Supplemental Data


Abstract
Full Text
Dyslexia: Cultural Diversity and Biological Unity
E. Paulesu, J.-F. Démonet, F. Fazio, E. McCrory, V. Chanoine, N. Brunswick, S.F. Cappa, G. Cossu, M. Habib, C.D. Frith, U. Frith

Supplementary Material

Note 14. Methods and results of behavioural study comparing dyslexics and controls in the three countries. Male, right-handed students subjects with tertiary education, participated in the study. Subjects details. Italy: 40 controls (mean age: 21.5; SD: 2.4); 18 dyslexics (mean age: 21.7; SD: 2.3). France: 18 controls (mean age: 28.2; SD: 4.8); 18 dyslexics (mean age: 27.2; SD: 5.9); United Kingdom: 18 controls (mean age: 23.5; SD: 2.9); 18 dyslexics (mean age: 23.6; SD: 4.7). All subjects were tested with the Wechsler Adult Intelligence Test. In addition, subjects were tested with tasks designed to assess reading accuracy and speed, and phonological processing.

Word reading tests. Specially constructed lists of words and nonwords were presented on a computer and naming latency was recorded via a voice-key. Accuracy was also recorded. The stimuli were highly concrete and familiar nouns. They were two- and three-syllable words, avoiding, in the case of French and English tests, irregular spelling patterns (in Italian, spelling is regular by definition). Nonwords were created from the words by maintaining the "word envelope" while changing internal consonants. In this test, 4 blocks each of 20 words or pseudowords were presented in an ABBA design. The words were highly concrete and highly familiar nouns. Each word was displayed for a maximum of 3 seconds. Participants were asked to read each word/pseudoword as soon as it appeared on the screen. Once the subject had responded and the latency had been recorded via a voice key, the word disappeared; there was a 1-second interval before the next stimulus was presented. Word and nonword recognition latencies exhibited a linear relationship between means and SDs. Hence, a reciprocal transformation was applied. As a baseline measure of response latency we also measured simple reaction times for a dot stimulus.

Spoonerisms. The Spoonerism task involves the segmentation and manipulation of the constituent sounds of words (1). Subjects heard pairs of words with the instruction to repeat back the two words after having swapped the initial sound around (e.g., Basket and Lemon repeated as Lasket and Bemon). The 24 words used in the Spoonerism task were two syllable highly familiar concrete words selected on the basis that they had clear syllable divisions and no consonant clusters in their onsets. Time taken to complete the test was recorded with a stopwatch from just before the first pair was given until the last Spoonerism was completed (in the Italian sample, only the cumulative time taken to produce the spoonerism after stimuli presentation was recorded, that is, the time taken to present the stimuli was not measured).

Auditory short-term memory for short and long words (2). Before testing, participants were shown the words to be used in the task. These were 7 short words (e.g., worst; sum; yield; harm; bond; hate; twice) and 7 long words (e.g., immediately; university; organisation; individual; opportunity; association; representative). Participants heard lists of 6 of the words spoken at the rate of one word every second; as soon as the experimenter had spoken the last word from a list, the participant was prompted to recall the words in the order of presentation. If a word could not be remembered participants were told to use the word "something" to maintain the order of the surrounding words. Only words recalled in the appropriate position were scored as correct. Ten lists of short words and ten lists of long words were presented in alternating order, and the number of words recalled correctly were summed across the two lengths of list. In the French sample instead, the span was measured for short and long-words separately; here span corresponds to the longest list length that subjects could repeat without errors in two out of three occasions.

Digit naming (3). In this task participants were asked to read aloud, as fast as possible, strings of 50 single digits. Digits were chunked into blocks of 5 (e.g., 68248 83542 99634) although participants were told to read each digit as a single number, i. e. the string 51368 should be read as "five, one, three, six, eight". The task was presented twice with different strings of 50 digits. The time taken to read each string was recorded with a stopwatch, starting from the experimenter saying the word "go" of "ready, steady, go", until the last digit had been said. A mean score, in seconds, was obtained over the two trials.
Tests used the first screening phase of Italian dyslexics. All tests were delivered in university classes.

Dictation of words and nonwords. Subjects wrote 20 words and 20 nonwords under paced conditions (1 stimulus dictated every 3 seconds).

Span for nonwords. Subjects wrote under paced conditions 10 lists of 4 nonwords. Subjects started written serial recall at the end of the presentation of each list. The number of correct responses (item identity and item position in the list) were scored.

Stress assignment task. The task consisted of a list of 90 printed words, which all had a length of three syllables and consonant/vowel structure: half of the words were stressed on the antepenultimate syllable (e.g., tavolo), and half on the penultimate (e.g. catena). The stress pattern of such words cannot be extracted by orthographic information alone and requires phonological recoding of the orthographic string. Subjects were given 3 minutes to underline the stressed syllable in each word, and the number of correct responses was scored.

Table 1. Wechsler IQ, reading and phonological tasks performance. Scaled scores on Wechsler subtests in dyslexics and controls. In bold: dyslexics significantly impaired in comparison with their controls: � = P < 0.0001; * = P < 0.001; + = P < 0.01; � = P < 0.03. Dyslexics were consistently impaired on Digit Span and tended to be impaired on Arithmetic and Digit symbol subtests. Comparisons are based on t-test. French and English dyslexics made significantly more errors in reading than Italian dyslexics for both words and nonwords (Mann-Whitney P < 0.001). The lower part of the table shows means and Sds for the experimental phonological tests. Comparisons are based on Mann-Whitney U tests. In all cases the tests revealed significant impairments of the dyslexic groups, compared with their controls. The absolute values of the RTs are not directly comparable between the different countries due to slight differences in hardware and administration procedures in different countries. Spoonerisms: the Italian data do not include the presentation time of the stimuli. Digit naming: direct cross-cultural comparison of digit naming times is not possible as the syllabic structure of the digit names is different across languages (e.g., Italian digits from 1 to 9 all have two syllables; corresponding English digits all have one syllable, except 7). Short-term memory for the French participants was measured as a word span analogous to digit span. In the Italian and English groups, the score represents items recalled in the correct order out of a maximum of 60 (10 trials, 6 words in length). STM = short-term memory.

Supplemental Table 1.
FranceItalyUK
ControlsDyslexicsControlsDyslexicsControlsDyslexics
Wechsler IQ measurements
Full IQ125121119116116.7111.7
(14)(8.3)(7.5)(7.8)(9.9)(9.6)
Verbal IQ128.5120.0�116.3113.4117.2109�
(11.9)(9.0)(8.2)(8.2)(11.8)(9.3)
Performance IQ114.7119.5119.8117.3111.8112.5
(13.3)(10.4)(9.2)(9.2)(9.8)(12.9)
Comprehension15.516.1131312.913.7
(2.3)(2.0)(2.8)(0.6)(2.7)(2.6)
Similarities14.914.212.712.212.212.8
(4.4)(3.4)(1.9)(1.8)(2.0)(2.2)
Arithmetic12.810.0*12.112.712.19.1*
(5.4)(3.5)(1.9)(1.8)(2.8)(4.7)
Digit span12.19.8�12.210.3+12.28.4*
(2.9)(2.8)(2.4)(2.1)(3.7)(3.7)
Vocabulary15.214.613.412.612.612.0
(2.3)(2.7)(2.1)(2.1)(4.5)(7.57
Digit Symbol11.410.213.712�11.29.5�
(1.9)(2.6)(2.4)(2.8)(5.1)(3.3)
Picture completion11.512.112.012.39.811.1
(3.4)(3.9)(2.3)(1.8)(4.1)(4.7)
Block design12.213.413.713.814.214.2
(3.1)(3.0)(2.2)(2.1)(5.6)(9.3)
Object assembly11.712.212.712.711.611.6
(2.7)(2.7)(3.3)(2.5)(4.4)(5.9)
Reading and phonological tasks
Word readingRT555727468570587782
(msec)(48.9)(201)(41)(56)(72)(137)
Word reading39.539.039.939.6+4039+
(accuracy)(0.7)(1.4)(0.3)(1.0)(0)(1.7)
Nonword reading RT6991136527.87367881333
(msec)(123)(385)(45)(90)(207)(322)
Nonword reading38.733.839.938.4+39.133.5
(accuracy)(1.3)(5.4)(0.3)(2.4)(1.0)(5.2)
Digit naming14.219.927.634.51420.4
(sec)(19.9)(3.9)(3.1)(5.3)(2.8)(3.9)
Spoonerism107209+48.111383.9202
(sec)(31)(80)(24)(68)(33.2)(115)
STM short words5.34.5+48.839.8*4934
(span Fr, items It - UK)(0.7)(0.6)(9.4)(7.3)(7.0)(10.7)
STM long words4.53.6*39.329.5+30.719.3*
(span Fr, items It - UK)(0.7)(0.6)(9.8)(9.9)(8.3)(7.6)


Note 18. Methods of PET experiments. There were two PET scan experiments involving 72 of the above subjects (36 subjects for each experiment, 24 for each country, half of whom were dyslexics). In the explicit reading experiment, subjects read words and nonwords aloud. The lists of words and the nonwords included those used in the behavioural reading experiment. The baseline was resting state. The rate of presentation on the computer screen was 2 seconds on and 1 second off. In the implicit reading experiment participants did not read aloud but performed a feature detection task. This involved detecting the presence or absence of ascenders (graphic features which go above the midline of the word, e.g., "b", "l", and "t" as opposed to "a", "c", and "o") within visually presented words, nonwords and false font strings. The false font was created by substituting letters in the real words with nonletters matched for size and presence or absence of ascenders [e.g., "cannon" and "meter" (see Scheme 1)]. The requirements of the task remained constant across stimuli: subjects pressed one key of a response box with their right hand index finger if one or more ascender was present, and another key with their right middle finger if no ascenders were present. The stimuli included the bisyllabic words and nonwords used in the other PET experiment, and were presented at the same rate. These studies were approved by the Ethics Committees of the Institute of Neurology (London) and Institute H San Raffaele (Milan). Informed consent was obtained after the nature and possible consequences of the studies were explained to the volunteers.

Data analysis. Regional cerebral blood flow (rCBF) was measured by recording the distribution of radioactivity following the intravenous injection of 15O-labeled water (H215O) with the a CTI Siemens Ecat HR+ PET scanner (CTI Inc., Knoxville, TN, USA) in London and the GE-Advance scanner (General Electric Medical System, Milwaukee, WI) in Milan. French subjects were scanned in London. Twelve consecutive scans were obtained for each subject in each experiment. The three stimulus conditions were presented in a counter-balanced order. Task-related differences in regional cerebral blood flow were examined using Statistical Parametric Mapping (SPM'96) software (Wellcome Department of Cognitive Neurology, London, UK) on stereotactically normalized and smoothed PET images (4, 5). For each experiment, data were analysed according to a random effects model: replications of each task were collapsed into average images so that only one average scan per reading task per subject was left and the residual variance of subsequent statistical analyses incorporated the appropriate inter and intra-subject variance components, permitting a mixed effects analysis appropriate for population inference (6). The analysis was based on a 2 (Controls versus dyslexics) × 3 (French, English, Italian subjects) × 2 (implicit, explicit reading) × 3 (words, nonwords, baseline) factorial design. The pattern of activation associated with reading was identified as the conjunction of the 6 main effects of reading (reading minus baseline) in each of the six groups of controls, and in each of the six groups of dyslexics. We then calculated the differences between controls and dyslexics as the conjunction of the 6 groups × task interaction effects. The interaction effects were computed on the voxels identified by the linear contrast of the relevant main effects.

Table 2. Brain activation data for reading in normal and in dyslexic readers.Localisation is based on stereotactic coordinates. These coordinates refer to the location of maximal activation indicated by the highest Z score in a particular anatomical structure (numbers in brackets indicate Brodmann areas). Distances are relative to the intercommissural (AC-PC) line in the horizontal (x), antero-posterior (y) and vertical (z) directions. Z scores indicate the magnitude of the statistical significance. Four neighbouring regions in the left hemisphere (superior, middle and inferior temporal gyrus, and middle occipital gyrus) were significantly more activated in the controls than in the dyslexics. The maximum peak of activation in this whole region was in the middle temporal gyrus. No region was found to show greater activation for dyslexics than for controls.

Supplemental Table 2.
LeftRight
Activations in controlsxyzZ scorexyzZ score
Inferior frontal gyrus (44)-468164.90----
Inferior frontal gyrus (44)-406225.34----
Inferior frontal gyrus (45)----6028-25.19
Precentral premotor cortex (6)-50-4325.9760-8444.82
Precentral motor cortex (4)-50-16304.31----
Ventral premotor cortex (6)-548104.47----
Ventral premotor cortex (6)-482225.12----
Anterior insula/inferior frontal-3822125.07----
Insula-322225.23----
Insula-346104.81----
Postcentral gyrus (43, 3,21)-60-10144.33----
Medial planum temporale (22)-42-38144.64----
Lateral planum temporale (22)-54-42164.83----
Superior temporal gyrus (22/21)-66-2626.0568-204.27
Superior/middle temporal gyrus (22)-64-44126.17----
Superior/middle temporal gyrus (22)-64-3666.18----
Middle temporal gyrus (21)-44-44-65.36----
Middle temporal gyrus (21)-58-5484.52----
Inferior temporal gyrus (37)-46-54-228.43----
Fusiform gyrus (37)-42-42-146.35----
Thalamus-14-2445.3222-1844.70
Putamen-280105.11----
Gl. Pallidum-24-22-24.4624-844.14
Brainstem-8-28-25.742-36-203.97
Cerebellum-4-44-84.838-42-224.11
Cerebellum-26-50-304.47----
Activations in dyslexicsxyzZ scorexyzZ score
Inferior frontal gyrus (45)-4424143.54----
Inferior frontal gyrus (44)-4616144.14----
Precentral gyrus (6)-521283.88441883.45
Superior temporal gyrus (22)-60-38106.2450-3885.50
Superior temporal gyrus (22)-566-23.71----
Superior/middle temporal gyrus (22)-68-2624.63----
Insula----3414144.22
Gl. pallidum-20-664.66----
Putamen-24264.16----
Thalamus-12-8163.68----
Activations greater in controls than in dyslexicsxyzZ scorexyzZ score
Superior temporal gyrus (22)-54-50143.70----
Middle temporal gyrus (21)-60-5605.30----
Inferior temporal gyrus (37)-52-60-145.06----
Middle occipital gyrus (37)-52-64-64.15----

References

  1. D. Perin, Br. J. Psychol.74, 129-144 (1983).
  2. A. D. Baddeley, N. Thomson, N. Buchanan, J. Verbal Learn. Verbal Behav.14, 575-589 (1975).
  3. M. B. Denckla, R. G. Rudel, Neuropsychologia14, 471-479 (1976).
  4. K. J. Friston, A. P. Holmes, K. J. Worsley, J.-B. Poline, C. D. Frith, R. S. J. Frackowiak, Hum. Brain Mapp.2, 189-210 (1995).
  5. K. J. Friston, J. Ashburner, J.-B. Poline, C. D. Frith, J. D. Heather, R. S. J. Frackowiak, Hum. Brain Mapp.2, 165-189 (1995).
  6. L. Frison, S. J. Pocock, Stat. Med. 11, 1685-704 (1992).