Your model of thinking is something like idealized bayesian one, not like human. If your mind decided that something is true with sufficient probability, it then fails to see alternative explanations. This "something" will be a reality to you, not just a belief about reality. But it is not the all. Your mind have some ideas associated with cow you've seen, and those ideas also becomes beliefs of yours. Implicit beliefs, you are probably not aware of them, you could notice this implicit beliefs only if they will begin to contradict evidence in a sharp way. For example, you can implicitly decide that this is a soft tempered cow, that would like to lick you in a face, if you come near. It was not important when you saw the model of a cow, so you didn't become consiously aware of your idea of a cow temper. But it was planted in you idea of reality. Maybe you would have an intention to come near the cow to be licked in the face, and you might be unaware of this intention. Human mind can easily manage such tricks.
And it leads to a funny thing. You saw the model of a cow, and it make you believe that there is a cow in the field and that you saw a cow. Then you could find a heap of poo, and you will strengten your beliefs futher. You might find a lot of evidence and it all will be explained under assumption that you saw a cow. And this evidence will strenghten your belief that you will be licked in the face, when you come near the cow.
But you didn't saw the cow that made this heap of poo. The real cow is pitch black, with a horns of gigantic size and they are really sharp. The real cow has red glowing eyes and it is going to kill you. But before you see the real cow itself, all the evidence that would point that there is a cow would also reinforce the idea of soft tempered black and white cow. The longer you manage to keep youself oblivious to real cow traits, the more surprised you will become when you find the real cow.