Psychology had to be a science studying behaviour and mind of living beings.
There is a separate part of it studying specifically human behaviour and mind.
However, there is absolutely no any definition of how exactly human behaviour and mind different from non-human ones and how to separate one from another.
So, psychology can't even give an answer to the very basic question that obviously should precede any further study - is some person mind and behaviour human or non-human?
Psychology could have been very useful instrument to detect those with non-human behaviour and mind among us with scientific precision, but it was purposedly turned into pseudoscience bullshit to not even allow that question.
Exactly, that's why a materialist approach to psychology doesn't work. You can't appeal to nature (hardware) to show you what the software (mind, soul) is. This is most evident in the field of ethics - looking at nature can't tell you what's right or wrong - it just is. Only a evaluation by a mind that has conception of morality can do that and concepts are not found in the material world or subject to empirical observation.