Virtual Echo Research Articles

Biosonar sampling strategies in frequency-modulated echolocating bats

Echolocating bats dynamically control multiple aspects of their biosonar emissions (emission rate, frequency, bandwidth, duration, and direction) in parallel as a function of their surroundings and current goals. As environments become more difficult to navigate and tasks become more complex, bats converge on sampling strategies that have less variability in the timing and spatial changes of their echolocation. We investigated these biosonar dynamics within a virtual echo target presentation paradigm where we challenged big brown bats sitting on a platform to localize a single echo target, which was either stationary or moved unpredictably in azimuth. Acoustic clutter was also added at varying distances to investigate its effect on their sampling strategies during the task. Bats modified their biosonar strategies differently depending on the distance of added acoustic clutter and the distance that a target shifted, and individuals tended to converge on similar strategies. We also show that certain perceptual contexts can lead to unexpected biosonar strategies in individual bats, such as the use of longer-duration emissions with less emission ‘clustering’ when localizing a virtual target against nearby clutter.

Abstract 92: Using Innovative Technology and Collaborative Efforts to Reduce Disparities and Inequities in Cancer Care and Improve the Lives of Patients in Low-Middle Income Countries in Sub-Saharan Africa: South African and Lesotho Experience of the ECHO Model

Abstract Purpose: Sub-Saharan Africa has huge disparities and inequities in cancer care. Some low resource countries have no facilities or trained oncologists and other healthcare professionals for cancer care. Patients often must travel long distances to access specialised cancer care such as radiotherapy, chemotherapy and palliative care. Patients with cancer in Lesotho who needed chemotherapy had to be flown to India; those who needed radiotherapy were referred to South Africa. Majority of the cancers diagnosed in the Northern cape province and Lesotho are in late stages and need treatment with chemotherapy and radiotherapy as part of the multimodality therapy. Methods: The Northern Cape Cancer Centre of Excellence and Research (NCCanCER) at Kimberley Hospital in South Africa collaborated with the Senkatana Hospital in Lesotho. Oncologists, specialist oncology nurses and IT personnel were trained at Project ECHO Institute in Albuquerque, NM to use the ECHO model for training, transfer of skills and mentorship. NCCanCER assisted Lesotho to set up a chemotherapy facility at Senkatana Hospital. An initial visit to the Kimberley Hospital Oncology Department for benchmarking was done by oncology staff from Lesotho. NCCanCER oncology staff went to Lesotho to provide on-site training in chemotherapy administration. Weekly virtual ECHO clinics were run from the Hub at Kimberley with spoke sites in Lesotho, Upington, Springbok and Kuruman. At the ECHO clinics, management of patients are discussed using evidence-based management protocols for continued training, transfer of skills, support and mentorship. Results: Doctors, nurses, pharmacists, social workers, clinical psychologists and community healthcare workers have been trained to provide cancer care and palliative care services in the underprivileged and underserved areas of the Northern cape and Lesotho. The first chemotherapy facility was opened in Lesotho in July 2022 and patients in Lesotho are no longer flown to India for chemotherapy. Patients in remote areas of the Northern cape province of South Africa can now receive chemotherapy and palliative care closer to their homes. There is continuous training, transfer of skills, expertise and mentorship of oncology staff. Conclusion: The ECHO model is useful in democratizing knowledge, transfer skills and expertise to improve care to patients in low resource countries. Citation Format: Daniel Osei-Fofie, Kabelo Mputsoe Cekwane, Mobashshar Hassan, Sophie Victoria Masuabi, Pearl Ntsekhe. Using Innovative Technology and Collaborative Efforts to Reduce Disparities and Inequities in Cancer Care and Improve the Lives of Patients in Low-Middle Income Countries in Sub-Saharan Africa: South African and Lesotho Experience of the ECHO Model [abstract]. In: Proceedings of the 11th Annual Symposium on Global Cancer Research; Closing the Research-to-Implementation Gap; 2023 Apr 4-6. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(6_Suppl):Abstract nr 92.

Object-specific adaptation in the auditory cortex of bats.

Identifying behaviorally relevant sounds is a vital function of the auditory system. Echolocating bats must negotiate a wealth of sounds during navigation and foraging. They must detect relatively rare but behaviorally relevant echoes and segregate them from many unimportant background echoes. For this, the bat's auditory system might rely on neural deviance detection-a process influencing the excitability of a neuron depending on the frequency of occurrence of a stimulus. To investigate neural deviance detection in the auditory cortex (AC) of anesthetized bats (Phyllostomus discolor), we designed sequences of repetitive virtual echoes differing in the spectrotemporal envelope, resembling those that bats might perceive in their natural environment. A standard echo was repeatedly played 10 times in these sequences, followed by a deviant echo at the end. Time intervals between echoes within the sequences varied. Our results show that neurons in the AC of the bat P. discolor are sensitive to novel virtual echoes presented at the end of these repetitive sequences: In 49% (62/126) of cortical neurons, extracellularly recorded responses adapted to the standard echo but showed a strong response to the deviant echo presented at the end. This effect depended strongly on the time intervals between echoes, with stronger adaptation at shorter intervals. This type of response might indicate a form of neuronal deviance detection mechanism in the AC that could help the bats to detect echoes of novel and potentially important objects within a stream of homogeneous background echoes.NEW & NOTEWORTHY In this study, we show that neurons in the auditory cortex of the bat Phyllostomus discolor are sensitive to novel acoustic stimuli in the context of repetitive virtual echo sequences differing in spectrotemporal envelope. This represents a form of neuronal deviance detection that might help the bats to detect echoes of rare but relevant objects among the clutter.

Quantification of mitral regurgitation after transcatheter edge-to-edge repair: Comparison of echocardiography and patient-specific in silico models

BackgroundDoppler echocardiographic (echo) assessment of residual mitral regurgitation (MR) after transcatheter edge-to-edge repair (TEER) is challenging and often subjective. This study aimed to evaluate the accuracy and feasibility of standardized quantitative echo methods for assessment of MR severity after MitraClip repair by comparing measurements against a reference MR severity obtained from patient-specific in silico models. MethodsPost-procedure hemodynamics were simulated under five different MitraClip configurations in previously validated patient-specific in silico models for the treatment of functional MR. The residual regurgitant volume was calculated as in clinical practice using four quantitative virtual echo methods: pulsed Doppler, volumetric, proximal isovelocity surface area (PISA) and vena contracta area (VCA). Multiple permutations were performed for each method. Virtual echo MR results were evaluated against reference MR values directly extracted from the 5 patient-specific in silico models. ResultsThe echo methods with the greatest accuracy were the three-dimensional (3D) volumetric method (r = 0.957, bias −0.8 ± 1.2 ml, p = 0.01), the 3D VCA method wherein velocity time integrals were evaluated for each jet assessed (r = 0.919, bias −1.5 ± 1.7 ml, p = 0.03), and the 3D PISA method integrating surface areas throughout systole (r = 0.98, bias −2.0 ± 0.9 ml, p = 0.003). The pulsed Doppler and 2D volumetric methods had technical limitations that may result in a high underestimation or overestimation of the MR severity after TEER. In the case of multiple regurgitant jets, a more accurate MR assessment was obtained when all significant jets were evaluated. ConclusionsClinically, the 3D volumetric, 3D VCA and 3D PISA methods gave the most accurate MR quantification after TEER. Three-dimensional echo technologies harbor the potential of becoming the non-invasive imaging tool of choice for MR quantification after complex transcatheter mitral interventions.

ECHO Autism: Early Intervention Connecting Community Professionals to Increase Access to Best Practice Autism Intervention.

Autism spectrum disorder (ASD) is estimated to affect 1 in 44 children in the United States. Disparities exist related to socioeconomic, racial/ethnic and geographic demographics. Due to the shortages of autism specialists in diagnosis, treatment and education for people with ASD, novel approaches to improve access to best practices are needed to ensure quality services. ECHO Autism: Early Intervention clinic consists of biweekly sessions focused on early identification and management of evidence-based practices for young children with ASD. It is an adaptation of the ECHO Autism clinic that has been proven effective for primary care providers. The clinic provides a safe, virtual learning environment where diverse professionals who work with children at risk or diagnosed with ASD can collaborate and learn together. ECHO Autism: Early Intervention bridges the care gap between autism specialists, community intervention providers, and children with autism to increase capacity for autism intervention best practices in underserved communities. Through participation in this convenient, web-based small group, the providers get specific case guidance on children at risk or diagnosed with autism and share best practices for autism specific interventions. Finally, the clinic connects participants with community resources, and family/caregiver support. In our article, we address the current challenge of access to quality early intervention specific to ASD in rural and underserved communities and how this issue can be addressed through a virtual ECHO Autism clinic. The aim of this concept article is to describe the innovative ECHO Autism: Early Intervention clinic and discuss its benefits and impact in the field.

Horseshoe bats use not changes in echo delay but Doppler shift to perceive approaching objects

Echolocating bats use echo delay for target ranging and Doppler shift information for relative velocity recognition. However, how they perceive moving objects remains unclear. To investigate this question, we played back echolocation pulses in real-time as virtual echoes to Japanese horseshoe bats (Rhinolophus ferrumequinum nippon) on a perch in a flight room. Since echoes coming back from an approaching object are theoretically characterized by both changes in echo delay and the presence of Doppler shift, we reproduced an artificial approaching object by encoding these two acoustic parameters in the virtual echoes. As a result, only Doppler shift evoked bats flight reaction, showing that they use only Doppler shift and not change in echo delay to perceive approaching objects. Also, we played back only constant frequency (CF) component and confirmed that they use the CF component to detect Doppler shift. Furthermore, as a response to the Doppler shift in the perceived echo, bats increased the bandwidth of the terminal component of their pulse. Surprisingly, this response occurred in the very first pulse after Doppler shift, which indicates bats can adapt their echolocation pulse characteristics to changing situations within a pulse. [This work was supported by JSPS KAKENHI Grant Nos. 18H03786 and 16H06542.]

Amplitude discrimination is predictably affected by echo frequency filtering in wideband echolocating bats.

Big brown bats echolocate using wideband frequency-modulated (FM) ultrasonic pulses, perceiving target range from echo delay and target size from echo amplitude. Echolocation pulses contain two prominent down-sweeping harmonics (FM1, ∼55-22 kHz; FM2, ∼100-55 kHz), which are affected differently by propagation to the target and back to the bat. Previous work demonstrates that big brown bats utilize the low frequencies in FM1 for target ranging, while FM2 only contributes if FM1 is also present. The present experiments test the hypothesis that the bat's ability to discriminate echo amplitude is also affected by selectively attenuating FM1 or FM2 in target or nontarget echoes. Bats were trained to perform an amplitude discrimination task with virtual echo targets located 83 cm away. Echo delay was fixed and echo amplitude was varied, while either FM1 or FM2 was attenuated by highpass or lowpass filtering. Bats' performance decreased when lower frequencies were attenuated in target echoes and when higher frequencies were attenuated in nontarget echoes. Performance was reversed in the opposite filtering conditions. The bat's ability to distinguish between virtual targets varying in amplitude at the same simulated range indicates a high level of focused attention for perceptual isolation of target from non-target echoes.

Twentieth Century Sociological Intimations, Twenty-First Century Contradictions: Neutralizing Racism and Reclaiming Whiteness

In the virtual echo chamber of 21st-century social media, the replacement of primary social bonds with virtual secondary bonds has led to violence and death in the real world. Due to ideological demagoguery and acceptance of violence in far-right-wing groups, imaginary realms in cyber-space have become sites from which terroristic acts flow into non-virtual life. Sociological theory from the past century predicts the current situation and fosters an understanding of how such technology leads to concentrations of racist ideologies and a reversal of Enlightenment values. Twentyfirst-century research suggests that those who commit race-driven violence against civil society perceive their actions as non-deviant and necessary.

Multi-echo gradient-recalled-echo phase unwrapping using a Nyquist sampled virtual echo train in the presence of high-field gradients.

To develop a spatio-temporal approach to accurately unwrap multi-echo gradient-recalled echo phase in the presence of high-field gradients. Using the virtual echo-based Nyquist sampled (VENyS) algorithm, the temporal unwrapping procedure is modified by introduction of one or more virtual echoes between the first lower and the immediate higher echo, so as to reinstate the Nyquist condition at locations with high-field gradients. An iterative extension of the VENyS algorithm maintains spatial continuity by adjusting the phase rotations to make the neighborhood phase differences less than π. The algorithm is evaluated using simulated data, Gadolinium contrast-doped phantom, and in vivo brain, abdomen, and chest data sets acquired at 3 T and 9.4 T. The unwrapping performance is compared with the standard temporal unwrapping algorithm used in the morphology-enabled dipole inversion-QSM pipeline as a benchmark for validation. Quantitative evaluation using numerical phantom showed significant reduction in unwrapping errors in regions of large field gradients, and the unwrapped phase revealed an exact match with the linear concentration profile of vials in a gadolinium contrast-doped phantom data acquired at 9.4 T. Without the need for additional spatial unwrapping, the iterative VENyS algorithm was able to generate spatially continuous phase images. Application to in vivo data resulted in better unwrapping performance, especially in regions with large susceptibility changes such as the air/tissue interface. The iterative VENyS algorithm serves as a robust unwrapping method for multi-echo gradient-recalled echo phase in the presence of high-field gradients.

Two-dimensional shape discrimination by sighted people using simulated virtual echoes.

In this study, a new research method using psychoacoustic experiments and acoustic simulations is proposed for human echolocation research. A shape discrimination experiment was conducted for sighted people using pitch-converted virtual echoes from targets of dissimilar two-dimensional (2D) shapes. These echoes were simulated using a three-dimensional acoustic simulation based on a finite-difference time-domain method from Bossy, Talmat, and Laugier [(2004). J. Acoust. Soc. Am. 115, 2314-2324]. The experimental and simulation results suggest that the echo timbre and pitch determined based on the sound interference may be effective acoustic cues for 2D shape discrimination. The newly developed research method may lead to more efficient future studies of human echolocation.

Software for reconstruction of nonuniformly sampled NMR data.

Nonuniform sampling (NUS) of multidimensional NMR experiments is a powerful tool to obtain high-resolution spectra with less instrument time. With NUS, only a subset of the points needed for conventional Fourier transformation is recorded, and sophisticated algorithms are needed to reconstruct the missing data points. During the last decade, several software packages implementing the reconstruction algorithms have emerged and been refined and now result in spectra of almost similar quality as spectra from conventionally recorded and processed data. However, from the number of literature references to the reconstruction methods, many more multidimensional NMR spectra could presumably be recorded with NUS. To help researchers considering to start using NUS for their NMR experiments, we here review 13 different reconstruction methods found in five software packages (CambridgeCS, hmsIST, MddNMR, NESTA-NMR, and SMILE). We have compared how the methods run with the provided example scripts for reconstructing a nonuniform sampled three-dimensional 15 N-NOESY-HSQC at sampling densities from 5% to 50%. Overall, the spectra are all of similar quality above 20% sampling density. Thus, without any particular knowledge about the details of the reconstruction algorithms, significant reduction in the experiment time can be achieved. Below 20% sampling density, the intensities of particular weak peaks start being affected. MddNMR's IST with virtual echo and the SMILE algorithms still reproduced the spectra with the highest accuracy of peak intensities.

Using ECHO Clinics to Promote Capacity Building in Clinical Supervision

Project Extension for Community Healthcare Outcomes (ECHO™) is a hub-and-spoke knowledge-sharing network, led by expert teams who use multipoint videoconferencing to conduct virtual clinics with community providers in order to improve the quality of care. For this project, members of the Addiction Technology Transfer Center network applied this model in order to enhance workforce capacity to deliver clinical supervision for the treatment of substance use disorders. Clinical supervisors (n=66) employed in substance use disorder treatment programs were recruited to participate in this pilot study. The virtual ECHO clinic consisted of 12 total sessions, each lasting 1 hour and comprising a 15-minute mini-lecture on a clinical supervision topic and a 45-minute case presentation and review. All data were collected and analyzed between September 2016 and June 2017. Forty-eight staff attended at least one ECHO session (mean=6.38) and results are presented for 20 staff who completed the follow-up survey. Participants were highly satisfied with the overall intervention, organization of the clinic and the facilitation of Hub experts, relevance of the technical assistance to their work, and with the impact of the intervention on their effectiveness as a supervisor. Results also indicate that there were significant self-reported improvements in clinical supervision self-efficacy following participation in the ECHO clinic. Results from this pilot study suggest that ECHO virtual clinics are feasible to implement for the purpose of workforce development, are well liked by participants, and can enhance clinical supervision self-efficacy among participants. Further research should explore the impact of self-efficacy on the effective implementation of clinical supervision practices. This article is part of a supplement entitled The Behavioral Health Workforce: Planning, Practice, and Preparation, which is sponsored by the Substance Abuse and Mental Health Services Administration and the Health Resources and Services Administration of the U.S. Department of Health and Human Services.

Social media echo chambers and satisfaction with democracy among Democrats and Republicans in the aftermath of the 2016 US elections

ABSTRACTThere is widespread evidence that individuals select information that supports their convictions and worldviews. This behavior yields the formation of echo chambers – environments in which an individual’s own political beliefs are repeated and amplified and dissenting opinions are screened out. Recent research demonstrates that social networking sites such as Facebook or Twitter can facilitate this selection into homogenous networks. Using data from a representative nation-wide online survey, we consider the degree to which respondents’ social media networks resemble virtual echo chambers. We then analyze the effect of these social media echo chambers on satisfaction with democracy among Democrats and Republicans in the aftermath of the 2016 US elections. Our findings reveal that virtual echo chambers boost democratic satisfaction among Republicans but they do not have an effect on system support by self-identified Democrats. Our paper therefore adds to a growing literature linking online behaviors to mass attitudes about politics.

Impact mitigation in layered polymeric structures

Impact mitigation in layered polymeric structures is studied to quantify the importance of impact impedance mismatch and energy dissipation modes on the overall transmission of a pressure wave. Internal reflection within the laminate structure is enhanced by optimizing the impedance between the laminate layers creating a virtual echo chamber for the impact wave. The high internal reflection potential of the structure enhances the residence of the energy within an energy dissipating viscoelastic layer. All the laminates of this research are composed of commonly available polymeric materials. A novel approach to measurement employs a Newton's cradle to correctly and accurately account for all input and output energies. As much as 90% of the theoretical transferrable energy can be dissipated by this mechanism. Statistical analysis of transmission and dissipation data shows that dissipative modes are of primary importance for mitigating impact forces, while other factors are of secondary importance. The most significant model is obtained when both dissipation and impedance are accounted for. The effect of increasing internal reflection within the dissipative structure results in the most significant variable for energy dissipation and transmission being the dissipative potential of a viscoelastic layer as determined from its tan-δ envelope. A dynamic finite element analysis technique has also been developed that models the time evolution of energy within the laminate structure following an idealized impact, and verifies the experimental results.

Personality traits and echo chambers on facebook

In online social networks, users tend to select information that adhere to their system of beliefs and to form polarized groups of like minded people. Polarization as well as its effects on online social interactions have been extensively investigated. Still, the relation between group formation and personality traits remains unclear. A better understanding of the cognitive and psychological determinants of online social dynamics might help to design more efficient communication strategies and to challenge the digital misinformation threat. In this work, we focus on users commenting posts published by US Facebook pages supporting scientific and conspiracy-like narratives, and we classify the personality traits of those users according to their online behavior. We show that different and conflicting communities are populated by users showing similar psychological profiles, and that the dominant personality model is the same in both scientific and conspiracy echo chambers. Moreover, we observe that the permanence within echo chambers slightly shapes users' psychological profiles. Our results suggest that the presence of specific personality traits in individuals lead to their considerable involvement in supporting narratives inside virtual echo chambers.

T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging.

A new acquisition and reconstruction method called T2 Shuffling is presented for volumetric fast spin-echo (three-dimensional [3D] FSE) imaging. T2 Shuffling reduces blurring and recovers many images at multiple T2 contrasts from a single acquisition at clinically feasible scan times (6-7 min). The parallel imaging forward model is modified to account for temporal signal relaxation during the echo train. Scan efficiency is improved by acquiring data during the transient signal decay and by increasing echo train lengths without loss in signal-to-noise ratio (SNR). By (1) randomly shuffling the phase encode view ordering, (2) constraining the temporal signal evolution to a low-dimensional subspace, and (3) promoting spatio-temporal correlations through locally low rank regularization, a time series of virtual echo time images is recovered from a single scan. A convex formulation is presented that is robust to partial voluming and radiofrequency field inhomogeneity. Retrospective undersampling and in vivo scans confirm the increase in sharpness afforded by T2 Shuffling. Multiple image contrasts are recovered and used to highlight pathology in pediatric patients. A proof-of-principle method is integrated into a clinical musculoskeletal imaging workflow. The proposed T2 Shuffling method improves the diagnostic utility of 3D FSE by reducing blurring and producing multiple image contrasts from a single scan. Magn Reson Med 77:180-195, 2017. © 2016 Wiley Periodicals, Inc.

Aural localization of silent objects by active human biosonar: neural representations of virtual echo-acoustic space.

Some blind humans have developed the remarkable ability to detect and localize objects through the auditory analysis of self-generated tongue clicks. These echolocation experts show a corresponding increase in 'visual' cortex activity when listening to echo-acoustic sounds. Echolocation in real-life settings involves multiple reflections as well as active sound production, neither of which has been systematically addressed. We developed a virtualization technique that allows participants to actively perform such biosonar tasks in virtual echo-acoustic space during magnetic resonance imaging (MRI). Tongue clicks, emitted in the MRI scanner, are picked up by a microphone, convolved in real time with the binaural impulse responses of a virtual space, and presented via headphones as virtual echoes. In this manner, we investigated the brain activity during active echo-acoustic localization tasks. Our data show that, in blind echolocation experts, activations in the calcarine cortex are dramatically enhanced when a single reflector is introduced into otherwise anechoic virtual space. A pattern-classification analysis revealed that, in the blind, calcarine cortex activation patterns could discriminate left-side from right-side reflectors. This was found in both blind experts, but the effect was significant for only one of them. In sighted controls, 'visual' cortex activations were insignificant, but activation patterns in the planum temporale were sufficient to discriminate left-side from right-side reflectors. Our data suggest that blind and echolocation-trained, sighted subjects may recruit different neural substrates for the same active-echolocation task.

Biosonar resolving power: echo-acoustic perception of surface structures in the submillimeter range

The minimum distance for which two points still can be separated from each other defines the resolving power of a visual system. In an echo-acoustic context, the resolving power is usually measured as the smallest perceivable distance of two reflecting surfaces on the range axis and is found to be around half a millimeter for bats employing frequency modulated (FM) echolocation calls. Only few studies measured such thresholds with physical objects, most often bats were trained on virtual echoes i.e., echoes generated and played back by a computer; moreover, bats were sitting while they received the stimuli. In these studies differences in structure depth between 200 and 340 μm were found. However, these low thresholds were never verified for free-flying bats and real physical objects. Here, we show behavioral evidence that the echo-acoustic resolving power for surface structures in fact can be as low as measured for computer generated echoes and even lower, sometimes below 100 μm. We found this exceptional fine discrimination ability only when one of the targets showed spectral interferences in the frequency range of the bats′ echolocation call while the other target did not. This result indicates that surface structure is likely to be perceived as a spectral quality rather than being perceived strictly in the time domain. Further, it points out that sonar resolving power directly depends on the highest frequency/shortest wavelength of the signal employed.

Virtual-Echo Projection Method for Suppression of Noise in UWB-SAR Imaging Systems

The conventional time-domain back-projection (BP) imaging method typically suffers from performance degradation when the echo signals are interfered by noise. In this letter, a virtual-echo projection imaging method is proposed for noise suppression, including the suppression of the additive white Gaussian noise and the irrelevant colored noise. First, the proposed method calculates a number of coarse imaging maps by projecting the realistic echoes on the virtual echoes. Second, the fine imaging maps are calculated by accumulating all the coarse imaging maps coherently. The performance of the proposed method is numerically investigated in comparison to that of the traditional BP method. The results indicate that the proposed method outperforms the conventional BP method in suppressing both the additive white Gaussian noise and the colored noise.

Bats’ avoidance of real and virtual objects: Implications for the sonar coding of object size

Fast movement in complex environments requires the controlled evasion of obstacles. Sonar-based obstacle evasion involves analysing the acoustic features of object-echoes (e.g., echo amplitude) that correlate with this object's physical features (e.g., object size). Here, we investigated sonar-based obstacle evasion in bats emerging in groups from their day roost. Using video-recordings, we first show that the bats evaded a small real object (ultrasonic loudspeaker) despite the familiar flight situation. Secondly, we studied the sonar coding of object size by adding a larger virtual object. The virtual object echo was generated by real-time convolution of the bats' calls with the acoustic impulse response of a large spherical disc and played from the loudspeaker. Contrary to the real object, the virtual object did not elicit evasive flight, despite the spectro-temporal similarity of real and virtual object echoes. Yet, their spatial echo features differ: virtual object echoes lack the spread of angles of incidence from which the echoes of large objects arrive at a bat's ears (sonar aperture). We hypothesise that this mismatch of spectro-temporal and spatial echo features caused the lack of virtual object evasion and suggest that the sonar aperture of object echoscapes contributes to the sonar coding of object size.