1 RUNNING HEAD: Frequency Discrimination and Reading Language Skills, but not Frequency Discrimination, Predict Reading Skills in Children At Risk of Dyslexia Margaret J. Snowling University of Oxford Debbie Gooch University College London Genevieve McArthur Macquarie University, Australia Charles Hulme University of Oxford
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RUNNING HEAD: Frequency Discrimination and Reading
Language Skills, but not Frequency Discrimination, Predict Reading Skills in Children At
Risk of Dyslexia
Margaret J. Snowling
University of Oxford
Debbie Gooch
University College London
Genevieve McArthur
Macquarie University, Australia
Charles Hulme
University of Oxford
2Frequency Discrimination and Reading
Abstract
This study evaluated the claim that auditory processing deficits are a cause of reading
and language difficulties. We report a longitudinal study of 245 children at family risk of
dyslexia, children with preschool language impairments, and controls. Children with
language impairments had poorer frequency discrimination thresholds than controls at 5½
years but children at family risk of dyslexia did not. A model assessing longitudinal
relationships between frequency discrimination, reading, language, and executive skills
showed that frequency discrimination was predicted by executive skills but was not a
longitudinal predictor of reading or language skills. Our findings contradict the hypothesis
that frequency discrimination is causally related to dyslexia or language impairment, and
suggest that individuals at-risk for dyslexia, or who have language impairments, may perform
poorly on auditory processing tasks because of comorbid attentional difficulties.
FREQUENCY DISCRIMINATION AUDITORY DEFICITS
RISK OF DYSLEXIA LANGUAGE DISORDER EXECUTIVE SKILLS
3Frequency Discrimination and Reading
Language Skills, but not Frequency Discrimination, Predict Reading Skills in Children At-
Risk of Dyslexia
Developmental dyslexia is a learning disorder primarily affecting the ability to learn
to read and spell. The predominant causal explanation for dyslexia is that it reflects a
2006a (t2); CELF-4 UK; Semel, Wigg, & Secord, 2006b (t3)), the child heard sentences of
different syntactic structures and had to select, from a choice of four, the picture that
conveyed its meaning. In a Sentence Repetition test designed for the project, the child had to
repeat 20 sentences varying in length (short versus long) and complexity (transitive versus
10Frequency Discrimination and Reading
ditransitive; e.g. “a lady pushed the bike to work” and “the busy teacher promised the clever
boy a sticker”). The total number of sentences repeated correctly was recorded.
Vocabulary. At 4½ (t2), children completed the Receptive One Word Picture
Vocabulary Test (ROWPVT; Brownell, 2000). The child heard a word and was asked to select
the corresponding picture, from a choice of four. At 5½ (t3), children completed an
Expressive Vocabulary measure (CELF-4 UK; Semel et al., 2006b), where the child was
asked to name objects or to describe what a person is doing.
Reading Measures
Regular and Irregular Word Reading. At age 4½ (t2) and 5½ (t3), children
completed the Early Word Reading subtest from the York Assessment of Reading for
Comprehension (YARC; Hulme et al., 2009). The child read aloud 30 single words, graded in
difficulty. Half of the words were phonemically regular (decodable), and the other half were
irregular. Each correct response scored 1 point; testing was discontinued if the child made 10
consecutive reading errors.
Single Word Reading. At 5½ (t3) and 8 (t5), children completed the YARC Single
Word Reading test (Hulme et al., 2009), which involved reading a list of 60 words of
increasing difficulty. Testing was discontinued after five consecutive errors/refusals. At age 8
(t5), they completed the Exception Word subtest from the Diagnostic Test of Word Reading
Processes (Forum for Research in Language and Literacy, 2012).
Nonword Reading. At age 8 (t5), children completed the Graded Nonword Reading
Test (Snowling, Stothard & McLean, 1996) (t5) which involved reading 20 nonwords (10
one-, 10 two-syllables).
Executive Function Measures
Visual Search. At age 4½ (t2), children completed the Apples Task (Breckenridge,
2008). The child was given one minute to search an array to identify targets (18 red apples)
11Frequency Discrimination and Reading
whilst ignoring distractors (81 red strawberries and 81 white apples). The number of targets
identified and the number of commission errors made (pointing to a distractor; false alarms)
were recorded. A visual search efficiency score (total targets correctly identified –
commission errors)/60 seconds) was calculated; a high score reflects better selective
attention.
Self regulation. At age 4½ (t2), children completed the Head Toes Knees and
Shoulders test (HTKS; Burrage et al., 2008). In this measure of behavioural inhibition, the
child had to do the opposite of what the examiner said (e.g. touch their toes if asked to touch
their head and vice versa). If the child was able to inhibit on 5/10 trials, they went on to
complete a further block of 10 harder trials with additional commands (e.g. to touch their
shoulders if asked to touch their knees and vice versa). Each correct response received two
points. Self-corrected responses (partial inhibitions, whereby the child moved towards the
incorrect, intuitive response but demonstrated the correct final response) received 1 point.
(maximum score = 40).
Visuo-spatial Memory. At age 4½ (t2), children completed Block Recall (Working
Memory Test Battery for Children, Pickering & Gathercole, 2001) a measure of visuo-spatial
memory. The child saw the examiner tap a sequence of blocks on a board and then recalled
the sequence by tapping the blocks in the same order. The task was discontinued after two
consecutive failures for sequences of the same length (maximum score 52).
Frequency Discrimination Measure
Frequency discrimination was measured at age 4½ (t2) and 5½ (t3) years using a task
based on one shown by McArthur, Ellis, Atkinson, and Coltheart (2008) to be highly
sensitive to deficits in dyslexic children. This task has good reliability across time and
correlates well with other measures of frequency discrimination (McArthur & Bishop, 2004).
The task is an adaptive three-interval, two-alternative forced choice AXB procedure with a
12Frequency Discrimination and Reading
maximum of 60 trials. Each trial comprised three 100ms pure tones (including 10ms offset
ramps) presented at 83dB SPL and separated by an ISI of 300ms. The “standard” tone (X) set
at 1000Hz was always presented as the second tone. In each trial, either the first tone (A) or
third (B) tone was randomly allocated to match the frequency of the standard tone. The
remaining tone became the “target” tone that was set at a higher frequency than the standard
tone using a modified PEST procedure (Taylor & Creelman, 1967). There were 100 different
possible target tones ranging from 1005-1500Hz in 5Hz steps. This range is commonly used
in discrimination tasks because it represents the approximate range of the first two formants
of many speech sounds (the most important formants for speech recognition). In early trials,
the PEST procedure ensured that trials were relatively easy by allocating a large frequency
difference between the standard and target tones (i.e., the target tone was set at 1500 Hz).
After two consecutive correct responses, the algorithm reduced the frequency difference in
large step sizes (200 Hz) until an error was made. At this point – called a “reversal” – the
algorithm decreased the step size (e.g., to 100 Hz) and made the discrimination easier by
increasing the frequency of the target tone relative to the standard tone. The step size was
halved progressively with each reversal. The smallest step size was 5 Hz. This final step size
was chosen instead of a more typical final step size of 0.1 Hz because our sample was much
younger (4½ years) than those in previous studies (9+ years) and hence had less fine-grained
frequency discrimination.
Children were given the following instructions for completing the task:
“Here are two baby snails (experimenter points to the two small snail pictures displayed on
the screen) and a mummy snail (the experimenter points to the large snail picture displayed
in the centre of the screen above the two smaller snails). One of the baby snails sounds
different (the target) from the mummy snail. Can you hear which one sounds different from
the mummy?” The child was instructed to indicate their response by touching the target snail
13Frequency Discrimination and Reading
- this was demonstrated by the examiner. If the child touched the mummy snail they were
prompted with ‘listen carefully – it is one of the baby snails which sounds different from the
mummy’.
Children could have up to 20 practice trials to familiarise themselves with the task;
however, once they obtained 3 consecutive correct responses the test trials began. The PEST
procedure continued until there had been 8 reversals in the adjustment of the target tone, or
the child had completed 60 trials (whichever came first). The child's threshold was calculated
as the mean value (in Hz) of the last 4 reversals of the target tone. This represented the child's
threshold for discriminating between the frequency of the standard and target tones. A higher
threshold score reflects poorer discrimination.
At the end of the task, the examiner rated both their judgement as to how well the
child understood the task and the child’s attention during it, each on a 5-point scale (0-poor to
5-excellent). A subsample of the cohort completed a second phase of testing a week later to
calculate test re-test reliability (r = .57).
Results
Following data screening, we conducted a series of one way ANOVAs comparing the
TD, FR and LI groups on cognitive skills (reading, language, executive function). Follow-up
Bonferroni tests were used to test for statistically significant differences between groups. A
similar set of analyses examined group differences in frequency discrimination. Finally, a
structural equation model examined the longitudinal relationships between frequency
discrimination at age 4½ (t2) and 5½ (t3), measures of language and reading at 5½ and
reading at age 8 (t5).
Group Differences in Cognitive Skills
Table 1 shows the reliabilities and the means and standard deviations for the
measures used at each time point together with Cohen’s d for the differences between the TD
14Frequency Discrimination and Reading
and the FR and LI groups, respectively. In general, measures were well distributed although
there were floor effects for reading measures at age 4½ (t2) and for the FR and LI groups on
sentence repetition (N=16) and self-regulation (N=10) measures. There was a consistent step-
wise pattern between the group means for most measures, with the TD group having better
scores than the FR group who had better scores than the LI group. As mentioned previously,
there were no significant differences in language, reading or executive skills between the LI
subgroups (FR vs noFR; these data are therefore not given).
15
Table 1
Raw scores (means and sds) for TD, FR and LI groups across measures of language, reading and executive skills at t2 (4½ years) t3 (5½
years) and t5 (8years) with effect sizes for group differences in means
Reliabilitya TD FR LI F(3, 225) Cohen’s d (95% CIs)
Measure TD vs FR TD vs LI
Language Sentence
Structure t21
.78 18.07a
(2.26)
17.56 a (2.34) 13.75 b
(3.75)
49.14, p < .001 .22 [.08,52] 1.48 [1.04, 1.79]
Sentence
Structure t31
21.72 a
(2.81)
21.44 a (2.86) 18.19 b
(4.34)
39.74, p < .001 .10 [-.21,.41] 1.26 [.88, 1.62]
Sentence
Repetition t22
.78 8.04 a (4.00) 5.81 b (3.23) 2.29 c (2.66) 42.87, p < .001 .62 [.29, .94] 1.63 [1.22, 2.05]
Sentence
Repetition t32
10.53 a
(4.21)
8.20 b (4.49) 5.37 c (4.06) 24.14, p < .001 . 53 [.21,.84] 1.24 [.87, 1.61]
Vocabulary3
t2
.95 65.11 a
(7.60)
63.62 a (9.93) 50.64 b
(8.60)
55.07, p < .001 .17 [-.14,.47] 1.79 [1.39, 2.18]
Vocabulary t34 .78 31.69 a
(6.01)
28.73 b (7.90) 18.88 c
(7.43)
59.02, p < .001 .42 [.10, .73] 1.91 [1.50, 2.31]
Reading Regular word .98 4.11 a (4.80) 2.76 a (3.91) .90 b (2.30) 11.50, p < .001 .31 [.002,.62] .83 [48, 1.17]
16Frequency Discrimination and Reading
reading t25
Regular word
reading t35
12.38 a
(3.31)
10.67 b (3.98) 7.59 c (4.40) 26.27, p < .001 .46 [.15, .78] 1.24 [.87, 1.61]
Irregular word
reading t26
.98 1.39 a (3.41) .67 b (1.97) .29 b (1.91) 3.43, p=.03 .26 [-.04,.57] .39 [.04, .73]
Irregular word
reading t36
7.77 a (5.22) 5.72 b (5.30) 2.47 c (3.62) 20.66, p < .001 .39 [.08, .70] 1.16 [.80, 1.52]
Single word
reading t37
.98 14.44 a
(9.83)
9.94 b (9.64) 4.44 c (7.50) 20.15, p < .001 .42 [.15, .78] 1.13 [.77, 1.49]
Irregular word
reading t58
.97 22.63 a
(4.52)
19.37 b (7.19) 17.22 b (6.8) 12.25, p < .001 .53 [.21, 86] 0.95 [.51, 1.31]
Single word
reading t57
.98 40.93 a
(7.96)
35.0 b (12.63) 30.95 b
(11.55)
14.16, p < .001 .55 [.23, .87] 1.02 [.66, 1.38]
Nonword
reading t59
.78 16.58 a
(3.32)
14.30 b (5.71) 13.33 b
(5.40)
7.84, p < .001 .48 [.16, 79] 0.74 [.39, 1.09]
Executive
Function
Visual search
t210
.54b .18 a (.05) .17 a (.06) .12 b (.07) 16.38, p < .001 .21 [-.10,.52] .98 [.62, 1.34]
Self-regulation
t211
.52 b 25.96 a
(9.66)
22.43a
(11.49)
9.90 b
(10.01)
40.74, p < .001 .33 [.02,.64] 1.64 [1.24, 2.03]
17Frequency Discrimination and Reading
Visuo-spatial
memory t212
.63 c 16.93 a
(3.41)
15.53 a, b
(4.21)
14.27 b
(3.75)
7.79, p < .001 .36 [.05, .67] .75 [.39, 1.10]
Table Notes 1 CELF Sentence Structure; 2 Experimental Sentence Repetition test; 3 ROWPT; 4 CELF Expressive Vocabulary; 5 YARC Early Word Recognition Test, regular words; 6 YARC Early Word Recognition Test irregular words; 7 Single word reading (SWRT); 8 Diagnostic Test of Word Reading Processes 9 Graded Nonword Reading test 10Visual search efficiency; 11 Head, Toes, Knees and Shoulders; 12 WMB-C Block Recall. aCronbach α unless otherwise stated; bStability t2-> t3; cTest re-test reliability. Values with the same subscript do not differ significantly.
18
Group Differences in Frequency Discrimination
Table 2 shows the numbers of children from each group for whom a threshold for
frequency discrimination (FD) was obtained at age 4½ (t2) and age 5½ (t3) as well as the
mean FD thresholds and ratings of how well the children understood and attended to the task.
Children who did not complete the task because they were unable to pass the practice
criterion (three consecutive correct responses in 20), could not understand the instructions, or
refused to co-operate, were recorded as ‘missing’. In addition, a small number of children
exited the task prematurely (2-9 children across groups at age 4½ (t2); 1-2 at age 5½ (t3)).
There was a larger percentage of missing data from the LI than from the other groups,
particularly at age 4½ (t2). It seems likely that this missing data resulted from poor
understanding of task instructions as rated by the assessors (concurrent correlations between
measures of language and judgments regarding comprehension of instructions were .31-.49).
19
Table 2
Group comparisons of frequency discrimination threshold for the TD, FR and LI groups
TD FR LI F Cohen’s d (95% CIs)Time 2 (4½ years)
TD-FR TD-LI
N (% threshold available)
74 (86%) 91(81%) 64 (40%) n/a n/a
Mean FD Threshold (Hz)
320.3 a (158.4) 278.0 a (170.0) 345.13 a (162.3) 2.03, p=.13 -.26 [-.05, .56] -.15 [-.49, .18]
4.4 a (.72) 4.11 a (.97) 3.21 b (1.21) 8.12, p=.000 .33 [-.02, .64] 1.21 [.85, 1.58]
Attention during task1
4.30a (.78) 4.14 a (.84) 3.72 b (.96) 7.52, p=.001 .20 [-.11, .50] .67 [.32, 1.10]
Table notes 1 = 0 (poor) - 5 (excellent) 2 Test-retest reliability of threshold estimate at t3 = .572 3 Value on an arbitrary scale relating to size of detectable difference in frequency at each of the last 4 reversals; multiply by 5 for values in Hz.
21
At age 4½ (t2), more than 80% of the FR and the TD children obtained a threshold,
whereas only around 40% of the LI children did so. For children contributing data, the group
differences in frequency discrimination were not statistically significant at age 4½ (t2)
(F(2,157) = 2.03, p = .13). There were improvements in children’s thresholds from age 4½
(t2) to age 5½ (t3), and these improvements were largest in the TD group, followed by the FR
group, followed by the LI group. At age 5½ (t3), most children tested obtained a threshold,
including those in the LI group. At this age there was a significant group difference in
frequency discrimination (F (2,216) = 11.5, p<.001) indicating that the LI group had
significantly poorer thresholds than either the TD and FR groups, which did not differ
significant from each other. The finding that poor frequency discrimination appears to be
associated with poor language rather than with family-risk of dyslexia per se was tested
further using an ANOVA to assess the effects of family risk (FR), language impairment (LI)
and their interaction on FD threshold at age 5½ (t3)(see Supplementary Table 1 for data from
the FRLI and LI subgroups separately). There was a significant effect of LI, (F(1,213 =
22.41, p < .001) but not of FR, (F(1,213 = 0.75, p= 0.39) and the interaction LI * FR, was
not significant (F(1,213 =0.01).
Ratings of attention during the task for each group are also shown in Table 2. At both
age 4½ (t2) and 5½ (t3), children with LI were rated as attending less well than those in the
other two groups. Given that the LI group had poorer scores on executive function tasks
(Table 1) and also showed poorer attention in the FD task (Table 2), it seems likely that the
poor thresholds obtained by these children in the frequency discrimination task were due to
difficulties in maintaining attention in the task.
Longitudinal Relationships between Frequency Discrimination, Reading, Language and
Executive Function
22Frequency Discrimination and Reading
The correlations between measures for the whole sample are shown in Table 3 (N = 241).
Intercorrelations between language measures were moderate-strong across time.
Intercorrelations between reading measures across time were strong. Executive measures
correlated moderately with each other and with reading and language. The correlation
between frequency discrimination at age 4½ (t2) and 5½ (t3) was moderate (r = .36).
Correlations between frequency discrimination and cognitive measures were low to moderate
at age 4½ (t2), though stronger at age 5½ (t3).
23
Table 3
Correlations between measures of frequency discrimination, reading, language and executive function across time points