Washington: In a key breakthrough which
could be used to improve sight for robots, scientists have for
the first time mapped crab vision.
An international team has worked out how fiddler
crabs -- who`ve all-round vision including overhead provided
by 9000 separate eye facets, or ommatidia -- actually perceive
the world and respond to it."Unlike our eyes, the crab`s eyes do not move, so it
uses different parts of its visual field for different tasks.
Some require a sharp focus and some of which require just a
general lookout to be maintained.
"Our work is aimed at understanding how they
process the visual signals they receive and convert them into
behaviour, a process common to all visual organisms, ourselves
included," Dr Jan Hemmi, who led the team, said.
The team has demonstrated that the sharpest vision
in the crab is in the horizontal plane immediately in front of
it. Its eyes here are really adapted to fine detail. This it
uses for identifying and communicating with potential mates.
The crab also sees quite well horizontally to either
side with especially good spatial perception enabling it to
see how far objects are from one another -- it uses this to
keep watch for rival crabs and monitor how far it is from its
own burrow, so it can run for cover, the scientists said.
The eye cells that make up its overhead and rear
vision are much more thinly spread, sufficient just to provide
warning of the approach of a predator like a gull, outlined
against the bright sky.
"We know that high levels of alcohol consumption can
increase the risk of becoming alcohol dependent in those who
have a genetic make up that predisposes to dependence. This is
a case of interaction between genes and environment.
"Indeed, in our study we found that, higher alcohol
consumption in humans was positively correlated with alcohol
dependence. However, because different sets of genes seem to
influence the level of alcohol consumption, as opposed to
propensity for alcohol dependence, we are confronted with
great variation in humans."Individuals with a set of genes that predisposes
them to drink moderate amounts of alcohol may still have the
genetic predisposition to lose control over their drinking
behaviour, and perhaps become alcohol dependent.
"Conversely, individuals with a genetic predisposition
to drink high amounts of alcohol may not have the genes that
predispose them to become dependent," lead researcher Boris