Comparing the impact of the method of adjustment and forced-choice methodologies on subjective visual vertical bias and variability.

Abstract

Previous research suggested that the method of adjustment and forced choice variants of the subjective visual vertical (SVV) produce comparable estimates of both bias and variability. However, variants of the SVV that utilize a method of adjustment procedure are known to be heavily influenced by task parameters, including the stimulus rotation speed, which was not accounted for in previous SVV research comparing the method of adjustment to forced-choice. The aim of the present study was to determine if (1) the SVV with a forced-choice procedure produces both bias and variability estimates that are comparable to those obtained using a method of adjustment procedure, (2) to see if rotation speed impacts the comparability of estimates and (3) quantify correlations between the estimates produced by different procedures. Participants completed a variant of the SVV which utilized a forced-choice procedure as well as two variants of the SVV using a method of adjustment procedure with two different rotation speeds (6°/s and 12°/s). We found that the bias estimates were similar across all three conditions tested and that the variability estimates were greater in the SVV variants that utilized a method of adjustment procedure. This difference was more pronounced when the rotation speed was slower (6°/s). The results of this study suggest that forced-choice and method of adjustment methodologies yield similar bias estimates and different variability estimates. Given these results, we recommend utilizing forced-choice procedures unless (a) forced-choice is not feasible or (b) response variability is unimportant. We also recommend that clinicians consider the SVV methods when interpreting a patient's test results, especially for variability metrics.