Computational protocol: Anchoring the Self to the Body in Bilateral Vestibular Failure

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Protocol publication

[…] Visual stimuli consisted of a colored 3D rendering of a room with three visible walls. The left and right walls were yellow and contained from 0 to 3 blue balls aligned horizontally. In the middle of the room and at the center of the screen, an avatar was shown sitting on a cube placed on the room floor. Two sets of pictures were created: female avatars were always shown to female participants, and male avatars were always shown to male participants. The avatar faced the left or right wall of the 3D room. The spatial arrangement of the balls was manipulated to create situations where the participant and avatar could “see” the same number of balls on the walls (i.e., congruent viewpoint), or a different number of balls (i.e., incongruent viewpoint) (). In total, for both female and male avatars and for both avatar orientations (i.e., facing the left or right wall), 10 visual stimuli were created to balance the number of trials with congruent and incongruent viewpoints (following procedures from Ref. []).Visual presentation was controlled, and responses were collected by using PsychoPy2 v1.82.01 []. Each trial started with the presentation of a white fixation cross on a black background for 750 ms. This was followed by the presentation of the question “How many blue balls do you see?” for 1500 ms and the presentation of a number (0, 1, 2 or 3) for 1000 ms. Then, one of the visual scenes was presented. Participants were instructed to indicate as quickly and accurately as possible whether the number of balls they saw matched the number specified after the question. The response time was not limited. Participants pushed one of two buttons on a keyboard to respond: half of the participants had to press a button with their right index finger to answer “yes” or another button with their right middle index finger to answer “no”; the other participants had a reverse configuration for the response buttons. As soon as participants pressed a button, the visual scene disappeared and the next trial started. Although participants had to count the number of balls according to their first-person perspective, the presence of the avatar in the visual scene allowed for measuring implicit third-person perspective taking (IPT), i.e. the extent to which the avatar’s viewpoint interfered with the participant’s viewpoint.In half of the trials (“matching trials”), the number specified after the question matched the number of balls visible from the participant’s viewpoint (). For the trials involving a congruent viewpoint, the number shown after the question corresponded to the quantity of balls visible from both the participant’s and avatar’s viewpoints. For the trials involving an incongruent viewpoint, the number corresponded to the quantity of balls visible only from participant’s viewpoint. In the other half of the trials (“mismatching trials”), the number specified after the question differed from the quantity of balls the participant could see. For the trials involving a congruent viewpoint, the number shown after the question corresponded to one of the three quantities of balls that did not match the quantity of balls visible from the participant’s and avatar’s viewpoints. For the trials involving an incongruent viewpoint, the number corresponded to the quantity of balls visible only from the avatar’s viewpoint. Following the procedures from Ref. [], we created six “filler trials” corresponding to a visual scene containing no ball on the left and right walls and for which the number “0” shown after the question was the correct answer. Visual stimuli were presented as 35 × 20 cm images on a computer screen. [...] We calculated the mean response time and percentage of correct answers for the matching trials. Data for mismatching trials and filler trials were discarded from the analysis according to previous studies []. Trials yielding incorrect answers were discarded from the analysis of the response times and we removed trials for which response times exceeded 2 standard deviations of the participant’s grand average. We focused on response times, shown to be more sensitive than accuracy to multisensory conflicts [–]. For the three tasks, response times were analyzed by repeated-measures ANOVAs with Statistica, Version12 SP3 (StatSoft Inc.), with Viewpoint (congruent vs incongruent) as a within-subject factor and with Group (BVF patients vs controls) and Gender (female vs male) as between-subject factors. Main effects and interactions were considered significant at p<0.05. We also calculated a congruency effect (CE), adapted from the cross-modal CE used to investigate visual-tactile and visuo-vestibular conflicts [–]. For each of the three tasks, CE was calculated as the difference in response times between the incongruent and congruent viewpoints. […]

Pipeline specifications

Software tools PsychoPy, Statistica
Applications Miscellaneous, Neuropsychology analysis
Organisms Homo sapiens
Diseases Nervous System Diseases, Peripheral Nervous System Diseases, Renal Insufficiency