Facing ambiguity: What we do in the space between stimulus and response

Decades of research in human and non-human animals has examined responses to clear valence, including stimuli that either represent a relatively clear threat (e.g., electric shock) or a clear reward (e.g., money). But daily life is replete with events or situations that are ambiguous - they could be threatening and/or rewarding. This review describes work that examines the wide inter-individual variability with which humans respond to this dual-valence ambiguity. Although some individuals more readily categorize these events as negative, others are prone to arrive at more positive categorizations. This predilection to lean in a more positive versus negative direction represents a stable, trait-like difference, and is referred to as valence bias. Valence bias is generalizable across categories of dual-valence ambiguity and has important implications for health and well-being. Here we focus on extensive findings that lend support for the Initial Negativity Hypothesis, which posits that the initial or default response is negative across people, and that positivity relies on an additional regulatory mechanism that helps to overcome the initial negativity. Together, the present review describes the cognitive and brain mechanisms underlying the valence bias, including emphasizing the importance of a broad set of systems that support human responses to ambiguity.