Late auditory evoked potentials in elderly long-term hearing-aid users with unilateral or bilateral fittings

This study investigated the effects of long-term unilateral and bilateral amplification on central auditory processing in elderly people with symmetrical hearing loss using late auditory evoked potentials. It was hypothesized that in the unilateral setting stimulation of the aided ear would yield an acclimatization effect with larger amplitudes and shorter latencies of the components P1, N1 and P2 compared to those of the unaided ear. Auditory evoked potentials were elicited by 500, 1000 and 2000 Hz pure tones at 55, 70 and 85 dB SPL presentation level delivered either to the left or right ear. Unilaterally and bilaterally fitted experienced hearing-aid users and a control group of normally hearing adults, all aged at least 60 years, participated. The responses of the unilateral hearing-aid users did not differ significantly for any of the components P1, N1 or P2 between the aided and unaided ears, but a significant interaction between ear and frequency was present for P2 amplitudes. P2 amplitudes were significantly smaller for the 0.5- and 1-kHz stimuli and tended to be larger for the 2-kHz stimulus in the aided ear suggesting an acclimatization effect. Larger P2 amplitudes were observed in the unilaterally fitted group, which was interpreted as a correlate of more effortful auditory processing in unilaterally fitted people.

from Hearing Research

Alterations in visual and auditory processing in hemispatial neglect; an evoked potential follow-up study

Hemispatial neglect is common after cerebrovascular stroke in the right hemisphere. Cortical electrophysiological studies, especially investigations of both visual and auditory processing in subjects with neglect are sparse. Our purpose was to assess whether and to which extent subjects with neglect may show impairments in both visual and auditory processing. Thereby, we assessed the evolution of changes in sensory processing and neglect symptoms over a 6 months follow-up period. Twenty-one stroke subjects with hemispatial neglect were studied at baseline, 3 weeks later and at 6 months follow-up. At enrollment, 12 patients were in Acute/subacute and 9 were in Chronic stage of stroke. Visual and auditory evoked potentials (EP) were elicited with unilateral stimulations and electrophysiologic data were registered with high-density EEG. Primary visual and auditory cortex activations seen in EP components were analyzed at three time points in order to detect alterations. Both sensory modalities revealed differences between hemispheres in processing stimuli coming from a unilateral source. Amplitudes of visual and auditory EP components elicited by left-sided stimuli were smaller compared to those elicited by right-sided stimuli in the Acute/subacute group. The behavioral neglect was more severe in those who had smaller EP amplitudes (e.g. EP amplitude after right auditory stimulus was significantly associated with total behavioral neglect score, r=.57). The main hemispheric differences diminished by the follow-up 6 months later along with the decreasing severity of neglect in the Acute/subacute group.

from the International Journal of Psychophysiology

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Learning-induced plasticity in human audition: Objects, time, and space

The human auditory system is comprised of specialized but interacting anatomic and functional pathways encoding object, spatial, and temporal information. We review how learning-induced plasticity manifests along these pathways and to what extent there are common mechanisms subserving such plasticity. A first series of experiments establishes a temporal hierarchy along which sounds of objects are discriminated along basic to fine-grained categorical boundaries and learned representations. A widespread network of temporal and (pre)frontal brain regions contributes to object discrimination via recursive processing. Learning-induced plasticity typically manifested as repetition suppression within a common set of brain regions. A second series considered how the temporal sequence of sound sources is represented. We show that lateralized responsiveness during the initial encoding phase of pairs of auditory spatial stimuli is critical for their accurate ordered perception. Finally, we consider how spatial representations are formed and modified through training-induced learning. A population-based model of spatial processing is supported wherein temporal and parietal structures interact in the encoding of relative and absolute spatial information over the initial post-stimulus onset. Collectively, these data provide insights into the functional organization of human audition and open directions for new developments in targeted diagnostic and neurorehabilitation strategies.

from Hearing Research

Motion-onset auditory-evoked potentials critically depend on history

The aim of the present study was to determine whether motion history affects motion-onset auditory-evoked potentials (motion-onset AEPs). AEPs were recorded from 33 EEG channels in 16 subjects to the motion onset of a sound (white noise) virtually moving in the horizontal plane at a speed of 60 deg/s from straight ahead to the left (−30°). AEPs for baseline and adaptation were compared. A stimulus trial comprised three consecutive phases: 2,000 ms adaptation phase, 1,000 ms stationary phase, and 500 ms test phase. During the adaptation phase of the adaptation condition, a sound source moved twice from +30° to −30° to top up preceding adaptation. In the baseline condition, neither top-up nor pre-adaptation were exerted. For both conditions, a stationary sound was presented centrally in the stationary phase, moving leftwards in the test phase. Typical motion-onset AEPs were obtained for the baseline condition, namely a fronto-central response complex dominated by a negative and a positive component, the so-called change-N1 and change-P2 after around 180 and 250 ms, respectively. For the adaptation condition, this complex was shifted significantly into the positive range, indicating that adaptation abolished a negativity within a time window of approximately 160 to 270 ms. A respective shift into the negative range was evident at occipito-parietal sites. In conclusion, while adaptation has to be taken into account as a potential confound in the design of motion-AEP studies, it might also be of benefit in order to isolate AEP correlates of motion processing.

from Experimental Brain Research

Auditory Brainstem Response at the Detection Limit

from JARO — Journal of the Association for Research in Otolaryngology

Abstract Specific predictions regarding the level dependence of auditory evoked responses near the detection limit were made in a companion modeling study (Lütkenhöner, J Assoc Res Otolaryngol 9:102–121, 2008). Here, these predictions are experimentally tested for auditory brainstem responses (ABR) to Gaussian-shaped 4-kHz tone pulses (full width at half maximum = 0.5 ms) that were presented at sound levels close to the subjective threshold. In the average of over about one million stimulus repetitions (repetition period = 16 ms), the amplitude of ABR wave V showed a smooth transition from a proportional to a logarithmic growth with increasing sound intensity. The latter type of growth corresponds to a linear increase with respect to sound level measured in decibels. Alternatively, the ABR amplitude near the detection limit may be considered a linear function of sound pressure, although—according to the model—this is only an approximation. Data and model are consistent with the view that a sensory threshold does not exist for the auditory modality, in accordance with signal detection theory. Even so, the model may be used to define a quasithreshold that is comparable to the subjective threshold.

Auditory Brainstem Response at the Detection Limit

from JARO — Journal of the Association for Research in Otolaryngology

Abstract Specific predictions regarding the level dependence of auditory evoked responses near the detection limit were made in a companion modeling study (Lütkenhöner, J Assoc Res Otolaryngol 9:102–121, 2008). Here, these predictions are experimentally tested for auditory brainstem responses (ABR) to Gaussian-shaped 4-kHz tone pulses (full width at half maximum = 0.5 ms) that were presented at sound levels close to the subjective threshold. In the average of over about one million stimulus repetitions (repetition period = 16 ms), the amplitude of ABR wave V showed a smooth transition from a proportional to a logarithmic growth with increasing sound intensity. The latter type of growth corresponds to a linear increase with respect to sound level measured in decibels. Alternatively, the ABR amplitude near the detection limit may be considered a linear function of sound pressure, although—according to the model—this is only an approximation. Data and model are consistent with the view that a sensory threshold does not exist for the auditory modality, in accordance with signal detection theory. Even so, the model may be used to define a quasithreshold that is comparable to the subjective threshold.

Auditory Brainstem Response at the Detection Limit

from JARO — Journal of the Association for Research in Otolaryngology

Abstract Specific predictions regarding the level dependence of auditory evoked responses near the detection limit were made in a companion modeling study (Lütkenhöner, J Assoc Res Otolaryngol 9:102–121, 2008). Here, these predictions are experimentally tested for auditory brainstem responses (ABR) to Gaussian-shaped 4-kHz tone pulses (full width at half maximum = 0.5 ms) that were presented at sound levels close to the subjective threshold. In the average of over about one million stimulus repetitions (repetition period = 16 ms), the amplitude of ABR wave V showed a smooth transition from a proportional to a logarithmic growth with increasing sound intensity. The latter type of growth corresponds to a linear increase with respect to sound level measured in decibels. Alternatively, the ABR amplitude near the detection limit may be considered a linear function of sound pressure, although—according to the model—this is only an approximation. Data and model are consistent with the view that a sensory threshold does not exist for the auditory modality, in accordance with signal detection theory. Even so, the model may be used to define a quasithreshold that is comparable to the subjective threshold.