Speech intelligibility under various degrees of anoxia.

Publisher Website
Google Scholar
Abstract
Twelve male college students, 18-21 yrs., free from systemic defects at medical examination, served as subjects. The method of observing effects of O2 deprivation involved the subjects'' ability to hear and to indicate on a check-list words in common speech at sea level, and at simulated altitudes of 13,600, 16,900 and 20,100 ft. in a nitrogen dilution chamber of 450 cu. ft. capacity. Temp. was constant at 74[degree] F with 60% rel. humidity. Air samples by Haldane-Henderson-Baily gas analysis did not deviate from the desired altitudes more than 600 ft. CO2 content averaged 0.52%. The altitudes corresponded to O2 percentages of 12.5, 10.3, and 8.85, respectively. Uniform difficulty of test materials was assured in the control and exptl. periods by use of 8 lists of recorded stimulus words. Test batteries for any one of the 4 conditions were made up of the same word lists but presented in varying order. They were derived from standard word lists by the Bell Telephone Laboratories. Intelligibility for vowel sounds was tested by monosyllabics having the same initial and final consonants; e.g., "suit", "sit", "set", etc. Consonant intelligibility involved a consonant vowel sound but a variation in initial and final consonant; e.g., "nor", "bore", "yore". There were 11 vowel items and 24 consonant items in each list. The lists were recorded on high fidelity equipment at N.B.C. Studios, New York City and put in semi-permanent form by R.C.A. of Camden, N. J. The recordings were played back in the chamber through a Fair-child pick-up coupled with a Presto amplifier and Western Electric earphones. Oxygen masks were worn by experimenter and subjects at all times in the chamber, so that the subjects were not aware of sea level runs. Following recorded instructions, Test 1 was given at sea level at high sound intensity (30 lb. with vowel articulation 98% and consonant articulation 94%). Test 2 came at exptl. altitude and same intensity after a 15 min. adjustment period. Tests 3-10 followed at same altitude but low intensity (24 lb. with vowel articulation 92% and consonant articulation 50%). Test 11 was given at altitude with a return to high sound intensity, and test 12 at sea level with high intensity. The average time of simulated ascent was 14 min. with an over-all time in chamber of 75 min. The mean articulation values for vowels, consonants and standard syllables dropped systematically as altitude increased. Standard syllable articulation values were calculated by the Fletcher-Steinberg formula S = (l[long dash]VC 2)0.9. At sea level this value was 24.6%; at 13,600 ft 21.6%; at 16,900 ft., 8.0%; and at 20,100 ft., 3.7%. Values for vowels and consonants showed a similar trend with the vowel values very much better than those for consonants under all conditions. The character of this drop is very definitely a function of initial difficulty at sea level, for when mean syllable articulation was 55.5% at sea level there was only an 8% drop at 18,500 ft. (previous study), whereas with a 24.6% sea level value in the present instance, decrements of 16.6% at 16,900 ft and 20.9% at 20,100 ft. occurred. That the ability to perceive speech sounds is affected by increased anoxia was demonstrated by the fact that 67% of the subjects showed some loss of efficiency at 13,600 ft.; 92% were affected at 16,900 ft., and 100% at 20,100 ft. The large decrement in performance at 13,600 ft. suggests the importance of oxygen equipment on long flights even at low altitude if effective communications are to be maintained.

This publication has 0 references indexed in Scilit: