Fast detection of unexpected sound intensity decrements as revealed by human evoked potentials

Abstract

The detection of deviant sounds is a crucial function of the auditory system and is reflected by the automatically elicited mismatch negativity (MMN), an auditory evoked potential at 100 to 250 ms from stimulus onset. It has recently been shown that rarely occurring frequency and location deviants in an oddball paradigm trigger a more negative response than standard sounds at very early latencies in the middle latency response of the human auditory evoked potential. This fast and early ability of the auditory system is corroborated by the finding of neurons in the animal auditory cortex and subcortical structures, which restore their adapted responsiveness to standard sounds, when a rare change in a sound feature occurs. In this study, we investigated whether the detection of intensity deviants is also reflected at shorter latencies than those of the MMN. Auditory evoked potentials in response to click sounds were analyzed regarding the auditory brain stem response, the middle latency response (MLR) and the MMN. Rare stimuli with a lower intensity level than standard stimuli elicited (in addition to an MMN) a more negative potential in the MLR at the transition from the Na to the Pa component at circa 24 ms from stimulus onset. This finding, together with the studies about frequency and location changes, suggests that the early automatic detection of deviant sounds in an oddball paradigm is a general property of the auditory system.

Figure 1. The three stimulation conditions.

Stimuli were clicks of 100 µs duration, presented binaurally through headphones. The onset-to-onset interval varied randomly in 8-ms steps between 256 and 344 ms, with a mean of 300 ms A. In the oddball blocks, two types of stimuli were presented randomly. Standard stimuli, indicated in black, were presented with an intensity of 50 dB SL and a probability of 6/7. Deviant stimuli, indicated in grey, were presented with an intensity of 40 dB SL and a probability of 1/7. B. In the reversed oddball blocks, the intensities of standards and deviants were exchanged. Probabilities and colors are as in A. C. In the control blocks seven different stimuli with intensities of 10, 20, 30, 40, 50, 60 or 70 dB SL, each with a probability of 1/7 were presented randomly.

Figure 2. ABRs to the control stimuli.

A. Single-subject recording to control stimuli of 70 dB SL at FCz. ABR components are labeled with Roman numerals. B. Grand-average response (N = 23) to the control stimuli of 10 to 70 dB SL at FCz. C, D. Mean Wave V peak amplitudes (C) and latencies (D) at FCz in response to the control stimuli presented at 20 to 70 dB SL. Error bars indicate +/- 1 standard error. Significant differences between adjacent control stimuli are indicated with an asterisk (p<0.05).

Figure 3. MLRs to the control stimuli.

A, B. Grand-average AEP (N = 23) filtered for the MLR in response to control stimuli of 10 to 30 dB SL (A) and 40 to 70 dB SL (B) at Fz. C,D. Mean peak amplitudes (C) and latencies (D) of the Na component in response to the control stimuli of 20 to 70 dB SL at the electrode Fz (N = 18). Error bars indicate +/- 1 standard error. Significant differences between adjacent control stimuli are indicated with an asterisk (p<0.05).

Figure 4. ABRs to standards, deviants and controls.

Grand-average response (N = 23) to deviants and standards (A), deviants and controls (B) and standards and controls (C) at FCz. The grey shaded bars denote the time window of the mean amplitudes used for statistics.

Figure 5. Deviance-related changes in the MLR.

Grand-average response (N = 23) at FCz, FC3 and Fz elicited by deviants and standards. The grey shaded fields mark the time window of the mean amplitudes used for statistics. The difference waveforms reveal a negative displacement of the response to deviants compared to the one to standards.

Figure 6. MLRs to the same physical stimulus presented in different conditions.

A−C. Grand-average MLR responses (N = 23) to deviants, standards and controls at Fz. The grey shaded areas and the framed area mark the time windows of the mean amplitudes used for statistics. D. Mean amplitudes from 21 to 27 ms after stimulus onset (grey shaded field in A−C) in response to deviant (dev), standard (std) and control (con) at Cz, FCz, Fz, FC3 and FC4.