The phantom effect in information visualization

Recent research focuses on understanding what triggers cognitive biases and how to alleviate them in the context of visualization use. Given its role in decision-making in other research fields, the Phantom Effect may hold exciting prospects among known biases. The Phantom Effect belongs to the category of decoy effects, where the decoy is an optimal yet unavailable alternative. We conducted a hybrid design experiment (N=76) where participants performed decision tasks based on information represented in different visualization idioms and phantom alternative's unavailability presentation delays. We measured participants’ perceptual speed and visual working memory to study their impact on the expression of the Phantom Effect. Results show that visualization usually triggers the Phantom Effect, but two-sided bar charts mitigate this bias more effectively. We also found that waiting until the participant decides before presenting the decoy as unavailable helps alleviate the Phantom Effect. Although we did not find measurable effects, results also suggest that visual working memory and visualization literacy play a role in bias susceptibility. Our findings extend prior research in visualization-based decoy effects. They are the first steps to understanding the role of individual differences in the susceptibility to cognitive bias in visualization contexts. © 2024 The Authors