Optimizing the stimulus used to elicit the acoustic change complex: Evaluation of the pre-transition stimulus duration and stimulus complexity in normal hearing adults

Introduction: 

The Acoustic Change Complex (ACC), a cortical auditory evoked potential elicited by sound changes, is a promising measure of speech discrimination for populations unable to perform speech perception tests. However, its clinical utility is limited by long measurement times, which could be reduced by optimizing the signalto-noise ratio (SNR). 

Objectives: 

To study the effect of 1) varying the pre-transition duration (PTD) and 2) tonal complexity on ACC outcomes, including N1-P2 amplitude, baseline noise, SNR, and efficiency (SNR divided by measurement time). 

Methods: 

ACC responses were measured in 18 normal-hearing adults using pure-tone stimuli with a frequency change (1 to 1.1 kHz) and PTDs of 0.25, 0.5, 1, 2 and 3 s, as well as a complex tone with a 1-second PTD. 

Results: 

N1-P2 amplitude increased with PTD up to 2 s. PTD 0.25 s was excluded due to response overlap. Increasing PTD from 0.5 s to 1 s increased efficiency and SNR, reducing estimated measurement time by 78.8 %. ACC presence increased with PTD (100 % for PTD 3 s), but SNR and efficiency gains were absent beyond PTD 1 s. The complex tone showed no difference in N1-P2 amplitude or SNR compared to the pure tone, but increased ACC presence by 22.5 % points. 

Conclusion: 

A PTD of 1 s is recommended over 0.5 s. Increasing tonal complexity and the PTD beyond 1 s seems promising to enhance ACC specificity without compromising SNR or efficiency. These findings support stimulus optimization to improve clinical feasibility of ACC measurements.