MDR-PS-Speech

[Update Nov. Some of this is now outdated. Oral communication while at depth was indeed done, via clicking.]

Speech, though completely dependent upon the
mouth/larynx, is not particularly sensorial. Eating, breathing,
sniffing, sneezing are all face-sense-related, talking isn't. Talking
is all about internal air valve control.

One cannot talk underwater, yet if not for underwater air valve
control, speech would not have happened.

In a way, both speech (audio sense only) and physical gestures (visual
sense only) require an absence/reduction of other of senses, otherwise
risking interference. (Compare the small eyes of echolocating
cetaceans (especially river dolphins, which are almost blind) vs huge
eyes of ancient non-echolocating marine reptiles.)

What is the physiological opposite of the anaerobic MDR Mammalian
Divers Reflex which occurs at depth? Instant exhalation
(photic/pressure/thermal induced) & aerobic breathing at surface, with
optional controlled exhalation vocalized speech. Has anyone
immediately upon surfacing from a *long* dive, spoken during the first
exhale? I think humans are programmed/selected not to, just like
seals. First exhale, then speak/bark. Not sure though.

I think also that the LCA Hominoid/Hominid could not call while
floating vertically, possibly due to (water) pressure on the
throat/sac/hyoid/thyroid cartilage. Only when pressure was eased,
could a vocal sound be produced (compare to having a "knot in ones
throat" or feeling choked up), I guess. This allowed breathing clearly
through the nose during floating, then upon grasping and lifting up or
wading, the air sac pressure is off, and oral breathing and calling
can start.

[{Highly significant}]
This might have been a predecessor of being able to suction feed in
Homo underwater, having the oral breathing disconnected during
submersion, allowing the open pharynx for feeding and swallowing, then
upon re-emergence to light/pressure change, the larynx reopens to the
mouth and instantly exhales but with no vocalization, just a pure
instant complete air exchange of the lungs, trachea, mouth. Only the
little air in the nasal area is not forcibly exchanged. Why? Either
because the sinuses and eustacean tubes were pre-flooded with seawater
(per Seb Murat), or because of some other reason (high-pressure nasal
sneeze might cause damage to delicate nasal
veins/arteries/turbinates/olfactory nerves/middle ear/inner ear
barotrauma).

Today's scuba divers and free divers instead keep their chin down near
the throat, with their eyes 60 to 90 degrees from the streamlined linear
posture (and more like a vertical floating ape posture), which differs
from this ancient diving technique, and may indicate why the photic
sneeze "doesn't work" in today's divers.