A self-training program for sensory substitution devices

Correction: A self-training program for sensory substitution devices

[This corrects the article DOI: 10.1371/journal.pone.0250281.].

Cross-modal correspondence enhances elevation localization in visual-to-auditory sensory substitution

Introduction

Visual-to-auditory sensory substitution devices are assistive devices for the blind that convert visual images into auditory images (or soundscapes) by mapping visual features with acoustic cues. To convey spatial information with sounds, several sensory substitution devices use a Virtual Acoustic Space (VAS) using Head Related Transfer Functions (HRTFs) to synthesize natural acoustic cues used for sound localization. However, the perception of the elevation is known to be inaccurate with generic spatialization since it is based on notches in the audio spectrum that are specific to each individual. Another method used to convey elevation information is based on the audiovisual cross-modal correspondence between pitch and visual elevation. The main drawback of this second method is caused by the limitation of the ability to perceive elevation through HRTFs due to the spectral narrowband of the sounds.

Method

In this study we compared the early ability to localize objects with a visual-to-auditory sensory substitution device where elevation is either conveyed using a spatialization-based only method (Noise encoding) or using pitch-based methods with different spectral complexities (Monotonic and Harmonic encodings). Thirty eight blindfolded participants had to localize a virtual target using soundscapes before and after having been familiarized with the visual-to-auditory encodings.

Results

Participants were more accurate to localize elevation with pitch-based encodings than with the spatialization-based only method. Only slight differences in azimuth localization performance were found between the encodings.

Discussion

This study suggests the intuitiveness of a pitch-based encoding with a facilitation effect of the cross-modal correspondence when a non-individualized sound spatialization is used.

Shape detection beyond the visual field using a visual-to-auditory sensory augmentation device

Current advancements in both technology and science allow us to manipulate our sensory modalities in new and unexpected ways. In the present study, we explore the potential of expanding what we perceive through our natural senses by utilizing a visual-to-auditory sensory substitution device (SSD), the EyeMusic, an algorithm that converts images to sound. The EyeMusic was initially developed to allow blind individuals to create a spatial representation of information arriving from a video feed at a slow sampling rate. In this study, we aimed to use the EyeMusic for the blind areas of sighted individuals. We use it in this initial proof-of-concept study to test the ability of sighted subjects to combine visual information with surrounding auditory sonification representing visual information. Participants in this study were tasked with recognizing and adequately placing the stimuli, using sound to represent the areas outside the standard human visual field. As such, the participants were asked to report shapes' identities as well as their spatial orientation (front/right/back/left), requiring combined visual (90° frontal) and auditory input (the remaining 270°) for the successful performance of the task (content in both vision and audition was presented in a sweeping clockwise motion around the participant). We found that participants were successful at a highly above chance level after a brief 1-h-long session of online training and one on-site training session of an average of 20 min. They could even draw a 2D representation of this image in some cases. Participants could also generalize, recognizing new shapes they were not explicitly trained on. Our findings provide an initial proof of concept indicating that sensory augmentation devices and techniques can potentially be used in combination with natural sensory information in order to expand the natural fields of sensory perception.

A case study in phenomenology of visual experience with retinal prosthesis versus visual-to-auditory sensory substitution

The phenomenology of the blind has provided an age-old, unparalleled means of exploring the enigmatic link between the brain and mind. This paper delves into the unique phenomenological experience of a man who became blind in adulthood. He subsequently underwent both an Argus II retinal prosthesis implant and training, and extensive training on the EyeMusic visual to auditory sensory substitution device (SSD), thereby becoming the first reported case to date of dual proficiency with both devices. He offers a firsthand account into what he considers the great potential of combining sensory substitution devices with visual prostheses as part of a complete visual restoration protocol. While the Argus II retinal prosthesis alone provided him with immediate visual percepts by way of electrically stimulated phosphenes elicited by the device, the EyeMusic SSD requires extensive training from the onset. Yet following the extensive training program with the EyeMusic sensory substitution device, our subject reports that the sensory substitution device allowed him to experience a richer, more complex perceptual experience, that felt more "second nature" to him, while the Argus II prosthesis (which also requires training) did not allow him to achieve the same levels of automaticity and transparency. Following long-term use of the EyeMusic SSD, our subject reported that visual percepts representing mainly, but not limited to, colors portrayed by the EyeMusic SSD are elicited in association with auditory stimuli, indicating the acquisition of a high level of automaticity. Finally, the case study indicates an additive benefit to the combination of both devices on the user's subjective phenomenological visual experience.

Multi-Sensory Color Code Based on Sound and Scent for Visual Art Appreciation

The development of assistive technologies is improving the independent access of blind and visually impaired people to visual artworks through non-visual channels. Current single modality tactile and auditory approaches to communicate color contents must compromise between conveying a broad color palette, ease of learning, and suffer from limited expressiveness. In this work, we propose a multi-sensory color code system that uses sound and scent to represent colors. Melodies express each color’s hue and scents the saturated, light, and dark color dimensions for each hue. In collaboration with eighteen participants, we evaluated the color identification rate achieved when using the multi-sensory approach. Seven (39%) of the participants improved their identification rate, five (28%) remained the same, and six (33%) performed worse when compared to an audio-only color code alternative. The participants then evaluated and compared a color content exploration prototype that uses the proposed color code with a tactile graphic equivalent using the System Usability Scale. For a visual artwork color exploration task, the multi-sensory color code integrated prototype received a score of 78.61, while the tactile graphics equivalent received 61.53. User feedback indicates that the multi-sensory color code system improved the convenience and confidence of the participants.