Publications

Abstract

There is a growing interest in the use of webcams to conduct eye-tracking experiments over the internet. We assessed the performance of two webcam-based eye-tracking techniques for behavioral research: manual annotation of webcam videos (manual eye-tracking) and the
automated WebGazer eye-tracking algorithm. We compared these methods to a traditional
infrared eye-tracker and assessed their performance in both lab and web-based settings. In
both lab and web experiments, participants completed the same battery of five tasks, selected
to trigger effects of various sizes: two visual fixation tasks and three visual world tasks testing
real-time (psycholinguistic) processing effects. In the lab experiment, we simultaneously collected infrared eye-tracking, manual eye-tracking, and WebGazer data; in the web experiment, we simultaneously collected manual eye-tracking and WebGazer data. We found that the two webcam-based methods are suited to capture different types of eye-movement patterns. Manual eye-tracking, similar to infrared eye-tracking, detected both large and small effects. WebGazer, however, showed less accuracy in detecting short, subtle effects. There was no notable effect of setting for either method. We discuss the trade-offs researchers face when choosing eye-tracking methods and offer advice for conducting eye-tracking experiments over the internet.

Abstract

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 et al. (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.

Abstract

Language comprehension involves the derivation of the meaning of sentences by combining the meanings of their parts. In some cases, this can lead to ambiguity. A sentence like Every hiker climbed a hill allows two logical representations: One that specifies that every hiker climbed a different hill and one that specifies that every hiker climbed the same hill. The interpretations of such sentences can be primed: Exposure to a particular reading increases the likelihood that the same reading will be assigned to a subsequent similar sentence. Feiman and Snedeker (2016) observed that such priming is not modulated by overlap of the verb between prime and target. This indicates that mental logical representations specify the compositional structure of the sentence meaning without conceptual meaning content. We conducted a close replication of Feiman and Snedeker’s experiment in Dutch and found no verb-independent priming. Moreover, a comparison with a previous, within-verb priming experiment showed an interaction, suggesting stronger verb-specific than abstract priming. A power analysis revealed that both Feiman and Snedeker’s experiment and our Experiment 1 were underpowered. Therefore, we replicated our Experiment 1, using the sample size guidelines provided by our power analysis. This experiment again showed that priming was stronger if a prime-target pair contained the same verb. Together, our experiments show that logical representation priming is enhanced if the prime and target sentence contain the same verb. This suggests that logical representations specify compositional structure and meaning features in an integrated manner.