Proprioceptive Cues Research Articles

Deep learning model for doors detection: A contribution for context-awareness recognition of patients with Parkinson’s disease

Freezing of gait (FoG) is one of the most disabling motor symptoms in Parkinson’s disease, which is described as a symptom where walking is interrupted by a brief, episodic absence, or marked reduction, of forward progression despite the intention to continue walking. Although FoG causes are multifaceted, they often occur in response of environment triggers, as turnings and passing through narrow spaces such as a doorway. This symptom appears to be overcome using external sensory cues. The recognition of such environments has consequently become a pertinent issue for PD-affected community. This study aimed to implement a real-time dl-based door detection model to be integrated into a wearable biofeedback device for delivering on-demand proprioceptive cues. It was used transfer-learning concepts to train a MobileNet-SSD in TF environment. The model was then integrated in a RPi being converted to a faster and lighter computing power model using TensorFlow Lite settings. Model performance showed a considerable precision of 97,2%, recall of 78,9% and a good F1-score of 0,869. In real-time testing with the wearable device, dl-model showed to be temporally efficient (∼2.87 fps) to detect with accuracy doors over real-life scenarios. Future work will include the integration of sensory cues with the developed model in the wearable biofeedback device aiming to validate the final solution with end-users.

Holitouch: Conveying Holistic Touch Illusions by Combining Pseudo-Haptics With Tactile and Proprioceptive Feedback During Virtual Interaction With 3DUIs

Virtual reality technology and immersive virtual environments often support realistic hand representations via hand-posture-sensing controllers or hand tracking for natural hand-based interaction. However, one limiting factor remains as the lack of realistic haptic feedback including tactile and proprioceptive cues; even for simple haptic interactions like touching a virtual object. This paper introduces the Holitouch technique to improve the haptic realism of essential 3D user interface elements such as buttons. Holitouch is a feedback technique based on a wearable device that combines different types of haptic feedback (i.e., 1) pseudo-haptic, 2) tactile, and 3) proprioceptive) to convey the holistic sensation of stiffness, contact, and activation while interacting with 3D buttons. Our approach provides these sensations by utilizing redundant multisensory cues, i.e., congruent feedback, to create plausible illusions of touch. The results of two experiments show that the proposed feedback combination contributes to delivering a holistic sensation when interacting with buttons in VR while having high user acceptance.

The “Kinesthetic HMD”: Inducing Self-Motion Sensations in Immersive Virtual Reality With Head-Based Force Feedback

The sensation of self-motion is essential in many virtual reality applications, from entertainment to training, such as flying and driving simulators. If the common approach used in amusement parks is to actuate the seats with cumbersome systems, multisensory integration can also be leveraged to get rich effects from lightweight solutions. In this paper, we introduce a novel approach called the “Kinesthetic HMD”: actuating a head-mounted display with force feedback in order to provide sensations of self-motion. We discuss its design considerations and demonstrate an augmented flight simulator use case with a proof-of-concept prototype. We conducted a user study assessing our approach’s ability to enhance self-motion sensations. Taken together, our results show that our Kinesthetic HMD provides significantly stronger and more egocentric sensations than a visual-only self-motion experience. Thus, by providing congruent vestibular and proprioceptive cues related to balance and self-motion, the Kinesthetic HMD represents a promising approach for a variety of virtual reality applications in which motion sensations are prominent.

Human movements do not look the same in a tilted world: Gravitational constraints influence the perception of biological motion.

We investigated whether gravitational constraints influence the interaction of visual, proprioceptive and vestibular cues for Biological Motion Perception (BMP). Participants were asked to distinguish between plausible and random point-light movements, while passively placed in either an upright or a tilted body orientation. Manipulating the body orientation with respect to gravity leads to different gravitational signals transmitted by the visual, proprioceptive, and vestibular systems. Participants were overall faster in distinguishing plausible point-light movements than random movements. Critically, response times for biologically plausible point-light movements - but not for random movements - were significantly prolonged in the tilted body orientation. Our results suggest that BMP depends not only on the spatial-temporal cues embedded in point-light movements but also rely on the congruency between current gravitational signals detected by the sensory systems and our previous knowledge of terrestrial gravity. STATEMENT OF RELEVANCE: As humankind is preparing for a new space age, understanding how gravity influences behaviour and cognition has never been more pressing. All living organisms have evolved to survive in a terrestrial gravitational field. Although we cannot consciously feel gravity, it has an impact in our life: it affects how we move and interact with the external environment. The sensory signals from the vestibular system are continuously combined with visual and proprioceptive cues to help us in maintaining a stable representation of the world. Here we placed participants in a tilted body orientation and were able to determine that a conflict between prior gravitational knowledge and what was actively sensed about gravity affected human Biological Movement Perception. Humans suffer changes in perception under non-terrestrial gravity conditions that may potentially compromise performance during space exploration.

A Comparison of Balance Performance of the Sensory Organization Test to the Head Shake Sensory Organization Test in Healthy Adults

To compare equilibrium scores between computerized dynamic posturography tests of the Sensory Organization Test (SOT) to the Head Shake-Sensory Organization Test (HS-SOT) in healthy adults. Approximately 50% of the brain's pathways are related to vision and many of these pathways are susceptible to injury in concussion. Visual-motor disruptions occur in 65%-90% of concussed patients. These disruptions impair balance and can be measured. The SOT is a computerized postural test that evaluates balance by altering visual, proprioceptive, and vestibular cues. The HS-SOT modifies 2 of the standard SOT conditions by including dynamic head motions that stimulate the semicircular canals within the vestibular system. Participants completed the Dizziness Handicap Inventory, Activities of Balance Confidence Scale, SOT, and HS-SOT in one session. Twenty-five individuals (17 females, 8 males; mean age, 21.08 ± 4.10 years, range, 18-33 years) completed outcome measures and 3 trials of testing. There was a significant difference in mean values between the SOT and the HS-SOT for both condition 2 (t(16) = 3.034, p = 0.008) and 5 (t(16) = 5.706, p < 0.001). Additionally, there was a significant difference in mean values between the SOT and the foam HS-SOT for condition 2 (t(16) = 4.673, p < 0.001) and condition 5 (t(16) = 7.263, p < 0.001). There was not a significant difference in means between the foam and without foam for HS-SOT for condition 2 (t(16) = 1.77, p = 0.095) and condition 5 (t(16) = 1.825, p = 0.087). The HS-SOT may quantify subtle balance deficits and enhance the clinical standard use of the SOT. Unlike the SOT where the head is static, the HS-SOT requires head movements, as if saying no repeatedly at approximately 100°/second as measured by an accelerometer. The HS-SOT may quantify subtle balance deficits and enhance the clinical standard use of the SOT.

Impact of Canal-Otolith Integration on Postural Control.

Roll tilt vestibular perceptual thresholds, an assay of vestibular noise, have recently been shown to be associated with suboptimal balance performance in healthy older adults. However, despite the strength of this correlation, the use of a categorical (i.e., pass/fail) balance assessment limits insight into the impacts of vestibular noise on postural sway. As a result, an explanation for this correlation has yet to be determined. We hypothesized that the correlation between roll tilt vestibular thresholds and postural control reflects a shared influence of sensory noise. To address this hypothesis, we measured roll tilt perceptual thresholds at multiple frequencies (0.2 Hz, 0.5 Hz, 1 Hz) and compared each threshold to quantitative measures of quiet stance postural control in 33 healthy young adults (mean = 24.9 years, SD = 3.67). Our data showed a significant linear association between 0.5 Hz roll tilt thresholds and the root mean square distance (RMSD) of the center of pressure in the mediolateral (ML; β = 5.31, p = 0.002, 95% CI = 2.1–8.5) but not anteroposterior (AP; β = 5.13, p = 0.016, 95% CI = 1.03–9.23) direction (Bonferroni corrected α of 0.006). In contrast, vestibular thresholds measured at 0.2 Hz and 1 Hz did not show a significant correlation with ML or AP RMSD. In a multivariable regression model, controlling for both 0.2 Hz and 1 Hz thresholds, the significant effect of 0.5 Hz roll tilt thresholds persisted (β = 5.44, p = 0.029, CI = 0.60–10.28), suggesting that the effect cannot be explained by elements shared by vestibular thresholds measured at the three frequencies. These data suggest that vestibular noise is significantly associated with the temporospatial control of quiet stance in the mediolateral plane when visual and proprioceptive cues are degraded (i.e., eyes closed, standing on foam). Furthermore, the selective association of quiet-stance sway with 0.5 Hz roll tilt thresholds, but not thresholds measured at lower (0.2 Hz) or higher (1.0 Hz) frequencies, may reflect the influence of noise that results from the temporal integration of noisy canal and otolith cues.

Visual-haptic integration, action and embodiment in virtual reality.

The current generation of virtual reality (VR) technologies has improved substantially from legacy systems, particularly in the resolution and latency of their visual display. The presentation of haptic cues remains challenging, however, because haptic systems do not generalise well over the range of stimuli (both tactile and proprioceptive) normally present when interacting with objects in the world. This study investigated whether veridical tactile and proprioceptive cues lead to more efficient interaction with a virtual environment. Interaction in the world results in spatial and temporal correlation of tactile, proprioceptive and visual cues. When cues in VR are similarly correlated, observers experience a sense of embodiment and agency of their avatars. We investigated whether sensorimotor performance was mediated by embodiment of the avatar hands. Participants performed a Fitts' tapping task in different conditions (VR with no haptics, active haptics, passive haptics, and on a real touchscreen). The active-haptic condition provided abstract tactile cues and the passive haptic condition provided veridical tactile and proprioceptive cues. An additional (hybrid haptics) condition simulated an ideal passive haptic system. Movement efficiency (throughput) and embodiment were higher for the passive than for the active and no-haptics conditions. However, components of embodiment (perceived agency and ownership) did not predict unique variance in throughput. Improved sensorimotor performance and ratings of presence and realism support the use of passive haptics in VR environments where objects are in known and stable locations, regardless of whether performance was mediated by the sense of embodiment.

Motor Cortical Excitability Changes in Preparation to Concentric and Eccentric Movements

Specific neural mechanisms operate at corticospinal levels during eccentric and concentric contractions. Here, we investigated the difference in corticospinal excitability (CSE) when preparing these two types of contraction. In this study we enrolled 16 healthy participants. They were asked to perform an instructed-delay reaction time (RT) task involving a concentric or an eccentric contraction of the right first dorsal interosseus muscle, as a response to a proprioceptive cue (Go signal) presented 1 s after a warning signal. We tested CSE at different time points ranging from 300 ms before up to 40 ms after a Go signal. CSE increased 300–150 ms before the Go signal for both contractions. Interestingly, significant changes in CSE in the time interval around the Go signal (from −150 ms to +40 ms) were only revealed in eccentric contraction. We observed a significant decrease in excitability immediately before the Go cue (Pre_50) and a significant increase 40 ms after it (Post_40) with respect to the MEPs recorded at Pre_150. Finally, CSE in eccentric contraction was lower before the Go cue (Pre_50) and greater after it (Post_40) compared to the concentric contraction. A similar result was also found in NoMov paradigm, used to disentangle the effects induced by movement preparation from those induced by the movement preparation linked to the proprioceptive cue. We could conclude that different neural mechanisms observed during concentric and eccentric contractions are mirrored with a different time-specific modulation of CSE in the preparatory phase to the movement.

Importance of vision in tandem running during colony relocation in an Indian ant

AbstractVisual inputs are important for navigation, and several studies have investigated its importance in ants in the context of foraging. Little is known about the importance of visual cues when the whole colony engages in the goal‐oriented task of colony relocation. In this study, we investigated the role of vision for a tandem‐running tropical ant Diacamma indicum during colony relocation by impairing the vision in both eyes of all colony members and comparing our findings with ants having unimpaired vision. Colonies relocated successfully under zero‐lux conditions and when all colony mates were visually impaired, without compromising their colony cohesion. On examining 265 tandem runs performed by visually impaired ants, we found that they had lower efficiency as compared to ants with normal vision. They traveled along longer routes at lower speeds and often lost their followers, leading to significant increase in transportation time. The absence of visual inputs did not influence the number of tandem leaders that participated nor did it negatively impact their ability to recruit their visually impaired followers from becoming tandem leaders. Visually impaired tandem leaders were not able to minimize their relocation path in an open arena but were capable of doing so in defined paths. Our results suggest that these ants use thigmotactic or proprioceptive cues in order to navigate to their new nest in the absence of visual inputs. Our understanding of tandem‐running recruitment would be incomplete until we delineate the role of multiple sensory inputs involved in conducting this mode of recruitment successfully.

Additive effect of “Brahma Mudra” on pain, proprioception and functional abilities in non-specific mechanical neck pain

ObjectiveBeing the second highest musculoskeletal problem irrespective of age, gender and occupation, the etiology of neck pain is predominantly mechanical in nature. This can lead to dysfunction with time and recurrence. Altered joint position sense (JPS) from soft tissues can alter the cervical biomechanics by compromising the cephalo spatial orientation, which depends on the visual, vestibular and proprioceptive cues. This study was done to observe the additive effect of “Brahma mudra” (BM) a yogic tool on non-specific mechanical neck pain and its clinical implication on pain, proprioception and functional abilities. MethodsIt was a quasi-experimental pre –post study design involving 30 individuals from a software firm between the age group of 18–45 years. The conventional treatment group received standard physiotherapy regime and in the BM group BM was incorporated in addition to standard physiotherapy regime. Independent sample student t-test/Mann Whitney test were used to compare continuous variables between two groups. Paired sample test/Wilcoxon signed rank test were used for within groups. ResultsThere was a significant reduction in pain, improved functional abilities and proprioception in BM group when compared to conventional treatment group with 0.01 level of statistical significance. ConclusionIt may be concluded that practice of BM had an added effect to conventional standard physiotherapy regime in reduction of pain, improvement of proprioception and functional abilities among individuals with chronic non-specific mechanical neck pain.

Aligning one’s sights: The pulvinar provides context for visual information processing

The pulvinar (lateral posterior [LP]), like other higher-order thalamic nuclei, receives input from-and sends output to-multiple neocortical structures. In this issue of Neuron, Blot etal. (2021) demonstrate that LP integrates multimodal inputs to put visual information in context.

Detection of passive movement in lower limb joints is impaired in individuals with Parkinson’s disease

ObjectiveSensory information is crucial when performing daily activities, and Parkinson’s disease may diminish sensitivity to sensory cues. This study aimed to examine the detection threshold of passive motion of knee and ankle joints in individuals with Parkinson’s disease. MethodsEighteen individuals in the early stages of idiopathic Parkinson’s disease (age: 62.7 ± 7.3 years) and 18 healthy matched controls (age: 62.5 ± 7.1 years) first performed a simple reaction time test. Participants were asked to perform ten trials, during which they had to watch a square on a screen and press a button as quickly as possible when the square lit up. Thereafter, the participants were tested for their detection threshold of passive motion of their lower limb joints. Participants were seated in a specially designed chair and their knee or ankle joint was passively moved at a velocity of 0.5º/s. Participants kept their eyes closed and were instructed to press a button as quickly as possible when any joint motion was detected. ResultsIndividuals with Parkinson’s disease needed more time to perform the reaction time test than did the control participants. Individuals with Parkinson’s disease also needed larger angular displacement, even when reaction time was used as a covariate measure, to detect any passive motion, in both knee (0.70º ± 0.20º) and ankle (1.03º ± 0.23º) joints than did the control participants [(0.57º ± 0.20º) and (0.84º ± 0.27º), respectively]. ConclusionImpaired joint proprioception can be observed in the early stages of Parkinson’s disease, which may compromise the use of proprioception cues from lower limbs.

Serotonergic inhibition of responding for conditioned but not primary reinforcers

Serotonin is widely implicated as a modulator of brain reward function. However, laboratory studies have not yielded a consensus on which specific reward-related processes are influenced by serotonin and in what manner. Here we explored the role of serotonin in cue-reward learning in mice. In a first series of experiments, we found that acute administration of the serotonin reuptake inhibitors citalopram, fluoxetine, or duloxetine all reduced lever pressing reinforced on an FR1 schedule with presentation of a cue that had been previously paired with delivery of food. However, citalopram had no effect on responding that was reinforced with both cue and food on an FR1 schedule. Furthermore, citalopram did not affect nose poke responses that produced no auditory, visual, or proprioceptive cues but were reinforced with food pellets on a progressive ratio schedule. We next performed region-specific knock out of tryptophan hydroxylase-2 (Tph2), the rate-limiting enzyme in serotonin synthesis. Viral delivery of Cre recombinase was targeted to dorsal or median raphe nuclei (DRN, MRN), the major sources of ascending serotonergic projections. MRN but not DRN knockouts were impaired in development of cue-elicited approach during Pavlovian conditioning; both groups were subsequently hyper-responsive when lever pressing for cue presentation. The inhibitory effect of citalopram was attenuated in DRN but not MRN knockouts. Our findings are in agreement with prior studies showing serotonin to suppress responding for conditioned reinforcers. Furthermore, these results suggest an inhibitory role of MRN serotonin neurons in the initial attribution of motivational properties to a reward-predictive cue, but not in its subsequent maintenance. In contrast, the DRN appears to promote the reduction of motivational value attached to a cue when it is presented repeatedly in the absence of primary reward.

An elasticity-curvature illusion decouples cutaneous and proprioceptive cues in active exploration of soft objects.

Our sense of touch helps us encounter the richness of our natural world. Across a myriad of contexts and repetitions, we have learned to deploy certain exploratory movements in order to elicit perceptual cues that are salient and efficient. The task of identifying optimal exploration strategies and somatosensory cues that underlie our softness perception remains relevant and incomplete. Leveraging psychophysical evaluations combined with computational finite element modeling of skin contact mechanics, we investigate an illusion phenomenon in exploring softness; where small-compliant and large-stiff spheres are indiscriminable. By modulating contact interactions at the finger pad, we find this elasticity-curvature illusion is observable in passive touch, when the finger is constrained to be stationary and only cutaneous responses from mechanosensitive afferents are perceptible. However, these spheres become readily discriminable when explored volitionally with musculoskeletal proprioception available. We subsequently exploit this phenomenon to dissociate relative contributions from cutaneous and proprioceptive signals in encoding our percept of material softness. Our findings shed light on how we volitionally explore soft objects, i.e., by controlling surface contact force to optimally elicit and integrate proprioceptive inputs amidst indiscriminable cutaneous contact cues. Moreover, in passive touch, e.g., for touch-enabled displays grounded to the finger, we find those spheres are discriminable when rates of change in cutaneous contact are varied between the stimuli, to supplant proprioceptive feedback.

Failure Handling of Robotic Pick and Place Tasks With Multimodal Cues Under Partial Object Occlusion.

The success of a robotic pick and place task depends on the success of the entire procedure: from the grasp planning phase, to the grasp establishment phase, then the lifting and moving phase, and finally the releasing and placing phase. Being able to detect and recover from grasping failures throughout the entire process is therefore a critical requirement for both the robotic manipulator and the gripper, especially when considering the almost inevitable object occlusion by the gripper itself during the robotic pick and place task. With the rapid rising of soft grippers, which rely heavily on their under-actuated body and compliant, open-loop control, less information is available from the gripper for effective overall system control. Tackling on the effectiveness of robotic grasping, this work proposes a hybrid policy by combining visual cues and proprioception of our gripper for the effective failure detection and recovery in grasping, especially using a proprioceptive self-developed soft robotic gripper that is capable of contact sensing. We solved failure handling of robotic pick and place tasks and proposed (1) more accurate pose estimation of a known object by considering the edge-based cost besides the image-based cost; (2) robust object tracking techniques that work even when the object is partially occluded in the system and achieve mean overlap precision up to 80%; (3) contact and contact loss detection between the object and the gripper by analyzing internal pressure signals of our gripper; (4) robust failure handling with the combination of visual cues under partial occlusion and proprioceptive cues from our soft gripper to effectively detect and recover from different accidental grasping failures. The proposed system was experimentally validated with the proprioceptive soft robotic gripper mounted on a collaborative robotic manipulator, and a consumer-grade RGB camera, showing that combining visual cues and proprioception from our soft actuator robotic gripper was effective in improving the detection and recovery from the major grasping failures in different stages for the compliant and robust grasping.

Caenorhabditis elegans learning in a structured maze is a multisensory behavior

SummaryWe show that C. elegans nematodes learn to associate food with a combination of proprioceptive cues and information on the structure of their surroundings (maze), perceived through mechanosensation. By using the custom-made Worm-Maze platform, we demonstrate that C. elegans young adults can locate food in T-shaped mazes and, following that experience, learn to reach a specific maze arm. C. elegans learning inside the maze is possible after a single training session, it resembles working memory, and it prevails over conflicting environmental cues. We provide evidence that the observed learning is a food-triggered multisensory behavior, which requires mechanosensory and proprioceptive input, and utilizes cues about the structural features of nematodes' environment and their body actions. The CREB-like transcription factor and dopamine signaling are also involved in maze performance. Lastly, we show that the observed aging-driven decline of C. elegans learning ability in the maze can be reversed by starvation.

The role of vestibular cues in postural sway.

Controlling posture requires continuous sensory feedback about body motion and orientation, including from the vestibular organs. Little is known about the role of tilt vs. translation vs. rotation vestibular cues. We examined whether intersubject differences in vestibular function were correlated with intersubject differences in postural control. Vestibular function was assayed using vestibular direction-recognition perceptual thresholds, which determine the smallest motion that can be reliably perceived by a subject seated on a motorized platform in the dark. In study A, we measured thresholds for lateral translation, vertical translation, yaw rotation, and head-centered roll tilts. In study B, we measured thresholds for roll, pitch, and left anterior-right posterior and right anterior-left posterior tilts. Center-of-pressure (CoP) sway was measured in sensory organization tests (study A) and Romberg tests (study B). We found a strong positive relationship between CoP sway and lateral translation thresholds but not CoP sway and other thresholds. This finding suggests that the vestibular encoding of lateral translation may contribute substantially to balance control. Since thresholds assay sensory noise, our results support the hypothesis that vestibular noise contributes to spontaneous postural sway. Specifically, we found that lateral translation thresholds explained more of the variation in postural sway in postural test conditions with altered proprioceptive cues (vs. a solid surface), consistent with postural sway being more dependent on vestibular noise when the vestibular contribution to balance is higher. These results have potential implications for vestibular implants, balance prostheses, and physical therapy exercises.NEW & NOTEWORTHY Vestibular feedback is important for postural control, but little is known about the role of tilt cues vs. translation cues vs. rotation cues. We studied healthy human subjects with no known vestibular pathology or symptoms. Our findings showed that vestibular encoding of lateral translation correlated with medial-lateral postural sway, consistent with lateral translation cues contributing to balance control. This adds support to the hypothesis that vestibular noise contributes to spontaneous postural sway.

Hypoxia and standing balance.

Standing balance control is important for everyday function and often goes unnoticed until impairments appear. Presently, more than 200 million people live at altitudes > 2500m above sea level, and many others work at or travel to these elevations. Thus, it is important to understand how hypoxia alters balance owing to implications for occupations and travelers. Herein, the influence of normobaric and hypobaric hypoxia on standing balance control is reviewed and summarized. As postural control relies on the integration of sensorimotor signals, the potential hypoxic-sensitive neurophysiological factors that contribute to balance impairments are also reviewed. Specifically, we examine how hypoxia impairs visual, vestibular, and proprioceptive cues, and their integration within subcortical or cortical areas. This systematic review included a literature search conducted via multiple databases with keywords related to postural balance, hypoxia, and altitude. Articles (n = 13) were included if they met distinct criteria. Compared to normoxia, normobaric hypoxia worsened parameters of standing balance by 2-10% and up to 83 and 240% in hypobaric hypoxia (high-altitude and lab-based, respectively). Although balance was onlydisrupted during normobaric hypoxia atFIO2 < ~ 0.15, impairments consistently occurred during hypobaric hypoxia at altitudes > 1524m (~ FIO2 < 0.18). Hypoxia, especially hypobaric, impairs standing balance. The mechanisms underpinning postural decrements likely involve alterations to processing and integration of sensorimotor signals within subcortical or cortical structures involving visual, vestibular, and proprioceptive pathways and subsequent motor commands that direct postural adjustments. Future studies are required to determine the sensorimotor factors that may influence balance control in hypoxia.

Multisensory Interactions in Head and Body Centered Perception of Verticality.

Percepts of verticality are thought to be constructed as a weighted average of multisensory inputs, but the observed weights differ considerably between studies. In the present study, we evaluate whether this can be explained by differences in how visual, somatosensory and proprioceptive cues contribute to representations of the Head In Space (HIS) and Body In Space (BIS). Participants (10) were standing on a force plate on top of a motion platform while wearing a visualization device that allowed us to artificially tilt their visual surroundings. They were presented with (in)congruent combinations of visual, platform, and head tilt, and performed Rod & Frame Test (RFT) and Subjective Postural Vertical (SPV) tasks. We also recorded postural responses to evaluate the relation between perception and balance. The perception data shows that body tilt, head tilt, and visual tilt affect the HIS and BIS in both experimental tasks. For the RFT task, visual tilt induced considerable biases (≈ 10° for 36° visual tilt) in the direction of the vertical expressed in the visual scene; for the SPV task, participants also adjusted platform tilt to correct for illusory body tilt induced by the visual stimuli, but effects were much smaller (≈ 0.25°). Likewise, postural data from the SPV task indicate participants slightly shifted their weight to counteract visual tilt (0.3° for 36° visual tilt). The data reveal a striking dissociation of visual effects between the two tasks. We find that the data can be explained well using a model where percepts of the HIS and BIS are constructed from direct signals from head and body sensors, respectively, and indirect signals based on body and head signals but corrected for perceived neck tilt. These findings show that perception of the HIS and BIS derive from the same sensory signals, but see profoundly different weighting factors. We conclude that observations of different weightings between studies likely result from querying of distinct latent constructs referenced to the body or head in space.

Do near-field cues enhance the plausibility of non-individual binaural rendering in a dynamic multimodal virtual acoustic scene?

It is commonly believed that near-field head-related transfer functions (HRTFs) provide perceptual benefits over far-field HRTFs that enhance the plausibility of binaural rendering of nearby sound sources. However, to the best of our knowledge, no study has systematically investigated whether using near-field HRTFs actually provides a perceptually more plausible virtual acoustic environment. To assess this question, we conducted two experiments in a six-degrees-of-freedom multimodal augmented reality experience where participants had to compare non-individual anechoic binaural renderings based on either synthesized near-field HRTFs or intensity-scaled far-field HRTFs and judge which of the two rendering methods led to a more plausible representation. Participants controlled the virtual sound source position by moving a small handheld loudspeaker along a prescribed trajectory laterally and frontally near the head, which provided visual and proprioceptive cues in addition to the auditory cues. The results of both experiments show no evidence that near-field cues enhance the plausibility of non-individual binaural rendering of nearby anechoic sound sources in a dynamic multimodal virtual acoustic scene as examined in this study. These findings suggest that, at least in terms of plausibility, the additional effort of including near-field cues in binaural rendering may not always be worthwhile for virtual or augmented reality applications.