Charlie99 once bubbled...
What article was this?
I was not able to find the article I more recently read that referenced the study, but that's ok the whole thing sounded very familiar. So I dug through some books and sure enough, I found a more original source of the study.
It was a 1965 study by Tom Mount and Dr. Gilbert Milner to determine the effects of anticipated behavior modeling in diving students with respect to narcosis. Three control groups of 4 student divers each were used in the study along with a group of 10 experienced deep divers who were tested concurrently with the students.
Group 1 was taught that a diver would get narcosis at 130 ft and that there was a very high probablility that symptoms would be severe.
Group 2 was taught about the existance of narcosis with symptoms normally occurring about 100 ft, but were not given an intimidating lecture or told that it was an insurmountable barrier.
Group 3 were given a full three hour lecture on narcosis on symptoms, risk factors, dangers, and known research. They were also told that dvers with strong will power could mentally prepare themselves and greatly reduce the effects.
Various baseline tests of mental acuity and dexterity were done an all groups at 50 ft. consiting of handwriting, peg bopard testing, math and other tests like placing a ball bearing in a long necked bottle. the test protocols were then modified to prevent the students from performing the tasks from memory during the actual testing at depth.
The initial test depth was at 130 ft and the Goup 1 divers had minor to above average narcosis symptoms while Groups 2 and 3 showed no significant effects on test performance.
At 180 ft, two Group 1 divers had severe narcosis symptoms and were removed from the study. All the Group 2 divers experienced about a 50% reduction in test performance and the Group 3 divers showed minor impairment based on overall test performance.
At 200 ft., All Group 1 divers were terminated from the study due to severe symptoms and two divers from Group 2 were dropped due to narcosis and apprehension. Group 3 divers actually showed a slight overall improvement in test scores.
At 240 ft, one diver from both Groups 2 and 3 were dropped from the study due to severe narcosis. The remaining Group 2 diver and the remaining three Group 3 divers showed some impairment overall but again the test scores showed overall improvement over the previous depth level. One female Group 3 diver showed her highest scores on all the tests at the 240 ft level.
As for the experienced deep divers, 7 of the 10 showed no decrease in test performance down to 200 ft and the remaining 3 finished the test (2 with perfect scores) but required adiditonal time to complete the tasks.
At 240 ft, 5 of the 10 performed all tests with no decrease in performance. One had problems with the ball bearing task but comleted all the other tasks successfully. Two other divers showed up to a 42% deficit and had problems comleting thew tests.
The conclusions were that performance at depth and tolerance to narcosis is subject to adaptation (the more you dive to depths the more likely you are to perform better) and that modeling is a key factor as most divers will experience what they expect to experience. So if you teach divers to expect to be debilitated by narcosis, they will be.
This was paraphrased from Bret Gilliam's 1995 revised edition of " Deep Diving. An advanced Guide to Physiology, Procedures and Systems". The conclusion at the end of the chapter is that diving as deep as deep as 200' on air is possible with experience, frequent exposure to deep diving and a high degree of training. But also that divers need to be cautious and prudent, obtain experience before attempting progressively deeper dives and should seek training under an experienced deep diving instructor before diving below sport diving limits.
I'd love to find the actual journal article and look at the methodolgy used and explore the reliability and validity of the study in more detail, but the results agree what I have found at depths down to 150 ft on air.
I doubt that I would want to do something extreme like dive the Andrea Doria on air, but then I also do not agree with the overly conservative views on depth limits with air either. I also do not agree with scaring students about diving below 60, 100 or 130 ft and about the effects of narcosis as a means of promoting saftey in the industry.