People interact with user interfaces daily to perform tasks such as web browsing, sending emails, watching videos and playing games. Many of their interactions will involve making judgements and decisions, such as judging the duration of software updates, the quality of video recommendations and deciding whether to examine word suggestions above a mobile keyboard. However, prior work from psychology and behavioural economics literature exhibits that people are susceptible to cognitive biases and perceptual distortions, implying that they can influence judgements and decisions in interaction. Examples of these effects relevant to this thesis include perceiving time as longer or shorter than it is, the Barnum effect (people’s tendency to assign higher quality ratings to personality descriptions presented as personalised for them than identical descriptions presented as generally true of people), and prob- ability weighting (the tendency to overweight small probabilities and underweight large probabilities).

If cognitive biases and perceptual distortions apply in interaction, user interface designers must be aware of them, and helping designers understand them can lead to opportunities for improving user experiences. Therefore, the primary goal of this thesis is to provide novel knowledge and insights for improving research and practice in HCI by investigating the influence of cognitive biases and perceptual distortions in interaction. In addressing this goal, this thesis presents three empirical studies.

Study 1 explored the influence of audio effects and attention on users’ perceived duration of interaction. This study was motivated by computer delays leading to user frustration, prior psychology literature of factors such as audio and attention influencing time perception, and the opportunity to extend from a previous HCI study demonstrating distortions in users’ duration judgements using audio effects. Study 1 had two stages: estimation of a wait duration (indicated with a progress bar) and pairwise comparisons between the duration of two interactive experiences with different effects. The first stage results revealed that perceived duration varied across different audio conditions, and the second stage results confirmed previous findings that increasing-tempo beeps could shorten the perceived duration but also extended these findings to interactions involving visual feedback (progress bar) and direct interaction (playing a game). These findings suggest that designers can use audio to alter users’ time perception during wait periods and reduce the adverse effects of computer delays.

Study 2 examined the effect of purported personalisation on users’ perceived quality of system recommendations. This study was motivated by the prevalence of recommender systems in contemporary user interfaces and the widely observed Barnum effect. The experiment showed participants a set of identical movie recommendations that were purportedly personalised or non-personalised. Opposite to the Barnum effect, the results showed that personalised recommendations had lower mean quality scores but no significant difference. This result suggests that Barnum-like effects of personalisation have minimal influence on perceived quality and that designers should be cautious about depending on this effect to improve user experience.

Study 3 investigated the probability weighting function influencing users’ decisions to examine or ignore text entry suggestions. The probability weighting function implies that users will exhibit a bias in which they overuse suggestions at low accuracy and underuse them at high accuracy, which can harm their text entry time. This study tested this prediction by having participants interact with five text entry suggestion systems, each with a unique probability of showing the participant their required word each time the suggestions were updated and examining users’ decisions to examine or ignore the suggestions. Experimental results confirmed the prediction, suggesting that designers should be wary of users exhibiting this bias and harming their performance. Moreover, as part of analysing users’ bias, this study contributes a method for analysing and modelling text entry to examine the costs and benefits of text entry suggestions.

In summary, this thesis makes four primary contributions: (1) a review of prior work on a set of cognitive biases and perceptual distortions and their potential influence in interactive contexts; (2) an investigation of audio effects and attention influencing users’ perceived duration; (3) an investigation of the Barnum effect influencing users’ perceived quality of recommendations; and (4) an investigation of the probability weighting function in text entry suggestion interaction.