Signal-to-noise ratio (SNR) values were transformed to be used as independent variables in the linear mixed effects modeling analysis in order to test specific patterns regarding the relationship between visual enhancement (VE) and SNR.

(A) Mean-centered and scaled raw SNR values. This variable presupposes a linear relationship between VE and SNR, which was used to test the pattern that the AV benefit varies linearly with SNRs, and is greatest at the highest SNRs or at the lowest SNRs. (B) The second-degree polynomial of the linear SNR values. This variable presupposes a quadratic relationship between VE and SNR, which was used to test the pattern that the AV benefit peak at intermediate SNR of −12, and drop for SNRs above and below.