How much I moved: Robust biases in self-rotation perception

Abstract

Vestibular cues are crucial to sense the linear and angular acceleration of our head in three-dimensional space. Previous literature showed that vestibular information precociously combines with other sensory modalities, such as proprioceptive and visual, to facilitate spatial navigation. Recent studies suggest that auditory cues may improve self-motion perception as well. The present study investigated the ability to estimate passive rotational displacements with and without virtual acoustic landmarks to determine how vestibular and auditory information interact in processing self-motion information. We performed two experiments. In both, healthy participants sat on a Rotational-Translational Chair. They experienced yaw rotations along the earth-vertical axis and performed a self-motion discrimination task. Their goal was to estimate both clockwise and counterclockwise rotations' amplitude, with no visual information available, reporting whether they felt to be rotated more or less than 45°. According to the condition, vestibular-only or audio-vestibular information was present. Between the two experiments, we manipulated the procedure of presentation of the auditory cues (passive vs. active production of sounds). We computed the point of subjective equality (PSE) as a measure of accuracy and the just noticeable difference (JND) as the precision of the estimations for each condition and direction of rotations. Results in both experiments show a strong overestimation bias of the rotations, regardless of the condition, the direction, and the sound generation conditions. Similar to previously found heading biases, this bias in rotation estimation may facilitate the perception of substantial deviations from the most relevant directions in daily navigation activities.

Keywords: Audition; Navigation; Vestibular.

Fig. 1

The RT-Chair (a). The 3D Tune-In Toolkit interface (b) with the representation of the three auditory landmarks (at azimuth -90°, the keyword sound, at azimuth 0° a water sound, at azimuth 90° a copy machine sound)

Fig. 2

Experimental setup. The considered points of reference at azimuth -90°, 0°, and 90° are highlighted in red. In the example, the participant is rotated 60° clockwise, being closer to azimuth 90°. With clockwise rotation, the delivered auditory landmarks were the sound of the water at azimuth 0° and the sound of the keyboard at azimuth 90°, black in the picture

Fig. 3

The experimental procedure in a Multisensory trial in Experiment 1. First, the participant press the start button (1); then, the two auditory landmarks were presented (2); afterwards, participant is rotated (3) and finally the two sounds are played a second time (4)

Fig. 4

Trial history for the Psi adaptive procedure from one participant (Vestibular-only condition, clockwise rotation). Since the first four trials were training trials, only experimental ones are represented (trials from 5 to 54). The upper dashed grey line represents the investigated rotational amplitude at 45°. The lower dashed red line represents the mean of delivered motion stimuli following the Psi Procedure that approximates the point of subjective equality (PSE). White squares indicate the “closer to azimuth 0°” responses; black squares indicate the “closer to azimuth 90°” responses

Fig. 5

Example of psychometric fit (a). Individual subject data from the Vestibular-only condition with clockwise rotations are represented. The vertical dashed red line on the right indicates the unbiased estimate at 45°; the vertical solid grey line on the left indicates the point of subjective equality (PSE) (33°); the two vertical grey dashed lines on either side of the solid one represent PSE ± the just noticeable difference (JND); black points are datapoints whose size is proportional to the number of presentations for that particular stimulus displacement. Example of an overestimation bias (b). Here, the participant experiences a 30° clockwise rotation but perceives it as a 45° rotation, showing an overestimation bias of 15°

Fig. 6

Bias (a) and just noticeable difference (JND) (b) of all participants in Experiment 1. As depicted, participants showed a strong overestimation bias (bias > 0) in all conditions, and their variability did not differ among conditions and rotation directions. Data points represent individual biases and JNDs; error bars are standard errors. **** = p < 0.0001; *** = p < 0.001

Fig. 7

Bias (a) and just noticeable difference (JND) (b) of all participants in Experiment 2. As depicted, participants showed a strong overestimation bias (bias > 0) in both conditions, and their variability was similar between conditions. Data points represent individual biases and JNDs; error bars are standard errors. **** = p < 0.0001