Non-linear frequency compression in hearing aids

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Music perception in adult cochlear implant recipients (Leal et al., 2003)

The following sub-tests were included in this study:
Timbre: In order to obtain evaluative responses of perceptions of various timbres, the participants listened to short solo melodies produced by three commonly heard musical instruments representing different instrumental families and frequency ranges. These included wind (trombone), percussion (piano) and string families (violin). The participants were asked to identify each instrument. To reduce the structural variability of the phrases between instruments, all instruments were played using the same pitch scale.
The instrumental recordings played the same French nursery melody (single note) (Leal et al., 2003:827).
Pitch: Twelve pairs of items with identical temporal patterns but differences in frequency were used. The pairs of items were sometimes similar and pitch was changed in an increasingly difficult manner. In the pitch discrimination test the respondents were asked to indicate whether the pair of items was the same or different and in the pitch identification test they were asked whether the pitch became higher or lower and where this change occurred (beginning, middle or end) (Leal et al., 2003:827).
Rhythm: This test was similar to the pitch test. They evaluated changes in duration or intensity of the notes by presenting ten pairs of musical pieces separated by five seconds of silence. All stimuli were presented at the same frequency. In the first part of the test (discrimination), respondents were asked to discriminate whether the pair of items was the same or different. In the second part (identification) they were asked to determine the point of change (Leal et al., 2003:827).
Song recognition: For this task, they showed participants a list of 16 songs and asked which ones they were familiar with. Eight songs were selected that the participant was familiar with and these songs (closed set) were presented at random. The songs were presented first by an orchestra without verbal cues, then played on piano (single note) and finally by an orchestra with verbal cues. Participants were asked to identify the songs by name or by singing a part of the song (Leal et al., 2003:827).

Recognition of familiar melodies by adult cochlear implant recipients and normal hearing adults (Gfeller et al., 2002)

To conduct this study, the researchers included a familiar melody recognition task as well as a complex-tone discrimination task. Both of these are discussed below.
Familiar melody recognition task: To identify items likely to be familiar to nonmusicians, collections of songs commonly known to the general public in the United States were reviewed and a pool of song titles was submitted to a panel of university experts in music education, who verified that these were well-known melodies (Gfeller, et al., 2002:34). Adult volunteers were tested individually in open-set recognition of 35 selected songs, played on piano and recorded on cassette tape (Gfeller, et al., 2002:35).
From the most familiar items, a subset of 12 was chosen. As prior research indicates that normal hearing adults and adults with cochlear implants rely on rhythmic features for melodic recognition, melodies were selected that could be grouped into two categories based on rhythmic features: items with distinctive rhythmic features within the melody line (e.g. dotted eight notes, triplet figures, etc.) and items made of quarter notes (no distinctive rhythm) with a half note at the closure of the musical phrase Gfeller, et al., 2002:35). In addition to the 12 familiar melody items, the test included 12 foils, one for each of the familiar melodies. These newly composed items were created by using the durational values and the pitches of the familiar melodies, but in a new sequential order.
Each familiar melody and its foil were presented in melody only, and melody plus harmony (no lyrics). All melody lines were presented in the same fundamental frequency range; melody-only versions included a fundamental frequency range of 194-659 Hz.
Harmony versions consisted of the melody (figure) against background harmony (ground) (Gfeller, et al., 2002:35). The harmony versions included a fundamental frequency range of 87 to 659 Hz. The melodies were presented in C major, and at the same tempo (Gfeller, et al., 2002:36). The test was delivered via a computer with touch screen and external speakers in free field. The stimuli were transmitted through the speech processor and the sound level was set at 70 dB. First, the participant read standardized instructions for the test on the computer screen and practiced on two sample items. A total of 45 items (familiar and foils) were then presented in random order. Each familiar item was presented twice: melody-only and melody-plus-harmony format. Six item foils were presented in melody-only format and six in harmony format. A sub-group of nine items was repeated a second time during the test to determine internal consistency of participant responses (Gfeller, et al., 2002:36).

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1. ORIENTATION AND PROBLEM STATEMENT
1.1 INTRODUCTION
1.2 RATIONALE
1.3 PROBLEM STATEMENT AND RESEARCH QUESTION
1.4 CLARIFICATION OF TERMINOLOGY
1.5 ABBREVIATIONS
1.6 OVERVIEW OF CHAPTERS
1.7 CONCLUSION
1.8 SUMMARY
2. MUSIC PERCEPTION
2.1 INTRODUCTION
2.2 THE PERCEPTION OF MUSIC
2.3 PHYSIOLOGICAL AFFECT OF MUSIC
2.4 MUSIC PERCEPTION TESTS DESCRIBED IN THE LITERATURE
2.5 DEVELOPMENT OF A MUSIC PERCEPTION TEST FOR HEARING AID USERS
2.6 COMPUTERIZED-ADAPTIVE TESTS VS. SELF-ADAPTED TESTS
2.7 MUSIC PERCEPTION IN THE SOUTH AFRICAN CONTEXT
2.8 CONCLUSION
2.9 SUMMARY
3. NON-LINEAR FREQUENCY COMPRESSION IN HEARING AIDS
3.1 INTRODUCTION
3.2 FREQUENCY LOWERING TECHNOLOGY AND TERMINOLOGY ISSUES
3.3 PREVIOUS FREQUENCY LOWERING HEARING AIDS
3.4 FREQUENCY TRANSPOSITION
3.5 NON-LINEAR FREQUENCY COMPRESSION
3.6 HEARING HEALTH CARE IN THE SOUTH AFRICAN CONTEXT
3.7 CONCLUSION
3.8 SUMMARY
4. METHOD
4.1 INTRODUCTION
4.2 AIMS
4.3 RESEARCH DESIGN
4.4 ETHICAL ASPECTS REGARDING RESEARCH
4.5 PARTICIPANTS
4.6 MATERIAL AND APPARATUS FOR THE COLLECTION OF DATA
4.7 PROCEDURE
4.8 CONCLUSION
4.9 SUMMARY
5. RESULTS
5.1 INTRODUCTION
5.2 PRESENTATION OF THE RESULTS IN CORRESPONDENCE WITH THE SUB-AIMS
5.3 CONCLUSION
5.4 SUMMARY
6. DISCUSSION OF RESULTS
6.1 INTRODUCTION
6.2 DISCUSSIONS OF THE RESULTS ACCORDING TO THE SUB-AIMS
6.3 CONCLUSION
6.4 SUMMARY
7. CONCLUSION AND RECOMMENDATIONS
7.1 INTRODUCTION
7.2 CONCLUSIONS
7.3 CLINICAL IMPLICATIONS
7.4 CRITICAL EVALUATION OF RESEARCH
7.5 RECOMMENDATIONS FOR FUTURE RESEARCH
7.6 CLOSING STATEMENT
REFERENCES

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