Measuring implicit line orientation discrimination using fast periodic visual stimulation

Fast periodic visual stimulation (FPVS) is an electroencephalography (EEG) marker of discrimination between two classes of frequency tagged stimuli (standards and oddballs). Here, we develop FPVS as a probe of low-level visual function, with a view to its future use as a sensitive diagnostic marker of visuospatial cognitive impairment. Thirty participants (21 (±5) years, 7 males) completed five FPVS conditions that implicitly measured their ability to discriminate an oddball line orientation (1°,5°,10°,30°,80°), from a standard vertical line, as well as an equiprobable control condition. Twenty-four participants (24 (±5) years, 5 males) completed a retest session around one month later. Following 100s of recording, activity at the oddball presentation frequency, a neural signal of discrimination between standard and oddball stimuli, was observed in response to lines of 5° and above. The magnitude of this oddball response increased as oddball lines deviated more from vertical. Demonstrating consistency in individual participants, oddball responses were present in 30/30 participants in response to a deviation of 30° and 29/30 in response to a deviation of 80°. At larger deviations, oddball responses were highly reliable between sessions, measured using intraclass correlations. Overall, this study showed that FPVS can consistently and reliably measure line orientation discrimination in individual participants. The consistency and reliability of oddball responses in the cognitively healthy, could provide a strong baseline that clinical group’s performance could be compared to, guiding neurocognitive assessment.