Descartes uses three very similar arguments to open all our knowledge to doubt: The dream argument, the deceiving God argument, and the evil demon argument. The basic idea in each of these is that we never perceive external objects directly, but only through the contents of our own mind, the images the external objects produce in us. Since sense experience never puts us in contact with the objects themselves, but only with mental images, sense perception provides no certainty that there is anything in the external world that corresponds to the images we have in our mind. Descartes introduces dreams, a deceiving God, and an evil demon as ways of motivating this doubt in the veracity of our sense experience.
Now, once we take this point into consideration we can assume that every time we use our senses, the organs that we use, send signals to our brain. After that, our brain sends back signals to those organs, and thus we perceive. But if we were to think about it, what we perceive is actually our mind’s interpretation of those signals. Hence we can safely say that our perception can be deceived due to the simple reason that the world we know, is all in our mind, and that we will never be able to verify the credibility of our mind on whether it correctly portrays the external world.
"So, do we really respond to a thing? Don't we respond' only the electrical and chemical events that occur in the brain and nerves, and not to the alleged real object? Therefore, it is not things we are experiencing but chemical and electrical reactions. We don't see things directly. We see via chemical and electrical reactions in eyes, nerves and bits of brain. This appears to be true because: Without eyes, we don't see. Without optic nerves we don't see. Without certain bits of the brain, we don't see. So we never directly see what is out there, according to science.
From this we can accept that Descartes might have been right in suggesting that our senses can be deceived and that the world we believe we live could be virtual for all we know and everything that we have come accept as the truth could be just perceptions formed by our biased minds. But the circumstances of the world we live in does not allow us to think for ourselves but instead forces us to trust our senses so as to survive in the world and fit in.
However, I believe that we should not blindly trust our senses but should instead take into consideration the method suggested by Descartes. We should apply pure reason and interpret what our senses show us instead of blindly believing all the time.