Rapid FFR: A rapid method for obtaining Frequency Following Responses.

Objectives: Frequency-Following Responses (FFRs) are typically recorded using stimuli of 40-250 ms in duration separated by silent intervals. Because robust FFRs require averaging across approximately 3000 stimulus repetitions, conventional acquisition is time-intensive. We introduce the Rapid FFR, a technique that minimises recording time by presenting the stimulus continuously (i.e., without inter-stimulus intervals) and by averaging across individual response cycles. This study aimed to: (a) compare Rapid and Conventional FFR performance under time-matched conditions; (b) assess test-retest reliability of both methods, and (c) examine potential neural adaptation during extended Rapid FFR recordings. Design: All participants (37 in total) were young adults with clinically normal hearing. In Experiment 1, FFRs were elicited from 16 listeners using a 128 Hz sawtooth wave presented in two ways: (1) continuously over approximately 1 minute in each polarity for the Rapid FFR and (2) as discrete tone bursts (1500 trials per polarity) for the standard FFR. Signal-to-Noise ratios (SNRs), response amplitudes, and test-retest reliability were compared across techniques. In Experiment 2, the Rapid FFR was recorded continuously from 21 listeners for nearly nine minutes to assess potential adaptation over time. Results: The Rapid FFR produced significantly higher SNRs than the standard FFR, reflecting improved recording efficiency. Both techniques captured inter-individual differences reliably, with comparable frequency-domain response patterns across participants. In particular, measures derived from the Rapid FFR showed strong agreement with those from the standard FFR for lower harmonics (F0-H3). Higher harmonics (H4-H7) exhibited greater variability but remained consistent between techniques. In the prolonged recording condition, FFR amplitudes remained stable over time, with no significant decline across the nine minute recording. This indicates that continuous stimulation did not result in measurable neural adaptation or response fatigue. Conclusions: The Rapid FFR offers a time-efficient alternative to standard protocols, preserving signal fidelity and reliability while enabling shorter acquisition times. These findings suggest that the Rapid FFR is well-suited for use in populations where long recordings are challenging (e.g., in infants and the clinic) and can facilitate more extensive experimental designs within a single session. The method holds promise for advancing both research and clinical applications of the FFR. Future studies should explore its use across a broader range of sounds (in particular, dynamically varying ones) and listener groups.