Does zero mean nothing? Investigating the attentional mechanism of the hidden-zero effect in risky decision-making

The framing of risky choices can shape and alter individuals' risk preferences. Within every option in a risky choice (e.g., 70% chance to win $100), there is a naturally embedded but hidden zero outcome (e.g., 30% chance to win $0). Here, we tested the hidden-zero effect by comparing participants' risky choices between two different conditions (i.e., presenting options with or without explicit-zero outcomes) with a full range of risky probabilities (5%-95%). The results showed that presenting zero outcomes explicitly led to more risky choices (Studies 1 and 2). Moreover, combining eye-movement measurement and computational modeling, we then developed a series of models based on Expected Utility and Prospect Theory to quantify the attentional process underlying this hidden-zero effect. These results demonstrated that the hidden-zero effect is primarily driven by a choice bias toward the risky option, which was mediated by increased visual attention to the risky option. These findings suggest that the utility of zero does not simply equal zero; rather, presenting the often-omitted zero components may shift individuals' attention toward risky options, encouraging them to take more risks.