So I've taken the 16 personality type quiz about 6 times, all of which say I am ISFP. But hold up I've taken the congnitive quiz about 4 times and it never comes up with ISFP. It comes up with ISFJ, ESFJ and INFP. What does this mean?? :S
Well all those types you mentioned have a Introverted Sensation preference. ESFJ, ISFJ and INFP all have Ne/Si perception preferences. ISFP is an Extraverted Sensation type.
Essentially the difference is one of subjective perception. Introverted Sensation is where your own subjective perception of an object takes precedent over the object's actual qualities. The example we use is Van Gogh who would paint things as he saw them, but that may relate little to what the object actually looked like. Ansel Adams on the other hand, is probably an Extraverted Sensation type. Someone oriented to the object as it is, without interjecting anything personal (introversion) on to that perception. Extraverted Sensation just notices the details as they are, without reaching back into the person's unconscious to attach anything to that perception.
So for example, in my photography class, the Si-types often look at a picture and say "oh it reminds me of home," where home means something that only they personally know the significance. To me as a Se-type, I only see the house. The details of the carpet, the paint, the furniture, textures, colors, etc., but I don't interject my own feeling of 'home' or memories or anything else onto the image. Extraversion always takes the objective at surface value (whether we're talking thinking, sensation, intuition, values, or whatever). Introversion is subjective.
That being said the Introverted Sensation type (ISTJ, ISFJ, ESFJ, ESTJ, ENFP, ENTP, INFP, INTP) takes in sensory data and attaches some personal significance or whatever from within to that sensory experience. Thus they form a perception is reality mindset, because to them all perception is personal (this is why they need Extraverted Intuition to help remind them that how they perceive something may not be all there is).
The Extraverted Sensation type (ESFP, ESTP, ISFP, ISTP, ENFJ, ENTJ, INFJ, INTJ) simply sees the object at face value, thus they need Introverted Intuition to remind them that the object may have some personal significance or implication that is not physically apparent.
The reason an MBTI test might give you strange results is because of the way it tests. It doesn't differentiate out the difference between Extraverted and Introverted Sensation, for example (which is a problem considering how different those perspectives are) but rather tries to infer them by testing you on other stuff like J/P or I/E. But of course this may lead to false positives or someone thinking they are a type that they are not (J/P is the real culprit here. Rather than test for the actual functions you use, MBTI tries to figure out your J/P, based on its own self-definition, then decides from that if you are say an ISFJ or ISFP, but this is problematic because ISFP and ISFJ have no common functions, but might superficially resemble each other behaviorally).