Audiovisual speech perception in cochlear implant patients

Hearing with a cochlear implant (CI) is very different compared to a normal-hearing (NH) experience, as the CI can only provide limited auditory input. Nevertheless, the central auditory system is capable of learning how to interpret such limited auditory input such that it can extract meaningful information within a few months after implant switch-on. The capacity of the auditory cortex to adapt to new auditory stimuli is an example of intra-modal plasticity — changes within a sensory cortical region as a result of altered statistics of the respective sensory input. However, hearing deprivation before implantation and restoration of hearing capacities after implantation can also induce cross-modal plasticity — changes within a sensory cortical region as a result of altered statistics of a different sensory input. Thereby, a preserved cortical region can, for example, support a deprived cortical region, as in the case of CI users which have been shown to exhibit cross-modal visual-cortex activation for purely auditory stimuli. Before implantation, during the period of hearing deprivation, CI users typically rely on additional visual cues like lip-movements for understanding speech. Therefore, it has been suggested that CI users show a pronounced binding of the auditory and visual systems, which may allow them to integrate auditory and visual speech information more efficiently. The projects included in this thesis investigate auditory, and particularly audiovisual speech processing in CI users. Four event-related potential (ERP) studies approach the matter from different perspectives, each with a distinct focus. The first project investigates how audiovisually presented syllables are processed by CI users with bilateral hearing loss compared to NH controls. Previous ERP studies employing non-linguistic stimuli and studies using different neuroimaging techniques found distinct audiovisual interactions in CI users. However, the precise timecourse of cross-modal visual-cortex recruitment and enhanced audiovisual interaction for speech related stimuli is unknown. With our ERP study we fill this gap, and we present differences in the timecourse of audiovisual interactions as well as in cortical source configurations between CI users and NH controls. The second study focuses on auditory processing in single-sided deaf (SSD) CI users. SSD CI patients experience a maximally asymmetric hearing condition, as they have a CI on one ear and a contralateral NH ear. Despite the intact ear, several behavioural studies have demonstrated a variety of beneficial effects of restoring binaural hearing, but there are only few ERP studies which investigate auditory processing in SSD CI users. Our study investigates whether the side of implantation affects auditory processing and whether auditory processing via the NH ear of SSD CI users works similarly as in NH controls. Given the distinct hearing conditions of SSD CI users, the question arises whether there are any quantifiable differences between CI user with unilateral hearing loss and bilateral hearing loss. In general, ERP studies on SSD CI users are rather scarce, and there is no study on audiovisual processing in particular. Furthermore, there are no reports on lip-reading abilities of SSD CI users. To this end, in the third project we extend the first study by including SSD CI users as a third experimental group. The study discusses both differences and similarities between CI users with bilateral hearing loss and CI users with unilateral hearing loss as well as NH controls and provides — for the first time — insights into audiovisual interactions in SSD CI users. The fourth project investigates the influence of background noise on audiovisual interactions in CI users and whether a noise-reduction algorithm can modulate these interactions. It is known that in environments with competing background noise listeners generally rely more strongly on visual cues for understanding speech and that such situations are particularly difficult for CI users. As shown in previous auditory behavioural studies, the recently introduced noise-reduction algorithm "ForwardFocus" can be a useful aid in such cases. However, the questions whether employing the algorithm is beneficial in audiovisual conditions as well and whether using the algorithm has a measurable effect on cortical processing have not been investigated yet. In this ERP study, we address these questions with an auditory and audiovisual syllable discrimination task. Taken together, the projects included in this thesis contribute to a better understanding of auditory and especially audiovisual speech processing in CI users, revealing distinct processing strategies employed to overcome the limited input provided by a CI. The results have clinical implications, as they suggest that clinical hearing assessments, which are currently purely auditory, should be extended to audiovisual assessments. Furthermore, they imply that rehabilitation including audiovisual training methods may be beneficial for all CI user groups for quickly achieving the most effective CI implantation outcome

Aerospace medicine and biology: A continuing bibliography with indexes (supplement 317)

This bibliography lists 182 reports, articles and other documents introduced into the NASA scientific and technical information system in November, 1988

EVALUATION OF AUDITORY CORTICAL PLASTICITY FROM FIRST AMPLIFICATION TO ONE YEAR OF HEARING AID USE: THE RELATIONSHIP BETWEEN AIDED CORTICAL AUDITORY EVOKED POTENTIALS (ACAEPs) AND SPEECH PERCEPTION OUTCOMES AMONG HEARING-IMPAIRED ADULT PATIENTS

Over the last decade, aided cortical auditory evoked potentials (ACAEPs) have continued to be a focus of interest due to the lack of adequate tools to objectively assess cortical auditory activity in response to amplified stimuli. The majority of authors have investigated the direct relationship between behavioral thresholds and ACAEPs and the evolution of ACAEP waves among children with sensorineural hearing loss (SNHL) undergoing rehabilitation. In contrast, scarce data are available regarding changes in ACAEPs over time in adult hearing aid users, particularly in relation to speech perception outcomes. The main goal of this project was to investigate the relationship between ACAEPs and speech perception capability over time in post-lingual SNHL adult patients who were first-time hearing aid users. We hypothesized that, in patients with better speech understanding, a modification of the P1-N1-P2 complex could be expected as a result of neuroplastic changes due to hearing aid amplification. A longitudinal prospective clinical study was conducted on 72 new hearing aid users suffering from symmetrical, sloping SNHL. Patients were assessed at three different time points: baseline (T0), 6 months after the initial assessment (T6), and 12 months after the initial assessment (T12). All the participants went through the same evaluation protocol, which included pure-tone audiometry, speech audiometry tests, ACAEPs recorded with two different stimuli (1000 Hz and 2000 Hz) and questionnaires assessing hearing aid benefit. Analysis of amplitude values at the three different time points demonstrated an increasing tendency for all waves in both experimental conditions (p<0.01). Latencies seemed to become shorter from T0 to T12 for each wave and in the case of 1 kHz and 2 kHz stimuli. (p<0.05). Linear regression analysis found that only P2 amplitude showed a statistically significant increase in its variation while matrix sentence test (MST) and speech intellection threshold (SIT) decreased in both experimental conditions, even when the analysis was adjusted for age and daily hearing aid use (p<0.05). The data collected in this study provide new evidence regarding the relationship between ACAEPs and the speech recognition capability of adults who are new hearing aid users. In both experimental conditions, we observed larger P2 amplitude in patients with better speech perception outcomes. It should be underlined that, even though P2 may reflect auditory processing beyond sensation, its increase could be an expression of neural activity associated with the acquisition process driven by exposure to sounds and speech. The observation that P2 amplitude tended to improve as SIT and MST scores decreased might be, in the future, a further object of investigation to assess its reliability as a marker of speech perception improvement; it may assist hearing aid dispensers and audiologists as a source of feedback in the evaluation of listening benefits in hard-to-test patients

Effects of depression, stress and other factors on cradling bias in Saudi males and females

Several studies have reported a strong bias in both human and non-human species for cradling their infants to the left side of the body. Most studies suggest that the main reason this phenomenon is the predominance of the right hemisphere of the brain for the processing of emotions and its transference, through brain laterality, to the left side of the body. Many other variables, including handedness, footedness, stress and depression have also been found to have some effect on cradling side. However, no study has been published for an Arab population. Given the strong religious and cultural belief of most Arabs that only the right hand should be used for most daily tasks, this study investigated the affect on cradling side of this habit, in addition to the factors named above. 369 Saudi citizens took part in this study. 234 lived in Saudi Arabia and 135 had lived in the UK for five or more years. 267 were women and 102 were men. Each answered a questionnaire which asked about their ‘preferred’ cradling side and then the 102 men were videotaped spontaneously cradling a real infant and an infant-like doll. Unfortunately, only the male sample could be videotaped due to restrictions on filming females in Saudi Arabia. The results confirmed those of previous studies by showing a very strong bias to leftside cradling. No difference was found between males and females in cradling a doll, or between the Saudi-based sample and the UK-based sample but the bias was significantly reduced in men. Apart from the influence of gender, the factors that reduced the cradling bias for a real infant were found to be lack of experience of parenthood, depression, stress and greater age of the infant. In cradling a doll, the most influential variables were handedness, footedness and depression. Further work is required on Arab samples, especially in examining spontaneous cradling by women and its relation to depression and stress. A mother’s mental state is known to affect the health of the infant and cradling side could be a useful filter for neonatal women who might require psychiatric treatment. Further research could also shed light on gender differences in the processing of emotion

Aerospace medicine and biology: A cumulative index to a continuing bibliography (supplement 319)

This publication is a cumulative index to the abstracts contained in Supplements 307 through 318 of Aerospace Medicine and Biology: A Continuing Bibliography. Seven indexes are included -- subject, personal author, corporate source, foreign technology, contract number, report number and accession number

Aerospace medicine and biology: A cumulative index to a continuing bibliography (supplement 345)

This publication is a cumulative index to the abstracts contained in Supplements 333 through 344 of Aerospace Medicine and Biology: A Continuing Bibliography. Seven indexes are included -- subject, personal author, corporate source, foreign technology, contract number, report number, and accession number

Neuroplasticity of Ipsilateral Cortical Motor Representations, Training Effects and Role in Stroke Recovery

This thesis examines the contribution of the ipsilateral hemisphere to motor control with the aim of evaluating the potential of the contralesional hemisphere to contribute to motor recovery after stroke. Predictive algorithms based on neurobiological principles emphasize integrity of the ipsilesional corticospinal tract as the strongest prognostic indicator of good motor recovery. In contrast, extensive lesions placing reliance on alternative contralesional ipsilateral motor pathways are associated with poor recovery. Within the predictive algorithms are elements of motor control that rely on contributions from ipsilateral motor pathways, suggesting that balanced, parallel contralesional contributions can be beneficial. Current therapeutic approaches have focussed on the maladaptive potential of the contralesional hemisphere and sought to inhibit its activity with neuromodulation. Using Transcranial Magnetic Stimulation I seek examples of beneficial plasticity in ipsilateral cortical motor representations of expert performers, who have accumulated vast amounts of deliberate practise training skilled bilateral activation of muscles habitually under ipsilateral control. I demonstrate that ipsilateral cortical motor representations reorganize in response to training to acquisition of skilled motor performance. Features of this reorganization are compatible with evidence suggesting ipsilateral importance in synergy representations, controlled through corticoreticulopropriospinal pathways. I demonstrate that ipsilateral plasticity can associate positively with motor recovery after stroke. Features of plastic change in ipsilateral cortical representations are shown in response to robotic training of chronic stroke patients. These findings have implications for the individualization of motor rehabilitation after stroke, and prompt reappraisal of the approach to therapeutic intervention in the chronic phase of stroke

Perceptual abnormalities in amputees: phantom pain, mirror-touch synaesthesia and referred tactile sensations

It is often reported that after amputation people experience "a constant or inconstant... sensory ghost... faintly felt at time, but ready to be called up to [their] perception" (Mitchell, 1866). Perceptual abnormalities have been highlighted in amputees, such as sensations in the phantom when being stroked elsewhere (Ramachandran et al., 1992) or when observing someone in pain (Giummarra and Bradshaw, 2008). This thesis explored the perceptual changes that occur following amputation whist focusing on pain, vision and touch. A sample of over 100 amputees were recruited through the National Health Service. Despite finding no difference in phantom pain based on physical amputation details or nonpainful perceptual phenomena, results from Paper 1 indicated that phantom pain may be more intense, with sensations occurring more frequently, in amputees whose pain was triggerinduced. The survey in Paper 2 identified a group of amputees who in losing a limb acquired mirror-touch synaesthesia. Higher levels of empathy found in mirror-touch amputees might mean that some people are predisposed to develop synaesthesia, but that it takes sensory loss to bring dormant cross-sensory interactions into consciousness. Although the mirror-system may reach supra-threshold levels in some amputees, the experiments in Paper 3 suggested a relatively intact mirror-system in amputees overall. Specifically, in a task of apparent biological motion, amputees showed a similar, although weaker, pattern of results to normalbodied participants. The results of Paper 4 showed that tactile spatial acuity on the face was also largely not affected by amputation, as no difference was found between the sides ipsilateral and contralateral to the stump. In Paper 5 cross-modal cuing was used to investigate whether referred tactile sensations could prime a visually presented target in space occupied by the phantom limb. We conclude that perception is only moderately affected in most amputees, but that in some the sensory loss causes normally sub-threshold processing to enhance into conscious awareness