The effects of a second stimulus on the auditory steady state response (ASSR) from the inferior colliculus of the chinchilla

Abstract

The auditory steady-state response (ASSR) is an auditory evoked potential which follows the envelope of the stimulus. One of the advantages of the ASSR is that multiple stimulation frequencies can be tested simultaneously. In experiment 1, we evaluated the effects of simultaneously presenting two separate stimuli on ASSR response amplitude. In experiment 2, we evaluated the effects of presenting two ASSR-generating stimuli monotically vs. dichotically, either ipsilaterally or contralaterally to the recording electrode. Recordings were made from the chinchilla inferior colliculi, in response to tonebursts, two-tones, or sinusoidally-amplitude modulated tones. We found that the addition of a second stimulus resulted in a reduction in ASSR response amplitude at moderate to high stimulus levels. The amount of amplitude reduction was typically larger in the monotic (e.g. approximately 50%) vs. dichotic condition (e.g. approximately 10-20%), regardless of whether the responses were recorded ipsilaterally or contralaterally to the ear of stimulus presentation. In conclusion, central as well as peripheral interactions contribute to the reduction in ASSR amplitude in response to the simultaneous presentation of multiple stimuli.

Age-Related Changes in Processing Simultaneous Amplitude Modulated Sounds Assessed Using Envelope Following Responses

“…The decrease in response amplitudes using multiple AM tones of the same sound level (SNR of 0 dB) has also been previously seen using steady state potentials where significant interactions between the tones take place, especially at moderate to high sound levels of 40-80 dB SPL (Dolphin 1995;Lins and Picton 1995;McNerney and Burkard 2010). In these studies, responses to a given AM decreases in the presence of a separate AM of higher F C (Ross et al 2003;McNerney and Burkard 2010). Since it is contrary to the typical shapes of tuning curves in AN neurons which show a sharper slope and a higher intensity required for activation on the higher-frequency side (Liberman 1978;Schmiedt 1989), these results were explained as a result of Bnonenergetic masking^and Bcentral neural mechanisms.Ĥ owever, in a population response like the EFR, especially for suprathreshold sounds, contributing neurons would not be limited to those near the carrier frequency of the stimulus alone, but rather would encompass a much larger range through activation of the low-frequency tails of their tuning curves, as the results from the AN model show (Fig.…”

“…Psychophysical studies have demonstrated similar effects of a higher-frequency masker having a greater effect on the target (Bacon and Moore 1993;Mendoza et al 1995). The decrease in response amplitudes using multiple AM tones of the same sound level (SNR of 0 dB) has also been previously seen using steady state potentials where significant interactions between the tones take place, especially at moderate to high sound levels of 40-80 dB SPL (Dolphin 1995;Lins and Picton 1995;McNerney and Burkard 2010). In these studies, responses to a given AM decreases in the presence of a separate AM of higher F C (Ross et al 2003;McNerney and Burkard 2010).…”

“…Concurrent sAM stimuli have been used as a model for detection and segregation of auditory objects in which stimulus parameters can be modified in a controlled and predictable manner (Hall and Grose 1991;Bacon and Konrad 1993;Yost and Sheft 1994). These studies suggest varying degrees of interactions in the detection of competing sAM stimuli, depending on sound level and spectral content of each component (Lins and Picton 1995;Herdman and Stapells 2003;McNerney and Burkard 2010;Nakamoto et al 2010). However, the neurophysiological bases of processing competing sAM tones are poorly understood.…”

The auditory steady state response: Far-field recordings from the chinchilla

“…Previous studies in our lab (McNerney & Burkard, 2010) have found that there is a decrease in ASSR response amplitude recorded from near-fi eld electrodes implanted in the IC with the addition of a second ASSR-generating stimulus (i.e. sinusoidally-amplitude modulated tones, two-tone stimuli, or toneburst stimuli).…”

“…Paired t-tests were then used to compare ASSRs in response to single vs. multiple stimulus conditions, as well as in response to the anesthetized vs. awake state. One-tailed rather than two-tailed t-tests were used, as previous research in our lab on chinchillas has shown that anesthesia results in a decrease in ASSR amplitude relative to the awake state, and that the presentation of multiple ASSR-generating stimuli results in a decrease in response amplitude relative to the single stimulus condition (Szalda & Burkard, 2005;McNerney & Burkard, 2010). Figure 1 represents a raw ASSR waveform from an individual animal that was collected from the MASTER system.…”