Improving spatial updating accuracy in absence of external feedback.

Updating the position of an earth-fixed target during whole-body rotation seems to rely on cognitive processes such as the utilization of external feedback. According to perceptual learning models, improvement in performance can also occur without external feedback. The aim of this study was to assess spatial updating improvement in the absence and in the presence of external feedback. While being rotated counterclockwise (CCW), participants had to predict when their body midline had crossed the position of a memorized target. Four experimental conditions were tested: (1) Pre-test: the target was presented 30° in the CCW direction from participant's midline. (2) Practice: the target was located 45° in the CCW direction from participant's midline. One group received external feedback about their spatial accuracy (Mackrous and Simoneau, 2014) while the other group did not. (3) Transfer T(30)CCW: the target was presented 30° in the CCW direction to evaluate whether improvement in performance, during practice, generalized to other target eccentricity. (4) Transfer T(30)CW: the target was presented 30° in the clockwise (CW) direction and participants were rotated CW. This transfer condition evaluated whether improvement in performance generalized to the untrained rotation direction. With practice, performance improved in the absence of external feedback (p=0.004). Nonetheless, larger improvement occurred when external feedback was provided (ps=0.002). During T(30)CCW, performance remained better for the feedback than the no-feedback group (p=0.005). However, no group difference was observed for the untrained direction (p=0.22). We demonstrated that spatial updating improved without external feedback but less than when external feedback was given. These observations are explained by a mixture of calibration processes and supervised vestibular learning.

Generalization of vestibular learning to earth-fixed targets is possible but limited when the polarity of afferent vestibular information is changed.

To maintain perception of the world around us during body motion, the brain must update the spatial presentation of visual stimuli, known as space updating. Previous studies have demonstrated that vestibular signals contribute to space updating. Nonetheless, when being passively rotated in the dark, the ability to keep track of a memorized earth-fixed target (EFT) involves learning mechanism(s). We tested whether such learning generalizes across different EFT eccentricities. Furthermore, we ascertained whether learning transfers to similar target eccentricities but in the opposite direction. Participants were trained to predict the position of an EFT (located at 45° to their left) while being rotated counterclockwise (i.e., they press a push button when they perceived that their body midline have cross the position of the target). Overall, the results indicated that learning transferred to other target eccentricity (30° and 60°) for identical body rotation direction. In contrast, vestibular learning partly transferred to target location's matching body rotation but in the opposite rotation direction. Generalization of learning implies that participants do not adopt cognitive strategies to improve their performance during training. We argue that the brain learned to use vestibular signals for space updating. Generalization of learning while being rotated in the opposite direction implies that some parts of the neural networks involved in space updating is shared between trained and untrained direction.

Visuo-vestibular interaction: predicting the position of a visual target during passive body rotation.

Following body rotation, optimal updating of the position of a memorized target is attained when retinal error is perceived and corrective saccade is performed. Thus, it appears that these processes may enable the calibration of the vestibular system by facilitating the sharing of information between both reference frames. Here, it is assessed whether having sensory information regarding body rotation in the target reference frame could enhance an individual's learning rate to predict the position of an earth-fixed target. During rotation, participants had to respond when they felt their body midline had crossed the position of the target and received knowledge of result. During practice blocks, for two groups, visual cues were displayed in the same reference frame of the target, whereas a third group relied on vestibular information (vestibular-only group) to predict the location of the target. Participants, unaware of the role of the visual cues (visual cues group), learned to predict the location of the target and spatial error decreased from 16.2 to 2.0°, reflecting a learning rate of 34.08 trials (determined from fitting a falling exponential model). In contrast, the group aware of the role of the visual cues (explicit visual cues group) showed a faster learning rate (i.e. 2.66 trials) but similar final spatial error 2.9°. For the vestibular-only group, similar accuracy was achieved (final spatial error of 2.3°), but their learning rate was much slower (i.e. 43.29 trials). Transferring to the Post-test (no visual cues and no knowledge of result) increased the spatial error of the explicit visual cues group (9.5°), but it did not change the performance of the vestibular group (1.2°). Overall, these results imply that cognition assists the brain in processing the sensory information within the target reference frame.