Human echolocators adjust loudness and number of clicks for detection of reflectors at various azimuth angles

Auditory orientation and distance estimation of sighted humans using virtual echolocation with artificial and self-generated sounds

Active echolocation of sighted humans using predefined synthetic and self-emitted sounds, as habitually used by blind individuals, was investigated. Using virtual acoustics, distance estimation and directional localization of a wall in different rooms were assessed. A virtual source was attached to either the head or hand with realistic or increased source directivity. A control condition was tested with a virtual sound source located at the wall. Untrained echolocation performance comparable to performance in the control condition was achieved on an individual level. On average, the echolocation performance was considerably lower than in the control condition, however, it benefitted from increased directivity.

Human Echolocators Have Better Localization Off Axis

Here, we report novel empirical results from a psychophysical experiment in which we tested the echolocation abilities of nine blind adult human experts in click-based echolocation. We found that they had better acuity in localizing a target and used lower intensity emissions (i.e., mouth clicks) when a target was placed 45° off to the side compared with when it was placed at 0° (straight ahead). We provide a possible explanation of the behavioral result in terms of binaural-intensity signals, which appear to change more rapidly around 45°. The finding that echolocators have better echo-localization off axis is surprising, because for human source localization (i.e., regular spatial hearing), it is well known that performance is best when targets are straight ahead (0°) and decreases as targets move farther to the side. This may suggest that human echolocation and source hearing rely on different acoustic cues and that human spatial hearing has more facets than previously thought.

Object Surface Recognition Based on Standing Waves in Acoustic Signals

This paper proposes the use of the standing waves created by the interference between transmitted and reflected acoustic signals to recognize the size and the shape of a target object. This study shows that the profile of the distance spectrum generated by the interference encodes not only the distance to the target, but also the distance to the edges of the target surface. To recognize the extent of the surface, a high-resolution distance spectrum is proposed, and a method to estimate the points on the edges by incorporating observations from multiple measurement is introduced. Numerical simulations validated the approach and showed that the method worked even in the presence of noise. Experimental results are also shown to verify that the method works in a real environment.

Discrimination of 2D wall textures by passive echolocation for different reflected-to-direct level difference configurations

In this work, we study people's ability to discriminate between different 2D textures of walls by passive listening to a pre-recorded tongue click in an auralized echolocation scenario. In addition, the impact of artificially enhancing the early reflection magnitude by 6dB and of removing the direct component while equalizing the loudness was investigated. Listening test results for different textures, ranging from a flat wall to a staircase, were assessed using a 2 Alternative-Forced-Choice (2AFC) method, in which 14 sighted, untrained participants were indicating 2 equally perceived stimuli out of 3 presented stimuli. The average performance of the listening subjects to discriminate between different textures was found to be significantly higher for walls at 5m distance, without overlap between the reflected and direct sound, compared to the same walls at 0.8m distance. Enhancing the reflections as well as removing the direct sound were found to be beneficial to differentiate textures. This finding highlights the importance of forward masking in the discrimination process. The overall texture discriminability was found to be larger for the walls reflecting with a higher spectral coloration.

Effectiveness of time-varying echo information for target geometry identification in bat-inspired human echolocation

Bats use echolocation through flexible active sensing via ultrasounds to identify environments suitable for their habitat and foraging. Mimicking the sensing strategies of bats for echolocation, this study examined how humans acquire new acoustic-sensing abilities, and proposes effective strategies for humans. A target geometry identification experiment-involving 15 sighted people without experience of echolocation-was conducted using two targets with different geometries, based on a new sensing system. Broadband frequency-modulated pulses with short inter-pulse intervals (16 ms) were used as a synthetic echolocation signal. Such pulses mimic buzz signals emitted by bats for echolocation prior to capturing their prey. The study participants emitted the signal from a loudspeaker by tapping on Android devices. Because the signal included high-frequency signals up to 41 kHz, the emitted signal and echoes from a stationary or rotating target were recorded using a 1/7-scaled miniature dummy head. Binaural sounds, whose pitch was down-converted, were presented through headphones. This way, time-varying echo information was made available as an acoustic cue for target geometry identification under a rotating condition, as opposed to a stationary one. In both trials, with (i.e., training trials) and without (i.e., test trials) answer feedback immediately after the participants answered, the participants identified the geometries under the rotating condition. Majority of the participants reported using time-varying patterns in terms of echo intensity, timbre, and/or pitch under the rotating condition. The results suggest that using time-varying patterns in echo intensity, timbre, and/or pitch enables humans to identify target geometries. However, performance significantly differed by condition (i.e., stationary vs. rotating) only in the test trials. This difference suggests that time-varying echo information is effective for identifying target geometry through human echolocation especially when echolocators are unable to obtain answer feedback during sensing.

Increased emission intensity can compensate for the presence of noise in human click-based echolocation

Echolocating bats adapt their emissions to succeed in noisy environments. In the present study we investigated if echolocating humans can detect a sound-reflecting surface in the presence of noise and if intensity of echolocation emissions (i.e. clicks) changes in a systematic pattern. We tested people who were blind and had experience in echolocation, as well as blind and sighted people who had no experience in echolocation prior to the study. We used an echo-detection paradigm where participants listened to binaural recordings of echolocation sounds (i.e. they did not make their own click emissions), and where intensity of emissions and echoes changed adaptively based on participant performance (intensity of echoes was yoked to intensity of emissions). We found that emission intensity had to systematically increase to compensate for weaker echoes relative to background noise. In fact, emission intensity increased so that spectral power of echoes exceeded spectral power of noise by 12 dB in 4-kHz and 5-kHz frequency bands. The effects were the same across all participant groups, suggesting that this effect occurs independently of long-time experience with echolocation. Our findings demonstrate for the first time that people can echolocate in the presence of noise and suggest that one potential strategy to deal with noise is to increase emission intensity to maintain signal-to-noise ratio of certain spectral components of the echoes.

Perceptual constancy with a novel sensory skill

Making sense of the world requires perceptual constancy—the stable perception of an object across changes in one’s sensation of it. To investigate whether constancy is intrinsic to perception, we tested whether humans can learn a form of constancy that is unique to a novel sensory skill (here, the perception of objects through click-based echolocation). Participants judged whether two echoes were different either because: (a) the clicks were different, or (b) the objects were different. For differences carried through spectral changes (but not level changes), blind expert echolocators spontaneously showed a high constancy ability (mean d′ = 1.91) compared to sighted and blind people new to echolocation (mean d′ = 0.69). Crucially, sighted controls improved rapidly in this ability through training, suggesting that constancy emerges in a domain with which the perceiver has no prior experience. This provides strong evidence that constancy is intrinsic to human perception.

This study shows that people who learn a new skill to sense their environment - here: listening to sound echoes - can correctly represent the physical properties of objects. This result has implications for effectively rehabilitating people with sensory loss.

Stimulus uncertainty affects perception in human echolocation: Timing, level, and spectrum

The human brain may use recent sensory experience to create sensory templates that are then compared to incoming sensory input, that is, "knowing what to listen for." This can lead to greater perceptual sensitivity, as long as the relevant properties of the target stimulus can be reliably estimated from past sensory experiences. Echolocation is an auditory skill probably best understood in bats, but humans can also echolocate. Here we investigated for the first time whether echolocation in humans involves the use of sensory templates derived from recent sensory experiences. Our results showed that when there was certainty in the acoustic properties of the echo relative to the emission, either in temporal onset, spectral content or level, people detected the echo more accurately than when there was uncertainty. In addition, we found that people were more accurate when the emission's spectral content was certain but, surprisingly, not when either its level or temporal onset was certain. Importantly, the lack of an effect of temporal onset of the emission is counter to that found previously for tasks using nonecholocation sounds, suggesting that the underlying mechanisms might be different for echolocation and nonecholocation sounds. Importantly, the effects of stimulus certainty were no different for people with and without experience in echolocation, suggesting that stimulus-specific sensory templates can be used in a skill that people have never used before. From an applied perspective our results suggest that echolocation instruction should encourage users to make clicks that are similar to one another in their spectral content. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Navigation and perception of spatial layout in virtual echo-acoustic space

Successful navigation involves finding the way, planning routes, and avoiding collisions. Whilst previous research has shown that people can navigate using non-visual cues, it is not clear to what degree learned non-visual navigational abilities generalise to 'new' environments. Furthermore, the ability to successfully avoid collisions has not been investigated separately from the ability to perceive spatial layout or to orient oneself in space. Here, we address these important questions using a virtual echolocation paradigm in sighted people. Fourteen sighted blindfolded participants completed 20 virtual navigation training sessions over the course of 10 weeks. In separate sessions, before and after training, we also tested their ability to perceive the spatial layout of virtual echo-acoustic space. Furthermore, three blind echolocation experts completed the tasks without training, thus validating our virtual echo-acoustic paradigm. We found that over the course of 10 weeks sighted people became better at navigating, i.e. they reduced collisions and time needed to complete the route, and increased success rates. This also generalised to 'new' (i.e. untrained) virtual spaces. In addition, after training, their ability to judge spatial layout was better than before training. The data suggest that participants acquired a 'true' sensory driven navigational ability using echo-acoustics. In addition, we show that people not only developed navigational skills related to avoidance of collisions and finding safe passage, but also processes related to spatial perception and orienting. In sum, our results provide strong support for the idea that navigation is a skill which people can achieve via various modalities, here: echolocation.

Human Click-Based Echolocation of Distance: Superfine Acuity and Dynamic Clicking Behaviour

Some people who are blind have trained themselves in echolocation using mouth clicks. Here, we provide the first report of psychophysical and clicking data during echolocation of distance from a group of 8 blind people with experience in mouth click-based echolocation (daily use for > 3 years). We found that experienced echolocators can detect changes in distance of 3 cm at a reference distance of 50 cm, and a change of 7 cm at a reference distance of 150 cm, regardless of object size (i.e. 28.5 cm vs. 80 cm diameter disk). Participants made mouth clicks that were more intense and they made more clicks for weaker reflectors (i.e. same object at farther distance, or smaller object at same distance), but number and intensity of clicks were adjusted independently from one another. The acuity we found is better than previous estimates based on samples of sighted participants without experience in echolocation or individual experienced participants (i.e. single blind echolocators tested) and highlights adaptation of the perceptual system in blind human echolocators. Further, the dynamic adaptive clicking behaviour we observed suggests that number and intensity of emissions serve separate functions to increase SNR. The data may serve as an inspiration for low-cost (i.e. non-array based) artificial 'cognitive' sonar and radar systems, i.e. signal design, adaptive pulse repetition rate and intensity. It will also be useful for instruction and guidance for new users of echolocation.

The flexible action system: Click-based echolocation may replace certain visual functionality for adaptive walking

People use sensory, in particular visual, information to guide actions such as walking around obstacles, grasping or reaching. However, it is presently unclear how malleable the sensorimotor system is. The present study investigated this by measuring how click-based echolocation may be used to avoid obstacles while walking. We tested 7 blind echolocation experts, 14 sighted, and 10 blind echolocation beginners. For comparison, we also tested 10 sighted participants, who used vision. To maximize the relevance of our research for people with vision impairments, we also included a condition where the long cane was used and considered obstacles at different elevations. Motion capture and sound data were acquired simultaneously. We found that echolocation experts walked just as fast as sighted participants using vision, and faster than either sighted or blind echolocation beginners. Walking paths of echolocation experts indicated early and smooth adjustments, similar to those shown by sighted people using vision and different from later and more abrupt adjustments of beginners. Further, for all participants, the use of echolocation significantly decreased collision frequency with obstacles at head, but not ground level. Further analyses showed that participants who made clicks with higher spectral frequency content walked faster, and that for experts higher clicking rates were associated with faster walking. The results highlight that people can use novel sensory information (here, echolocation) to guide actions, demonstrating the action system’s ability to adapt to changes in sensory input. They also highlight that regular use of echolocation enhances sensory-motor coordination for walking in blind people.

Vision loss has negative consequences for people’s mobility. The current report demonstrates that echolocation might replace certain visual functionality for adaptive walking. Importantly, the report also highlights that echolocation and long cane are complementary mobility techniques. The findings have direct relevance for professionals involved in mobility instruction and for people who are blind.

Bat-inspired signal design for target discrimination in human echolocation

Echolocating bats exhibit sophisticated sonar behaviors using ultrasounds with actively adjusted acoustic characteristics (e.g., frequency and time-frequency structure) depending on the situation. In this study, the utility of ultrasound in human echolocation was examined. By listening to ultrasonic echoes with a shifted pitch to be audible, the participants (i.e., sighted echolocation novices) could discriminate the three-dimensional (3D) roundness of edge contours. This finding suggests that sounds with suitable wavelengths (i.e., ultrasounds) can provide useful information about 3D shapes. In addition, the shape, texture, and material discrimination experiments were conducted using ultrasonic echoes binaurally measured with a 1/7 scaled miniature dummy head. The acoustic and statistical analyses showed that intensity and timbre cues were useful for shape and texture discriminations, respectively. Furthermore, in the discrimination of objects with various features (e.g., acrylic board and artificial grass), the perceptual distances between objects were more dispersed when frequency-modulated sweep signals were used than when a constant-frequency signal was used. These suggest that suitable signal design, i.e., echolocation sounds employed by bats, allowed echolocation novices to discriminate the 3D shape and texture. This top-down approach using human subjects may be able to efficiently help interpret the sensory perception, "seeing by sound," in bat biosonar.