Schematic overview of trials used in the experiments.

<p>Both panels (A, B) represent the time course (x-axis) of the platform position (y-axis) used in the experiments. In both experiments, each experimental trial comprises two intervals lasting from 0-1s and 1-2s after platform motion onset respectively. In each interval, visual motion is presented (gray areas) between 0.25–0.75s after the start of the interval. It is therefore presented around the peak velocity of the vestibular stimulation. A. In experiment 1, radial optic flow that is either congruent (Cong) or incongruent (Incong) with the platform motion direction (forward) is presented in one interval, while in the other noise dots are presented. B. In experiment 2, leftward or rightward optic flow that is either congruent or incongruent with the platform motion (leftward) is presented in one interval, while in the other interval noise dots are presented. In both experiments, the presentation order of optic flow and noise dots intervals was counterbalanced across trials.</p

Average motion coherence threshold across observers for radial optic flow.

<p>In the left panel, the average motion coherence threshold across observers (y-axis) is depicted for the incongruent, congruent and stationary condition (x-axis). The center panel shows the average motion coherence threshold across observers for each visual motion direction (expanding, contracting optic flow). The right panel depicts the average motion coherence threshold across observers for the incongruent, congruent and stationary condition separated per motion direction. In all panels, error bars indicate ± 1 SEM. An asterisk indicates a significant difference between conditions.</p

Vestibular discrimination results.

<p><b>A)</b> Example results for an individual subject shown in the same format used for the individual identification data (Fig. 2A). Plot illustrates the physical stimulus (x-axis, PSE) perceived equivalent to each investigated reference direction (y-axis). Error bars represent JNDs. <b>B)</b> Mean (+/−SD) bias across subjects in the discrimination procedure (black). Horizontal error bars represent SD of the PSEs. For comparison, mean bias in the identification procedure (grey) is replotted from Fig. 3A. <b>C)</b> Mean (+/−SD) variability (i.e. JND) across subjects in the discrimination procedure (black). Horizontal error bars represent SD of the PSEs. For comparison, mean variability in the identification procedure (grey) is replotted from Fig. 3D.</p

Distribution of preferred directions (top row) and resulting population vector decoding predictions (bottom row).

<p><b>A)</b> Preferred directions of otolith afferents. <b>B)</b> Preferred directions of MSTd neurons for vestibular heading stimuli. <b>C)</b> Preferred directions of MSTd neurons for visual heading stimuli. <b>D)</b> Afferent predicted (black) and observed (grey) vestibular bias. <b>E)</b> MSTd predicted and observed vestibular bias. <b>F)</b> MSTd predicted and observed visual bias. Note, panels B), C), and predictions in E), and F) reproduced from Gu et al 2010.</p

Vestibular discrimination results for one subject at one investigated direction (−90°).

<p><b>A)</b> Trial history for 1U1D staircase block. Upper and lower panels represent the two interleaved staircases that converged from above and below the investigated direction. Dashed line indicates mean of staircase reversals which approximates the PSE. <b>B)</b> Trial history for 1U2D and 2U1D staircase block. Upper and lower panels represent the two interleaved staircases that converged from above and below the mean PSE from the 1U1D block. <b>C)</b> Psychometric function fit to all data from the staircase blocks shown in A) and B). Error bars show 95% and 99% confidence intervals of the fit at the 20%, 50%, and 80% correct points.</p

Overview of stimulus parameters used in the current study and two prior studies reporting contradictory findings.

<p>Overview of stimulus parameters used in the current study and two prior studies reporting contradictory findings.</p

Average motion coherence threshold across observers for leftward/rightward optic flow.

<p>In the left panel, the average motion coherence threshold across observers (y-axis) is depicted for the incongruent, congruent and stationary condition (x-axis). The center panel shows the average motion coherence threshold across observers for each visual motion direction (leftward, rightward optic flow). The right panel depicts the average motion coherence threshold across observers for the incongruent, congruent and stationary condition separated per motion direction. In all panels, error bars indicate ± 1 SEM. An asterisk indicates a significant difference between conditions.</p

Visual and vestibular bias (top row) and variability (bottom row) across modalities.

<p>Error bars represent SD. <b>A, </b><b>D)</b> Vestibular identification procedure. <b>B, </b><b>E)</b> Visual identification procedure. <b>C)</b> Data from A) and B) re-plotted without error bars to facilitate comparison. <b>F)</b> Data from D) and E) re-plotted without error bars to facilitate comparison. Note, asterisks indicate heading angles for which bias was <i>most</i> significant, i,e, p<0.05 before Bonferroni correction. The correction is not applied here for illustrative purposes only.</p

Bayesian model and predictions.

<p><b>A)</b> Standard deviation of visual (dotted) and vestibular (solid) likelihoods as a function of heading angle used in the model (adapted from Gu et al. 2010). <b>B)</b> Best-fitting prior distributions for visual and vestibular identification data. Each curve is a sum of two Gaussians centered at +90° and −90°, with equal SD. σ_prior equals 17° and 50° for visual and vestibular priors, respectively. <b>C)</b> Predicted (black) and observed (grey) vestibular biases. <b>D)</b> Predicted and observed visual biases.</p

Illustrations of experimental procedures.

<p><b>A)</b> Example movement. On each trial, subjects experienced a movement in the horizontal plane, for example 45°, as shown here. <b>B)</b> Response dial for identification task. Subjects indicated their heading direction after each movement by adjusting the orientation of an arrow within a dial on the screen. The setting shown here matches the movement from panel A). <b>C)</b> Investigated heading directions for the identification procedure (grey) and the control procedure (black).</p