While adults can readily report another agent’s false belief, theories of belief processing typically assume that this process requires the inhibition of one’s own salient current knowledge: belief processing involves overcoming an initial “egocentric bias” towards one’s own knowledge. However, evidence for the presence of egocentric bias during tasks in which adults explicitly report another agent’s false belief is surprisingly limited, with some studies providing conflicting results (e.g., Wang & Leslie, 2016; Rubio-Fernandez, 2017), failures to replicate (e.g., Ryskin & Brown-Schmidt, 2014; Samuel et al., 2018) or data that do not clearly support the presence of an egocentric bias (e.g., Back & Apperly, 2010). In this online psychology experiment (n = 267), we used computer mouse tracking to attempt to measure, in adults, egocentric bias during an unexpected transfer false belief task. Mouse tracking allows researchers to measure the online competition between different response options when one makes a decision, and thus has the potential to reveal attraction to response options that reflect participants’ own knowledge during a false belief task. Participants viewed video scenarios in which an agent had either a true belief (“TB-scenarios”) or a false belief (“FB-scenarios”) as to the location of a toy. In each video, the agent first watched the toy hidden in one of two cups. The keys were then moved to the other cup either in the agent's presence (TB-scenarios) or absence (FB-scenarios). At the end of each video participants used a mouse to answer questions presented on the screen by moving the mouse from the bottom centre of the screen to click on one of two response boxes located in the top left and right of the screen. Key experimental questions required participants to answer: “Which cup does HE think the toy is in NOW?” (belief question); “Which cup do YOU think the toy is in NOW?” (reality question); “Which cup do YOU think the toy was in FIRST?” (memory question). Answers to all questions were always either "Red" or "Blue", and the location of the response box corresponding to these two possible answers remained fixed for participants across all trials. On each trial participant response accuracy, response time, time taken to first move the mouse, and time-stamped mouse coordinates as they made their response were recorded. Participants received 12 experimental question trials (2 of each Scenario x Question combination). Participants did not receive any practice trials of these experimental questions: combined with the low number of total trials, these conditions should reduce the impact of any practice effects on participants' performance. Critically, on belief questions only on FB scenarios the alternative incorrect answer reflects participants’ own knowledge (if the agent thinks the toy is in the "red" cup, then the participant will know that the toy is in fact in the "blue" cup). In contrast, on belief questions following TB scenarios the correct answer reflects participants' own knowledge. For both reality and memory questions, however, irrespective of scenario the correct response is consistent with what participants’ themselves know. If there is an egocentric bias towards one’s own knowledge when processing another's false belief, then one would predict a statistical interaction between question-type and scenario. One would predict that any differences between question-types (e.g., in errors, response times or mouse path deviation towards the incorrect answer) to be greater following FB-scenarios relative to TB-scenarios. We did not find statistically significant interactions of question and scenario in our data.This project investigates the fundamental cognitive processes underlying our ability to understand other people's beliefs about the world, specifically when those beliefs are different to our own. Human beings have been described as "egocentric creatures": even as adults we often assume that other people share our perceptions, desires and knowledge about the world. However, the exact cognitive processes that lead to such errors in adults, in particular when thinking about other people's beliefs, are currently not well understood. Research within psychology has traditionally focused on the egocentricism of children under 5 years of age. Young children show a profound difficulty in reporting that another person has a belief that differs from current reality. Imagine your friend watches you put some chocolate in the kitchen cupboard, and the leaves the room. While she is out, you then move the chocolate into the fridge. If asked "where does she think the chocolate is", as an adult you could relatively easily reply: "in the cupboard", even though you know it is now in the fridge (your "true belief" or "current knowledge"). Young children, however, typically will reply "the fridge", as though they expect their absent friend to also share their current knowledge. Many explanations of this error focus on the immature ability of young children to inhibit their own current true belief, or knowledge. These theoretical accounts claim that thinking about a belief that you know to be false fundamentally involves inhibiting what you know to be true, and it is this process that young children struggle with. These accounts predict that even in adults, who can report another person's false belief with ease, processing the false belief, just as in children, requires successful inhibition of an egocentric bias towards one's current knowledge. In the last decade, psychology has seen increasing research into the processes involved when adults attribute beliefs and other mental states to other people. Understanding how adults process beliefs is of key importance for understanding not only how we as adults are able to socially interact with each other, but also for understanding the developmental changes required for children to develop these abilities. A number of researchers have recently attempted to address whether adults show an egocentric bias towards their own knowledge when processing a false belief, as predicted by many developmental theories. Research to date, however, has failed to provide a definitive answer to this long-standing question. In this project, we will address this issue by using the novel technique of mouse-tracking. Mouse-tracking allows researchers to measure the on-line attraction to different possible responses while participants make a decision. While it has been used across a range of fields in psychology, it has yet to be widely used within theory of mind research. We will use this technique to measure whether adults show an egocentric bias towards their own current knowledge when they are asked to report the false belief of another person. Across 4 experiments, we will use mouse-tracking to: (i) Establish a direct measure of the egocentric bias in belief processing that has been claimed to be present when adults process another person's false belief. (ii) Investigate the nature of this egocentric bias in order to understand what specific aspects of belief processing causes it in adults. This project tests critical assumptions of long-standing theoretical accounts of belief processing in both adults and children, and as such will be of key interest to psychologists, neuroscientists and philosophers investigating social cognition. Furthermore, by improving our understanding of adult belief processing, in the long-term this project will also benefit those working with groups that typically have difficulty understanding other people's beliefs, such as in autism and acquired brain injury.

Computer mouse tracking data from on online psychology experiment (n = 267). On each trial, participants viewed a video either from a false belief or true belief scenario and answered a question that appeared onscreen. Participants answered the question by moving their computer mouse from the bottom centre of the screen to click on one of two response boxes located in the top left and top right of the screen. On each trial participants' accuracy, response times and time-stamped mouse coordinates were recorded. Participants were recruited through the Prolific online participant recruitment platform. All participants reported that they were fluent English speakers and normally used a computer mouse with their right hand. Participants received financial compensation (£3) for their time (20 mins) through the Prolific platform.