Psychophysical validation of calibrated white-noise and tuned-noise auditory masks for transcranial focused ultrasound
Martin T.W. Scott, Patti N. Limon, Gerald Popelka, Kim Butts Pauly, Anthony M. Norcia, Ryan T Ash
2026 · 10.64898/2026.07.29.741617
Abstract
Auditory confounds have proven to be a major hurdle in the elucidation of veridical neuromodulation effects with transcranial ultrasound stimulation (TUS). Auditory noise masks are an essential method to reduce the audibility of TUS and have shown promise in several studies. Here we describe a novel approach for design, calibration, and psychometric validation of auditory noise masks to reduce the perceptibility of TUS. White noise masks and spectrum-tuned masks matched to a TUS protocol that generates highly salient auditory costimulation (487.5 Hz pulse repetition frequency, 10% duty cycle, 68 W/cm2 pulse-peak average intensity, 500 kHz acoustic frequency) were generated, and dB(A) levels were calibrated with an artificial ear. The masker levels needed to reduce TUS detection performance in a two-interval forced choice task were determined with an adaptive QUEST+ staircase in 20 neurotypical participants. Detection performance of this highly salient TUS protocol was driven to near chance performance (<55%) in 17/20 participants with white-noise and 18/20 participants with spectrum-tuned noise. However, high masker levels approaching safety limits were needed to render TUS inaudible for the majority of participants, indicating the need for formal masker calibration for these TUS settings. Additionally, against expectation the spectrum-tuned masker did not significantly outperform the white-noise masker, suggesting that perceptibility of TUS auditory costimulation does not lawfully follow the sound expected from its pulse envelope and the known spectrum of human hearing.
Abstract via crossref.
Exposures
Exposure 1: 500 kHz TUS, 487.5 Hz PRF, beam steered to 70 mm, placed above left ear
Target: other — “placement above the left ear with a 10-degree angled gel pad”
Device: NeuroFUS · Sonic Concepts (sold by Brainbox) · NeuroFus CTX-500 with TPO-203 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.287 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 487.5 | ✓✓✓ |
| Duty cycle (%) | 14pulse duration × PRF gives 13.991% | ✓✓✓⚑ |
| Sonication duration (s) | 0.96 | ✓✓✓⚑ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported | |
| Isppa, domain unspecified (W/cm²) | 68 | ✓✓✓⚑ |
Each trial had two 960 ms intervals separated by 50 ms; TUS (487.5 Hz PRF, 14% duty cycle) occurred in one of the two intervals, and the participant reported which. 125 trials per masker condition.
Flags from extraction
exposures[0].timing.duty_cycle_pct— Abstract states 10% duty cycle; Methods and Figure 2 state 14%. Methods value recorded (also consistent with 0.287 ms x 487.5 Hz).exposures[0].timing.sonication_duration_s— Methods give 'pulse train = 0.960ms' (apparent unit typo); the 960 ms TUS interval per trial is recorded as the sonication duration.exposures[0].unspecified_domain.isppa_w_cm2— 68 W/cm2 spatial peak pulse average intensity; paper does not say whether free-field or in situ.exposures[0].target.terms— No anatomical target; transducer placed above left ear without neuronavigation, 70 mm beam steering; paper says placement approximates their LGN experiments.exposures[0].device.family— Paper names 'NeuroFus CTX-500' with TPO-203 drive system.