Vibrotactile feedback systems are widely used in assistive technology, wearable devices, and virtual environments to deliver precise tactile information. The timing of interstimulus intervals (ISIs) plays a critical role in determining how accurately users perceive and interpret vibrotactile patterns. The optimal use of ISIs can increase the effectiveness of these systems, improve user interaction, and enable reliable, intuitive feedback in diverse applications. We examined how different interstimulus intervals ISIs impact the accuracy of vibrotactile pattern recognition. Participants wore a forearm-mounted device with six voice coil actuators arranged in a 3 × 2 grid, delivering Braille-based vibrotactile patterns sequentially at ISIs ranging from 10 to 2500 ms. Eight participants performed identification tasks involving Icelandic Braille patterns categorized as either short (2–3 actuators) or long (4–5 actuators). A repeated measures ANOVA was conducted to assess the effects of ISI, pattern type, and practice (across two testing blocks) on pattern recognition accuracy. For short patterns, accuracy was highest (92%–98%) at ISIs of 50–700 ms, with peak performance at 300 ms. For long patterns, accuracy reached 86%–94% at ISIs of 100–500 ms, peaking at 400 ms. Participants were more accurate with short patterns, and performance improved significantly over time for both short and long patterns, highlighting the importance of training for vibrotactile pattern recognition. These results underscore the importance of careful selection of ISIs in vibrotactile feedback systems for accurate pattern identification. The findings provide valuable insights for conveying tactile information using wearable devices, contributing to better tactile feedback and performance in applications requiring precise vibrotactile information delivery.

When two brief vibrotactile stimulations are sequentially applied to observers’ lower back, there is systematic mislocalization of the stimulation: if the second stimulation is of higher intensity than the first one, observers tend to respond that the second stimulation was above the first one, and vice versa when weak intensity stimulation follows a strong one. This haptic mislocalization effect has been called the intensity order illusion . In the original demonstration of the illusion, frequency and amplitude of the stimulation were inextricably linked so that changes in amplitude also resulted in changes in frequency. It is therefore unknown whether the illusion is caused by changes in frequency, amplitude or both. To test this, we performed a multifactorial experiment, where we used L5 actuators that allow independent manipulation of frequency and amplitude. This approach enabled us to investigate the effects of stimulus amplitude, frequency and location, and to assess any potential interactions among these factors. We report four main findings: (1) we were able to replicate the intensity order illusion with the L5 tactors; (2) the illusion mainly occurred in the upwards direction, or in other words, when strong stimulation following a weaker one occurred above or in the same location as the first stimulation; (3) the illusion did not occur when similar stimulation patterns were applied in the horizontal direction; and (4) the illusion was solely due to changes in amplitude, whereas changes in frequency (100 Hz vs 200 Hz) had no effect.

This article presents an investigation into the perceptual vibrotactile thresholds for a range of frequencies on both the inside and outside areas of the wrist when exciting the skin with parallel vibrations, realized using the L5 actuator made by Lofelt GmbH. The vibrotactile threshold of 30 participants was measured using a modified audiometry test for the frequency range of 25–1,000 Hz. The average threshold across the respective frequencies was then ultimately determined from acceleration minima. The results show that maximum sensitivity lies in the range of 100–275 Hz (peaking at 200 Hz) for the inside and 75–250 Hz (peaking at 125 Hz) for the outside of the wrist and that thresholds are overall higher for the hairy skin on the outside of the wrist than for the glabrous skin on the inside. The results also show that the vibrotactile thresholds varied highly between individuals. Hence, personalized threshold measurements at the actuator locations will be required to fine-tune a device for the user. This study is a part of an ongoing research and development project where the aim is to develop a tactile display device and a music encoding scheme with the purpose of augmenting the musical enjoyment of cochlear implant recipients. These results, along with results from planned follow-up experiments, will be used to determine the appropriate frequency range and to cast light on the dynamic range on offer for the tactile device.

While previous research on spatial sound perception investigated the physical mechanisms producing the most relevant elevation cues, how spectral notches are generated and related to the individual morphology of the human pinna is still a topic of debate. Correctly modeling these important elevation cues, and in particular the lowest frequency notches, is an essential step for individualizing Head-Related Transfer Functions (HRTFs). In this paper we propose a simple computational model able to predict the center frequencies of pinna notches from ear meshes. We apply such a model to a highly controlled HRTF dataset built with the specific purpose of understanding the contribution of the pinna to the HRTF. Results show that the computational model is able to approximate the lowest frequency notch with improved accuracy with respect to other state-of-the-art methods. By contrast, the model fails to predict higher-order pinna notches correctly. The proposed approximation supplements understanding of the morphology involved in generating spectral notches in experimental HRTFs.

Electronic travel aids (ETAs) have been in focus since technology allowed designing relatively small, light, and mobile devices for assisting the visually impaired. Since visually impaired persons rely on spatial audio cues as their primary sense of orientation, providing an accurate virtual auditory representation of the environment is essential. This paper gives an overview of the current state of spatial audio technologies that can be incorporated in ETAs, with a focus on user requirements. Most currently available ETAs either fail to address user requirements or underestimate the potential of spatial sound itself, which may explain, among other reasons, why no single ETA has gained a widespread acceptance in the blind community. We believe there is ample space for applying the technologies presented in this paper, with the aim of progressively bridging the gap between accessibility and accuracy of spatial audio in ETAs.

A novel sensory substitution algorithm based on the sonification of depth maps into physically based fluid flow sounds is described. Spatial properties are extracted from depth maps and mapped into parameters of an empirical phenomenological model of bubble statistics, which manages the generation of the corresponding synthetic fluid flow sound. Following minimal training, the proposed approach was tested in a preliminary experiment with 20 normally sighted participants and compared against the well-known vOICe sensory substitution algorithm. Although the accuracy in recognizing visual sequences based on the corresponding sonification is comparable between the two systems, an overwhelming support for the fluid sounds compared to the vOICe output in terms of pleasantness was recorded. Collected data further suggests that ample margins of performance improvement are achievable following thorough training procedures.