PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Parallel task contexts in QoE testing. Can EEG help to understandthe results?
Jan HOLUB1; David Pánek2
1

Faculty of Electrical Engineering, Czech Technical University in Prague, Czech Republic
2

Faculty of Physical Education and Sport, Charles University, Czech Republic

ABSTRACT
Improved intelligibility of distorted speech has been observed after a parallel psycho-motor task has been
introduced. Electroencephalographic activity has been recorded and analyzed for several test situations –neutral, a plain intelligibility test, an intelligibility test with parallel aimed shooting, and an intelligibility testwith parallel hit counting. Our findings indicate increased brain activity in the area of the central auditory
circles, which evaluate the content of audio information during a parallel cognitive and motor task when thecomplex motor parallel task is considered to be primary (more important).
Keywords: Sound quality, speech intelligibility, parallel task, EEG

1. INTRODUCTION
Speech intelligibility is a measure of the clearness of speech, and subjective testing of speech
intelligibility has been standardized, e.g., in (1). The application of appropriate statistical methods (2)enables statistically significant assessments of compared technologies to be made, or a reliability
statement can be made when a minimum intelligibility threshold has been defined. The main issue,
however, is the validity of the fundamental assumption that under lies all currently used test methods:
in standardized tests, the subjects are seated in an anechoic or semi-anechoic test room and are focusedon listening to the tested samples only. In many real communication scenarios, however, users perform
multiple tasks in parallel (jogging, watching TV or driving a car while talking on the phone, forexample).
Existing subjective test methods and related recommendations are based on the simple assumptionthat laboratory tests with the subjects fully concentrated on the test procedure provide the mostsensitive results. In other words, it is assumed that the test samples will generate higher intelligibility
scores than any real-life scenario in which users are distracted by multitasking. However, it isnecessary to verify the validity of the assumption that tests based on fully-concentrated andundistracted subjects necessarily achieve the highest score.
An interesting way to bring subjective tests closer to reality while keeping them in a controlledlaboratory environment is to introduce a parallel task. The test subjects are asked to perform aphysically and mentally challenging secondary task while listening to and evaluating the samples. The
recently approved ETSI Technical Report (3) includes state-of-the-art approaches that have been usedin various published scientific experiments, and also necessary recommendations, classifications,types of subjects, and various examples of scenarios as a guide for researchers when organizing
parallel task-based subjective tests.
In 2018, interesting counter-intuitive results were reported in (4) from intelligibility tests
deploying a parallel task. In some situations, it is reported that the intelligibility scores were
statistically significantly higher with a parallel task than without it. EEG activity monitoring has been
proposed as a way to investigate why this effect was observed (5).
Electroencephalography (EEG) is a widely-used neurophysiological diagnostic method that
displays electric brain activity in a defined spectrum. The main advantage of EEG is its
non-invasiveness, which allows repeated and prolonged recording of brain activity during periods of
1
2

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holubjan@fel.cvut.cz
david.panek@seznam.cz

resting and also periods of movement. It is regularly used for monitoring key indicators of the onset of
fatigue, performance motivation and a range of other cognitive functions. Our study uses the EEG
method in a general way, focusing in greater detail on standardized low -resolution electromagnetic
tomography (sLORETA) (6), a widely-used inverse solution technique that estimates the intracranial
distribution of electrical activity in the cortex based on an a priori defined head conductivity model.
sLORETA estimates the sources underlying scalp EEG data in a 3-D cortical space. The spatial volume
units (voxels)that are used to calculate the distribution of current densities are defined on the basis of
the Talairach atlas and the corresponding digital probability brain atlas (7). sLORETA determines thecurrent densities in a total of 6 239 voxels with a spatial resolution of 5 mm3 (6).

2. EXPERIMENTS
2.1 Experiment design
In our experiment, multiple intelligibility tests were performed, always using the same set of
distorted speech samples, played out in different random orders. The initial test followed thestandardized methodology, with no additional activity of the subjects. The other intelligibility tests
then deployed two different parallel tasks, designed to require different amounts of mental andadditional physical effort from the test subjects. The EEG activity wa s monitored in the steady-state
situation (with closed eyes and also with open eyes), during a regular intelligibility test and two
intelligibility tests deploying parallel tasks.
The selected parallel task (aiming a handgun at a moving target and shooting or, alternatively,
counting the successful hits of another shooter) generates a well -defined and highly repeatable
psycho-motoric load, as opposed to the purely physical tasks (e.g., a stationary bicycle) or the purely
mental tasks (e.g., mathematical quizzes) described in (3). This kind of task is chosen to avoid thesensitivity of the test to the physical or mental skills inequity of the test subjects.
2.2 Methods
All tests were performed in an acoustically treated critical listening laboratory conforming to (8) –with a reverberation time of 185ms, and background noise less than 30dB SPL(A), with no fluctuationsin frequency spectra. Sennheiser HD280Pro closed circumaural headphones were used for sample
playout. A professional voting device was used to collect the subjectsʼ responses.
The intelligibility tests followed the Modified Rhyme Test (MRT) methodology, as described in (1).
48 samples selected from the MRT sample list were used, and due to the limited capacity of the voting
device, only five answer options were used, instead of the originally proposed six options. The
samples had been recorded using the voices of two male English native narrators, using 24 recordings
from each of them. The distorted samples were produced using a network simulator depl oying a set ofa contemporary regular and low bit-rate coder and background noise options: Pulse Code Modulation(PCM) (9) at 64kbit/s (16 reference samples) and a low bit-rate coder (Mixed-Excitation Linear
Predictive enhanced - MELPe) (10), operating at 2.4kbit/s (32 samples). 16 MELPe samples (out of a
total of 32) were mixed with car interior background noise at Signal-to-Noise ratio SNR=0dB. A diotic
presentation level of 73dB SPL (A) was used. Further details about the structure of the sample and theway in which it was created are available in (4). For some samples, the intelligibility scores werehigher with the parallel task than without the parallel task, see Tab. 1 (adapted from (4)):
Table 1 – Selected speech samples where the intelligibility was measured to be higher with a parallel task
than without a parallel task, deploying over 50 respondents (after (4)):
Intelligibility
Sample Number

without parallelIntelligibility withSTD

task (%)

the parallel task

STD

(%)

17

60

6,9

78

5,9

36

51

7,0

70

6,3

42

37

6,7

56

7,0

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2.3 Test procedure
Six subjects (three female and three male) in the age range from 19 – 45 were tested. All of themwere native English speakers. The experiment consisted of four phases. First, a steady -state EEG wasrecorded with open eyes and with closed eyes (5 minutes each). Then, regular intelligibility tests were
performed with EEG activity monitored (COUNTER and SHOOTER). One session lasted
approximately 12 minutes.
This experiment had four phases:
Resting EEG with closed eyes (PRE CE) and with open eyes (PRE OE)Intelligibility test without a parallel task (WORDS)Intelligibility test with a parallel task – one subject played the role of the ‘shooterʼ (SHOOTER)Intelligibility test with a parallel task – one subject played the role of the ‘counterʼ (COUNTER)
The third and fourth phases repeated the intelligibility test (with different randomization), but witha parallel task. The parallel task deployed a professional laser shooting simulator. This part of the test
was always performed by two subjects. In the third phase of the test, one of the subjects played the roleof the ‘shooterʼ while the other subject acted as the ‘counterʼ. In the last (fourth) phase, the subjects
swapped their roles (‘shooterʼ vs. ‘counterʼ) and repeated the intelligibility test for the last time. The
two subjects (‘shooterʼ and ‘counterʼ) performed the intelligibility test in parallel. The order of phases
2, 3 and 4 was randomly generated to minimize the influence of the learning effect in the intelligibility
test. Further details about the voting process and about intelligibility data acquisition are available in(4).
A professional laser shooting simulator was used for generating the parallel task. For the EEG
measurements, we used the Electro-Cap, Inc. Nicolet EEG wireless 32/64 Amplifier with a telemetric32-channel (Natus 98 Neurology, Inc. USA). The EEG data was recorded with 19 electrodes: Fp1, Fp2,
F7, F3, Fz, F4, F8, T5, T3, C3, Cz, C4, T4, T6, P3, Pz, P4, O1, O2. The electrodes were localizedaccording to the 10–20 international system [11]. The sampling frequency was set to 512 Hz, with aband-pass filter from 0.5–70 Hz, and the electrode impedance was kept below 10 kΩ.
All EEG data were subjected to editing procedures, using Neuroguide software (Neuroguide ©
NG-2.4.6; Applied Neuroscience Inc., St. Petersburg, Fla., USA). We used Neuroguide to select 30
seconds of artifact-free data. After transformation to the average reference, the EEG activity of at least
15 two-second epochs of artifact-free resting EEG were averaged to calculate the cross-spectra insLORETA for six non-overlapping frequency bands: delta (1.5–6 Hz), theta (6.5–8 Hz), alpha-1 (8.5–
10 Hz), alpha-2 (10.5–12 Hz), beta-1 (12.5–18 Hz), beta-2 (18.5–21 Hz), and beta-3 (21.5–30 Hz).
Using the sLORETA transformation matrix, the cross spectra of each subject and for each frequency
band were then transformed to sLORETA files. This resulted in the corresponding 3D cortical
distribution of the electrical neuronal generators for each subject (12). The computed sLORETA image
displayed the cortical neuronal oscillators in 6239 voxels, with a spatial resolution of 5 mm (6).
The localization of the differences in brain electrical activity within the groups was assessed by avoxel-by-voxel paired t-test of the sLORETA images, based on the power of the estimated electric
current density, which resulted in t-statistic three-dimensional images. In the sLORETA images,
cortical voxels of statistically significant differences were identified by a nonparametric approach,using a randomization strategy that determined the critical probability threshold values for an actuallyobserved statistical item, with corrections for multiple testing (13).
In each group, we compared the difference on a level of significance of p≤0,05, under the following
circumstances:‘Shooterʼ versus resting EEG with open eyes –SHOOTER vs. PRE OE‘Counterʼ versus resting EEG with open eyes – COUNTER vs. PRE OE‘Counterʼ versus the intelligibility test, without a parallel task – COUNTER vs. WORDS

3. RESULTS
3.1

Alpha activity pre-test

All participants generated alpha activity during resting EEG with closed eyes, so all participants
were able to produce this alpha activity when in a relaxed state.

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3.2

Words vs. PRE OE

We observed statistically significant differences p≤0,05 in the delta band when comparing theintelligibility test without a parallel task (WORDS) versus the resting EEG with open eyes (PRE OE).
We found increased activity in the delta band in the right dorsolateral prefrontal cortex (DLPFC),
which is responsible for higher cortical functions associated with executive functions and motor
planning (Fig. 1).

Figure 1 - Statistical non-parametric map (SnPM) of sLORETA differences in delta current density whencomparing the intelligibility test without a parallel task (WORDS) versus the resting EEG with open eyes
(PRE OE). Yellow and red shades indicate a significant increase in delta sources (at the 0.05 significancelevel after correction for multiple comparisons.) in BAs 10,11, 46 and 47 (frontal gyrus). The structuralanatomy is shown in grey scale (L – left; R – right).
3.3 Shooter vs. PRE OEWhen comparing the intelligibility test with the parallel task - shooter (SHOOTER) versus resting
EEG with open eyes (PRE OE), we observed significant changes in the beta -2 and beta-3 band only.
We found decreased activity in the beta-1 band in the posterior cingulum (BA 31), which is responsiblefor integrating stimuli and their emotional experience. Increased activity in beta-3 occurs in the
middle-temporal lobe (BA 21), which is involved in processing complex sounds, in selective
processing of text and speech, and in semantic processing (Fig 3).

Figure 2 - Statistical non-parametric map (SnPM) of sLORETA differences in the beta-2 current density
comparing the intelligibility test with the parallel task - shooter (SHOOTER) versus the resting EEG with
open eyes (PRE OE). Blue shades indicate a significant decrease in beta-2 sources (at the 0.05 level ofsignificance, after correction for multiple comparisons.) in BA 31 (gyrus cinguli posterior). The structural6153

anatomy is shown in grey scale (L – left; R – right).

Figure 3 - Statistical non-parametric map (SnPM) of sLORETA differences in the beta-3 current density,
comparing the intelligibility test with the parallel task - shooter (SHOOTER) versus resting EEG with openeyes (PRE OE). Yellow and red shades indicate a significant decrease in beta-3 sources (at the 0.05 level ofsignificance, after correction for multiple comparisons.) in BA 21 (middle temporal gyrus). The structuralanatomy is shown in grey scale (L – left; R – right).
3.4

Counter vs. PRE OE

We found statistically significant differences (level p≤0,05) in the beta-3 band when comparing theintelligibility test with the parallel task – (COUNTER) versus resting EEG with open eyes (PRE OE).
The increased activity in the beta-3 band occurs in the dorsolateral prefrontal cortex (DLPFC) - BAs
10, 11, 46 and 47 on both sides, which are responsible for the execution function, and in the righttemporal lobe - BA 38, corresponding to a higher level of integration of the auditory stimulus, and tosemantic processing, and it participates in speech processing.

Figure 4 - Statistical non-parametric map (SnPM) of sLORETA differences in the beta-3 current density,
when comparing the intelligibility test with the parallel task – counter (CALCULATOR) versus resting EEG
with open eyes (PRE OE). Yellow and red shades indicate a significant decrease in beta-3 sources (at the 0.05
level of significance, after correction for multiple comparisons.) in BAs 10, 11, 46 and 47 (frontal gyrus) andBA 38 (temporal gyrus). The structural anatomy is shown in grey scale (L – left; R – right).

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3.5 Counter vs. Words
When comparing the intelligibility test with the parallel task – counter (COUNTER) versus theintelligibility test without a parallel task (WORDS), we found statistically significant differences inthe beta-3 current density in the left dorsolateral prefrontal cortex - BAs 10, 11, 46 and 47,
corresponding with the higher execution functions.

Figure 5 - Statistical non-parametric map (SnPM) of sLORETA differences in the beta-3 current density,
when comparing the intelligibility test with a parallel task – counter (COUNTER) versus the intelligibility
test without a parallel task (WORDS). Yellow and red shades indicate a significant increase in beta-3 sources(at the 0.05 level of significance, after correction for multiple comparisons) in BAs 10, 11, 46 and 47 (frontal
gyrus). The structural anatomy is shown in grey scale (L – left; R – right).

4. DISCUSSION
Central auditory processing follows two major pathways, both originating in the primary auditory
cortex (temporal cortex BAs 41, 42): Pathway 1. the ventral auditory stream from the posterior middle
and inferior temporal gyrus to the anterior, middle temporal gyrus (MTG) for identifying auditory
objects, including speech. This is called the WHAT system for sounds recognition. Pathway 2. th edorsal auditory stream into the superior temporal cortex and the parietal cortex for analyzing spatialaspects of sounds, including motion in space. This is called the WHERE system for auditory spatial
analysis (14,15,16,17).
A difference is found between the roles of simple intelligibility test (WORDS) and counting whileobserving a shooter (COUNTER). During the plain intelligibility test (WORDS), we observe activity
only in the right dorsolateral prefrontal cortex (DLPFC). However, during the intelligib ility test
performed together with watching the shooter (COUNTER), we can observe activity above both
frontal lobes, with dominance on the right and in the temporal area of the right temporal lobe BA 38,
which indicates activity of the ventral/WHAT auditory circle (14,17). The finding of increased activity
in the temporal area can correlate with the increased action in the region for processing the meaning of
the perceived word. The heightened activity above the frontal lobes can be associated with theso-called behavior inhibitory system (BIS), which indicates a rather negative reaction to the current
situation and the behavior activation system (BAS), which is activated during a positive emotional
reaction to the ongoing situation (19,18). During the plain intelligibility test (WORDS), dominanceabove the right frontal lobes is observed, which can indicate BIS activity, probably indicating negative
subject attitude during this test. During the role COUNTER, conversely, there is increased activity
over the right frontal lobe, which matches BAS activation with a positive emotional response,suggesting that the subject’s attention may have been taken by the shooter. In general, activity in the
DLPFC area is connected with executory functions, motorical scheduling, and learning (20).
During the role of SHOOTER, we observe decreased activity in the dorsal cingular cortex BA 31.
Together with the anterior cingular cortex, BA 31 has a strong reciprocal connection with the lateralprefrontal cortex, and through this connection, they partake in executory functions of the working
memory and motoric planning (21). The dorsal singular cortex participates in spatial navigation and inprocessing surrounding scenes (22, 23). Depressed activity during this experiment may indicate acertain attenuation of motoric movement perception and reduced emotional reactions. The finding of6155

raised activity for SHOOTER in the area of the middle temporal lobe BA 21, correlates with theincreased activity in the ventral/what auditory circle and is in response to raised analyzing processes of
the auditory stimulus (14,17).
Although we did not capture activity in the primary auditory zones BAs 41, 42 of the temporal lo be,
activity in COUNTER and in SHOOTER was observed in the ventral/WHAT auditory circle and inassociated areas of the prefrontal lobe that integrate those primary acoustical stimuli into anunderstandable form, enabling it to be perceived and evaluated in a complex manner.
Although alpha activity was measured during resting EEG in all participants, it was not registeredduring the experiment itself. This finding is probably connected with the major cerebral activity that isneeded for processing acoustical information together with an accompanying activity. Consequently, if
we want to pass on some information through an acoustic stimulus, it can be processed more intensely
if the listener simultaneously performs a parallel activity.
The results indicate that the intelligibility results for plain listening during a standard laboratory
intelligibility test can be outperformed by a test procedure that is enhanced by the introduction of aparallel task. The EEG measurements indicated that the higher auditory and cognitive brain functions
are enhanced during parallel tasks that engage the subject in the test procedure and/or during paralleltasks that reduce the “internal dialogue” of the subjects. Internal dialogue occurs involuntarily
during regular laboratory intelligibility tests not involving any parallel task, and probably cannot be
controlled consciously by ordinary test subjects. These counter-intuitive results imply the need for
substantial changes not only in subjective intelligibility testing methodology but also in perception
stimulation in highly demanding professional scenarios, in rehabilitation and in education.

5. CONCLUSIONS
EEG activity has been recorded and analyzed for several test situ ations. Distinct differences inbrain processing of auditory content were found among three groups of subjects, referred to as
WORDS, COUNTER, and SHOOTER. The listening-only group (WORDS) shows changes only in thereal prefrontal cortex area, indicating increased activity in the circles that participate in thecomprehensive evaluation of all input information. The listening and observing group (COUNTER)
also has increased activity in these areas of the prefrontal lobe, but on both sides of it, and, at the sametime, there is increased activity in the left temporal lobe, corresponding to zones of complex
processing of the auditory stimulus. This area is involved in central auditory circuits that evaluate thecontent of the acoustic stimulus. Increased activity in these areas is also found in the listening andshooting group (SHOOTER). At the same time, however, activity in the limbic area is reduced, which
can indicate reduced emotional manifestations and efficiency of the psycho -motoric parallel task.
These findings indicate increased brain activity in the area of the central auditory circles that areevaluating the content of audio information during parallel cognitive and motor tasks when a complex
motoric parallel task is considered to be primary (more important).
The results of this experiment show that the brain analysis of the content of the stimuli may behigher during parallel operation. This effect is reflected primarily in content -rich auditory informationthat requires deeper analysis.

ACKNOWLEDGEMENTS
Authors would like to Tomáš Drábek and Milan Martínek for their assistance during the tests.

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