No abstract
. "Phywrul Dam ami Physiulii..!)-»f K\iil..liiu, "f ,h.. A ». ühliiol.. «ml Lnrynuul.. Itt;«. 41. 7111-7711. IIMKIII of (be Auditory Nerve." Ann. Otol..-■IIH-"normal hmrinit" mom. will » u h. stilly b.-i.-t.-ri-.tl to »s "normal»." •I perimental session the thresholds on each ear for discomfort, tickle, and pain were determined for given frequencies and then repeated. In other words the thresholds were determined for the right ear then the left ear, followed by a repeat series of measurements on the right ear and the left ear. Kxcept in a few instances there were six consecutive sessions one week apart for each subject. In most cases thresholds of acuity were determined before and after testing for tolerance thresholds. This latter procedure was introduced in the course of the experiment to determine what effect exposure to high intensity stimuli might have on the threshold of acuity. 2. Speech tolerance-There were 30 normal ears and 30 hard-of-hearing ears exposed to the complete experimental procedure. These subjects were subdivided into three groups (1, 2, and 3) of 10 normal and 10 hardof-hearing ears each. The basis of division between groups 1 and 2 was the order of testing of ears with the time interval between sessions remaining constant. Groups 1 and 3 differed in the time interval between session* with the order of testing of ears remaining constant. An experimental session consisted of determination of thresholds of acuity for speech, and discomfort, tickle, and pain thresholds four times for each ear. All subjects were exposed to four sessions of speech tolerance testing as contrasted witli six sessions for pure tone tolerance. The fact that the speech tolerance threshold curves were reaching asymptotes as a function of experience determined the number of sessions. Study of change of tolerance a) Change with experience: The change of tolerance (which subsequently proved to be upward) for pure tones and speech as a function of number of consecutive testing sessions was studied. b) Retention of tolerance: The retention of tolerance for speech as a function of given time intervals from date of last test was investigated. c) Contralateral tolerance: The effect of tolerance tests for speech and pure tones of one ear on the opposite ear was studied. This phenomenon is defined as contralateral tolerance. d) Transfer tolerance: The effect on tolerance for pure tones as a result of exposure to speech tolerance procedure was investigated. This phenomenon is defined as transfer tolerance. el Methods of elevating tolerance: When it was noted that the testing procedure, per se, elevated tolerance, it was decided to make a deliberate experimental attempt to increase tolerance in hard-of-hearing ears through exposure of the subject to two different levels of high intensity speech. Therefore, a third group of 10 hard-of-hcaring subjects was exposed at four weekly experimental sessions. The right ears of this group were exposed to one level of stimulation and the left ears to another level.
The phonetically-balanced monosyllabic word lists of the Psycho-Acoustic Laboratory have proved clinically useful for assessing practical auditory discrimination. A new set of recordings has been prepared that provides (1) short intervals between items, (2) accurate monitoring of intensity, and (3) uniformity of a given item as it occurs in different scramblings. The uniformity was obtained by dubbing the original material (spoken by Dr. Ira Hirsh) to magnetic tape, cutting the tape, reassembling the pieces in random order, dubbing to a disk, scrambling the same pieces again for another dubbing, etc. Four scramblings each of six 50-word lists have been used to determine the properties of the new recordings. For a team of twelve trained normal listeners, the articulation curve rises from zero at an intensity just above the threshold of detectability. Its initial slope is about 4 percent per db and its shape is convex upward throughout, rather than sigmoid. Its shape is convex upward throughout, rather than sigmoid. At 35 db re: 0.002 microbar it has reached 85 percent. From there the increase is quite steady at 0.5 percent per db, but the score does not reach 98 percent until 60 db re: 0.0002 microbar. Masking with white noise at successive signal-to-noise ratios yields approximately the same curve. An S/N ratio of 24 db lowers the articulation score to 90 percent. The most difficult words are in each case those containing weak sibilants among their terminal consonants. On the basis of an item analysis of the errors and with elimination of some of the less familiar words we are preparing for clinical use several shorter lists that will be closely comparable with one another in all scramblings and that will have the same distribution of difficulty as the original 50-word lists.
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