This work investigates the effect of display polarity on cognitive load, using eye-tracking and subjective measures, and emotional reactions to assess whether the popularity of negative polarity displays is related to affective qualities or true physiological benefits. Younger and older adults tested positive and negative polarities under bright and dim environments for writing and search tasks. Eye-tracking results showed higher cognitive load using negative polarity, reflected in increased search time and pupil diameter for older adults in a bright environment and younger adults in a dim environment. For older adults, mental effort scores were higher using negative polarity for the search task in a bright environment. This group reported more positive emotions using positive polarity, while younger adults expressed more interest in negative polarity. These results suggest that older adults use positive polarity to avoid mental fatigue, while younger adults use negative polarity in a dim environment for aesthetic reasons. Practitioner summary: The effects of negative polarity on cognitive load and users' preferences are often unclear. Eye-tracking and subjective data reveals that negative polarity displays elicit higher cognitive load for older adults in a bright environment and younger adults in a dim environment, suggesting older adults prioritise reduced fatigue while younger adults prioritise the feel of the interface.
Keywords: Display polarity; age; cognitive load; emotion; eye-tracking.