Sentence:  (4) the unipolar-<WSD>bipolar</WSD> distinction is important in regard to these personality variables; the trait of extraversion (associated as it is with positive affectivity) may mean that individual variation here leads to a more <WSD>bipolar</WSD> pattern; ... 
Meaning of the word marked with <WSD> tags:  Involving or having both extremes or poles at the same time.