Naming Speed in Children with Dyslexia Angela J ... - CiteSeerX

Naming Speed and Dyslexia

Naming Speed in Children with Dyslexia

Angela J. Fawcett and Roderick I Nicolson Department of Psychology University of Sheffield

Journal of Learning Disabilities, (1994), 27, 641-646


Abstract Seven groups of children, comprising three groups of children with dyslexia with mean ages 8, 13, and 17 years; three groups of normally achieving children matched for age and IQ with the dyslexic groups; and a group of 10 year old children with mild learning difficulties (slow learners) matched for reading age with the youngest dyslexic group, undertook a series of tests of naming speed in discrete reaction time format. The children with dyslexia were significantly slower than even their chronological age controls, and equivalent to their reading age controls, on naming colors, digits, and letters, and significantly slower than even their reading age controls on naming pictures of common objects. Overall, performance of the 17 year old children with dyslexia was closest to that of the 8 year old controls. Performance of the slow learners was equivalent to that of the youngest children with dyslexia. The results show that children with dyslexia have persistent, and unexpectedly severe, problems in naming speed for any stimuli, regardless of whether the stimulus requires grapheme-phoneme decoding.

Requests for reprints should be addressed to Dr. Angela Fawcett, Department of Psychology, PO Box 603, University of Sheffield, Sheffield S10 2UR, UK. Acknowledgements The research reported here was supported by a grant from the Leverhulme Trust to the University of Sheffield. We thank Alan Baddeley and Tim Miles for valuable suggestions for the design of the studies. We acknowledge gratefully the dedicated support of the participants and their parents, and the support of the teachers and pupils at Ecclesall Junior School and Silverdale Secondary School, Sheffield.


Specific developmental dyslexia is normally characterised by unexpected problems in learning to read for children of average or above average intelligence. There is still considerable debate over diagnostic methods, but a standard definition adopted in the UK is that provided by the World Federation of Neurology:—“a disorder in children who, despite conventional classroom experience, fail to attain the language skills of reading, writing and spelling commensurate with their intellectual abilities” (1968, p26). Much recent research on dyslexia has been targeted on the sub-skills underlying reading, and there is now solid evidence of a deficit in early phonological skills in children with dyslexia (Bradley & Bryant, 1983; Snowling, Goulandris, Bowlby, & Howell, 1986; Stanovich, 1988; Vellutino, 1979). Unfortunately (from the diagnostic viewpoint), pure phonological deficits diminish with age, making it difficult to use such deficits for diagnosis after about 10 years of age, although deficits may still be revealed using more complex phonological tasks (Pennington, Van Orden, Smith, Green, & Haith, 1990; Olson, Gillis, Rack, DeFries, & Fulker, 1991; Scarborough, 1983). Furthermore, there is some evidence that children of generally low IQ (slow learners) have similar, or more marked, phonological deficits at the critical pre-reading ages (Shaywitz, Shaywitz, Liberman, Fletcher, Shankweiler, Duncan, Katz, Liberman, & Francis, 1991). In addition to the well-established phonological deficits, there is evidence that children with dyslexia show impaired speed of processing, including choice reactions to an auditory tone (Nicolson & Fawcett, 1993), ability to detect visual flicker (Lovegrove, Garzia, & Nicholson, 1990), and neuroanatomical irregularities in the transient visual system (Livingstone, Rosen, Drislane, & Galaburda, 1991). However, the strongest and best-established evidence for processing speed deficits has been derived from the Rapid Automatised Naming (RAN) paradigm (Denckla & Rudel, 1976a; Denckla, 1972). The basic technique for RAN is to present a card containing several rows and columns of stimuli, and ask the subject to name each stimulus in order, as fast as possible. The time taken is the dependent variable. There is now a wealth of data showing deficits on RAN using a variety of stimuli (e.g., Badian, Duffy, Als, & McAnulty, 1991; Bowers & Wolf, 1992; Denckla & Rudel, 1976a,b; Rudel, Denckla, & Broman, 1981; Spring & Capps, 1974; Swanson, 1987; Wolf, 1984; Wolf, Bally, & Morris, 1986; Wolf & Obregon, 1992). One of the most intriguing aspects of the RAN task, in terms of diagnosis, is the finding (Denckla & Rudel, 1976b) that RAN differentiates children with dyslexia from other groups with learning disabilities, such as children of normal IQ with minimal brain damage but no reading disabilities. There is also some evidence to suggest that children with dyslexia perform less well on naming speed than slow learners (Gough & Tunmer, 1986; Wolf & Obregon 1989; 1992). Continued problems with the RAN have been identified with both digits and letters in adolescents and adults with dyslexia (see e.g., Bowers, Steffy, & Tate, 1988; Denckla & Rudel, 1976a; Wolff,


Michel, & Ovrut, 1990), but not in subjects with attention-deficit disorder (Felton, Wood, Brown, & Campbell, 1987). Explanations of impaired RAN speed include phonological deficits (Katz, 1986; Mann & Brady, 1988; Stanovich, 1990), and deficits in the precise timing mechanisms needed to integrate the phonological and orthographic codes in reading (Bowers & Wolf, 1993). However, a significant problem in the interpretation of RAN deficits is that a variety of underlying problems would lead to qualitatively similar results. It might be, for instance, that a child had difficulty keeping place on the page of stimuli, or difficulties recovering from an error, or mild attentional problems which caused occasional lapses of concentration. It might be that he or she had a continuous workload problem and found the lengthy paced task particularly difficult, or, being less automatic on the naming tasks, had to try harder to name the stimulus quickly, and therefore tired more quickly. It might even be that children with dyslexia merely have a slower rate of articulation. Each of these deficits has been suggested by dyslexia researchers, and any or all of them would lead to a RAN deficit. One approach is to reduce task variables by using discrete trials (where stimuli are presented individually) but this technique has produced mixed results. Several studies (Bowers & Swanson, 1991; Katz, 1986; Scarborough, 1990; Wolff et al., 1990) have found evidence of speed deficit, whereas others have found no such evidence (Perfetti, Finger & Hogaboam, 1978; Stanovich, 1981; Stanovich, Feeman, & Cunningham, 1983; Stanovich, 1990). Results appear to vary with age, with significant differences in picture naming in the early grades, but mixed evidence of deficits in letter and digit naming by around grade 4. Wolf (1991) notes that the RAN task includes errors and hesitations, whilst the discrete trial format, by contrast, often explicitly excludes errors together with outlier reaction times. Wolf and Obregon (1992) note that deficits in speed of object naming may be attributable either to lack of speed or to lack of vocabulary. Using the Boston Naming Test, in which the subject has to name pictures of objects, they established that children with dyslexia obtained equivalent scores to slow learners, even though their receptive vocabulary was better (assessed by multiple choice on the Boston Naming Test pictures). A further methodological issue was identified by Bowers and Swanson (1991) who showed that poor readers were differentially impaired by use of a paced continuous discrete trial procedure, as opposed to a 1.5 second interstimulus interval. In summary, the RAN procedures lead to robust effects in terms of naming speed deficit, but the complexity of the RAN task allows interpretations in terms of rapid tiring, vigilance, placekeeping, and error-recovery, thereby clouding theoretical interpretation. The discrete trials procedure rules out the above interpretations and so provides a more sensitive index of pure processing speed than the RAN task, but uncertainty over the extent, developmental duration, and task specificity of the speed deficit with a discrete trials procedure has made theoretical interpretation equally problematic. The objective of the research reported here was to facilitate


theoretical interpretation by administering the range of naming speed tests to children at various ages, including children with dyslexia, slow learners, and normally achieving children. A further hope was that the results would inform the construction of a processing speed test which could be used to augment a phonological skill test in a diagnostic battery for dyslexia for children of 8 years through adulthood.

Method Participants In order to monitor longitudinal change, three age groups of children with dyslexia (mean age = 8, 13, and 17 years) were studied, together with three groups of normally achieving children matched for age and IQ. This design allows not only the standard chronological age match comparison, but also a reading age match comparison (by comparing the children with dyslexia with the younger controls), and even a ‘twice chronological age match’ comparison (by comparing the oldest children with dyslexia with the youngest controls). All the children with dyslexia had been diagnosed as dyslexic between the ages of 7 and 10, based on discrepancies of at least 18 months between chronological and reading age, together with a full scale IQ of at least 90 on the WISC-R (Weschler, 1976). A group of slow learning children (full scale IQ between 70 and 90) with mean age 10 years was also studied. The slow learner group was matched for reading age with the youngest dyslexic children. All but one of the children were white, drawn from social classes 1, 2, and 3 (i.e., middle class or skilled working class), and were predominantly male, apart from the 8 year old group of children with dyslexia and the slow learners, which both included four females. The slow learning children were in special school placements. Further details are provided in Table 1. ** Insert Table 1 about here

Experimental Tasks Four tests, namely object, color, digit and letter naming, were used. One would expect a developmental improvement in speed of naming for each of these tasks, but comparison between the reading-related tasks (letters and digits) and the non-reading-related tasks (objects and colors) might well prove a useful discriminant between the different groups. The procedure for each task was essentially the same. The experiment was carried out on a 4 MByte LCII Apple Macintosh micro, using the Naming Speed test of the COMB multimedia battery (Nicolson, 1993). Stimuli were pre-stored and presented in pseudo-random order under experimental control. Subjects were instructed to say the name of the stimulus as quickly as


possible. Voice onset was picked up by a microphone which interrupted the computer, thereby allowing voice onset latency to be recorded automatically. The experimenter typed in the specific response uttered. All instructions were presented in synthesized speech, and further explained by the experimenter, who emphasised the need for speed with accuracy. Following calibration of the microphone, a short familiarization session was given, in which the pictures were named in synthesized speech, and the experimenter ensured that the subjects were able to name the pictures correctly. After a short practice, with spoken feedback, and the resolution of any uncertainties, the main experiment began with the presentation of first the pictures, then the colors, next the digits, and finally the letters. The task was in an unpaced, single trial format. Following each trial, the experimenter initiated the next trial when the subject was ready, and the next stimulus was presented at a random interval between 1 and 1.5 seconds later. No results feedback was given during the main experiment. Each stimulus was presented once only, with order of presentation randomized across stimuli. For picture naming, 12 pictures were used, namely leaf, house, nose, bird, mouse, cat, table, frog, cup, pig, hat, tree. Their names were all single syllable words with AA frequency (Thorndike & Lorge, 1944) and an early age of acquisition (Carroll & White, 1973) and the pictures were presented as simple line drawings. For color naming, the six colors used were clear primary colors (red, blue, black, yellow, green, white), presented as a block of color (size 5 x 3.5 cms) in the center of the screen. For digit naming, the eight digits used were 1, 2, 3, 4, 5, 6, 7, 8 presented in 24 point Times font in the center of the screen. For letter naming, the eight letters used were c, o, b, a, d, t, w, s presented in 24 point lower case Times font in the center of the screen. Data Analysis Maturational changes were assessed by using three age groups of children with dyslexia. If a significant difference between the groups has been found in an overall analysis, three separate issues are of interest in the statistical analyses for each experiment. First it is important to identify whether children with dyslexia perform worse than their same-age controls (excluding the slow learning children). This analysis (CA and Dyslexia) has two factors: chronological age (8, 13 and 17) and dyslexia (present/absent). The second analysis (RA and Dyslexia) also excludes the slow learners and involves comparison with reading age controls (excluding the oldest controls and the youngest children with dyslexia). It also has two factors, namely reading age (13 and 8), and dyslexia (see Note). The third analysis (SL and Dyslexia) involves a 1 factor comparison between the 8 year old children with dyslexia and the slow learners.


Results For each experiment, since reaction time distributions are skewed, the median latencies were derived to avoid the danger of outliers biasing the means. The group means of the median results for picture, color, digit and letter naming latency, including both correct and error data, are presented in Table 2. Accuracy was near ceiling for the first three tasks, but there were some errors in the letter naming task for all the dyslexic groups. Consequently accuracy data are presented only for the letter naming task. ** insert Table 2 about here For clarity of presentation, the results of the inferential statistical analyses have been collated and tabulated, and are shown in Table 3. It may be seen that the children with dyslexia performed significantly slower than their chronological age controls on all four tasks. When compared with their reading age controls, their performance was not significantly different for three of the tasks, but was significantly slower for picture naming. For all four tasks, speed of naming increased significantly with age. Two interactions were significant: the chronological age analyses of digit naming and letter naming. Inspection of Table 2 indicates that the interactions arise because the youngest children with dyslexia were very much slower than the other groups. This no doubt reflects the low reading age of the youngest children with dyslexia, and their poorer letter and number knowledge (as indicated by their lower accuracy in letter naming). **Insert Table 3 about here.

Discussion In undertaking this research we wished to address four incompletely resolved issues: first, whether children with dyslexia show any deficit in discrete trials naming speed; next, if there were a deficit, would it be confined to the reading-related tasks, and would it be confined only to the younger children with dyslexia; and finally, would the deficit be more severe than for slow learners matched for reading age? Our results showed that the children with dyslexia were significantly slower at naming colors, digits and letters than their chronological age controls, and equivalent to their reading age controls. For pictures, their performance was significantly worse than even their reading age controls. The answer to the first two questions therefore appears clear-cut. There are clear deficits, and they apply to all four tasks. Furthermore, all three groups of children with dyslexia showed a clear deficit, with the 17 year old children with dyslexia performing only at the level of the 8 year old controls for picture naming and letter naming. This resolves the third issue. These results suggest that children with dyslexia have persistent, and unexpectedly severe, problems in naming speed for any stimuli, regardless of whether the stimulus requires grapheme-


phoneme decoding. Finally, the 10 year old slow learners performed at an equivalent speed to that of the 8 year old children with dyslexia, in line with their reading ages. This result contrasts with that of Wolf and Obregon (1989), who found that their groups with dyslexia performed significantly slower than poor readers of the same age on picture, letter and digit naming. The difference between the studies appears to derive from the performance of the poor readers, in that Wolf and Obregon’s poor readers performed at close to normal speed. Interpretation of these differences is problematic, since Wolf and Obregon used the standard RAN task and avoided the use of IQ measures in determining their slow learners. If we turn to our fifth, applied issue, it seems that the discrete trials naming speed task is unlikely to discriminate children with dyslexia from slow learners, and so it may well be that the RAN task would prove more valuable as part of a diagnostic battery. In terms of theoretical interpretation of these results, the deficit in discrete trial naming speed for children with dyslexia rules out explanations in terms of hesitations, greater effort, speed of articulation and the like which might well apply to the RAN procedure. Furthermore, the deficits in color and picture naming as well as the reading-related tasks suggest that there must be some generalised deficit in speed of access to the lexicon. These results are not unexpected in that in earlier research using the same groups of children (Nicolson & Fawcett, 1993) we established that the children with dyslexia showed speed deficits both in lexical decision time (saying whether or not a stimulus was a valid word) and also in selective choice reaction (pressing a button on hearing a low tone, while making no response when a high tone was presented). Interestingly, however, the voice onset latency of the children with dyslexia when naming a pre-specified word was equivalent to that of their chronological age controls, as was their speed of simple reaction to an auditory tone (Nicolson, Fawcett, & Baddeley, 1992; Nicolson & Fawcett, 1993). A parsimonious account of the pattern of results in the studies presented here, together with this previous research is that children with dyslexia do not have a fundamental deficit in speed of reaction, but that their deficit increases as the number of possible responses increases, in line with the amount of processing required (cf. Hick, 1952). It is interesting to note that latencies for all groups were slower for the picture naming task than for the color, digit and letter naming. This is presumably because there are many more possible objects which could be presented than digits, colors or letters. The fact that the slow learning children also showed more marked deficits as the alternatives increased is consistent with a number of such findings in the reaction time literature (e.g., Vernon, 1981). One possible explanation for apparent discrepancies in the literature is that the RAN deficit is additive, reflecting not only the discrete trials deficit but also effects involving slower articulation, greater hesitation, tiring, and the like. If one assumes that the slow learners show few of these extra effects, it is likely that the slow learners would in fact outperform the children with dyslexia on the RAN task (as found by Wolf & Obregon) whilst performing at


equivalent levels on the discrete trials naming test. Further research is needed to explore this possibility. In conclusion, this study replicates and extends the standard findings for the RAN task, demonstrating that there are severe and persistent problems in naming speed for children with dyslexia, in even the simplest discrete trial format. This deficit was found not only with alphanumeric stimuli, but also with colors and simple line drawings of objects which should be well within the vocabulary of the average 8 year old. In this condition, the performance of the children with dyslexia was slower than even their reading age controls. The results indicate that children with dyslexia may have impaired speed of access to their lexicon for all types of stimuli, regardless of the mode of stimulus presentation.


Note. In order to match the groups for reading age, the two lowest achieving 17 year old dyslexics were excluded from this analysis.


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Table 1. Psychometric data on the seven groups of participants. The three groups of children with dyslexia are labeled D17, D13 and D8, with the suffix indicating the mean age. Similarly the three groups of normally achieving children are labeled C17, C13 and C8. The group of slow learners are labeled SL10.

Group

N

IQ (WISC-R) Mean

Range

Chronological Age Mean

Reading Age

Range

Mean

Range [15.0 to 15.0] [8.2 to 14.6] [10.9 to 14.6]}b

C17

11

107.3

[92 to 130]

17.4

[17:0 to 18:0]

D17

13 {11}b

105.0 {105.0

[88 to 126] [92 to 126]}b

17.4

[16:0 to 18:2]

15.0a 12.5 {13.2

C13

11

111.6

[96 to 129]

13.4

[13:0 to 14:4]

13.7

[12.8 to 14.6]

D13

10

111.2

[101 to 128]

13.3

[11:7 to 14:9]

9.9

[7.9 to 12.3]

C8

10

115.1

[101 to 133]

8.2

[7:0 to 8:8]

9.2

[7.7 to 11.1]

D8

12 {11}b

113.4 {113.4

[96 to 133] [96 to 133]}b

8.7

[7:7 to 9:9

6.6 {6.5

[5.5 to 7.9] [5.5 to 7.7]}b

SL10

10

77.6

[68 to 83]

10.0

[9:1 to 11:1]

6.4

[5.3 to 7.3]

a 15 represents ceiling on the Schonell test of reading age used. All this group were reading at this level, and the majority had reached this level at around the age of 15. b In order to improve the match for reading age with the 13 year old controls, two subjects were omitted from the reading age analysis. Figures in {brackets} show the psychometric data excluding these subjects. The same technique was adopted for the 8 year old children with dyslexia.


Table 2. Mean Data for the Four Naming Tasks

Dyslexia Group

D8

D13

Picture naming latency

0.84

0.72

Color naming latency

0.65

Digit naming latency

D17

Control

Slow Learner

C8

C13

0.64

0.66

0.57

0.58

0.85

0.58

0.49

0.56

0.45

0.44

0.66

0.70

0.55

0.48

0.51

0.45

0.44

0.73

Letter naming latency

0.81

0.61

0.54

0.56

0.50

0.46

0.84

Letter naming accuracy (%)

89

96

97

100

100

C17

100

SL10

98

Note: Latency data are in seconds. The accuracy data for all groups for the three conditions other than letter naming were 98% or better.


Table 3. Summary of the Statistical Analyses on the Four Tasks

Task

Chronological Age and Dyslexia Dyslexia

Age

Reading Age and Dyslexia

SL vs dyslexia

Interaction Dyslexia Reading Age Interaction

Pictures

F(1,61)=20.5 ****

F(2,61)=8.7 ***

F(2,61)=1.8 F(1,38)=4.6 F(1,38)=12.1 F(1,38)=0.0 * ***

F(1,19)=0.0

Colors

F(1,61)=16.9 F(2,61)=14.7 **** ****

F(2,61)=1.3 F(1,38)=0.4 F(1,38)=12.6 F(1,38)=0.0 ***

F(1,19)=0.0

Digits

F(1,61)=32.7 ****

F(2,61)=21.6 ****

F(2,61)=5.1 F(1,38)=1.2 **

F(1,38)=8.5 **

F(1,38)=0.1

F(1,19)=0.1

Letters

F(1,61)=45.5 ****

F(2,61)=25.5 ****

F(2,61)=5.6 F(1,38)=2.3 **

F(1,38)=8.4 **

F(1,38)=0.2

F(1,19)=0.2

F(2,61)=2.2 F(1,38)=3.7 F(1,38)=0.3

F(1,38)=0.3

% correct F(1,61)=11.5 F(2,61)=2.2 ** (letters) Key:

* p < .05;

** p < .01;

*** p < .001;

F(1,19)=5.2 *

**** p < .0001.

Note Data (except for the bottom row) are the median latencies for voice onset when naming the stimulus.