A big debate about perception involves how it is we perceive anything at all. There are perhaps three stances we could take toward the issue of perception. First, we have direct access to the world outside of us through our senses. Second, we have indirect access to the world outside of us through our senses and a mediating Representation. Third, we have no access to the world outside of us but only Representations.
First possibility: We have direct access to the world outside of us through our senses. (direct realism)
Consider this first possibility. It is what is often called "direct realism." So when I look at my laptop, for example, I am seeing my laptop. Sure, there's a complicated story to tell about how the brain does it, and a complicated physiological story about how my eyes work, but basically there's a one-to-one correspondence between my seeing to see a laptop and that I see a laptop. But consider the perception again. What I see isn't an object with all of its 4 dimensions. I see one aspect of what I assume to be an object. I see, for example, this side from this distance, under this light, etc. I can't see the back of the laptop nor can I see underneath it. All of this gives me some suspicion that what I see is not exactly something else directly in the world but certain aspects of what could be directly out there in the world.
You could say the same about optical illusions and rainbows. Optical illusions are basically the brain's failure to perceive something for what it objectively is and instead perceive patterns, distances, and directions that are not there. Rainbows seem to be objects that eventually touch the ground but the closer you are to them they recede.
Rainbows, optical illusions, and the talk of the laptop suggest the second or third possibility. So let's consider...
Second possibility: We have indirect access to the world through our senses and a mediating Representation (indirect realism).
I capitalize Representation here so as to distinguish the word from at least one philosophical tradition that requires that representations are representations of some other object and to define it instead as some complex manifold of percepts, what might have to be given a better understanding through neuroscience or some of the other natural sciences.
Setting that issue aside, the view espoused here is often called "indirect realism," indirect because there is something intermediary between us and the world. Given that when I reflect on what I perceive I realize I never perceive anything in its totality. But maybe that is not exactly right. Surely I do not see everything in its totality only certain aspects of it, but this is to say nothing yet of the other senses. For example, it does not even seem intelligible to me to say that I did not taste a bite of food 'in its totality.' I can say, however, that I "half-heard a conversation," but regarding smell it might seem stranger to say that I 'partially' smelled it. Or regarding touch, the touch of something often appears immediate.
This diversity of perception and the way the world subsequently seems to us coupled with my reflections about what it seems appropriate to say might say more about language than it does about the five senses. Nevertheless, it seems to hint that the only reason we infer the existence of objects in the world and a world outside of our perception is because we are so designed to operate as if everything we perceive is natural and so. Furthermore, we can rationalize that the world is so and that objects are actually there and perdure through time because that seems to be an inference to the best explanation: If there were not a world external to the mind/brain, it would be a lot of information for little old me to carry around in his head absent some world of objects providing me with input.
Third possibility: We have no access to the world outside of us but only our Representations (idealism).
Assume for the moment that I perceive that the world is such because of evolution and a kind of mental confabulation that allows me to believe that there is a world and it is a place full of persons and other entities. If this much were true, then we would have the position often called "idealism." I want to give some credence to idealism if it is properly construed.
If the claim and this whole direct-realism, indirect-realism, idealism debate is really about our epistemic limitations, then idealism looks to be correct. I mean, if this third possibility "idealism" really means "We cannot know that there is a world outside of us, only that we have Representations," that much seems to be true. If it is a claim about metaphysics, meaning "There is no world outside of us but only our Representations," that position would be more difficult to affirm.
As far as epistemology goes, we could go right on assuming that the world is metaphysically full of people and objects and so on but it is just that, an assumption. As far as the limited position we're in, we can't ever know for sure that the Representations have some reality correspondence. We just have to build theories that are intelligible and explanatory to understand how the world seems to work and modify our thinking after that.