Blindfolded Subjects Research Articles

Visual Mental Imagery and Neural Dynamics of Sensory Substitution in the Blindfolded Subjects

Although one can recognize the environment by soundscape substituting vision to auditory signal, whether subjects could perceive the soundscape as visual or visual-like sensation has been questioned. In this study, we investigated hierarchical process to elucidate the recruitment mechanism of visual areas by soundscape stimuli in blindfolded subjects. Twenty-two healthy subjects were repeatedly trained to recognize soundscape stimuli converted by visual shape information of letters. An effective connectivity method called dynamic causal modeling (DCM) was employed to reveal how the brain was hierarchically organized to recognize soundscape stimuli. The visual mental imagery model generated cortical source signals of five regions of interest better than auditory bottom-up, cross-modal perception, and mixed models. Spectral couplings between brain areas in the visual mental imagery model were analyzed. While within-frequency coupling is apparent in bottom-up processing where sensory information is transmitted, cross-frequency coupling is prominent in top-down processing, corresponding to the expectation and interpretation of information. Sensory substitution in the brain of blindfolded subjects derived visual mental imagery by combining bottom-up and top-down processing.

Proprioceptive acuity for landmarks on the hand and digits.

Previous work using visually guided reaches to localize landmarks on a hidden hand has suggested that proprioceptive acuity for hand targets is low and representation of hand dimensions is highly distorted (e.g., hand width estimated to be 60% wider than actual hand width). We re-examined these issues using a pure proprioceptive task in which 20 blindfolded subjects reached in a single movement without terminal corrections to touch the right index-tip to landmarks of the left hand placed in various locations in 3D space. Subjects were also tested with vision allowed to estimate minimal errors. Based on previous reports of high proprioceptive acuity for some hand landmarks, we hypothesized that the proprioceptive representation of the hand was much less distorted than described previously and that errors were not correlated with target hand location. Mean distance errors in proprioceptively guided reaches to the landmarks averaged less than 3cm and were only 0.5-1.3cm larger than when vision was allowed. Errors were not correlated with hand location in most subjects. Distortions of hand width averaged less than 20% wider than actual width and were not correlated with hand location in most subjects. We conclude that relatively accurate proprioceptive awareness of locations of hand/digit structures and dimensions is available for use in control of hand movements, which are executed largely subconsciously. Studying acuity of proprioception using conscious perceptual tasks and involving vision may not provide accurate measures of proprioceptive acuity as used by the motor system.

Beat Detection Recruits the Visual Cortex in Early Blind Subjects.

Using functional magnetic resonance imaging, here we monitored the brain activity in 12 early blind subjects and 12 blindfolded control subjects, matched for age, gender and musical experience, during a beat detection task. Subjects were required to discriminate regular (“beat”) from irregular (“no beat”) rhythmic sequences composed of sounds or vibrotactile stimulations. In both sensory modalities, the brain activity differences between the two groups involved heteromodal brain regions including parietal and frontal cortical areas and occipital brain areas, that were recruited in the early blind group only. Accordingly, early blindness induced brain plasticity changes in the cerebral pathways involved in rhythm perception, with a participation of the visually deprived occipital brain areas whatever the sensory modality for input. We conclude that the visually deprived cortex switches its input modality from vision to audition and vibrotactile sense to perform this temporal processing task, supporting the concept of a metamodal, multisensory organization of this cortex.

Knee Valgus during Jump Landing Is Related to the Inaccuracy of Knee Position Recognition in Healthy Young Women.

ABSTRACTObjective:Knee valgus during jump landing is a cause of knee injuries during sports activities. Body recognition is important for maintaining the knees and other body parts in their proper positions. The aim of this study was to investigate whether knee valgus during jump landing in healthy young women is related to the inaccuracy of recognition of bilateral knee positions in the squatting position.Methods:In 39 healthy young women, the degree of knee valgus was evaluated during the drop vertical jump test using the ratio of the knee separation distance to the ankle separation distance. The accuracy of recognition of bilateral knee positions in the squatting position was evaluated by having the blindfolded subjects indicate with their index fingers the subjective positions of their bilateral patellae by placing their fingers on a horizontal bar positioned in front of them 3 cm below the navel. The difference ratio of the recognized distance to the actual distance between the bilateral patellae was measured as an inaccuracy index.Results:The degree of knee valgus during the drop vertical jump test was positively correlated with the degree of inaccuracy of the recognized knee position with the knees in the neutral position (r=0.358, P=0.025).Conclusions:In healthy young women, knee valgus during jump landing was significantly correlated with the inaccuracy in knee position recognition in the squatting posture. This finding suggests that the assessment of knee position recognition in the squatting position could be useful as a screening tool for preventing knee injuries on jump landing during sports activities.

Integrating Wearable Haptics and Obstacle Avoidance for the Visually Impaired in Indoor Navigation: A User-Centered Approach.

Recently, in the attempt to increase blind people autonomy and improve their quality of life, a lot of effort has been devoted to develop technological travel aids. These systems can surrogate spatial information about the environment and deliver it to end-users through sensory substitution (auditory, haptic). However, despite the promising research outcomes, these solutions have met scarce acceptance in real-world. Often, this is also due to the limited involvement of real end users in the conceptual and design phases. In this article, we propose a novel indoor navigation system based on wearable haptic technologies. All the developmental phases were driven by continuous feedback from visually impaired persons. The proposed travel aid system consists of a RGB-D camera, a processing unit to compute visual information for obstacle avoidance, and a wearable device, which can provide normal and tangential force cues for guidance in an unknown indoor environment. Experiments with blindfolded subjects and visually impaired participants show that our system could be an effective support during indoor navigation, and a viable tool for training blind people to the usage of travel aids.

A comparative study of auditory reaction time among blind and blindfolded sighted subjects

A comparative study of auditory reaction time among blind and blindfolded sighted subjects

Characterizing Individual Differences in a Dynamic Stabilization Task Using Machine Learning

INTRODUCTION: Being able to identify individual differences in skilled motor learning during disorienting conditions is important for spaceflight, military aviation, and rehabilitation.METHODS: Blindfolded subjects (N = 34) were strapped into a device that behaved like an inverted pendulum in the horizontal roll plane and were instructed to use a joystick to stabilize themselves across two experimental sessions on consecutive days. Subjects could not use gravitational cues to determine their angular position and many soon became spatially disoriented.RESULTS: Most demonstrated minimal learning, poor performance, and a characteristic pattern of positional drifting during horizontal roll plane balancing. To understand the wide range of individual differences observed, we used a Bayesian Gaussian Mixture method to cluster subjects into three statistically distinct groups that represent Proficient, Somewhat Proficient, and Not Proficient performance. We found that subjects in the Not Proficient group exhibited a suboptimal strategy of using very stereotyped large magnitude joystick deflections. We also used a Gaussian Naive Bayes method to create predictive classifiers. As early as the second block of experimentation (out of ten), we could predict a subject's final group with 80% accuracy.DISCUSSION: Our findings indicate that machine learning can help predict individual performance and learning in a disorienting dynamic stabilization task and identify suboptimal strategies in Not Proficient subjects, which could lead to personalized and more effective training programs.Vimal VP, Zheng H, Hong P, Fakharzadeh LN, Lackner JR, DiZio P. Characterizing individual differences in a dynamic stabilization task using machine learning. Aerosp Med Hum Perform. 2020; 91(6):479-488.

Comparison of auditory spatial bisection and minimum audible angle in front, lateral, and back space

Although vision is important for calibrating auditory spatial perception, it only provides information about frontal sound sources. Previous studies of blind and sighted people support the idea that azimuthal spatial bisection in frontal space requires visual calibration, while detection of a change in azimuth (minimum audible angle, MAA) does not. The influence of vision on the ability to map frontal, lateral and back space has not been investigated. Performance in spatial bisection and MAA tasks was assessed for normally sighted blindfolded subjects using bursts of white noise presented frontally, laterally, or from the back relative to the subjects. Thresholds for both tasks were similar in frontal space, lower for the MAA task than for the bisection task in back space, and higher for the MAA task in lateral space. Two interpretations of the results are discussed, one in terms of visual calibration and the use of internal representations of source location and the other based on comparison of the magnitude or direction of change of the available binaural cues. That bisection thresholds were increased in back space relative to front space, where visual calibration information is unavailable, suggests that an internal representation of source location was used for the bisection task.

Roll tilt self-motion direction discrimination training: First evidence for perceptual learning

Perceptual learning, the ability to improve the sensitivity of sensory perception through training, has been shown to exist in all sensory systems but the vestibular system. A previous study found no improvement of passive self-motion thresholds in the dark after intense direction discrimination training of either yaw rotations (stimulating semicircular canals) or y-translation (stimulating otoliths). The goal of the present study was to investigate whether perceptual learning of self-motion in the dark would occur when there is a simultaneous otolith and semicircular canal input, as is the case with roll tilt motion stimuli. Blindfolded subjects (n = 10) trained on a direction discrimination task with 0.2-Hz roll tilt motion stimuli (9 h of training, 1,800 trials). Before and after training, motion thresholds were measured in the dark for the trained motion and for three transfer conditions. We found that roll tilt sensitivity in the 0.2-Hz roll tilt condition was increased (i.e., thresholds decreased) after training but not for controls who were not exposed to training. This is the first demonstration of perceptual learning of passive self-motion direction discrimination in the dark. The results have potential therapeutic relevance as 0.2-Hz roll thresholds have been associated with poor performance on a clinical balance test that has been linked to more than a fivefold increase in falls.

Proprioceptive identification of joint position versus kinaesthetic movement reproduction

Regarding our voluntary control of movement, if identification of joint position, that is independent of the starting condition, is stronger than kinaesthetic movement reproduction, that implies knowledge of the starting position and movement’s length for accuracy, is still a matter of debate in motor control theories and neuroscience.In the present study, we examined the mechanisms that individuals seem to prefer/adopt when they locate spatial positions and code the amplitude of movements.We implemented a joint position matching task on a wrist robotic device: this task consists in replicating (i.e. matching) a reference joint angle in the absence of vision and the proprioceptive acuity is given by the goodness of such matching.Two experiments were carried out by implementing two different versions of the task and performed by two groups of 15 healthy participants. In the first experiment, blindfolded subjects were asked to perform matching movements towards a fixed target position, experienced with passive movements that started from different positions and had different lengths. In the second experiment, blindfolded subjects were requested to accurately match target positions that had a different location in space but were passively shown through movements of the same length.We found a clear evidence for higher performances in terms of accuracy (0.42±0.011/°) and precision (0.43±0.011/°) in the first experiment, therefore in case of matching positions, rather than in the second where accuracy and precision were lower (0.36±0.011/° and 0.35±0.011/° respectively). These results suggested a preference for proprioceptive identification of joint position rather than kinaesthetic movement reproduction.

Kinesthetic Senses.

The kinesthetic senses are the senses of position and movement of the body, senses we are aware of only on introspection. A method used to study kinesthesia is muscle vibration, which engages afferents of muscle spindles to trigger illusions of movement and changed position. When vibrating elbow flexors, it generates sensations of forearm extension, when vibrating extensors, sensations of forearm flexion. Vibrating the elbow joint produces no illusion. Vibrating flexors and extensors together at the same frequency also produces no illusion, because what is perceived is the signal difference between antagonist muscles of each arm and between arms. The size of the illusion depends on how the muscle has been conditioned beforehand, due to a property of muscle called thixotropy. When measuring the illusion, blindfolded subjects may carry out a matching or pointing task. In pointing, signals from muscle spindles are less important than in matching. Afferent signals from kinesthetic receptors project to areas of somatosensory cortex to generate sensations of detection and location. This is referred to the body model, which provides information about size and shape of body parts. Kinesthesia, together with vision and touch, is associated with the sense of body ownership. All three can combine or each, on its own, can generate ownership. Related is the sense of agency, the sense of being responsible for one's own actions. In recent times, much progress has been made using neuroimaging techniques to identify the various areas of the brain likely to be responsible for generating these sensations. © 2017 American Physiological Society. Compr Physiol 8:1157-1183, 2018.

Learning dynamic control of body yaw orientation.

To investigate the role of gravitational cues in the learning of a dynamic balancing task, we placed blindfolded subjects in a device programmed with inverted pendulum dynamics about the yaw axis. Subjects used a joystick to try and maintain a stable orientation at the direction of balance during 20 100s-long trials. They pressed a trigger button on the joystick to indicate whenever they felt at the direction of balance. Three groups of ten subjects each participated. One group balanced with their body and the yaw axis vertical, and thus did not have gravitational cues to help them to determine their angular position. They showed minimal learning, inaccurate indications of the direction of balance, and a characteristic pattern of positional drifting away from the balance point. A second group balanced with the yaw axis pitched 45° from the gravitational vertical and had gravity relevant position cues. The third group balanced with their yaw axis horizontal where they had gravity-dependent cues about body position in yaw. Groups 2 and 3 showed better initial balancing performance and more learning across trials than Group 1. These results indicate that in the absence of vision, the integration of transient semicircular canal and somatosensory signals about angular acceleration is insufficient for determining angular position during dynamic balancing; direct position-dependent gravity cues are necessary.

Effects of training procedures and target positions on lower arm movements

The aim of a series of experiments, which included three groups of six blindfolded subjects, 19-23 years of age, was to find out effects of different ways of training on some spaciotemporal aspects of different movements by lower arms. The subjects were trained to make 20, 40,60, 80 degree movements on a kinaesthesiometer. The direction of movements was ventral-lateral and lateral- ventral in the relation to the body. One of the groups was trained first by dominant arm, and then non-dominant, while the second group had the opposite sequences of training. The third group, however, was trained bibrachially. After the training, the three groups took part in a series of arm movement experiments, where the task time (TT), movement time (MT) and the deviation from lite target (error) were recorded for the two arms separately, as well as bibrachially. The smallest deviations from the target were obtained in all the situations, when the target was positioned more ventrally, regardless of the amplitude or the direction of the movements. This was attributed to a higher differential sensitivity of the proprioceptors affected by the ventral movements in comparisi on to those affected by the lateral movements.

Haptic Guidance in Dynamic Environments Using Optimal Reciprocal Collision Avoidance

Human guidance in situations where the users cannot rely on their main sensory modalities, such as assistive or search-and-rescue scenarios, is a challenging task. In this letter, we address the problem of guiding users along collision-free paths in dynamic environments, assuming that they cannot rely on their main sensory modalities. In order to safely guide the subjects, we adapt the optimal reciprocal collision avoidance to our specific problem. The proposed algorithm takes into account the stimuli which can be displayed to the users and the motion uncertainty of the users when reacting to the provided stimuli. The proposed algorithm was evaluated in three different dynamic scenarios. A total of 18 blindfolded human subjects were asked to follow haptic cues in order to reach a target area while avoiding real static obstacles and moving users. Three metrics such as time to reach the goal, length of the trajectories, and minimal distance from the obstacles are considered to compare results obtained using this approach and experiments performed without visual impairments. Experimental results reveal that blindfolded subjects are successfully able to avoid collisions and safely reach the targets in all the performed trials. Although in this letter we display directional cues via haptic stimuli, we believe that the proposed approach can be general and tuned to work with different haptic interfaces and/or feedback modalities.

The role of smell, taste, flavour and texture cues in the identification of vegetables

It has been shown that the identification of many foods including vegetables based on flavour cues is often difficult. The effect of providing texture cues in addition to flavour cues on the identification of foods and the effect of providing taste cues only on the identification of foods have not been studied. The aim of this study was to assess the role of smell, taste, flavour and texture cues in the identification of ten vegetables commonly consumed in The Netherlands (broccoli, cauliflower, French bean, leek, bell pepper, carrot, cucumber, iceberg lettuce, onion and tomato). Subjects (n = 194) were randomly assigned to one of four test conditions which differed in the sensory cues available for vegetable identification: taste, smell (orthonasal), flavour (taste and smell) and flavour-texture (taste, smell and texture). Blindfolded subjects were asked to identify the vegetable from a list of 24 vegetables. Identification was the highest in the flavour-texture condition (87.5%). Identification was significantly lower in the flavour condition (62.8%). Identification was the lowest when only taste cues (38.3%) or only smell cues (39.4%) were provided. For four raw vegetables (carrot, cucumber, onion and tomato) providing texture cues in addition to flavour cues did not significantly change identification suggesting that flavour cues were sufficient to identify these vegetables. Identification frequency increased for all vegetables when perceived intensity of the smell, taste or flavour cue increased. We conclude that providing flavour cues (taste and smell) increases identification compared to only taste or only smell cues, combined flavour and texture cues are needed for the identification of many vegetables commonly consumed in The Netherlands.

Gravitational and Somatosensory Influences on Control and Perception of Roll Balance

Blindfolded subjects used a joystick to orient themselves to the direction of balance in a device programmed to exhibit inverted pendulum behavior in the roll plane; they indicated with a trigger press when they were at that location. Our goal was to determine how otolith and somatosensory information about the gravitational vertical influenced the ability to locate the direction of balance. The subjects (N = 12) were tested in each of three orientations of the body roll plane: vertical (Upright), 45° back (45_Degree), and 90° back (Supine), which provided progressively less salient otolith and somatosensory information about roll orientation with regard to the direction of gravity. For each pitch plane, subjects were tested with three directions of balance: 0° (aligned with the gravitational vertical in the Upright condition) and 30° right or left. The mean achieved and indicated orientations for the Upright and 45_Degree conditions were significantly displaced away from the direction of balance in the direction of gravity, with indicated angles less displaced. In the Supine condition, the mean achieved and indicated angles were closer to the direction of balance, but their within-trial standard deviations were significantly larger than in the Upright and 45_Degree conditions, which did not differ. This greater variability resulted from the frequent side to side "drifting" behavior that was a characteristic feature of the Supine condition only. These findings indicate that in the absence of vision accurate dynamic orientation requires gravity dependent shear forces on the otolith organs and body surface.Panic AS, Panic H, DiZio P, Lackner JR. Gravitational and somatosensory influences on control and perception of roll balance. Aerosp Med Hum Perform. 2017; 88(11):993-999.

Learning dynamic balancing in the roll plane with and without gravitational cues.

We determined the relative contributions of gravity-dependent positional cues and motion cues to the learning of roll balance control. We hypothesized that gravity-dependent otolith and somatosensory shear forces related to body orientation would yield better initial performance, more rapid learning, and better retention. Blindfolded subjects rode in a device programmed to roll with inverted pendulum dynamics in a vertical (UPRIGHT) or horizontal plane (SUPINE), and used a joystick to align themselves with the direction of balance. Each subject completed five blocks of four 100s long trials on two consecutive days in one of four groups (n=10 per group): Group 1, UPRIGHT balancing both days; Group 2, SUPINE both days; Group 3, UPRIGHT then SUPINE; and Group 4, SUPINE then UPRIGHT. On Day 1, UPRIGHT subjects showed better initial performance and greater improvement in performance than SUPINE subjects, who showed improvements only in having fewer deviations exceeding ±60deg from the direction of balance. Subjects tested UPRIGHT on both days showed full retention of learning across days and additional Day 2 learning, but subjects tested SUPINE on both days showed partial retention of their marginal learning from Day 1 and little improvement on Day 2. Subjects tested SUPINE on Day 2 after being tested UPRIGHT on Day 1 showed no better performance than subjects tested SUPINE on Day 1. By contrast, there was transfer from SUPINE on Day 1 to UPRIGHT on Day 2. We conclude that absence of gravitationally dependent otolith and somatosensory cues degrades balance performance.

Cooperative Navigation for Mixed Human–Robot Teams Using Haptic Feedback

In this paper, we present a novel cooperative navigation control for human–robot teams. Assuming that a human wants to reach a final location in a large environment with the help of a mobile robot, the robot must steer the human from the initial to the target position. The challenges posed by cooperative human–robot navigation are typically addressed by using haptic feedback via physical interaction. In contrast with that, in this paper, we describe a different approach, in which the human–robot interaction is achieved via wearable vibrotactile armbands. In the proposed work, the subject is free to decide her/his own pace. A warning vibrational signal is generated by the haptic armbands when a large deviation with respect to the desired pose is detected by the robot. The proposed method has been evaluated in a large indoor environment, where 15 blindfolded human subjects were asked to follow the haptic cues provided by the robot. The participants had to reach a target area, while avoiding static and dynamic obstacles. Experimental results revealed that the blindfolded subjects were able to avoid the obstacles and safely reach the target in all of the performed trials. A comparison is provided between the results obtained with blindfolded users and experiments performed with sighted people.

Spatial Cues Provided by Sound Improve Postural Stabilization: Evidence of a Spatial Auditory Map?

It has long been suggested that sound plays a role in the postural control process. Few studies however have explored sound and posture interactions. The present paper focuses on the specific impact of audition on posture, seeking to determine the attributes of sound that may be useful for postural purposes. We investigated the postural sway of young, healthy blindfolded subjects in two experiments involving different static auditory environments. In the first experiment, we compared effect on sway in a simple environment built from three static sound sources in two different rooms: a normal vs. an anechoic room. In the second experiment, the same auditory environment was enriched in various ways, including the ambisonics synthesis of a immersive environment, and subjects stood on two different surfaces: a foam vs. a normal surface. The results of both experiments suggest that the spatial cues provided by sound can be used to improve postural stability. The richer the auditory environment, the better this stabilization. We interpret these results by invoking the “spatial hearing map” theory: listeners build their own mental representation of their surrounding environment, which provides them with spatial landmarks that help them to better stabilize.

Assessment of texture discrimination ability at the sole of the foot in subjects with chronic stroke compared with young and elderly subjects with no neurological deficits: a reliability and validity study

Purpose: To examine validity and test–retest reliability of a sensory test developed to evaluate ability of elderly subjects with/out a stroke to discriminate between textures with the sole of their foot.Methods: Subjects poststroke, old adults and young subjects were tested twice. Twelve materials relevant to foot function (e.g., gravel, sand) were used. Blindfolded subjects were requested to discriminate with the sole of each foot one outstanding texture among three textures presented in each of 12 subtests. ANOVA, ICC and Bland–Altman tests were used to determine group/leg differences and test-retest reliability.Results: Discrimination ability of the involved lower extremity poststroke is significantly reduced. Ability in individuals with no neurological impairment is age related. Good test–retest (ICC = 0.81) reliability was demonstrated for the impaired foot of subjects poststroke. The 95% repeatability ranges were age related with the highest range demonstrated for the involved foot poststroke. A significant fair negative correlation was demonstrated between texture discrimination ability and tactile detection threshold measured by Semmes–Weinstein monofilaments for the involved foot in poststroke subjects.Conclusion: This newly developed assessment tool demonstrates concurrent and known-groups validity and is reliable for determining texture discriminative ability of the foot in individuals post-stroke and in older adults with no neurological impairment.Implications for rehabilitationThe texture discrimination test presented here is a valid and reliable tool, providing quantitative assessment of sensory function at the sole of the foot in older adults with no neurologic deficits and in subjects poststroke.Lower extremity texture discrimination test is easy to administer in the clinic and might suggest directions for individually tailored, lower extremity, sensory retraining protocols.