With regard to tables 1, 2 and 3, there was no
significant difference between the dyslexics and controls for the number of pairs correctly matched with the exception of
the 14.5 group. There was a significant increase in the
mean number of correct identifications made as the age of the groups increased. These results can be accounted for by the subjects’ increased manual dexterity and the dyslexic's
strategy of turning over a significantly larger number of cards as age increases. Older age groups made significantly more incorrect matchings and the dyslexic group as a whole made significantly more matchings than the control group.
These findings confounded the hypothesis advanced by many researchers (Vernon, 1970; Bakker and Satz, 1970; Naidoo, 1972), that dyslexics suffered from a maturational lag. However, the dyslexic group did make significantly more incorrect matchings than the control group. This was interest ing in as much as it substantiated the overall hypothesis
that dyslexics were fundamentally less efficient processors of all kinds of information. It will be observed that as the age of the groups increased and greater manual dexterity was facilitated, so the number of attempts increased. This
increase was initially dramatic for the dyslexic group while the control groups increase was less so. The contention of
Miles and Wheeler (1974), Wheeler, (1977), Ellis and Miles (1978)
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and Thompson and Wilsher (1978) that dyslexics suffered from a specific limitation in short-term memory was further supported by these results.
There was a significant difference between the dyslexic and control groups for the total number of attempts, further more as the age groups increased the total number of attempts made by the dyslexic group dramatically increased from
77.1 at 13.5 tp 150.5 at 16.5 (a difference of 73.4 attempts) while for the control group the increase was from 61.0 at
13.5 to 115.5 at 16.5 (a difference of 54.5). The difference at each age group between the dyslexic and control subjects were progressively larger.
The control group had a significantly better hit-rate than the dyslexic group, however there was no significant change in the hit-rate as the age of the group increased. Furthermore there was no differential change in the hit-rate for the dyslexic as opposed to the control group. These findings are interesting when considered in conjunction with the total number of attempts. It will be observed that the increase in total number of attempts did not lead to a better hit-rate for the dyslexic group and this factor might be
explained in terms of the dyslexic child’s inefficient
ability to use the information which he received. This added support to the short-term memory deficit hypothesis.
It will also be observed that the dyslexic group needed significantly more mean exposures per correct
identification than did the control group and it is hypothesized that they were functioning at a less efficient level than
the control group for all age groups. The dyslexic subjects*
mean efficiency was 8.02 exposures per correct identification and the controls 4.55. This confirmed the hypothesis that dyslexics suffered from a smaller capacity in short-term memory store. The controls were able to store more *bits*
of information in memory. There was no significant change in the mean number of exposures per correct identification
as the age of the group increased and there was no differential change in the mean number of exposures per correct identification for the dyslexics as opposed to the control group. Control
subjects were significantly more efficient than dyslexics as indicated by their higher hit-rate.
The dyslexic subjects were able to overcome some of the effects of their limitation in short-term memory by working at a faster rate, thereby reducing the temporal load on
short-term memory. However, as explained, this strategy did not enable them to obtain a better hit-rate or more correct matchings.
6E SUMMARY
The experiment was designed to investigate dyslexics1 spatial information processing ability over a specific duration of time, 300 seconds; to ascertain whether there was a limitation in short-term memory and further whether there was a maturational lag which was associated with this limitation. Two groups of 30 children were selected, namely non-dyslexic (control) and dyslexic, comprising of three distinct age ranges, 13.5, 14.5 and 16.5 years. The task consisted of matching 36 pairs of cards displayed in a randomized order. There was no significant difference between the dyslexic and non-dyslexic subjects for the number of
pairs correctly guessed. However, age was a significant factor, as subjects get oldertheir performance improved. Dyslexics made significantly more incorrect responses than controls. Younger subjects made significantly fewer
incorrect responses than older groups. Control subjects
were significantly more efficient than dyslexics as indicated by their higher hit-rate. Age was not a significant factor.
The concept of a maturational lag was not tenable since the performance of neither the dyslexic nor control group" increased with age. The dyslexics were able to overcome some of the effects of this limitation in short-term memory by working at a faster rate thereby reducing the temporal
load on short-term memory. However, using this strategy did
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not enable them to obtain a better hit-rate or more
correct matchings. The results were compatible with the
concept that dyslexia was characterized by a 'general limitation* in short-term memory which manifested itself with an increasing information load.
CHAPTER 7
A FINAL DISCUSSION OF THE EXPERIMENTAL PROGRAMME