Stéphanie Bertet

Auditory and visual 3D virtual reality therapy for chronic subjective tinnitus: theoretical framework

It is estimated that ~10% of the adult population in developed countries is affected by subjective tinnitus. Physiopathology of subjective tinnitus remains incompletely explained. Nevertheless, subjective tinnitus is thought to result from hyperactivity and neuroplastic reorganization of cortical and subcortical networks following acoustic deafferentation induced by cochlear or auditory nerve damage. Involvement of both auditory and non-auditory central nervous pathways explains the conscious perception of tinnitus and also the potentially incapacitating discomfort experienced by some patients (sound hypersensitivity, sleep disorders, attention deficit, anxiety or depression). These clinical patterns are similar to those observed in chronic pain following amputation where conditioning techniques using virtual reality have been shown both to be theoretically interesting and effectively useful. This analogy led us to develop an innovative setup with dedicated auditory and visual 3D virtual reality environments in which unilateral subjective tinnitus sufferers are given the possibility to voluntarily manipulate an auditory and visual image of their tinnitus (tinnitus avatar). By doing so, the patients will be able to transfer their subjective auditory perception to the tinnitus avatar and to gain agency on this multimodal virtual percept they hear, see and spatially control. Repeated sessions of such virtual reality immersions are then supposed to contribute to tinnitus treatment by promoting cerebral plasticity. This paper describes the theoretical framework and setup adjustments required by this very first attempt to adapt virtual reality techniques to subjective tinnitus treatment. Therapeutic usefulness will be validated by a further controlled clinical trial.

Investigation on localisation accuracy for first and higher order ambisonics reproduced sound sources

Ambisonics and higher order ambisonics (HOA) technologies aim at reproducing sound field either synthesised or previously recorded with dedicated microphones. Based on a spherical harmonic decomposition, the sound field is more precisely described when higher-order components are used. The presented study evaluated the perceptual and objective localisation accuracy of the sound field encoded with four microphones of order one to four and decoded over a ring of loudspeakers. A perceptual test showed an improvement of the localisation with higher order ambisonic microphones. Reproduced localisation indices were estimated for the four microphones and the respective synthetic systems of order one to four. The perceptual and objective analysis revealed the same conclusions. The localisation accuracy depends on the ambisonic order as well as the source incidence. Furthermore, impairments linked to the microphones were highlighted.

Investigation on the restitution system influence over perceived Higher Order Ambisonics sound field: a subjective evaluation involving from first to fourth order systems

Among the spatial audio reproduction techniques over loudspeakers, the Higher Order Ambisonics (HOA) approach is based on a sound field spherical harmonics decomposition. By truncating the decomposition to the Mth order, it remains a finite number of components that form the spatial HOA format. The more components are used to encode the sound field, the finer the spatial resolution is. Similarly, the size of the area where the sound field is accurately recreated is proportional to the order. For an Mth encoding order, N=2M+2 equally distributed loudspeakers are recommended for a homogeneous reproduction in the horizontal plane. Adding loudspeakers does not change the spatial resolution. However, what is the influence of the restitution system on the perceived sound field? An experiment was designed in order to compare four systems (from first to fourth order) and a reference one, using similarity ratings obtained from pairwise comparisons. Two sound scenes were used, simulating an audio conference and a s...

Off-Centre Localisation Performance of Ambisonics and HOA For Large and Small Loudspeaker Array Radii

Ambisonics and Higher Order Ambisonics (HOA) are scalable spatial audio techniques that attempt to present a sound scene to listeners over as large an area as possible. A localisation experiment was carried out to investigate the performance of a first and third order system at three listening positions one in the centre and two off-centre using a 5 m radius loudspeaker array. The results are briefly presented and compared to those of an earlier experiment on a 2.2 m loudspeaker array. In both experiments the off-centre listeners were placed such that the ratio of distance from the centre to the array radius was constant in both experiments. The test used a reverse target-pointer adjustment method to determine the error, both signed and absolute, for each combination of listening position and system. The results for both arrays were found to be very similar, suggesting that the relative amplitude of the loudspeakers, which were the same in both cases, was more dominant for localisation than the arrival time differences, which differed between array sizes.