Normal-hearing Ears Research Articles

The tone decay test.

The purpose of this investigation was to estimate: (1) The correlation between tone decay degree and topographical diagnosis, age and pure tone threshold. (2) The significance of applying different test frequencies. A total of 2123 ears were tested in 500, 2000 and 4000 Hz by means of a manual method. A strict correlation was found, on the one side, between a high degree of tone decay and cerebello-pontine angle tumours and on the other side a low degree or missing tone decay in normal hearing ears. In six diagnostic groups the per stimulatory threshold shift was unequally distributed among the different test frequencies. The age factor does not influence the tone decay noticeably, while the degree of hearing loss in some cases seems to be an important factor. Two test frequencies are recommended, 500 and 2000 Hz.

Delayed speech feedback in normal hearing and conductive hearing loss, with and without a functioning stapedius muscle.

Normal ears, otosclerotic ears with normal hearing after stapedectomy, and ears with pure conductive hearing loss from otosclerosis and packing of the ear canal, were subjected to a delayed speech feedback test (DSF-test). The results showed no difference in the DSF-effect between the normal ears and the normal hearing operated otosclerotic ears. Neither was there any difference between the nonoperated otosclerotic and the normal hearing ears with an artificial hearing loss. The results suggest that activity in the stapedius muscle has no influence on the DSF-effect in normal hearing ears and in ears with conductive hearing impairment. The DSF-effect, however, was almost double in the non-operated otosclerotic ears and in ears with artificial hearing loss. This may be due to the acoustic energy from the earphones, in the pure conductive hearing losses of about 40 dB, reaching the cochlea both by air and bone conduction in almost equal amounts.

Effect of masking on induced conduction deafness.

It has been demonstrated that masking with 80 db. of white noise re normal threshold (95 db. re 0.0002 dyne per square centimeter) can for clinical purposes eliminate a normal hearing ear while testing the opposite ear by bone conduction. With this degree of masking there is no significant overmask. 1 It is frequently necessary to use masking in an ear which has some degree of conduction deafness. There is no experimentally confirmed knowledge of the degree of masking necessary in such an ear or the effectiveness of usually employed intensities in various degrees of conduction deafness. The object of this study is to determine the difference in response to masking of a normal ear and of one with experimentally induced conduction deafness as measured by crossed bone conduction. Material and Method For the purposes of this investigation 20 subjects with unilateral complete deafness were selected. This degree of deafness