A number of stimulus presentation features of the tone burst-evoked N1-P2 cortical response were investigated to identify any advantage over simple stimulation when the test is used for hearing threshold estimation. The speed of establishing objective thresholds at 1, 3, and 8 kHz in both ears was also measured in what was designed to be an efficient test protocol, together with the precision of the threshold estimates with reference to subjects' conventional audiograms.
Twenty-four volunteer subjects were recruited and tested by both behavioral and electrophysiological methods. A low-intensity, 3-kHz stimulus was used when the stimulus features were studied. The parameter was the N1-P2 amplitude.
Changing the side of presentation (randomly or by alternating ears), varying the interstimulus interval and inserting a 10-second recovery period midway though an averaging run had no demonstrable effect on response amplitude, both individually or in combination, contrary to earlier reports. Establishing the 6 threshold estimates took an average 20.6 minutes. The mean error in the N1-P2 threshold estimate was 6.5 dB, with no significant effect of frequency. After correcting for this bias, 94% of individual threshold estimates were within 15 dB of the behavioral threshold and 80% were within 10 dB.
This study suggests that cortical electric response audiometry has a performance that is as good as or better than the auditory brain stem response for threshold estimation in adults and that sophisticated stimulation techniques do not appear to be required. An efficient test protocol that automates many laborious tasks reduces the test time to less than half that previously reported in the literature for this response.
"They found that speech identification abilities decreased when exposed to poorer signal-to-noise ratios with the performance decrement paralleled by both increased N1 latencies and decreased N1 amplitudes. More importantly, the latency and amplitude of the N1 significantly correlated with behavioral assessments of signal detectability (Martin et al., 1997) with electrophysiological thresholds closely approximating behavioral thresholds (Lightfoot and Kennedy, 2006). These findings suggest that AEPs provide a sensitive measure of signal audibility, which may prove useful at evaluating the effects of age-related hearing loss on central auditory processing. "
[Show abstract][Hide abstract] ABSTRACT: Aging is often accompanied by hearing loss, which impacts how sounds are processed and represented along the ascending auditory pathways and within the auditory cortices. Here, we assess the impact of mild binaural hearing loss on the older adults' ability to both process complex sounds embedded in noise and to segregate a mistuned harmonic in an otherwise periodic stimulus. We measured auditory evoked fields (AEFs) using magnetoencephalography while participants were presented with complex tones that had either all harmonics in tune or had the third harmonic mistuned by 4 or 16% of its original value. The tones (75 dB sound pressure level, SPL) were presented without, with low (45 dBA SPL), or with moderate (65 dBA SPL) Gaussian noise. For each participant, we modeled the AEFs with a pair of dipoles in the superior temporal plane. We then examined the effects of hearing loss and noise on the amplitude and latency of the resulting source waveforms. In the present study, results revealed that similar noise-induced increases in N1m were present in older adults with and without hearing loss. Our results also showed that the P1m amplitude was larger in the hearing impaired than in the normal-hearing adults. In addition, the object-related negativity (ORN) elicited by the mistuned harmonic was larger in hearing impaired listeners. The enhanced P1m and ORN amplitude in the hearing impaired older adults suggests that hearing loss increased neural excitability in auditory cortices, which could be related to deficits in inhibitory control.
Frontiers in Systems Neuroscience 01/2014; 8:8. DOI:10.3389/fnsys.2014.00008
"Also, rise times between 20 and 30 ms result in the largest N1 amplitudes with either no further change, or decrease, in amplitude with longer rise times [40, 41]. Perhaps different results may have been obtained using stimuli with more typical rise/fall times and overall durations, such as 20 ms rise time and 60 ms total duration [22, 23, 42–44], although a recent study by Easwar and colleagues  suggests little difference in SCPs to hearing-aid-processed stimuli with 7.5 ms versus 20 ms rise times. "
[Show abstract][Hide abstract] ABSTRACT: Slow cortical potentials (SCPs) are currently of great interest in the hearing aid fitting process for infants; however, there is conflicting evidence in the literature concerning the use of SCPs for this purpose. The current study investigated SCP amplitudes and latencies in young normal-hearing listeners in response to a 60 ms duration tonal stimulus (1000 Hz) presented at three intensities (30, 50, and 70 dB SPL) in aided and unaided conditions using three hearing aids (Analog, DigitalA, and DigitalB) with two gain settings (20 and 40 dB). Results showed that SCP amplitudes were smaller for the digital hearing aids compared with the analog hearing aid, and none of the hearing aids resulted in a reliable increase in response amplitude relative to the unaided across conditions. SCP latencies in analog conditions were not significantly different from latencies in the unaided conditions; however, both digital hearing aids resulted in significantly delayed SCP latencies. The results of the current study (as well as several previous studies) indicate that the SCP may not accurately reflect the amplified stimulus expected from the prescribed hearing aids. Thus, “aided-SCP” results must be interpreted with caution, and more research is required concerning possible clinical use of this technique.
International Journal of Otolaryngology 10/2012; 2012(1687-9201). DOI:10.1155/2012/921513
"As an example, the N1-P2 amplitude was expected to be 5 uV for 1 k, and 3 uV for higher frequencies at CAEP threshold. If the amplitude was larger, then threshold was equal to the stimulus presentation level minus 5 dB (Lightfoot & Kennedy 2006). Given the challenges of electrophysiological response recognition by visual detection methods, automated or machine scoring techniques have been applied. "
[Show abstract][Hide abstract] ABSTRACT: The detection of adult cortical auditory evoked potentials (CAEPs) can be challenging when the stimulus is just audible. The effectiveness of a statistic compared with expert examiners in (1) detecting the presence of CAEPs when stimuli were present, and (2) reporting the absence of CAEPs when no stimuli were present, was investigated. CAEPs recorded from ten adults, using two speech-based stimuli, five stimulus presentation levels, and non-stimulus conditions, were given to four experienced examiners who were asked to determine if responses to auditory stimulation could be observed, and their degree of certainty in making their decision. These recordings were also converted to multiple dependent variables and Hotelling's T2 was applied to calculate the probability that the mean value of any linear combination of these variables was significantly different from zero. Results showed that Hotelling's T2 was equally sensitive to the best of individual experienced examiners in differentiating a CAEP from random noise. It is reasonable to assume that the difference in response detection for a novice examiner and Hotelling's T2 would be even greater.
International journal of audiology 12/2009; 48(12):833-42. DOI:10.3109/14992020903140928 · 1.84 Impact Factor
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