This question is open to quite a lot of debate. You may fancy
asking it within the philosophy forum also, as it is a popular
topic within this field. I'll concentrate on giving a brief outline
of some of the more well known theories put forward, but there are
many more and can be taken to great depth! Perhaps the most
straightforward theory regarding senses is referred to as "direct
realism" (naive realism). This is the view that, quite simply, what
we experience corresponds directly to that which exists in the
external world. My computer exists outside my own perception in
exactly the state in which i perceive it. However, there have been
many criticisms raised against this position. The argument from
illusion states that direct realism is challenged by the fact that
we can experience optical illusions. A straight stick, when half
submerged in water, may appear bent, although in the external world
it still exists as a straight object. What's more, some debate
whether the colours we perceive are properties of an external
world- what we perceive as being green, for example, is purely the
result of light frequencies being absorbed and reflected. External
realm ---> Our perceptions. Indirect Realism (representative
realism) seems to overcome some of these problems. This theory
states that we do not experience the world directly, and that, in
between the external realm and are perceptions exist "sense data".
Things in the world are experienced via this data, which is
representative of objects in the real world. This can explain how
our perceptions are not always truly accurate representations of
the world (explaining optical illusions), but introduces another
problem: since all we experience is sense data, we can never check
the extent to which this really corresponds with objects in the
external world. We live behind a "veil of perception" which we can
never overcome, and this may lead to scepticism. However many have
argued that our sense data must be somewhat similar to the external
world or we would experience more difficulties in everyday life- if
we perceived flat ground where stairs existed in the external world
then this would be very impractical!! External realm --> Sense
Data ---> Our perceptions. Idealism challenges the idea of an
external realm possessing an objective existence, claiming that all
we can ever experience is ideas. Berkeley is particularly
associated with this stance- all we can ever hold as truth is that
what we perceive. He summed up his theory in the phrase "to be is
to be perceived." If a tree falls in a forest and no one is around
to hear, it does not make a sound. However, this seems to raise
some problems. If all we experience is subjective ideas, why do
people seem to experience similar things? And if objects only exist
when perceived, then this seems to go against the flow of time and
space, creating gaps: if an apple is placed in a drawer and cannot
be perceived, then it appears to cease to exist. In order to
overcome these problems, Berkeley argued that objects are
constantly perceived by god. Of course, this hinges upon a
unprovable metaphysical basis, which is difficult to justify!
Perhaps the other most widely known theory of perception is that of
phenomenalism. This theory maintains that objects do not exist in
themselves in the external world, but exist purely as clusters of
sensory stimuli or sense data. However, it is not whether a person
is physically perceiving an object which brings it into subjective
existence, but whether a person is capable of perceiving it. In
this way, when shutting an apple in a drawer, it does not disappear
because, theoretically, someone would still be capable of
perceiving it. This theory does not hinge upon god, and alters
Berkeley's phrase to "to be is to be perceivable". So there you go,
some (very brief) theories as to how we perceive. Maybe research
them online or in journals if you are interested in going into more
depth! :)
