Psychological egoism should be contrasted well with ethical egoism, which is the view that we always ought to be motivated by self-interest.
Max Stirner is known for holding this view of the human psyche. (He was also a proponent of ethical egoism.)
Because psychological hedonism makes a very strong claim (we are always motivated by self-interest), it appears to be quite easy to refute empirically.
See also: psychological hedonism
External links. More information can be found at http://www.utm.edu/research/iep/e/egoism.htm http://plato.stanford.edu/entries/egoism/