On chirp stimuli and neural synchrony in the suprathreshold auditory brainstem response

The chirp-evoked ABR has been regarded as a more synchronous response than the click-evoked ABR, referring to the belief that the chirp stimulates lower-, mid-, and higher-frequency regions of the cochlea simultaneously. In this study a variety of tools were used to analyze the synchronicity of ABRs evoked by chirp- and click-stimuli at 40 dB HL in 32 normal hearing subjects aged 18 to 55 years (mean=24.8 years, SD=7.1 years). Compared to the click-evoked ABRs, the chirp-evoked ABRs showed larger wave V amplitudes, but an absence of earlier waves in the grand averages, larger wave V latency variance, smaller FFT magnitudes at the higher component frequencies, and larger phase variance at the higher component frequencies. These results strongly suggest that the chirp-evoked ABRs exhibited less synchrony than the click-evoked ABRs in this study. It is proposed that the temporal compensation offered by chirp stimuli is sufficient to increase neural recruitment (as measured by wave V amplitude), but that destructive phase interactions still exist along the cochlea partition, particularly in the low frequency portions of the cochlea where more latency jitter is expected. The clinical implications of these findings are discussed. (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3436527

Use of a non-linear algorithm to improve the maximum length sequence auditory brainstem response

Background: The auditory brainstem response (ABR) is the most preferred tool in Universal Newborn Hearing Screening (UNHS) because of its high sensitivity and specificity and its ability to detect abnormalities up to auditory nerve. However, the testing time is considerably long does increase the cost of running UNHS. One of the possible techniques to shorten the ABR testing time is by using high stimulus repetition rate through linear Maximum Length Sequence (lMLS). This algorithm has been reported to have poor signal to noise ratio thus increase the testing time. The present study has developed a new non linear MLS (nlMLS) which aims to overcome the mismatch between the non-linearity of the auditory system and the linearity aspect of the algorithm. Aim This study is aimed to investigate the effect of using the novel nonlinear MLS (nlMLS) to the ABR results in newborn subjects. Methodology 30 newborn subjects whom passed the UNHS were involved in this study. ABR were recorded using MLS using both linear and non linear reconstruction at 180, 250, 500 and 836 cps using a custom built evoked potential system. In addition, the ABR was recorded using vertical electrode montage (non-inverting: high forehead, inverting: nape of neck and ground: shoulder). Next, the wave V amplitude and signal to noise ratio (SNR) were calculated for each ABR. The ABR wave V amplitude was calculated from the peak of wave V to the following trough while SNR was derived from variance ratio at single point (Fsp) formula. MLS ABR were recorded using order 6 with 160 trains for 180 cps, 240 trains for 250 cps, 280 trains for 500 cps and 320 trains for 836 cps. Results Results show that the nlMLS has significantly higher amplitude and better SNR value than ABR recorded with lMLS (RM ANOVA, p<0.05) at the same stimulus repetition rate. The amplitude of wave V value increase from 13.3 to 53.6% when changing from lMLS to nlMLS with the maximum increment observed in MLS ABR at 500 cps. The SNR increase from 19.8 to 63 % when changing from lMLS to nlMLS with the maximum increment observed in MLS ABR at 500 cps. Conclusion With these results, nonlinear algorithm is considered as a good tool to be applied in ABR recording in particular for UNHS as it can improve the SNR, amplitude and further more can save the recording tim

An update on retinal prostheses

Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cortex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration. There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included conjunctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely. Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a complex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field

Enhancing object contrast using augmented depth improves mobility in patients implanted with a retinal prosthesis

Purpose: Prosthetic vision shows promise for improving performance in orientation and mobility tasks. To date, prosthetic vision research has occurred mainly in high-contrast (e.g., black/white) environments with limited investigation of performance in environments with low contrast. In retinal implants, vision processing is critical for scene understanding including detecting objects of low contrast with their environment, and ensuring their visibility. The ability to detect objects that are poorly contrasted is impaired with the state-of-the-art vision processing, i.e., Intensity-based visual representations. We evaluated the effectiveness of an Augmented Depth-based vision processing algorithm (ADVP) compared to Intensity-based vision processing (IVP) and System Off (SO) for avoiding low-contrast trip hazards in retinal prosthetic vision. Methods: Two participants with profound vision loss (bare light perception) due to retinitis pigmentosa who were implanted with a 24-channel retinal prosthesis (400 or 600 &amp;#0956;m diameter) into the suprachoroidal space.&amp;lt;br /&amp;gt; &amp;lt;br /&amp;gt; Participants traversed a straight corridor (2.2 x 7.5 meters; dark floor, white walls) with dark ground-based obstacles that varied in number, size and placement. The presentation order was randomized for Visual Representation and the obstacle characteristics. Participants 1 and 2 completed 60 and 25 traversals,respectively, over a two-day period. The primary outcome measure was the number of contacts with the objects and walls per traversal. Results: ADVP (P1 n=21, mean=.714&amp;#0177;.784; P2 n=12, mean=1.33&amp;#0177;1.44) was associated with significantly fewer contacts than IVP (P1 n=22, mean=1.18&amp;#0177;.907, p=.025; P2 n=7, mean=3.14&amp;#0177;1.77, p=.025) and SO (P1 n=17, mean=1.76&amp;#0177;1.20, p=.002; P2 n=6, mean=6.17&amp;#0177;3.55, p=.001) for both participants. No significant difference was evident between IVP and SO in the number of collisions for either P1 (p=.237) or P2 (p=.067). Conclusions: Vision processing techniques that provide scene understanding through enhanced depth perception can improve the performance of a retinal prosthesis for detecting and avoiding low-contrast trip hazards compared to the standard Intensity-based visual representation and System Off. These findings highlight the need for robust vision processing methods in retinal prostheses especially given the display limitations of current devices

A prototype suprachoroidal retinal prosthesis enables improvement in a tabletop object detection task

Purpose: The Bionic Vision Australia consortium has been developing a suprachoroidal retinal prosthesis, which has an easily accessible surgical location, good device stability and minimal adverse events over a 2-year period. We have previously reported that this device improves light localisation and optotype recognition. The aim of this study was to investigate device efficacy using a tabletop object recognition task, which forms part of the Low Vision Assessment of Daily Activities (LoVADA) protocol. Methods: Two subjects with bare light perception from retinitis pigmentosa were implanted with a 24-channel suprachoroidal retinal prosthesis prototype. Four white household items (placemat, dinner plate, coffee mug, fork) were placed in random locations on a black table. Performance was scored by an occupational therapist, on the number of items (a) correctly identified and (b) accurately touched; results of both providing a overall performance score. Time was recorded for all assessments, and not restricted. Assessment was completed at baseline (no device), at the first ADL testing session, and again six months later. Device on and device off conditions were randomly presented. Usage of the device was restricted to the laboratory, thus limiting opportunity to learn between sessions. Results: The rate of accurate touch improved at each session with device-on. By the six-month session, one subject was able to accurately visually locate and touch 100% of the items with device on (vs. 0% with device off), whilst the other subject touched 75% with device on and 25% with device off. However, subjects were not able to reliably identify the household items by name. The task took more time to complete with the device on (average 4.5 minutes) vs. device off (average 2 mins) & baseline (average 42 seconds). Conclusions: The prosthesis improved the ability to visually locate and touch tabletop items. Whilst not able to name items, subjects believed they would be able to better interpret the information with more practice and training. These results are consistent with other retinal prosthesis groups, and show that the suprachoroidal implant can provide useful visual information in a static real world setting. Clinical testing of a second generation 'take-home' device is planned, where it is anticipated that functional outcomes will be improved through increased experience with the device and neuroplasticity

Preliminary results of the bionic vision australia suprachoroidal visual prosthesis pilot trial

Purpose: Visual prostheses have been shown to be efficacious in the restoration of basic visual percepts to patients with profound vision loss from retinitis pigmentosa (RP). Previous implants have been located in either the epiretinal, subretinal or intra-scleral spaces of the eye. Bionic Vision Australia has conducted a pilot clinical trial of a novel suprachoroidal implant. The purpose of this study was to evaluate the stability, safety and basic efficacy of the device. Methods: Three subjects with end-stage retinitis pigmentosa (bare light perception) were implanted with a prototype silicone and platinum suprachoroidal array containing 20 stimulating electrodes, which could be directly stimulated via a percutaneous connector. Intraocular array position was monitored over an 18-month period with weekly fundus photography and optical coherence tomography (OCT) scans. Lead wire and percutaneous connector stability were monitored using monthly X-ray and biannual computerized tomography (CT) imaging. Device efficacy was assessed using psychophysical methods, and assessment of performance in basic visual function tests such as the Basic Assessment of Light and Motion (BaLM), Berkeley Rudimentary Vision Test (BRVT), tumbling E and Landolt C tests. Results: From image analysis, both the intraocular array and extraocular connections remained in a stable position with respect to anatomical landmarks in the retinal plane. There was no damage to the devices, and the only device-related serious adverse events related to superficial skin infection around the percutaneous connector, which settled with topical or systemic antibiotics and no intraocular sequelae. All electrodes remained connected during the 18-month period. All three subjects perceived phosphene percepts, although there were significant differences in optimal stimulation parameters between them. All patients performed better with the device on than off for the laboratory based visual function tests, including achieving scores of between 72% and 100% on the light localisation subtest of the BaLM when the device was on. Conclusions: The suprachoroidal implant location is safe and provides excellent device stability. Visual function test performance was improved with device on vs. device off. As device efficacy and longevity is dependent on a stable electrode-tissue interface, suprachoroidal implantation appears a promising option for visual prostheses