pitch discrimination of tunned percussion instruments for cochlear implants users

7/24/2019 Pitch Discrimination of Tunned Percussion Instruments for Cochlear Implants Users

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Acoustic Laboratory December 2015, Argentina

PITCH DISCRIMINATION OF TUNED PERCUSSION INSTRUMENTS

FOR COCHLEAR IMPLANTS USERSCacavelos, Federico Nahuel

Ingeniera de Sonido, Universidad Nacional de Tres de [email protected]

AbstractThe present study focuses the analysis on the pitch discrimination of impulsive sounds. This study aims to

compare experimentally the competences of normal hearing (NH) and cochlear implant users (CI) by stimulatingwith tuned percussion instruments present in rhythmic patterns. The hypothesis of the study is impulsive signals

should be more complicated for discrimination than continuous note because the temporal fine structure. For this

reason different percussion instrument are tuned in an easily recognizable pitch for CI users and presented in

rhythmic patterns. ABX test was carried out in 21 NH subjects and 1 CI at the moment. The results are compared

with previous studies where the test signal was continuous tone. The result showed that in NH subjects the

discrimination rate is preserved. More CI is needed to test the hypothesis with large interval confidence.

1. INTRODUCTION

The research on music perception of Cochlear

Implant users (CI) has been developing during the

last years. Most of the studies investigate the abilityof melodic contour identification and timbre

recognition, as well as emotional communication,

rhythm and meter recognition. However, there are no

currently many studies addressing the perception of

impulsive signal sounds and possible identification

CI users. Therefore this study investigates the

identification of impulsive signals by using

percussion instruments that were tuned in toneswhere CI should easily distinguish.

In the current section are shown some results of

previous studies. Methods and procedures aredescribed in the second section. Results of the test

will be shown in third section and compared with

previous studies in the fourth section. The fifth

section is reserved to conclusions.

The central auditory processing in human been has

two possible mechanism to perceive pitch. One ofthem is based on the temporal theory, where the

perception of time periods smaller than 1 ms enabling

us to perceive frequencies up to 1 kHz. This is

essential to recognize the fine structure of signals. InCI this mechanism can be hampered by the low

stimulation rates used in some codification strategies.The other mechanism used by the central auditory

processing is the place theory, where describes how

resonances distributed in the basilar membrane

produce a frequency dispersal, commonly called the

tonotopic distribution [1]. In CI is not possible to

stimulate the cochlea in two sectors simultaneously

due to electrical interference between electrodes, this

way the codification strategies keep just the peaks

signal of a period, discarding the week intensity. This

is why CI users have difficult to detect fine structure

of pitch information and impulsive sounds.

Cognitive factors may also agree difficult to

identification process. Disturbance Auditory

Processing is a hearing impairment where exists an

impediment to analyze and / or interpret soundpatterns. In this sense is necessary to attend the

central auditory processing. [2]; [3]

It is well established that people with hearing

impairments, including CI users, perceive rhythm

approximately as well as those with normal hearing[4], [5], [6], and [1].

Gfeller et Lansing (1991) [7] administered a testcalled PMMA (Primary Measures of Music Audition

developed for Gordons in 1979) to 18 postlingually

deafened CI subjects. Mean scores on the rhythm

subtest (88%) were higher than on the tonal subtest(78%).

Leal et al. (2003) [8] conducted rhythm

discrimination tasks in twenty-nine postlingually

deafened adults scoring 95%.

Kong et al (2004) [9] found no significant difference

in performance among four tempo condition (60, 80,

100, and 120 beats per minute) in normal hearing and

cochlear implant users by an identification task where

asked to subjects to read and chose the musicalnotation displayed on the screen that corresponded to

the rhythmic pattern presented.The collective findings across a range of studies

indicate that CI users perform significantly worse

than NH controls on pitch-based tasks.

In the 1991 Gfeller study [7], CI subjects scored 78%

on the tonal subtest of the PMMA, by varying the

second note in four semitones, while NH scoredhigher than 95%.

Schulz & Kerber (1994) [13] assessed pitch

perception for eight users of a single-channel CI

programmed with a now-obsolete analogue

processing scheme. In the melodic-directionperception task, subjects were required to assess


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whether a tonal sequence played on the piano was

ascending, descending, or unchanging in pitch. Theresults of this assessment indicated that, subjects with

CIs scored between 68% and 84%, while NH scored

100% suggesting that although they could undertake

the task with varying degrees of accuracy and ease,

their overall scores were still significantly below thatof the NH control group. Also they asked todifferentiate whether two tones played on a piano

were the same or different in pitch. The results

indicated that whilst NH subjects could reliably

differentiate between notes one semitone apart, CI

group were able to differentiate intervals larger than a

major second or a minor third. The authors also

reported that these results were fairly consistent

across the 11 octave frequency range used in this

task.

Fujita & Ito (1999) [10] found that five of eight CI

users discriminated the higher of two notes between

four and ten semitones apart. However, the remainingthree subjects could not discriminate between two

notes, one octave (i.e. 12 semitones) apart.

Gfeller et al. (2002) [15] also investigated pitch

perception by comparing CI users with NH controls

in a higher/lower pitch discrimination task. Whereasthe mean difference limen for NH subjects was 1.13

semitones the CI populations performance was

highly variable with a mean difference of 7.56

semitones.

Eunoak Kim (2012) [5] also tested the CI capabilities

by using a synthesized piano tone in fourth basedfrequencies (185 Hz, 262 Hz, 330 Hz and 390 Hz).

The normal hearing group scored 96% (SD, 3%)correct while the CI listeners scored 70% (SD, 11%)

correct. These fourth based frequencies are used in

the current study for tune the different sound

material. This way can be compare both test results.

A recent study compared pitch discrimination ability

at 1 and 6 semitones using real-world stimuli of

sung vowels sounds. CI subjects were severely

impaired compared to NH subjects. NH performed

89% and CI 60% for the 6 semitone changecondition. On the 1 semitone change condition NH

perform on 81% and CI 49% of accuracy (Sucher and

McDermott, 2007) [4].

Phillips-Silver et al (2015) [11] test the capacity offeeling beat of drum music in CI users by playing

different latin merengue rhythms and analyze thebody movements by a accelerometer remote control.

They found that cochlear implant users are able to

synchronize dance-like body movement to drum

music (even as well as they entrain to visual and

auditory metronomes). In comparison with a group of

matched controls, however, the synchronizationperformance of CI users is worse across all

conditions. Also found evidence that pitch variations

would interfere with beat finding and

synchronization.

The objective of the present study is to evaluate the

pitch identification skills of percussive instrumentssounds that have strong impulsive information when

they are played in a simple rhythmic pattern. The

hypothesis is that CI users should perform worse on

pitch discrimination of impulsive signals (percussion

instrument) than in tone signals due to the finestructure.The method of analysis that this study propose is

using the same parameters discrimination pitch tone

signals from previous studies and thus compared with

the results founded of impulsive pitch sounds signals.

For this reason a three different tuned sounds was

made tanking into account enough harmonic

components difference being easily recognizable

even for CI users.

There are certain limitations of the study since some

parameters that cannot be controlled. The loudness

variation will depend strongly of the calibration

processor settings and physiological condition. Theuser can detect and discriminate the sounds only by

the loudness difference. Also cognitive aspects of

memory loss and attention may hamper the test,

where the difficulty of the discrimination does not

imply a hearing problem but rather a deficiency in thecentral auditory processing [2], [3].

Some previous studies explain that exist wide

variation on the perception skills in CI users [4], [5],

[6], [1], it can attach disadvantages when analyzing

the confidence intervals of the data collected. This is

because differences in the CI devices, codificationstrategies and the patient own adaptation.

2. PROCEDURE

2.1 Stimuli PreparationSource signal consist in rhythmic patterns made with

three percussion instruments as Kick, Snare and

Cymbal. Each percussion instrument was carefully

processed and transpose to the same frequency of

tone signals from previous studies.

Figure 1: The three pitched instrument spectrums used inthe patterns.

This way, each instrument has 6 semitones distance

from each other, F3 (170 Hz) for the kick, C4 (261

Hz) for snare and G4 (390 Hz) for ride cymbal, as is

possible to see by their spectrums on figure 1. This

distance was intended to bring clearly pitchidentification according to Eunoak Kim (2012) study


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[5]. The three sounds instrument was normalized in

peak amplitude because of peak method detectionused in the common coding strategies.

The three percussion instruments were used to create

different rhythmic patterns used as test material.

The test is divided in two parts with propose to

achieve more specify of the subjective identification.In the first part the same instrument is used to thewhole rhythmic pattern, and compares the three

instruments separated in each pattern. An example of

the MIDI sheets to the first part is shown in Figure 2.

Figure 2: The three signals of rhythmic patterns used forfirst part. Top: Ride cymbal in the whole pattern; Middle:

Snare in the whole pattern; Bottom: Kick in the whole

pattern.

The second study combines the three instruments in

each pattern and changes just one hit as it is possible

to see in figure 3. The first part attempts to discern if

they really perceive the difference in impulsive pitch

and the second aims to analyze discrimination in a

combined pattern of different instruments. This offers

more complex to understanding of the phenomena.

The number of hits for all rhythmic configuration was

6, showing good appreciation by Kim in 2012 [5]

after testing with different quantities of tones.

Figure 3: The three signals of rhythmic patterns used for

second part. Top: Ride cymbal hit change in combinedpattern; Middle: Snare hit change in combined pattern;

Bottom: Kick hit change in combined pattern.

The 15 combinations involve the repetition of tests on

the same subject in order to increase the number of

trials and improve the confidence interval. Since it is

expected more variation in the results of the second

part, the first part was repeated two times whilesecond part was repeated three times. For each

repetition a different pattern was used confronting the

subject always to different signals.

All sounds where made in Albeton Live 7.0 using an

Electric Drum Roland DR-909 and DR-707 andtranspose of drum rack of native software. The tempo

condition was 120 bpm following the results of Ying-

Yee Kong (2004) [14] where it does not find real

difference in de discrimination skills when the beatsper minute change.

2.2 Subjective Test

ABX test with 15 stimuli combinations was made

repeating two times the first part of test and threetimes the second part, each time the patterns waschange getting different type of stimuliavoiding thesubject to facilitate remembering the previous pattern

choice. The subjects has to identify if the last signal

(X signal) is equal to A (X=A) or if it is equal to B

(X=B).

The test was applied at the moment in 21 NH subjects

of 20-55 years old and 1 bilateral postlingual CI user

of 52 years old (3 years of experience with CI)

equipped with Nucleus 5 (22 electrodes and CP810

processor using ACE strategy). A Matlab algorithm

was used in order to apply order randomization of the

audio presentation. Test environment was differentbetween both groups of study. In the CI user the line

out of the processor was used to avoid the

characteristics of the acoustic environment, but in NH

subjects a headphone Audio Technica ATH-D49 was

used into a quiet room with acoustic treatment. In allcases a Notebook computer with Maudio FastTrack

was used to reproducing the audio test. Just one ear

was stimulated in all cases. Total time of test was 5

minutes in each subjectdepending on how long youuse each subject to choose the answer. To replay the

audio was not allowed but the subject can choose hisown conformably sound level.

There are some parameters that cannot be controlledin both groups. The most important factor is the

degree of attention that the subject can achieve at that

moment. This can be hampered by limited memory

capacity and slower processing speed since disorders

of the central auditory processing according to Oscar

Caete (2006) [3]. Also different models, settings and

codification strategy of the CI devices can add wide

variation to the identification process of the subject.Several authors also point out that there is greatvariation between the perceptual skills of users [6],

[1]. This happens because of the resilience of the

subjects to electrical stimulation of their particular

physiological characteristics.

3. RESULTS

The percentage of hits was calculated for all subjects

using Matlab software. In order to get the differences

between different instruments, the results are

presented by each comparison. The three first groupsof columns correspond to the first test and second

group of columns correspond to the second test.

By the assumption that the statically analysis of an

ABX test follows a binomial distribution, according

to J. Boley in 2009 [12]. It is possible to obtain by a95% of confident interval of each result.


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As is shown in the figure 4 and table 1, the normal

hearing identified nearly 100% in all the stimulipresented, showing just lower performance for the

second part of the test. From the three signals

presented in the second part, which corresponds to

the change of snare-ride has a slight increase of the

percentage of successes. This result is consistent withthe frequency of the tuning given distance.

Figure 4: Bar graphic of percentage of successes for

Normal Hearing subjects (NH) and Cochlear Implant users(CI), for first part of test (left columns) and second part

(right columns) with a 95% confident interval (black lines).

Table 1: Values of percentage of successes for Normal

Hearing subjects (NH) and Cochlear Implant users (CI) and

the 95% confident intervals.

May be notice that for the CI results it is not possible

to get a confidence interval useful to analyze the

results globally.

4. DISCUSSION

Normal hearing subjects perform better than 89 %

correct in the combined patterns and almost 100% forthe patterns with the same instrument. These results

can confirm some of the previous studies:

89% (Sucher CM, 2007) [4]

95% (Gfeller K, 1991) [7]

100% (Schulz and Kerber, 1994] [13]

Although, the numbers of trials to CI are insufficient

to permit a real data analysis, is possible to see that

CI user performed worse than any NH performance.

Results of the study evaluated to date in the only

cochlear implant user reveals lower performance than

previous studies:

60% (Sucher CM, 2007) [4]

78% (Gfeller K, 1991) [7]

68% - 84% (Schulz and Kerber , 1994) [13]

Is necessary to point that the previous studies use a

continuous note and this study is using an impulsive

sound, in this sense is expected lower performance

for impulsive sounds.Some errors with NH group may have been caused

by the subject poor attention. Although a drop in

performance was not shown with over time in both

groups.

The subject evaluated with CI showed some difficult

to some discrimination task, and the forced choice

was obliged to respond randomly. At the same way

he expresses that he was unable to identify certain

sounds but he can recognize the difference by not

because their pitch components but rather for their

loudness. One of the reasons of this event is because

CI users may have different performance of their

calibration. Sounds can match with specific channelshaving different impedance and thus generate

loudness differences, easy recognizable for the CI

users.

5. CONCLUTIONS

The hypothesis cannot be tested because the large

confident intervals of the CI users. This can be

improved by increasing the number of trials in CI

users, achieving more confidence results. This studyis currently in progress.

Possible future studies can include others factors by

using more frequencies in order to achieve greater

accuracy in the cochlear implant identification,

although previous studies of continuous tone showed

no variation in frequency scale.Some cochlear implant users can identify a difference

between samples but does not mean that they

perceive correctly the sound. For this reason, future

works may consider most number of instrument

sounds with different harmonic composition can

provide better specificity to the phenomenon

6.

REFERENCES[1] Valeriewei Lool, Music Perception of Cochlear

Users, Doctorate Thesis, Department ofOtolaryngology , University of Melbourne, (2006).

[2] I.J.R. Restrepo, J.R.C. Medina, Desrdenes del

procesamiento auditivo,IATREIA, 19(4), (2006).[3] Oscar Caete S., Central Auditory Processing

Disorder, Revista Otorrinolaringologica Cabeza

Cuello, 66, 263-273, (2006);

[4] Sucher CM and McDermott HJ., Pitch ranking of

complex tones by normally hearing subjects and

cochlear implant users, Hear Res, 230, 80-87, (2007).

[5] Eunoak Kim et al., Music Perception Ability of

Korean Adult Cochlear Implant Listeners, Clinical

Kick-Snare

(SAME)

Snare-Ride

(SAME)

Kick-Ride

(SAME)

Kick-Snare

(COMBINED)

Snare-Ride

(COMBINED)

Kick-Ride

(COMBINED)

NH 100% 95% 98% 90% 89% 94%

NH 95%

Confident

Interval

0% 6% 6% 9% 9% 7%

CI 100% 50% 100% 66% 58% 50%

CI 95%

Confident

Interval

0% 49% 0% 19% 39% 40%


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and Experimental Otorhinolaryngology, 5(1), S53-

S58, (2012).[6] P. Donnelly and C. Limb Music, Perception in

Cochlear Implant Users. The Johns Hopkins

University, Baltimore, Maryland (2009).

[7] Gfeller K and Lansing CR, Melodic, Rhythmic,

and Timbral Perception of Adult Cochlear ImplantUsers, Journal of Speech, Language and HearingResearch, 34, 916-920 , (1991).

[8] Leal M.C. et al., Music Perception in Adult

Cochlear Implant Recipients, Acta Oto-

Laryngologica, 123, 826-835, (2003).

[9] Kong YY et al., Music perception with temporal

cues in acoustic and electric hearing, Ear Hear, 25,

173185, (2004).

[10] Fujita S et al., Ability of nucleus cochlear

implantees to recognize music, Annals Otol

Rhinology Laryngology, 108, 634-40, (1999).

[11] J. Phillips-Silver, Cochlear implant users move

in time to the beat of drum music, Elsevier, (25-23).Canada (2015).

[12] J. Boley, Statistical Analysis of ABX Results

Using Signal Detection Theory. Audio Engineering

Society, 127, 7826, (2009).

[13] Schultz E, Kerber M., Music perception with theMED-EL implants, Advances in cochlear implants,

326332,(1994).

[14] Ying-Yee Kong et al., Music Perception with

Temporal Cues in Acoustic and Electric Hearing,

Lippincott Williams & Wilkins. Ear & Hearing,

25(2), (2004)

[15] Gfeller K et al., Recognition of familiar

melodies by adult cochlear implant recipients andnormal-hearing adults, Cochlear Implants, 3(29-53),

326332, (2002).

pitch discrimination of tunned percussion instruments for cochlear implants users

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