Speech Comprehension by Cochlear Implant Users Assessed with Evoked Potentials and Response Times.

INTRODUCTION: Cochlear implant (CI) users differ greatly in their rehabilitation outcomes, including speech understanding in noise. This variability may be related to brain changes associated with intact senses recruiting cortical areas from stimulation-deprived senses. Numerous studies have demonstrated such cross-modal reorganization in individuals with untreated hearing loss. How it is affected by regular use of hearing devices remains unclear, however. To shed light on this, the current study measured cortical responses reflecting comprehension abilities in experienced CI users and normal-hearing controls. METHODS: Using multichannel electroencephalography, we tested CI users who had used their devices for at least 12 months and closely matched controls (N = 2 × 13). Cortical responses reflecting comprehension abilities - the N400 and late positive complex (LPC) components - were evoked using congruent and incongruent digit-triplet stimuli. The participants' task was to assess digit-triplet congruency by means of timed button presses. All measurements were performed in speech-shaped noise 15 dB above individually measured speech recognition thresholds. Three stimulus presentation modes were used: auditory-only, visual-only, and visual-then-auditory. RESULTS: The analyses revealed no group differences in the N400 and LPC responses. In terms of response times, the CI users were slower and differentially affected by the three stimulus presentation modes relative to the controls. CONCLUSION: Compared to normal-hearing controls, experienced CI users may need more time to comprehend speech in noise. Response times can serve as a proxy for speech comprehension by CI users.

Does experience with hearing aid amplification influence electrophysiological measures of speech comprehension?

OBJECTIVE: To explore if experience with hearing aid (HA) amplification affects speech-evoked cortical potentials reflecting comprehension abilities. DESIGN: N400 and late positive complex (LPC) responses as well as behavioural response times to congruent and incongruent digit triplets were measured. The digits were presented against stationary speech-shaped noise 10 dB above individually measured speech recognition thresholds. Stimulus presentation was either acoustic (digits 1-3) or first visual (digits 1-2) and then acoustic (digit 3). STUDY SAMPLE: Three groups of older participants (N = 3 × 15) with (1) pure-tone average hearing thresholds <25 dB HL from 500-4000 Hz, (2) mild-to-moderate sensorineural hearing loss (SNHL) but no prior HA experience, and (3) mild-to-moderate SNHL and >2 years of HA experience. Groups 2-3 were fitted with test devices in accordance with clinical gain targets. RESULTS: No group differences were found in the electrophysiological data. N400 amplitudes were larger and LPC latencies shorter with acoustic presentation. For group 1, behavioural response times were shorter with visual-then-acoustic presentation. CONCLUSION: When speech audibility is ensured, comprehension-related electrophysiological responses appear intact in individuals with mild-to-moderate SNHL, regardless of prior experience with amplified sound. Further research into the effects of audibility versus acclimatisation-related neurophysiological changes is warranted.

Comparing Clinically Applicable Behavioral and Electrophysiological Measures of Speech Detection, Discrimination, and Comprehension.

Effective communication requires good speech perception abilities. Speech perception can be assessed with behavioral and electrophysiological methods. Relating these two types of measures to each other can provide a basis for new clinical tests. In audiological practice, speech detection and discrimination are routinely assessed, whereas comprehension-related aspects are ignored. The current study compared behavioral and electrophysiological measures of speech detection, discrimination, and comprehension. Thirty young normal-hearing native Danish speakers participated. All measurements were carried out with digits and stationary speech-shaped noise as the stimuli. The behavioral measures included speech detection thresholds (SDTs), speech recognition thresholds (SRTs), and speech comprehension scores (i.e., response times). For the electrophysiological measures, multichannel electroencephalography (EEG) recordings were performed. N100 and P300 responses were evoked using an active auditory oddball paradigm. N400 and Late Positive Complex (LPC) responses were evoked using a paradigm based on congruent and incongruent digit triplets, with the digits presented either all acoustically or first visually (digits 1-2) and then acoustically (digit 3). While no correlations between the SDTs and SRTs and the N100 and P300 responses were found, the response times were correlated with the EEG responses to the congruent and incongruent triplets. Furthermore, significant differences between the response times (but not EEG responses) obtained with auditory and visual-then-auditory stimulus presentation were observed. This pattern of results could reflect a faster recall mechanism when the first two digits are presented visually rather than acoustically. The visual-then-auditory condition may facilitate the assessment of comprehension-related processes in hard-of-hearing individuals.

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols.

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviors under elastohydrodynamic lubrication (EHL) conditions, as found inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that liquid 1-dodecanol undergoes a pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed inside the contact depending on the temperature and pressure conditions. Surprisingly, at a moderate temperature and pressure, 1-dodecanol forms a polymorph that exhibits robust macroscale superlubricity. The DAC and DSC experiments show that superlubricity is facilitated by the formation of lamellar, hydrogen-bonded structures of hexagonally close-packed molecules, which promote interlayer sliding. This novel superlubricity mechanism is similar to that proposed for the two-dimensional materials commonly employed as solid lubricants, but it also enables the practical advantages of liquid lubricants to be maintained. When the pressure is increased, 1-dodecanol undergoes a polymorphic transformation into a phase that gives a higher friction. The DAC and DSC experiments indicate that the high-friction polymorph is an orthorhombic crystal. The polymorphic transformation pressure coincides with the onset of a dimple formation in the EHL films, revealing that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. This is the first demonstration of a macroscale superlubricity in an EHL contact lubricated by a nonaqueous liquid that arises from bulk effects rather than tribochemical transformations at the surfaces. Since the superlubricity observed here results from phase transformations, it is continuously self-replenishing and is insensitive to surface chemistry and topology. This discovery creates the possibility of implementing superlubricity in a wide range of machine components, which would result in enormous improvements in efficiency and durability.