple: RD+AD+CD) are related to deficits
- at all levels: perceptual/motor, memory, verbal and academic (with the exception of attention)
- and is clearly distinguishable from single and double LD's.

However,
- double LD's (RD+AD, RD+CD, AD+CD) are hardly distinguishable from single RD and AD.

Table 1. Differences between age controls (N), single and general disabilities on classification variables.

Note. Bold scores differ from the other scores.

Table 2. Differences between age controls (N) and single disabilities on levels and tasks.

Note. First line indicates z-scores, second line Effect Size:
mean N - mean LD / s.d. N (s.d. of N z-score between brackets).
Bold scores differ significantly from italic scores.

Table 3. Differences between single RD and RD+ on levels and tasks.

Bold scores differ significantly from italic scores.
NB: ES not included.

Table 4. Differences between single AD and AD+ on levels and tasks.

Bold scores differ significantly from italic scores.
NB: ES not included.

See for a related study also: Van Daal, V., & Van der Leij, A. (1999). Developmental dyslexia: Related to specific or general deficits? Annals of Dyslexia, 49, 71-104.