Person perception refers to the different mental processes that we use to form impressions of other people. This includes not just how we form these impressions, but the different conclusions we make about other people based upon our impressions. It concerns social processing issues like what information we extract when we see other people, how we interpret what we see, and how this interpretation influences our subsequent behavior.

Research has highlighted the non-veridical nature of person perception, revealing a number of biases that are relied upon in order to cope with the enormous complexity of social information processing such as Attribution Errors, Context Effects, and social categorization.

Self-perception theory (SPT) is an account of attitude formation developed by psychologist Daryl Bem. It asserts that people develop their attitudes (when there is no previous attitude due to a lack of experience, etc.—and the emotional response is ambiguous) by observing their own behavior and concluding what attitudes must have caused it. The theory is counterintuitive in nature, as the conventional wisdom is that attitudes determine behaviors. Furthermore, the theory suggests that people induce attitudes without accessing internal cognition and mood states. The person interprets their own overt behaviors rationally in the same way they attempt to explain others’ behaviors.

The two postulates of the self-perception theory are:
1. When we want to know how a person feels, we look to see how he acts. Accordingly, when an individual himself wants to know how he feels, he may look to see how he acts. The first postulate of the self-perception theory was derived from this line of reasoning: Individuals came to “know” their own attitudes, emotions, and other internal states partially by inferring them from observations of their own overt behavior and/or the circumstances in which the behavior occurs.
2. The second postulate of the self-perception theory suggests a partial identity between self- and inter-personal perception: to the extent that internal cues are weak, ambiguous or uninterpretable, the individual is functionally in the same position as an outside observer, an observer who must necessarily rely upon those same external cues to infer the individual’s inner states.

It is important to emphasize that neither the interpersonal observer not the individual himself is confined to inferences based upon overt actions only. Experimental evidence of the self-perception theory was provided by the facial feedback experiment and the false confession experiment.

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“Person perception” is concerned with how we process information about people. It includes the mental processes involved in forming impressions about people, and the conclusions we make about other. Self- perception theory deals with a person’s attitude formation related to himself by observing own behavior. The first postulate states that person infers own attitude by observing own behavior and the circumstances in which they occur. Second postulate states that when internal cues are weak, person has to rely on external cues like an outside observer.

Sources:
Self perception theory, Daryl J. Bem
http://en.wikipedia.org/wiki/Self-perception_theory
http://psychology.about.com/od/socialpsychology/a/person-perception.htm
http://www.oxfordbibliographies.com/view/document/obo-9780199828340/obo-9780199828340-0136.xml