HUMAN BEHAVIOR PROGRAM 265 



Comparisons between the predive and postdive data were made to determine any possible 

 trends from the effects of prolonged pressure exposure on hearing levels. Again, a wide range 

 of individual differences was demonstrated. The differences between predive and postdive 

 thresholds were aggregated for all subjects and ears by test frequencies. Less than one-fifth 

 of the changes were in the direction of better hearing levels. Slightly less than one-fourth of 

 the threshold differences, when viewed in the same manner, showed no change between predive 

 and postdive levels. In contrast, more than half of the hearing-level changes were in the direc- 

 tion of hearing loss. Thus a trend toward acquired hearing loss is indicated. It should also be 

 pointed out that although changes were relatively small when postdive levels showed better 

 hearing (usually 5 to 10 db), the postdive hearing loss changes were more prevalent and 

 greater (up to 25 db). 



The conclusions from a pilot effort such as this should be viewed as tentative, but certain 

 implications are fairly obvious: 



1. Hearing levels of divers tend to reflect a pattern of acoustic trauma quite similar to 

 that of personnel exposed to high-intensity noise levels. Hearing ability of divers is also sub- 

 ject to additional deleterious effects from more than the usual amount and degree of ear pa- 

 thologies. Therefore, the need for a program of hearing conservation for these personnel is 

 indicated. 



2. The single episode of exposure to the environmental conditions of Sealab II resulted in 

 very little change in hearing levels for frequencies in the speech range (below 3000 cps), but a 

 trend was indicated for hearing loss at the higher test frequencies (3000 cps and above). 

 Therefore, any future projects of this nature should include a more comprehensive and care- 

 fully planned study of auditory functions. 



GENERAL DISCUSSION 



Psychomotor Tests 



The data at hand indicate that a general decrement in human performance occurs between 

 dry-land and shallow-water conditions, and increases under Sealab conditions. The trends of 

 the data indicate that short-term, simple performance, requiring little thinking and not depend- 

 ent on the use of the senses to any extent (e.g., strength test) is least affected, and that com- 

 plex, prolonged performance, calling on many human faculties (e.g., group assembly), is most 

 affected. This differential decrement effect can be seen most clearly in the data from the in- 

 dividual assembly test, where the task difficulty increases in terms of dexterity requirements 

 and the need to attend to spatial relations. 



There are indications in the data, as analyzed thus far, that some part of the performance 

 decrement is associated with personality variables. As previously mentioned, relative lack of 

 frustration tolerance, evidenced by expressed dislikes and complaints, is echoed in high 

 strength-test scores. It also appears that persons enjoying above-average choice as fellow 

 team members do well on the individual assembly test. This may reflect a desire to be with 

 persons who are careful and methodical in their work, virtues which would tend to be shown in 

 high scores on the individual assembly test. As examination of the data continues, other rela- 

 tionships of this type are expected to emerge. 



While these individual differences in underwater performance are important for the pur- 

 poses of team selection, task allocation, etc., the major issue is the observation of the average 

 performance decrement, particularly the sizeable decrements associated with the more com- 

 plex tasks. 



Helium Speech 



The problem of verbal communication in a helium atmosphere is well known. The differ- 

 ence in the density of the medium causes everyone to sound Uke Donald Duck. Upon entering 

 Sealab, many divers, especially those to whom the experience was novel, found the situation 



