The Dynamics of Attention Shifts Among Concurrent Speech in a Naturalistic Multi-Speaker Virtual Environment

Focusing attention on one speaker on the background of other irrelevant speech can be a challenging feat. A longstanding question in attention research is whether and how frequently individuals shift their attention towards task-irrelevant speech, arguably leading to occasional detection of words in a so-called unattended message. However, this has been difficult to gauge empirically, particularly when participants attend to continuous natural speech, due to the lack of appropriate metrics for detecting shifts in internal attention. Here we introduce a new experimental platform for studying the dynamic deployment of attention among concurrent speakers, utilizing a unique combination of Virtual Reality and Eye-Tracking technology. We created a Virtual Cafe in which participants sit across from and attend to the narrative of a target speaker. We manipulate the number and location of distractor speakers, manifest as additional patrons throughout the Virtual Cafe. By monitoring participants eye-gaze dynamics, we studied the patterns of overt shifts of attention among the concurrent speakers as well as the consequences of these shifts on speech comprehension. Our results reveal important individual differences in the gaze-pattern displayed during selective attention to speech. While some participants stayed fixated on a target speaker throughout the entire experiment, approximately 30% of participants frequently shifted their gaze toward distractor speakers or other locations in the environment, regardless of the severity of audiovisual distraction. Critically, the tendency for frequent gaze-shifts negatively impacted comprehension of the target speaker. We also found that gaze-shifts occurred primarily during gaps in the acoustic input, suggesting they are prompted by momentary unmasking of the competing audio, in line with glimpsing theories of processing speech in noise. These results open a new window into understanding the dynamics of attention as they wax and wane over time, and the different listening patterns employed for dealing with the influx of sensory input in multisensory environments. Moreover, the novel approach developed here for tracking the locus of momentary attention in a naturalistic virtual-reality environment holds high promise for extending the study of human behavior and cognition and bridging the gap between the laboratory and real-life.