The interest in “implicit bias” began with implicit memory as seen in patients with memory loss who are told jokes, forget the joke, but find retellings of the joke less and less funny. This led to research into implicit bias as measured in a test of associations of white & good versus black & bad and then the reverse.
This field of study began in cognitive psychology but was adopted by social psychology. There is controversy around the evidence supporting whether or not implicit attitudes actually affect behaviour.