Horizontal vHIT gain is unaffected by moderate cognitive load: evidence from a single-distance dual-task paradigm

To determine whether moderate cognitive load alters horizontal vestibulo-ocular reflex (VOR) gain during the video head impulse test (vHIT) and to evaluate the reliability of vHIT under dual-task conditions.

Thirty-three healthy young adults (mean age 21.3 ± 2.1 years) completed two vHIT conditions: (1) a baseline single-task condition and (2) a dual-task cognitive load condition involving serial subtraction aloud while fixating a constant target at a single distance. Horizontal VOR gains were measured bilaterally. Mental effort and dizziness were rated on 0 to 10 numerical rating scales.

Baseline VOR gains were 0.925 ± 0.063 (left) and 0.924 ± 0.074 (right). Under cognitive load, gains were 0.938 ± 0.084 and 0.938 ± 0.074, small increases of 1.4 to 1.5% that were non-significant (p > 0.40) and met equivalence criteria within ± 0.05 gain units. Reliability across conditions was excellent (ICC [3,1] = 0.90 left; 0.89 right). Cognitive engagement increased significantly (2.1 ± 1.1 to 7.3 ± 1.4; p < 0.001), while dizziness remained minimal. No meaningful correlation was observed between gain change and perceived effort or dizziness (Spearman's ρ < 0.05, p > 0.05).

Horizontal vHIT gain remained stable, statistically equivalent, and highly reliable under cognitive load, despite marked increases in perceived effort. These findings highlight the attentional resilience of the horizontal VOR, consistent with its brainstem-mediated circuitry. Consequently, horizontal vHIT appears robust for use in routine clinical settings where divided attention may be present.