Keywords
auditory perception - hearing tests - dyslexia
Introduction
The ability of temporal resolution is fundamental for comprehension of human speech
and is a prerequisite for linguistic abilities.[1]
[2] This ability acts in the auditory perception of verbal and nonverbal sounds; in
the perception of music, rhythms, and periodicity; and in the discrimination of steps,
duration, and phonemes.[3]
Alteration of the auditory perception may bring about problems in speech and language
development as well as in learning and socialization of children, adults, and the
elderly. The decoding of the spoken message involves the analysis of many signal components
including the acoustical, phonetic, phonological, lexical, suprasegmental, syntactical,
and semantic components.[4]
[5] For this decoding to occur, the acoustical cues of frequency, intensity, and timing
must be processed in a precise manner by the auditory system.[6]
[7]
Phonemes, the isolated sounds that make up the syllables, represent these rapid sound
stimuli in speech. Hence, the individual with altered perception would have difficulty
perceiving that words can be decomposed in those smaller isolated sounds. This ability,
called phonological conscience, is essential for one to master the alphabetical system in which the phonemes are
mapped as letters (graphemes). Therefore, the learning of this ability can be considered
essential when learning how to read[8] and at the same time is the main manifestation of the reading and writing disorders.
According to the World Health Organization,[9] dyslexia is defined as a disorder that manifests itself by specific difficulties in learning
how to read and write that are not attributable to any other kind of deficit related
to intelligence, motivation, learning opportunity, or sensorial acuity. Reading and writing disorder is described as a manifestation that features the difficulty in acquiring and/or
developing written language by children and presents both deficits in phonological
decoding and oral and/or written language comprehension.[10]
Keeping this relation in mind, subjects with phonological deviation and/or reading
and writing difficulties may present alterations in temporal auditory processing and
may need more time to detect gaps between auditory stimuli.
The goal of this study was to verify and compare the temporal resolution ability in
individuals diagnosed with a reading and writing disorder to those with dyslexia,
which may help in speech and language rehabilitation.
Methods
This study was approved by the Universidade Federal de São Paulo Ethics in Research
Committee (UNIFESP/EPM), process no. 1726/09. All the selected subjects were volunteers
and signed a free and willing consent form.
Participating subjects were divided in two groups: 11 with the diagnosis of dyslexia
(GD) and 15 with the diagnosis of reading and writing disorder (GSD). Subjects in
the GSD group were receiving speech and language treatment at the Nucleus for Teaching,
Assistance and Research of Reading and Writing Disorders – NEAPEL – UNIFESP. For patients
with a diagnosis of dyslexia, the Brazilian Association of Dyslexia and Infant Interdisciplinary
Nucleus of Neuropsychological Treatment were contacted.
To form this study sample, volunteers had to be between the ages of 10 and 15, of
either gender, without any history of evidence of psychiatric or neurologic impairment
or of hearing loss.
To constitute the control group, the work of Perez and Pereira[11] was used to establish normalcy reference criteria for youngsters of 11 and 12 years
of age of both genders. The threshold measure considered as the normal value followed
the criteria of a positive response for four of six presentations: a 5.0-millisecond
threshold for the right ear and 5.11 milliseconds for the left ear, and a total 71.99%
correct response for the right ear and 71.41% for the left. A stratified lottery based
on the studied age groups was performed and 21 subjects were selected.
All subjects completed a basic hearing assessment, including collection of a case
history, tonal threshold audiometry, speech audiometry, and tympanometry.
The procedure used to measure the behavior of temporal resolution was the Gaps-in-Noise
(GIN) test proposed by Musiek et al,[12] with a total of 60 silence intervals or gaps inserted in a noise segment, with a
time variation of silence between 2 and 20 milliseconds. Two kinds of responses were
analyzed: the temporal acuity threshold, which is the least value in milliseconds
in which the subject perceived the silence interval, and the total number of correctly
identified gaps, in percentage values.
The GIN test, presented from a CD, was applied using an Interacoustic MA-41 audiometer
attached to a Sony CD player (Interacoustics AS Drejervaenget, Assens0 Denmark) in
an acoustic cabin at a 50-dB SL (sensation level) intensity (according to the mean
auditory thresholds for 500, 1,000, and 2,000 Hz). All the results were recorded in
specific registration sheets. The CD is composed of a training track and four test
tracks. Each test track is composed of diverse stimuli of 6 seconds of white noise
with 5-second intervals between the stimuli.
The training track was applied before the beginning of the test to ensure that the
subject clearly understood what needed to be done. The test was applied to one ear
at a time. In the right ear, test track 2 was used, and in the left ear, test track
3. The instructions to the subjects were: “You will hear a noise and within this noise
there will be spaces or gaps in which the noise will be absent. The gaps will vary in size and you will have to
listen carefully, because some of them will be extremely small. Occasionally there
will be no gaps. You must raise your hand every time you hear a gap.”
The threshold considered was the perception of four of six presentations of the same
gap, that is, 66.66% of identification of a specific silence interval in milliseconds
according to the criteria of Musiek et al.[12]
To assess the answers in this study, in the three groups (control, diagnosis of reading
and writing disorder, diagnosis of dyslexia), the nonparametric test of Kruskal-Wallis
was used, followed by a procedure of multiple nonparametric comparisons. A nonparametric
test was applied because it was not possible to find a transformation that could stabilize
the variance in the responses of the three groups. The criteria adopted to determine
the significance was the level of 0.05 with the construction of confidence intervals
of 95%.
Results
[Table 1] shows the descriptive statistics for the responses obtained by the three groups:
the group with dyslexia, the group with reading and writing disorders, and the control
group. The GIN threshold was not the same for all groups for both the right (p < 0.001) and the left ears (p = 0.0015); it was significantly lower for the control group than for the other groups
(p < 0.05). There was no difference between the group with dyslexia and the group with
reading and writing disorders (p > 0.05).
Table 1
Descriptive measures of the gap thresholds (in milliseconds) and percentage of correct
gap identification for each group for the right and left ears
|
Group
|
Variable
|
Mean
|
SD
|
0%
|
25%
|
50%
|
75%
|
100%
|
No. of subjects
|
|
Control
|
GIN T RE
|
4.6
|
0.57
|
4
|
4
|
5
|
5
|
6
|
21
|
|
GIN T LE
|
5.0
|
0.89
|
4
|
5
|
5
|
5
|
8
|
21
|
|
% GIN RE
|
73.33
|
5.29
|
60.00
|
71.67
|
71.67
|
75.00
|
85.00
|
21
|
|
% GIN LE
|
72.65
|
6.01
|
58.33
|
70.00
|
73.33
|
76.67
|
81.67
|
21
|
|
GSD
|
GIN T RE
|
7.8
|
3.76
|
4
|
5.5
|
6
|
10
|
15
|
15
|
|
GIN T LE
|
7.4
|
2.72
|
4
|
4.5
|
8
|
10
|
12
|
15
|
|
% GIN RE
|
57.44
|
18.22
|
25.00
|
42.49
|
56.66
|
69.99
|
88.33
|
15
|
|
% GIN LE
|
60.67
|
16.39
|
31.66
|
47.49
|
61.66
|
75.00
|
85.00
|
15
|
|
GD
|
GIN T RE
|
7.1
|
1.16
|
5
|
6
|
8
|
8
|
8
|
11
|
|
GIN T LE
|
7.2
|
1.27
|
5
|
7
|
8
|
8
|
8
|
11
|
|
% GIN RE
|
55.60
|
5.83
|
43.33
|
53.33
|
56.66
|
58.33
|
65.00
|
11
|
|
% GIN LE
|
55.60
|
8.03
|
48.00
|
49.16
|
55.00
|
60.83
|
70.00
|
11
|
Abbreviations: GD, group with dyslexia; GIN, Gaps-in-Noise test; GSD, group with specific
reading and writing disorder; LE, left ear RE, right ear; SD, standard deviation;
T, threshold.
The percentage of correct responses for the GIN was not the same for the three groups,
for both the right (p < 0.001) and left ears (p < 0.001). The GIN percentage was significantly higher for the control group than
for the other groups (p < 0.05). There was no difference between the group with dyslexia and the group with
reading and writing disorders (p > 0.05).
Discussion
Analysis of the GIN test in our subjects with dyslexia and subjects with a reading
and writing disorder reinforce studies that indicate that phonological alterations
need a longer temporal processing, that is, need a longer interval to perceive the
difference between sounds. Some researchers indicated that school-aged children with
dyslexia may present temporal processing problems.[13] The perceptual abilities related to speech, language, and reading are extremely
dependent on the ability of temporal resolution, which may be assessed by the GIN
test.
In the present study, school-aged children in the group with dyslexia and the group
with reading and writing disorders presented a deficit in auditory temporal resolution
compared with the control group. There was no statistically significant difference
between the responses for the study group with dyslexia and the group with reading
and writing disorders.
Some studies verified that the phonological deficit must be caused by an auditory
processing deficit due to the fact that the altered auditory temporal processing may
hinder the perception of subtle signals in speech resulting in the observed difficulties
in phonological processing.[13]
[14]
[15]
[16] Boscariol et al studied the Random Gap Detection Test (RGDT) and found results of
13 milliseconds for the control group and 32.39 milliseconds for the GD group.[13] The RGDT and GIN tests assess the temporal resolution ability; however, they have
diverse investigation natures, hence there were differences in threshold limits for
the same sample between test protocols.[17]
Simões and Schochat assessed 40 children aged 7 to 12 years of age, 20 with dyslexia
and 20 in a group with auditory processing disorders.[14] The tests involved the abilities of auditory closure, figure-ground for linguistic
sounds, and temporal ordering. The subjects in the dyslexia group presented altered
responses only for the test that assessed temporal processing.
These researches agree with other studies that associate reading and writing abilities
to auditory temporal processing abilities.[15]
[18]
Regarding the descriptive measures of the auditory responses for the GIN test, we
observed a gap threshold for the right ear of 7.8 milliseconds for the group with
reading and writing disorders and a gap of 7.1 milliseconds for the group with dyslexia.
The left ear obtained the threshold of 7.4 milliseconds for the group with reading
and writing disorders and 7.2 milliseconds for the group with dyslexia. The found
percentage was 55.60% for both ears for the dyslexia group, and for the reading and
writing disorders was 57.44% for the right ear and 60.77% for the left ear.
The literature points to gap thresholds less than 6 milliseconds in subjects from
7 to 46 years of age. This confirms that the subjects with dyslexia and with reading
and writing disorders present worse results when compared with the control group.
Samelli and Schochat[19] observed similar gap detection thresholds for both ears when studying 100 young
adults age 18 to 31. The general mean of the gap thresholds was 3.98 milliseconds
and the mean percentage of correct gap detection was 78.89%. However, the author considered
a gap threshold to be 50% of presentations, that is, three correct responses of the
six presented. A study in school-aged children found values of 4.7 milliseconds and
73.6% in children of 8, 9, and 10 years of age[20] and 5.05 milliseconds and 71.70% in children age 11 and 12 years.[11]
The group with dyslexia and the group with the diagnosis of reading and writing disorders
in our study had lower mean response values than those obtained for the control group
and lower than that in the reviewed literature, indicating the presence of the inability
of temporal resolution in individuals with reading/writing difficulties.
Conclusion
After analyzing the data obtained in this study, subjects in the group with dyslexia
and in the group with reading and writing disorders presented worse responses in the
GIN test than the control group. This result can indicate a correlation between the
temporal processing abilities and the reading and writing abilities.
