What is the internal validity of Philosophy?

I remember one line of the philosophical inquiry into the perception process like this: By the logic that a perceiver must be separated from perceived, therefore there must exist ‘little man’ who observe what we observe in our brain. But then how does these ‘little man’ know what they observing? Then it require a little man inside another little man’s brain. We can easily see how this lead to an absurd conclusion. So the conclusion is either perception is logically impossible or there is something wrong with this picture, likely its hidden assumption.
I prefer the later since there are obvious logically error with the picture: Why must perceiver must be separated from perceived? Why can’t perceiver also perceiving itself? Where does this notion that perceiver must be separated from perceived, which sounds so natural to us, come from?

I am not interested to dwell into the actual psychological history of this idea. I only think it is very likely it is coming from the logical rule of our mind rather than fact of physical reality. It has everything to do with the habit of our mind to separate the perceiver and separated in our Cognitive process. Thus it is natural to infer from this logic that there must be some mechanism to observe what is observed, since it is assumed that the observer itself has no explanatory power. Observation is obviously different from the process of understanding, therefore we habitually separate them into two categories. It thus follows that there must be two set of brain cells devoted to two different neurological process, since in our mind it is ‘natural’ to place one category in one slot.(Against the Pigeonhole Principle in Discrete Mathematics.) When one set of brain cell is responsible for observation, then another set of brain cell must be responsible for analyze it. How logical is it to infer the process in Physical space from the bias inherent in our Cognitive Process in Psychological Space?

This, I see it as the example of the issue in Philosophical reasoning. If only we can obliterate all assumption then we can arrive at the best understanding of the world, otherwise we may think we are analyzing the world objectively while we are subtly biased in one way or another.