“I care about winning some but losing none!”—Attentional mechanism of mutable-hidden zero effect in economic choices

In risk-related economic choices, designating zero as “winning $0” or “losing $0” asymmetrical shapes subsequent decision preferences – a phenomenon known as the mutable-zero effect. However, little is known about whether mutable-zero effect pertains to risky decision-making and what cognitive mechanisms underlie it. Here, we examine this question by conducting an eye-tracking experiment where participants (N = 110) chose between certain and risky options. Critically, risky options (“p% to win $X” in the gain domain, and “p% to lose $X” in the loss domain) were companioned with either explicit zero outcomes as “(1-p)% to win $0” or “(1-p)% to lose $0”, or hidden zero outcomes. We found, in small to medium probability intervals, that participants were more risk-aversive when observing “win $0” yet more risk-seeking when observing “lose $0”. By combining attentional drift diffusion modeling (aDDM) with cumulative prospect theory (CPT), we tested whether it was attention or value computation that give rise to our mutable-zero findings. We found that the mutable-zero effect arose from attentional bias and the starting point in the aDDM rather than from CPT-related parameters. Specifically, the attentional mechanism was asymmetrically attributed to the non-zero outcomes when presented with “win $0” as well as zero outcomes when presented with “lose $0”. These findings provide insights into the attentional mechanism underlying the mutable-zero effect and shed light on the role of “null outcomes” in economic choices.