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We review recent trends and methodological issues in assessing and testing theories of emotion, and we review evidence that form follows function in the affect system. Physical limitations constrain behavioral expressions and incline behavioral predispositions toward a bipolar organization, but these limiting conditions appear to lose their power at the level of underlying mechanisms, where a bivalent approach may provide a more comprehensive account of the affect system.
Cacioppo et al. (Mon,) studied this question.