Table 1.

Mean ± SD thresholds for each condition of each vestibular experiment

	Earth horizontal/head horizontal	Earth horizontal/head vertical	Earth vertical/head horizontal	Earth vertical/head vertical
Vestibular heading
Two-interval	6.01 ± 2.31°	15.97 ± 4.60°	12.86 ± 3.88°	8.93 ± 3.70°
Equivalent one-interval threshold	4.25 ± 1.63°	11.29 ± 3.25°	9.09 ± 2.74°	6.31 ± 2.62°
Coarse discrimination (one-interval)	0.063 ± 0.025 m/s2	0.110 ± 0.029 m/s2	0.093 ± 0.023 m/s2	0.097 ± 0.034 m/s2
Amplitude discrimination
Two-interval	0.126 ± 0.071 m/s2	0.124 ± 0.059 m/s2	0.104 ± 0.054 m/s2	0.117 ± 0.078 m/s2
Equivalent one-interval threshold	0.089 ± 0.05 m/s2	0.088 ± 0.042 m/s2	0.074 ± 0.038 m/s2	0.083 ± 0.055 m/s2

Thresholds correspond to the 84% correct level for each task. Note that heading and amplitude discrimination thresholds were obtained from two-interval tasks (Fig. 3). To facilitate comparison across tasks, these thresholds have also been expressed as equivalent one-interval thresholds (computed by dividing by $\sqrt{2}$). This is because, in a single-interval task, the 84% correct threshold is equal to the SD of the underlying estimator, whereas in a two-interval task, it is $\sqrt{2}$ times the standard deviation of the underlying estimator (Ernst and Banks, 2002).