Data from objective, published studies suggest there is no psychomotor or behavioral adaptation, in terms of measurable test or task performance, resulting from repeated exposure to depth. They also indicate that subjective adaptation does occur. A potential danger of this dissociation, of actual performance from perceived performance, is that ‘depth trained’ divers do not perceive that they are impaired, although they are, and may make poor decisions regarding their ability to function at depth, resulting in injury or death to themselves or diving companions. Of course, one problem with drawing conclusions from these results is that the same tests demonstrate substantial inter-subject variability in the objective effects of narcosis on psychomotor and behavioral function, and in the subjective adaptation to narcosis. Some divers can demonstrate narcosis at relatively shallow depths (<100 ft), while others do not demonstrate substantive impairment even at depths normally associated with demonstrable narcotic effects (>150ft). That is part of the challenge of establishing guidelines for trimix use, for example. Some on SB won’t dive below 100 ft without it. Others apparently dive to 175 ft without it, and without documented performance problems and associated safety issues. Who is right?
Of course, an important by-product of this variability is that it gives SB posters something to argue about, just like the endless (and probably pointless) exchanges over the erosion of training standards, across agencies and over time.