In general it is thought that the temporal lobes of the brain are responsible for short-term memory and the ability to distinguish different sounds, while the occipital lobe is mostly responsible for the visual sense. Most memory is a function of the cortex, which is comprised of the occipital and temporal lobes along with the frontal, parietal, and limbic lobes.

This last example illustrates the difficulty with trying to narrowly isolate different parts of the brain: while we can see that one region or another is generally associated with certain processes, the brain is very complex and all parts are interdependent to some extent. For example, while the occipital lobe is primarily responsible for processing immediate visual inputs, other parts of the brain are also involved in the ability to interpret, recognize, and remember that information. The brain is complex, and nearly every activity requires, to some extent, a contribution from every part of the brain.

I just read today in Science magazine that scientists think the hippocampus may be involved in imagining the future.It's known to be involved in memory, because damaging it results in amnesia. The scientists were surprised that imagining the future might be in the same region of the brain. The article says the hippocampus is thought to encode new memories and send them to the cortex for long term storage.

You can search Google for sight and hearing in the brain. Sight happens a lot in the eyes, which are little blobs of brain sticking out of the skull; scientists are surprised at how much processing of visual signals happens already at the back of the eyeball, before the info goes down the optic nerve to the brain. The optic tectum is the region in the brain where sights are processed, but I don't know where that is.

Memory is dealt with in the forebrain, and generally sensory input is dealt with in the optic tectum, and then further manipulated in the forebrain. Of course, for vision, it starts with the eye - which, developmentally speaking, is itself part of the brain.

It is tenuous to definitively point out parts of the brain that are responsible for functions like sight and sound. These are complex processes that do not belong to just one area. But we know a good amount about the brain that we can give reasonable answers. Here it goes:

Memory: hippocampus (sea horse shaped cortex; imagine drawing a line on a face between the eyes and nose; now imagine taking a thin slice out of a brain where you drew that line. In the middle of that slice would be the hippocampus)

Sight: occipital cortex (part of the brain that is all the way opposite of the eyes, ironically; located pretty much in the back of your head)

Sound: temporal cortex (not too surprisingly, located by your ears and temples)