gms | German Medical Science

The aim of the difficult tests in speech audiometry is the development of diagnostics of the processes of central conversion of hearing information. Part I presents prepared single-mouth filtration tests basing on the ones published in 1993 by Pruszewicz and the, mentioned in 1993 [Ref. 8], new articulation lists for the Polish language, so-called NLA-93. In both ear testing two dichotic tests have been used – numeral and force test. The transported speech test was devised basing on Calearo for Italian.

The aim of the work was to devise tests for word audiometry difficult because of the language and acoustics used, and their check up on a group of people normally hearing aged differently

40 people aged 18–71 have been examined in the research, among them 23 women and 17 men. The examined were divided into 4 age groups, ten people each. The first group included people aged 18–35 with average age of 35 years, second group included people aged 44–55 with average age of 50 years, and third group included those aged 56-65 with average age of 59. The fourth group included people aged over 65 with the average age of 69. Hearing disorders have been ruled out basing on an interview, otolaryngologic examination and tone audiometry. Medium auditory threshold in tone audiometry for the respective age groups. For group 1 - UP 15 dB for UL 13 dB, for group 2 UP and UL 20 dB, for group 3 UP 22 dB, UL 23 dB, and group 4 UP 31 dB, UL 30 dB.

Both-ears tests have been conducted: numeral test and word test using minimal pairs divided into two channels with a computer programme Cool Edit Pro 2.0 with volume of 55dB HL and one-ear test with administering the signal with block bands for left and right. Using the same software the Transported Speech Test (according to Calearo) was conducted transmitted directly into the ears. People without any disorders in the central nervous system hear the test material in a continuous and understandable manner at the frequency of deploying 2-40x/s. The test used 3-syllable, 5-syllable and 10-syllable phrases.

The filtration was conducted using the programme Cool Edit Pro 2.0at the level of 55db HL. The following ranges of filtration have been used: high level capacity filter >500 Hz, low level capacity filter <500 Hz, high level capacity filter >1000 Hz, low level capacity filter <1000 Hz, high level capacity filter >1500 Hz and filter low level capacity filter <1500 Hz. Characteristic of the filters: steepness 24 dB, depth 85 dB.

Tests were conducted using Aurical audiometer produced by GN Otometrics A/S with HOLMOCO 95-01-08307 type earphones, produced by Holmberg GmbH and B-71 type bone earphones produced by Radioear, with an external CD Panasonic SL-S113.

As a result of the conducted research it has been observed that level of words recognition in all age groups was the highest during high level capacity filtering (removal of bands below 500 Hz) – it was 95.7% for the right ear and 96.4% for he left ear. Similar but slightly lower values in words recognition were present in high-level capacity filtering in all examined frequencies. No age group and no frequency generated any statistically significant differences between the right and the left year.

The lowest average percentage of recognition of the transmitted signal was present when blocking the bands over 500 Hz with low-level capacity filter. The percentage of understood words was on average 52.4% for the right ear and 57.8% for the left ear, slightly higher percentage of words’ understanding occurred with the low level capacity filter below

1000 Hz respectively 75.0% UP and 78.7% UL. For the low level capacity filtration below 1500 Hz the percentage of words’ understanding was the same as with the high level capacity filtration. Similarly as for the high level capacity filtration, no statistically significant differences between right and left ear occurred in nay age group and for any frequency (Table 1 [Tab. 1], Figure 1 [Fig. 1]).

In the respective age groups the percentage of understood words decreased with age with the most visible differences concerning the low level capacity filtration below 500 Hz. For the age group below 45 years the average percentage of words’ understanding was as high as 65.4% for UP and 72.1% for Ul comparing to the results for the age group over 65 years, where the average percentage of words’ understanding for the same filtration equalled to UP 37.7% UL 41.9% (Figure 2 [Fig. 2])

In both-ears test attention is given to increase in understanding of the signal of the speech with the dominating ear (right) at the cost of both-ears hearing. It occurs with age and so: for the age group below 45 the UP understanding equals to 26.6% and both-ear hearing (UP/UL) is as high as 69%, but already in the age group over 65 the right ear hearing (UP) equals to 54.6% as compared with 33.4% of both-ears hearing (UP/UL). Perception of the speech signal in the form of numerals is easier comparing to verbal test with age. In the numeral test, in the age group below 45, both-ear understanding equalled to 69%, while in verbal test - 49%. However, with the people aged over 65, both-ears hearing equalled to 33.4% and words’ understanding was as low 12% (Figures 3 [Fig. 3], 4 [Fig. 4]).

Similarly in the test of transported speech according to Calearo the percentage of the understood words decreased with age, and the lowest percentage of understood words occurred with 3-syllable words and equalled to 26% for people aged over 65 comparing to 88.9% in the group of people aged below 45 (Figure 5 [Fig. 5]).

Incorrect recognition of the word consisted in exchange, consonants dropping, adding consonants within the same phonetic type to which the sound belongs (Table 2 [Tab. 2]). Better recognition of vowels can explain their formant structure and comparatively highest relative energy of vowels and lexical similarity. According to Pruszewicz [Ref. 9] vowels are better recognizable because in the filogenetic development primordial speech was based mostly on singing vowel sounds.

The most essential bands for the Polish speech are 100-2300 Hz or 500-2000 Hz, and in optimal conditions even a 125-2000 Hz is enough. The biggest percentage of understandable words ranges within 1300-1600 Hz [Ref. 1], [Ref. 5]. Elimination of low tones below 1500 Hz impairs the understanding of speech in a slight degree, while elimination of high and medium tones makes the speech virtually unintelligible. According to Fletcher [Ref. 3] half of the acoustic energy of speech is included in band 100 to 350 Hz and the second half in band ranging from 350 to 10000 Hz. Limiting the speech reception to a range of 350 to 10000 Hz also causes the loss of 50% of volume and at the same time 98% of clearness of speech. Limiting the speech reception to a range of 100 to 350 Hz causes the loss of 50% of volume and only 2% of clearness of speech. Limiting the speech reception to band from 100 to 350 Hz causes a 50% volume loss but at the same time 98% of clearness of speech, what makes speech completely unintelligible. This is also confirmed by our research. According to Wedenberg [Ref. 2] percentage of understanding the speech signal for the respective frequencies ranges as follows: 125 Hz – 25%, 200 Hz - 4%, 500 Hz – 9%, 1000 Hz – 26%, 2000 Hz – 30%, 4000 Hz – 10% and 6000 Hz – 7%. The larger the information material included in the speech, the larger the degree to which the acoustic elements are supplemented on the level of central nervous system. Consequently, even seemingly very imperfect and fragmentary information combined with an efficient central nervous system is enough to understand speech.

According to Stach, Spretnjak, Jerger (1990) [Ref. 7] the percentage of central hearing disorders in elderly people is growing with age, from 17% (aged 50-54), through 58% (aged 65-69), 72% (aged 70-74), up to 95% in patients aged over 80. However, large-scale research has revealed smaller percentage of patients with central hearing disorders. Cooper and Gates (1991) [Ref. 7] recorded 23% cases of central hearing disorders in patients aged 70-79 and 47% cases in patients aged 80-89. The process of aging can cause changes on every level of hearing tract. Pathological changes connected with the process of aging have also been discovered in the nuclei of the brain stem (Hansen, Reske-Nielsen 1965) as well as in core structures (Adams and others 1984) [Ref. 7]. Deviations in the test results in some elderly people can be connected with involution changes of the nervous system. It has been observed in both-ears hearing tests that, with age, the hearing ability with left ear decreases while the predominance of the right one increases. (Rodrigez and others 1990) [Ref. 7]. The predominance of the right ear increasing with age has also been established in the case of other dichotic tests (Jerger, Alford and others) [Ref. 7].

The results of the conducted research confirm the general rule of replacing one type of sounds with others within a phonetic type to which the vowel belongs, or outside this phonetic type e.g. consonants always or almost always are replaced with consonants. Better recognition of consonants may explain their formant structure and comparatively highest relative vowel energy [Ref. 4], [Ref. 5].

Using both-ears tests plays an important role in the situation, when hearing clear tones and understanding speech without disruptions remains unchanging. These tests, the first and so far the only that have been devised for the Polish language, become indispensable in diagnosing the central disorders of auditory conversion.

As important is to prove the ear direction majority developing together with human growth process when the auditory thresholds of both ears are the same in right-handed people, which can be used to adjust the hearing aids in the elderly.