1. The effect of partial sleep
deprivation (24h) on gap
detection thresholds and
temporal ordering tasks
Petri Nel
Lezahn Prinsloo
Supervisors: Dr. L. Pottas & Dr. M. Soer
In partial fulfillment of the requirements for the degree B.
Communication Pathology in the Department of Speech-
Language Pathology and Audiology, Faculty of Humanities,
University of Pretoria
2. 2
Abstract
Objective: Temporal patterning abilities are connected with activity from the prefrontal
cortex, which has been shown to be one of the primary areas affected by sleep
deprivation. Therefore the main aim of this study was to determine the effect of partial
sleep deprivation for a period of 24 hours on temporal patterning abilities in young
adults with normal hearing and auditory processing abilities.
Design: The duration pattern test was used in both the humming and labeling method of
response to obtain results for temporal ordering tasks. The gaps-in-noise test was also
employed and generated two different measurements, an approximation threshold and
a percentage score. All measurements were obtained prior to sleep deprivation as well
as after sleep deprivation had occurred.
Study Sample: In the present study twenty healthy adult participants (9 females and 11
males, aged 22.65 0.72 years) were subjected to a preliminary screening protocol that
included a pure tone audiometry test, immittance testing and Dichotic Digits Test. If
participants met the selection criteria they were allowed to participate in the study.
Results: The results obtained in the present study indicated a significant statistical
difference for three out of the four measurements that were compared. No significant
difference in results was found for the duration pattern test, labeling method of
response.
Conclusion: The findings of this study demonstrated that sleep deprivation affects
temporal patterning abilities that are associated with the prefrontal cortex with the
exception to complex tasks that elicit a compensatory response.
Keywords: Temporal patterning, temporal resolution, sleep deprivation, prefrontal
cortex, Duration pattern test, Gaps-in-Noise test
3. 3
Plagiarism Declaration
DECLARATION
Full name: Petri Nel Full name: Lezahn Prinsloo
Student number: 11124432 Student number: 11135525
Degree: B. Communication Pathology Degree: B. Communication Pathology
We declare that the research report is our own original work. Where secondary
materials are used, this has carefully been acknowledged and referenced in accordance
with university requirements.
We understand what plagiarism is and are aware of the University of Pretoria's policy
with this regard.
______________________ _____________________
SIGNATURE DATE
______________________ _____________________
SIGNATURE DATE
UNIVERSITY OF PRETORIA
FACULTY OF HUMANITIES
DEPARTMENT OF SPEECH-LANGUAGE PATHOLOGY AND AUDIOLOGY
4. 4
Acknowledgements
Thank you to our supervisors, Dr. Pottas and Dr. Soer, for the guidance and
motivation throughout the completion of our research project.
A very special thank you to all 20 participants that took part in our study. We
really appreciate it and without them we would not have been able to complete
our project.
Thank you to Sandile for the completion of the statistical analysis as well as the
explanation and advice of the results.
Thank you to the Department of Communication Pathology for the provision of
the equipment that was required in order to complete our data collection.
5. 5
Table of Contents
List of Figures ............................................................................................................................................. 6
List of Tables............................................................................................................................................... 7
_____________________________________________________________________ ............................8
Introduction ............................................................................................................................................8
Methodology.........................................................................................................................................11
Aims of the study...............................................................................................................................11
Research design.................................................................................................................................11
Ethical considerations........................................................................................................................11
Participants .......................................................................................................................................12
Sampling method and sample size .................................................................................................12
Participant selection criteria ..........................................................................................................12
Materials and apparatus for preliminary screening protocol ..........................................................13
Procedures for screening protocol .................................................................................................14
Description of participants.............................................................................................................14
Materials and apparatus for gathering of data...................................................................................14
Audiometric equipment..................................................................................................................14
Gaps-in-Noise (GIN) .......................................................................................................................14
Duration Pattern Test (DPT)...........................................................................................................15
Procedures for data collection .......................................................................................................15
Data processing and analysis.................................................................................................................16
Results ..................................................................................................................................................17
Comparison of results of the BSL and post SD for DPT (humming method of response)......................17
Comparison of results of the BSL and post SD for DPT (labeling method of response) ........................18
Comparison of results of the BSL and post SD for GIN A.Th................................................................19
Comparison of results of the BSL and post SD for GIN percentage scores...........................................19
Discussion .............................................................................................................................................20
Conclusion.............................................................................................................................................24
Clinical implications...............................................................................................................................24
Recommendation..................................................................................................................................24
References ............................................................................................................................................25
6. 6
Appendices ................................................................................................................................................ 26
List of figures
Figure 1: Comparison of the average of the DPT BSL results and post SD for the
humming method of response (n=20)...............................................................................17
Figure 2: Comparison of the average of the DPT BSL results and post SD for the
labeling method of response (n=20) .................................................................................18
Figure 3: The mean scores of the GIN approximation thresholds (A.Th): BSL and post
SD results compared (n=20).............................................................................................19
Figure 4: The average of the GIN percentage scores: BSL and post SD results
compared (n=20) ...............................................................................................................20
7. 7
List of Tables:
Table 1: Screening apparatus used for participant selection...........................................13
8. 8
Abbreviations: CAP = Central auditory processing, CAPD = Central auditory
processing disorder, DDT= Dichotic Digits Test, DPT = Duration Pattern Test, SD =
Sleep deprivation, PFC = Prefrontal cortex, BSL = Baseline, GIN = Gaps-in-Noise,
STDEV= Standard deviation, LPFC = Lateral prefrontal cortex, CRH= Compensatory
Recruitment Hypothesis, A.Th = Approximation threshold, N= Norm
_____________________________________________________________________
Introduction
Sleep is a reversible state of consciousness that alternates with wakefulness and is
characterized by an increased threshold to sensory input and decreased motor output.
(Walker, 2009). These characteristic changes occur in the central and peripheral
physiologic processes and conscious awareness diminishes (Walker, 2009). Sleep has
important functions which include the homeostasis of energy systems, memory
processing, thermoregulation and cognitive performance (Walker, 2009).
In modern societies our lifestyles are associated with increased stress, and as a result,
a decrease in the quantity and quality of sleep (Liberalesso, D'Andrea, Cordeiro,
Zeigelboim, Marques, & Jurkiewicz, 2012). Several factors have been suggested that
could possibly cause this reduction of sleep. These factors include adjustments in the
environment and cultures such as increased environmental light, increased
industrialization and more people doing shift work (Chokroverty, 2009). The unfortunate
result of these factors is that sleep deprivation (SD) in adults have a prevalence of up to
20% (Hublin, Kaprio, Partinen, & Konskenvuo, 2001). Studies dating back as far as
1896 have demonstrated that insufficient sleep negatively affects cognitive performance
in humans (Dinges, 2005). Studies showed an impairment of performance when sleep
deprival occurred in humans proving sleep as a vital part of human functioning
(Chokroverty, 2009). Sleep deprivation (SD) experimentation also demonstrates that
sleep is essential for functioning, awareness, concentration and memory (Chokroverty,
2009).
It is considered that adults require approximately 7.5 to 8 hours sleep continuously in a
24 hour period (Chokroverty, 2009). A decline in the duration of sleep that individuals
obtain has been shown to negatively affect the immune, metabolic, and endocrine
9. 9
systems (Imeri & Opp, 2009). Partial SD occurs when an individual acquires less than
seven hours of sleep in a 24 hour period (Dinges, 2005).
SD and its effects on humans have been studied extensively; however, limited
information is available on SD and its effect on central auditory processing (Liberalesso
et al., 2012). ASHA (American Speech-Language Hearing Association) defines central
auditory processing (CAP) as the way in which the central nervous system uses
auditory information and stimuli (ASHA, 2005). CAP is cognitively responsible for
language comprehension and for the following behavioral phenomena: localization and
lateralization of sound; auditory pattern recognition; auditory discrimination; the
temporal aspects of audition or sounds (including auditory masking, auditory resolution,
integration, and ordering); as well as for the ability to compensate for auditory
performance with degraded acoustic signals (Geffner & Ross-Swain, 2007). Chermak
and Musiek (1997) state that speech reception and auditory processing of spoken
language is a process much more intricate than simply the arrival of speech and sound
at the eardrum (Mulder, Rogiers, & Hoen, 2010). Hearing involves a large number of
mechanical and neurobiological operations and thus is not limited to the detection of an
acoustic stimulus (Mulder et al., 2010). All these aspects of audition depend on the
conveyance of neural information and impulses across synapses (ASHA, 2005).
Auditory temporal resolution, a component of CAP, is a perceptual function connected
with activity from the prefrontal cortex (PFC) (Liberalesso et al., 2012). The PFC is one
of many brain regions that is first to be affected by SD (Zukerman, Babkoff, Fostick, &
Ben-Artzi, 2005). Temporal resolution is the capability of the auditory system to react to
fast alternations in the envelope of a sound over time and gap-detection models can be
used to measure a primary aspect of this ability (Plack & Viemeister, 1993). This CAP
task is essential for understanding speech in a quiet and noisy environment (Geffner &
Ross-Swain, 2007). Tasks highly reliant on optimal PFC functioning will display a
decrease in function, even with SD of a mild to moderate degree (24 hours) (Zukerman
et al., 2005).
10. 10
Multiple tests are available to measure temporal resolution, in which the auditory
systems' ability to resolve time, is assessed (Geffner & Ross-Swain, 2007). The Gaps-
in-Noise (GIN) test, developed by Chermak and Musiek (2005), measures the detection
of temporal modulation, duration discrimination and gap-duration discrimination.
According to Geffner and Ross-Swain (2007), the GIN test provides better specificity
than other temporal resolution measures as it has the smallest range and standard
deviations.
Another temporal processing skill is temporal ordering, which is the ability of an
individual to process two or more auditory stimuli in order of the occurrence in time
(Musiek & Chermak, 2007). Recognition of the temporal order of sounds is an essential
perceptual ability for speech-understanding and relies on memory (Fogerty, Humes, &
Kewley-Port, 2010). Information is stored in the working memory, but also needs to be
categorized according to its order of occurrence (Katz, Medwetsky, Burkard, & Hood,
2009). The lateral prefrontal cortex (LPFC) is responsible for formulating and execution
of plans and sequences of action (Katz et al., 2009). Therefore it is evident that since
sequencing is a critical role in working memory, it is likely to be involved in the receptive
aspects of ordering phonological information to develop its lexical representations and
sequencing (Katz et al., 2009). Working memory tasks typically rely on brain function
within the PFC, and the PFC has been identified as the brain region most vulnerable to
SD (Walker, 2009). According to Walker (2009), studies that examined the brain
function of tasks that rely on working memory following SD, have shown an increase
and decrease in activation of the cerebral response (Walker, 2009). Therefore the effect
of SD on the cerebral response to working memory demands remains unclear (Walker,
2009). It is speculated that the brain response to other working memory tasks possibly
relies on the specific nature of the task demands and the specific sub-regions within the
PFC underlying performance of those specific demands (Walker, 2009). Subsequently
the compensatory recruitment hypothesis (CRH) was formulated that may explain this
phenomenon. The CRH states that the brain possesses the ability to recruit additional
cognitive resources during task performance following SD that aids in execution of tasks
(Walker, 2009).
11. 11
Research has previously indicated that SD adversely affect processes associated with
the PFC, thus we can hypothesize that SD could impair the functioning of central
auditory processes that involve the PFC (Liberalesso, et al., 2012) and as a result it
may influence the reliability of auditory assessment. SD and its effects on humans have
been studied extensively; however, limited information is available on SD and its effect
on CAP (Liberalesso et al., 2012).
Therefore the primary aim of this study is to measure the effects of short periods of total
SD (i.e. 24 hours) on temporal auditory processing. This will be achieved by using gap-
detection thresholds and duration pattern tests to draw inferences on temporal
resolution and -ordering functioning.
Methodology
Aims of the study
The main aim of this study was to determine the effects of partial SD (i.e. 24 hours) on
temporal processing. The sub aims were to determine the effects of partial SD on
temporal ordering and temporal resolution skills, specifically using gap detection
thresholds and duration pattern percentage scores to determine the effect of SD.
Research design
A descriptive comparative research design was selected and a quantitative approach
was applied. This research design was employed due to the fact that two related
samples, "before and after" results within the same individual, were determined and
compared. The baseline (BSL) test results of adults with normal hearing were compared
to test results that were obtained after SD had occurred.
Ethical considerations
As required for undergraduate studies, approval was obtained by the Departmental
Research and Ethics Committee of the Department of Speech-Language Pathology and
Audiology, University of Pretoria before any data collection commenced (See Appendix
A). All participants signed an informed consent form prior to participation in testing
12. 12
procedures (See Appendix B). Confidentiality was maintained by allocating code
numbers to each participant (SASHLA, 2010). Participants were given the option to
withdraw from the study at any point in time (SASHLA, 2010).
Participants
Sampling method and sample size
Random stratified and purposive sampling was used for the purpose of this study. This
method was chosen as it increases the precision of the sample. (Ebrahim & Bowling,
2005). Participants were randomly selected from the University of Pretoria and
surrounding communities with specific reference to their age. The termination of data
collection occurred after 20 data sets were obtained.
Participant selection criteria
A sample of 20 participants, aged 18 to 30 years was recruited to participate in this
research study. Participants had to present with normal hearing sensitivity (0 dB to 15
dB) as this is a prerequisite for auditory processing testing (AAA, 2010). Normal
immittance results (Type A tympanogram; normal middle ear pressure -50 to +50 daPa,
static compliance 0.3 to 1.75 ml and ear canal volume 0.4 to 1.0 ml and acoustic
reflexes at 70 dB to 90 dB above threshold level were also considered as selection
criteria as several studies (Katz et al., 2009) have demonstrated the possible negative
impact that a peripheral hearing loss has on CAP test performance (AAA, 2010). In
order to rule out the presence of auditory processing disorders (APD), the Dichotic
Digits Test (DDT) was implemented. The DDT has been shown to be sensitive to
cortical lesions that may affect temporal processing (Bellis, 2003). A previous study
done by (Samelli & Schochat, 2008) also employed the DDT as a basic triage for
auditory processing abilities of their participants. Participants scoring ≤ 80% with the
DDT were excluded from the study as this is considered the norm for normal auditory
processing abilities (Bellis, 2003). According to AAA (2010) an individual's cognitive
status could influence their ability to complete complex behavioral measures of auditory
functioning, thereby leading to inaccurate interpretation of results and may also render
test results invalid. All participants were required to have competent cognitive status
and to be proficient in the language of instructions (Afrikaans and English) given. Use of
13. 13
medication was prohibited, due to the fact that many drugs act as a stimulant that
inhibits falling asleep (Walker, 2009) and may have an influence on the results.
Stimulants such as caffeine and Modafinil maintain cognitive performance during sleep
loss and thereby play a role in managing cognitive performance under a variety of
conditions (Wesensten, 2012).
Materials and apparatus for preliminary screening protocol
Apparatus: Screening for participant selection
Table 1 provides a summary of the materials and apparatus used during the preliminary
screening protocol as well as the motivation for use. Scoring sheets for each
corresponding test were utilized to record assessment results for each participant (See
Appendix C).
Table 1: Screening apparatus used for participant selection
Assessment materials and apparatus Motivation for use
Otoscopy (Welch-Allyn, Model 25270-MS)
Visual inspection of ear canal, eardrum and
bony structure of middle ear.
Immittance (GSI Tympstar)
(Calibration: January 2014)
Assess middle ear functioning including
compliance, ear canal volume and pressure.
Assess the presence of stapedial reflexes.
Hearing evaluation (GSI 61 Welch-Allyn
audiometer equipped with Telephonic – 50
earphones)
(Calibrated in January 2014)
Assessed pure tone hearing thresholds to
determine hearing sensitivity of individual.
Dichotic Digit Test (Sansui CD210 CD
player)
Assessed central auditory processing (CAP)
abilities namely; binaural integration and
binaural separation (Bellis, 2003).
14. 14
Procedures for screening protocol
All participants underwent a screening procedure prior to BSL testing in which they were
required to complete a case history form, score above 80% for the DDT, had to have
normal immittance and otoscopic findings, and normal pure tone thresholds (0 dB HL –
15 dB HL) across the frequency range i.e. 125 Hz to 8000 Hz. These tests were utilized
to ensure that participants met the criteria which are required.
Description of participants
The cohort included 9 females (45 %) and 11 males (55 %), with a mean age of 22.65
(standard deviation, 0.72).
Materials and apparatus for gathering of data
Audiometric equipment
Temporal processing tests was conducted using GSI 61 Welch-Allyn audiometer
equipped with Telephonic – 50 earphones (Calibration: January 2014). A Sansui CD210
CD player was used to present test materials to participants, while seated in a sound
proof booth
Gaps-in-Noise (GIN)
The GIN, developed by Frank Musiek and colleagues (Samelli & Schochat, 2008) was
used to clinically measure participant’s temporal resolution abilities. Testing material
consists of one practice list and four test lists, due to time constraints only the practice
list, test one and test two item lists were utilized. A study showed that the equivalent
forms reliability for the GIN test is high; therefore the choice of lists utilized does not
affect the outcome of the results (De Lange & Hattingh, 2012). Another study done by
Samelli et al. ((2008) demonstrated similar responses inter-lists and for both ears,
confirming the above mentioned. Each item was presented monaurally at 50 dB HL
above pure tone average (PTA). Ten practice items were presented to the participant to
ensure that clarity was achieved. The GIN is composed of a series of computer-
generated, equally distributed, broadband noise segments of six seconds in duration.
Each six second segment of noise consists of zero to three silent intervals ranging from
two to twenty ms embedded in six second segments of white noise. The position,
number and duration of gaps per noise segment are randomized throughout the test
15. 15
(Samelli & Schochat, 2008). Scoring for the GIN is administered by means of calculating
the GIN approximation threshold (GIN A.Th), followed by the GIN percentage score.
Adult norms for the GIN A.Th is considered to be less than or equal to 8msec per
segment of noise (Musiek & Chermak, 2007). The GIN percentage score cut off score
for adults is 54% any score lower is perceived as abnormal (Musiek & Chermak, 2007).
Duration Pattern Test (DPT)
The DPT, also developed by (Musiek & Chermak, 2007), was used to assess temporal
patterning abilities of participants.
The DPT as described by Musiek and Chermak (2007) is composed of three pure tones
per token; each tone is presented at 1000 Hz. These tones are either short (250 ms) or
long (500 ms) in duration. An inter-tone interval of 300 ms is used for testing. The DPT
consists of six randomizations (LLS, LSL, LSS, SLS, SLL and SSL) and uses a 6
second inter-pattern interval. The DPT was used with both methods of response,
‘humming’ and ‘labeling’.
Participants were instructed to; firstly, label the sounds they heard by categorizing the
sound as short or long, thereafter they were instructed to hum what was heard. A list of
20 items was presented monaurally for each method of response. One item consisted of
three tones. Participants had to correctly label or hum all three tones for the item to be
recorded as correct. The DPT was presented 50 dB HL above participant’s PTA. The
percentage scored correctly by participants was established for each of the variables.
Procedures for data collection
CAP assessment protocol
CAP was assessed with the use of the GIN and the DPT at two different periods of time,
BSL and after 24 hours post SD. The BSL CAP tests were conducted immediately after
the initial hearing evaluation on the subjects who adhered to the selection criteria. The
BSL results were obtained on participants in a normal (rested) state and the second test
was performed after participants had no sleep continuously for 24 hours. A researcher
remained with participants throughout the night to ensure participants did not fall asleep
and to ensure that the validity of results was maintained. Activities such as watching
television or playing computer games were the preferred choice of activity during the SD
16. 16
period. All participants were prohibited from smoking; consuming any medication,
stimulants, caffeine, or alcohol for the 24 hours between the BSL and 24 hours SD test
sessions.
Data processing and analysis
Data processing
The data collected was entered in master charts by the two primary researchers and
analyzed quantitatively using statistical methods. Thereafter the data were refined to a
single Microsoft Excel (2007) sheet, replacing the raw data with the corresponding
assigned coded values to the outcomes of each test.
The DPT consists of two ear specific lists of 25 items, each used correspondingly. This
score indicates the number of items out of 25 which the subject indicated correctly. The
following formula was employed to calculate percentage score per ear:
The GIN has two measures of analysis, the approximation threshold (A.Th) and the
overall percentage correct. The A.Th is the shortest gap duration for which there were at
least four of six correct (67%) identifications (Shinn, Chermak, & Musiek, 2009).The
number of gaps correctly identified represents the overall percentage score (Shinn,
Chermak, & Musiek, 2009). These percentages do not refer to the approximation
thresholds (A.Th) but to the gaps perceived (Samelli & Schochat, 2008). Results were
presented as means for both gap detection thresholds and percentage scores. The
approximation threshold (A.Th) and percentages of correct responses are unrelated and
independent variables (Samelli & Schochat, 2008).
Data analysis
The Statistical Software Package SPSS 15.0 was employed to analyze the data and
Microsoft Word and Excel were used to generate graphs, tables etc.
17. 17
Figure 1: Comparison of the average of the DPT BSL results and post SD for the
humming method of response (n=20)
The Kolmogorov-Smirnov test was used to determine if data was distributed normally.
Most of the variables relevant to this study, were not distributed normally, thus
nonparametric procedures was the more reliable method to use. Comparing two related
samples, according to Corder and Foreman (2009), the appropriate nonparametric test
is the Wilcoxon Signed Ranks test (Corder & Foreman, 2009).
The level of significance adopted for this study was <0.05 which is represented as the p-
value. If the p-value is < 0.05, it indicates that there is a statistically significant difference
at a 5% level of significance (Williams, Sweeney, & Anderson, 2009).
Results
The results of this study are discussed according to the set sub aims.
Comparison of results of the BSL and post SD for DPT (humming method of
response)
In order to determine the effect of SD on temporal ordering, the BSL results of the DPT
were compared to the post SD results.
In Figure 1 it is that evident that there was a decrease in the average scores (85.55%,
STDEV=16.88) after SD had occurred in comparison to the BSL (95.3%, STDEV= 6.66)
results The cut off score of 73% as set out by Bellis (2003) indicates that both scores
obtained fall within normal limits (Bellis, 2003). The average DPT (humming)
95.3
85.55
0
20
40
60
80
100
PercentageScores
Participants
DPT (Humming)
BSL
Post SD
18. 18
percentage scores following 24 hours of SD (24hSD) were significantly lower than those
observed during the BSL condition without SD. A p-value of <0.001 was calculated with
the Wilcoxon Signed-Rank test when results of the BSL and post SD were compared.
Comparison of results of the BSL and post SD for DPT (labeling method of
response)
The BSL percentage scores of the DPT were compared to the post SD scores for the
labeling method of response. Figure 2 indicates the results obtain by the participants for
DPT labeling method of response.
Figure 2 projects a slight visual difference between the results observed for BSL
(86.63%, STDEV= 16.97) and the post SD (82.65%, STDEV=17.09) for DPT labeling
method of response. Bellis (2003) set out a cut off score for DPT (labeling) of 73% for
both ears (Bellis, 2003). Both results obtained fall within normal limits. No significant
difference was obtained for this method of response in the DPT with a p-value of
<0.131, indicating that SD did not adversely affect the DPT in the case of labeling
method of response.
86.63
82.65
0
10
20
30
40
50
60
70
80
90
100
PercentageScores
Participants
DPT (Labelling)
BSL
PostSD
Figure 2: Comparison of the average scores for the DPT BSL results and post SD for the
labeling method of response (n=20)
19. 19
Comparison of results of the BSL and post SD for GIN A.Th
The first score calculated for the GIN was the approximation threshold (A.Th). The A.Th
is the shortest gap duration for which there were at least four of six correct (67%)
identifications. BSL results were compared to the results obtained post SD (Figure 3).
Figure 3 provides a clear representation of the threshold shift that occurred between the
BSL (A.Th=4.9, STDEV=0.83) and post SD (A.Th=5.68, STDEV= 0.91). The normative
value for A.Th is ≤ 8 ms, therefore both results obtained are within normal limits (Musiek
& Chermak, 2007). The Wilcoxon Signed-Rank test was used to compare the results
obtained in the two different conditions. The results indicate a statistically significant
difference with a p-value <0.006, demonstrating that SD had a significant effect on GIN
A.Th when BSL and post SD results were compared.
Comparison of results of the BSL and post SD for GIN percentage scores
The second score calculated for the GIN was a percentage score indicating the number
of gaps correctly identified. BSL results were compared to the results obtained post SD.
4.9
5.67
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
BSL Post SD
GINA.Th
BSL vs Post SD
Figure 3: The mean scores of the GIN approximation thresholds (A.Th): BSL and post
SD results compared (n=20)
20. 20
Figure 4: The average of the GIN percentage scores: BSL and post SD results
compared (n=20)
In Figure 4 it is evident that overall percent scores obtained by participants after 24hSD
(62.88%, STDEV=8.30) declined compared to results obtained during BSL (70.93%,
STDEV= 6.18) testing. The cut-off score for percent correct is ≤54% for adults, therefore
both scores obtained fall within normal limits (Musiek & Chermak, 2007). The p-value of
<0.000 as calculated by the Wilcoxon Signed-Rank indicated a significant statistical
difference between BSL results and post SD results.
Discussion
The overall aim of this study was to measure the impact of SD on temporal auditory
processing in a group of healthy adults, specifically the impact on temporal resolution
and temporal ordering skills. This was achieved by comparing results in the GIN and
DPT in a BSL (rested) condition as opposed to after 24 hours of SD. A significant
decline in performance was observed in three out of the four (75%) measurements that
were compared. In a study done by Liberalesso et al. (2012), two temporal processing
tests were employed, the Random Gap Detection Test (RGDT) and Staggered
Spondaic Word Test (SSWT), and were compared prior to SD and after 24hSD. The
70.93
62.88
58.00
60.00
62.00
64.00
66.00
68.00
70.00
72.00
GINPercentageScores
Participants
BSL
Post SD
21. 21
study revealed that both the RGDT and SSWT worsens after SD had occurred, which
substantiates the hypothesis that perceptual functions that are connected with PFC
activity are affected by SD (Liberalesso et al., 2012). Studies done by Harrison and
Horne (2000) have revealed that during wakefulness the PFC is the most active (i.e.
highest metabolic rate of all cortical regions) and that the PFC is one of the first brain
regions to suffer as a result from SD (Harrison & Horne, 2000). Therefore, the current
study was based on the premise that functions connected to PFC activity are primarily
affected by SD. This theory predicts that SD will influence complex tasks that require
higher cortical-related skills.
Temporal ordering: DPT
Firstly, the present study revealed a decrease in the ability of participants to correctly
sequence items presented during the DPT for the humming method of response, this
was determined by the mean scores of performance before and after SD. However, only
a slight decline in performance was observed for the DPT labeling method of response
(Fig. 2) and the results did not reveal a significant difference before and after SD. Due
to the increased complexity that accompanies the labeling method of response a
greater decline with the labeling method of response compared to the humming method
of response would be expected. To strengthen the argument, a study showed that
young South African adults performed better in the humming method of response
(94.83% left, 95.92% right), than in the labeling method of response (87.42% left,
86.08% right) (Veenstra & Buys, 2013). The inference of this being that humming is a
simpler task than labeling, therefore the impact of SD would be greater on the labeling
method response.
This discrepancy in these methods of response after SD had occurred for the DPT can
be explained by a study that demonstrated that an increase in task difficulty facilitates
the cerebral compensatory response in the presence of SD (Drummond, Brown,
Salamat, & Gillin, 2004). A verbal-learning task showed a significant increase in
cerebral responses in both the PFC and the parietal lobes following SD (Drummond et
al., 2004). Additionally, there have been multiple findings showing that SD has a more
deleterious effect on performance of lengthy and boring tasks than on those that are
22. 22
shorter and more interesting (Gosselin, De Koninck, Cambel, & Kenneth, 2005).
However Harrison and Horne (2000) demonstrated that tasks depending on the
prefrontal lobes were still greatly affected by SD even when tasks are interesting and
short (Harrison & Horne, 2000). The above mentioned thus can explain that due to the
increased difficulty that arises in the labeling method of response, a cerebral
compensatory was most likely elicited and therefore participants did not show a
significant decline in performance after 24hSD.
This finding is further supported by another study that indicated that tasks that rely on
working memory (i.e temporal ordering) may elicit a compensatory response in the
presence of SD, depending on the degree of attention that the task at hand demands
(Dinges, 2005). Studies using positron-emission tomography (PET) and functional
magnetic resonance imaging (fMRI) revealed that certain regions of the brain changed
in response to SD (Dinges, 2005). PET studies illustrated an overall decrease in
glucose metabolism throughout cortical and sub-cortical regions during SD (Dinges,
2005). However an increase in impairment of cognitive tasks after SD, showed that
glucose uptake decreased more specifically in the PFC, thalamus and posterior parietal
association cortices (Dinges, 2005). fMRI studies confirm that after 24hSD, attention-
demanding tasks increased thalamic activation and this is thought to demonstrate a
neuroanatomical correlate of increased "mental energy" that occurs during a low state
of arousal (Dinges, 2005). The study demonstrated that verbal working memory after
SD resulted in decreased temporal lobe activation and increased parietal lobe activation
(Dinges, 2005). This increase is associated with the preservation of working memory
function (Dinges, 2005). The above mentioned therefore suggests a possible
neurophysiological mechanism that uses posterior cortical systems to elicit a
compensatory response in the presence of SD and can thus explain the results
obtained in this study.
Temporal resolution: GIN
The outcome of this research study revealed a significant difference in thresholds
obtained pre- and post SD during the GIN test. Results indicated an incline in the GIN
23. 23
A.Th post SD, hence an increase in the length of the shortest gap duration perceived for
which there were at least four out of six correct (67%) identifications.
These results are confirmed by a recent study on the effects of SD on CAP that
indicated that the time period that was needed to recognize the gap of silence between
matching sound stimuli in the Random Gap Detection Test (RGDT) post SD, revealed a
negative impact of SD on temporal resolution ability (Liberalesso et al., 2012).
According to a study done by Babkof et al. (2005), 24 hours of SD reduces auditory
temporal resolution by 28% or more and affects higher level cognitive functions such as
language comprehension and auditory processing (Kerkhof & Van Dongen, 2010). With
regard to the GIN percentage scores the results of the current study indicated a decline
in the participants’ ability to accurately identify the number of gaps after SD. These
results can be explained by research indicating that the auditory function of temporal
resolution (including gap -detection) rely on the functioning of the PFC, which is affected
by SD (Kerkhof & Van Dongen, 2010).
Kerkhof and Van Dongen proposed a study that explains the ‘sleep- based
neuropsychological perspective’ that was first explained by Harrison and Horne in 1983,
which serves as an alternative to the ‘classical arousal hypothesis, in a detailed manner.
This research study suggest that the various parts of the brain are affected differently by
SD and that the area in the brain (PFC) involved in auditory processing or more
specifically, temporal resolution, is directly affected by SD (Kerkhof & Van Dongen,
2010).
The PFC, which is one of the first areas in the brain to be affected by SD, is most active
during wakefulness and plays a critical role in the perception of speech (Babkoff,
Zukerman, Fostick, & Ben-Artzi, 2005). As SD has an influence on the functioning of the
frontal lobe and consequently the PFC, it can also affect the expression and perception
of speech and language (Liberalesso, et al., 2012). As the current study indicated that
participants performed worse in temporal resolution tasks post SD it might consequently
affect their speech perception abilities, due to the fact that speech perception is highly
reliant on temporal resolution.
24. 24
Conclusion
In conclusion, the results presented in this study demonstrated that partial sleep
deprivation for a period of 24 hours is sufficient to significantly affect temporal
processing abilities, i.e. temporal ordering (humming method of response) and temporal
resolution, in healthy young adults. The decline in performance of participants confirms
that SD negatively affects the processes associated with the PFC. The impairment of
these abilities following sleep deprivation may be due the effects of SD on
neurobiological functions that are essential for the processing of auditory information
which include memory, attention, concentration, reaction time and stimulus perception.
Additionally, no significant decline in performance was observed for the DPT (labeling)
due to the elicitation of the cerebral compensatory response in tasks that had a higher
attention-demand and increased task difficulty.
Clinical implications
The results of this study revealed the significant effect that SD may have on CAP,
specifically temporal processing abilities, which are essential for speech perception.
Any CAP testing can thus be influenced by SD and therefore questions regarding
sleeping habits and/or sleeping disorders should be considered in the case history prior
to CAP testing. This will increase accuracy and reliability of results obtained from CAP
tests consequently enabling audiologists to make a more accurate diagnosis of central
auditory processing disorders (CAPD).
Recommendation
The recommendations for future research studies include the increase in sample size
that will enable researchers to make more reliable interpretations of the findings. The
present study was done according to a five day inter-test time frame due to time
constraints which might reduce the accuracy of the findings; therefore it is suggested
that the inter-test interval time should be increased to yield more accurate results.
25. 25
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29. 29
Appendix B: Informed consent
Dear Participant,
REQUEST FOR PARTICIPATION IN A RESEARCH STUDY
As final year students in B.Communication Pathology (Audiology) at the University of
Pretoria, it is required that we conduct a research study and submit a research report in
partial fulfillment of our degree. In our study we will examine the effects of partial sleep
deprivation (lack of sleep for 24 hours) on temporal auditory processing (the ability to
perceive time related changes in acoustic stimuli) and speech recognition in noise.
Due to the lack of information available on this topic, the results obtained in the study may
be valuable for future research studies
Participation in this study will require that you visit the Department of Communication
Pathology at the University of Pretoria. Upon arrival you will be asked to complete a short
background history pertaining to your hearing. A set of tests will be administered to ensure
that hearing and processing of sound is normal. You will then be required to return to the
department on a different date. On this day we require you to remain awake continuously
for 24 hours. Thereafter we will repeat the set on tests administered to measure the effects
on hearing and processing of sound.
Participation in this study is completely voluntary and participants may withdraw from the
study at any time without any negative consequences. Participation in this study does not
pose any risk for participations.
All identifying information of participants will be kept confidential. The data will be kept for
15 years for archiving and research purposes before being destroyed. The data obtained
will be available to our supervisors, Dr. L Pottas and Dr. M Soer, as well as the Head of
Department of Communication Pathology, Prof. B Vinck. All the relevant results will be
complied in a research report, which will be available at the University of Pretoria.
Participants may also request to view the results obtained.
By signing the informed consent, you agree to the following:
Having good sleeping behaviors
Not using any of the following stimulants on the day of testing:
Coffee and tea
Coca cola or any other soft drink containing caffeine, including Redbull and Monster
energy drinks
Alcohol
Smoking
Not using any medication
30. 30
If you require any additional information, you are welcome to contact us at 0849228064 or
0842932855.
Your participation will be greatly appreciated.
Yours Sincerely,
Petri Nel (Student) Lezahn Prinsloo (Student)
Dr. L Pottas (Supervisor) Dr. M Soer (Supervisor)
Prof. B Vinck
HEAD OF DEPARTMENT OF COMMUNICATION PATHOLOGY
