Fixation-related potentials during a virtual navigation task: The influence of image statistics on early cortical processing

Madison, Anna; Callahan-Flintoft, Chloe; Thurman, Steven M.; Hoffing, Russell A. Cohen; Touryan, Jonathan; Ries, Anthony J. · 2025 · Crossref

DOI: 10.3758/s13414-024-03002-5

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Summary

This study investigates how low-level image statistics—specifically luminance and spatial frequency—influence early cortical processing during naturalistic visual exploration. Historically, research on scene processing has relied on static stimuli with fixed gaze, limiting the generalizability of findings to real-world conditions where eye movements dynamically select visual information. To address this gap, the authors employed fixation-related potentials (FRPs), which time-lock electroencephalography (EEG) data to fixation onsets during free viewing. The primary objective was to determine if early visual components, namely the lambda response and N1, are modulated by image statistics independently of oculomotor covariates like saccade magnitude. The experiment involved 33 participants navigating a complex virtual environment to locate target objects while their eye movements and EEG were co-recorded. The researchers utilized a rigorous data processing pipeline to isolate neural activity from ocular artifacts and overlapping responses. First, they applied an optimized independent component analysis approach (OPTICAT) to remove eye-movement-related artifacts. Second, they employed linear deconvolution modeling using the Unfold Toolbox to correct for the temporal overlap of neural activity inherent in free-viewing paradigms. Image statistics were calculated post-hoc for 5° patches centered on each fixation, measuring average luminance and the slope of the amplitude spectrum as a metric for spatial frequency. The results demonstrated that early visual components of the FRPs are sensitive to both luminance and spatial frequency around the fixation point. Crucially, these modulations occurred separately from the effects of eye-movement characteristics, such as saccade size and duration. The study confirms that the lambda response and N1 amplitude vary with the visual properties of the scene at the moment of fixation, even when controlling for the confounding influence of oculomotor variables. These findings highlight the utility of combining FRPs with deconvolution modeling to study visual processing under naturalistic conditions. By effectively disentangling neural responses from overlapping activity and oculomotor covariates, this approach allows for a more accurate assessment of how low-level image statistics drive early cortical processing. The study bridges the gap between controlled laboratory experiments and real-world visual behavior, providing evidence that scene processing mechanisms observed in static paradigms also operate during dynamic, free-viewing navigation.

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• eye movements scanning