The Eyes are the Window of the Soul (and UX)? – Pupil Size as a Potential Indicator of Emotional Responses in UX Research
DOI:
https://doi.org/10.15170/MM.2026.60.KSZ.01.03Keywords:
pupil diameter, eye-tracking, emotions, mobile user experienceAbstract
THE AIM OF THE PAPER
The aim of this study is to interpret psychophysiological findings on pupil size changes by linking them to the conceptual framework of marketing and user experience (UX) research, thereby contributing to a more precise delineation of the role of pupil size in UX‑related investigations. The paper, in this context, identifies research gaps emerging in the fields of advertising, online retail, specific elements of user experience and methodological approaches, and, by means of a small‑scale qualitative eye‑tracking pilot study, provides illustrative examples of the potential relationship between pupil size changes and the frustration and positive experiences arising during the use of mobile applications.
METHODOLOGY
The study is based on a systematic literature review that organises research addressing the emotional and cognitive underpinnings of pupil size changes, with particular emphasis on the interrelations between negative emotions, cognitive load and user frustration. This is complemented by a small‑scale qualitative eye‑tracking pilot study (n=10), in which pupil size time series recorded during the use of retail mobile applications and semi‑structured interviews were analysed in order to identify pupil size changes associated with critical UX situations.
MOST IMPORTANT RESULTS
Based on the literature review, pupil size change (under appropriate measurement conditions) can be regarded as a reliable physiological indicator of negative emotions, increased cognitive load and user frustration, whereas responses associated with positive emotions tend to be shorter in duration and less consistent. The results of the qualitative eye‑tracking pilot support this pattern, showing that pronounced pupil size changes were primarily linked to non‑functioning or missing functions, overly complex tasks, longer waiting times and visual overload, while in the case of relevant products and promotions they also appeared as signs of heightened interest. The findings further indicate that pupil size is sensitive to environmental and contextual influences, which necessitates the careful and cautious application of this indicator.
RECOMMENDATIONS
Pupil size change can be used in UX research as a complementary indicator for identifying frustration points, particularly for mapping non‑functioning or missing functions, overly complex tasks, longer waiting times and visual overload. Its application is primarily recommended in controlled experimental designs, where lighting conditions and other contextual factors can be appropriately regulated, and where pupillometry, in combination with other qualitative and quantitative tools (interviews, questionnaires, behavioural data), serves as a guiding but not solely decisive source of information in the UX testing of mobile applications.
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