Moving visual world experiments online? A web-based replication of Dijkgraaf, Hartsuiker, and Duyck (2017) using PCIbex and WebGazer.js

The visual world paradigm is one of the most influential paradigms to study real-time language processing. The present study tested whether visual world studies can be moved online, using PCIbex software (Zehr & Schwarz, 2018) and the WebGazer.js algorithm (Papoutsaki et al., 2016) to collect eye-movement data. Experiment 1 was a fixation task in which the participants looked at a fixation cross in multiple positions on the computer screen. Experiment 2 was a web-based replication of a visual world experiment by Dijkgraaf, Hartsuiker and Duyck (2017). Firstly, both experiments revealed that the spatial accuracy of the data allowed us to distinguish looks across the four quadrants of the computer screen. This suggest that the spatial resolution of WebGazer.js is fine-grained enough for most visual world experiments (which typically involve a two-by-two quadrant-based set-up of the visual display). Secondly, both experiments revealed a delay of roughly 300 ms in the time course of the eye movements, possibly caused by the internal processing speed of the browser or WebGazer.js. This delay can be problematic in studying questions that require a fine-grained temporal resolution and requires further investigation.