Auditory brainstem response at the detection limit

Auditory signal detection appears to depend on temporal integration of subthreshold activity in auditory cortex

The threshold of hearing decreases with increasing sound duration up to a limit of a few hundred milliseconds, whereas other auditory time constants are orders of magnitude shorter. A possible solution to this resolution-integration paradox is that temporal integration occurs more centrally than computations depending on high temporal resolution. But this would require information about subthreshold events in the periphery to reach higher centers. Here we show that this prerequisite is fulfilled. The auditory evoked response to a just perceptible pulse series does basically not depend on whether single pulses are below or above behavioral threshold. The failure to find evidence of temporal integration up to response latencies of 30 ms suggests that the integrator is located more centrally than primary auditory cortex. By using noise to its advantage, the auditory system apparently has established a central integration mechanism that is about as efficient as the peripheral one in the visual system.

Baseline correction of overlapping event-related responses using a linear deconvolution technique

The time it takes an event-related response (ERR) to subside is often longer than the interval between successive events so that the response to a new event interferes with a baseline formed by responses to preceding events. Thus, without proper baseline correction, the interpretation of an event-triggered average (ETA) of recorded data can be problematic. As the spectral compositions of ERR and baseline typically overlap, filtering the ETA is not always an adequate solution. The approach introduced here exploits that ETA and ERR are linearly related. Unless the series of events is exactly periodic, the ERR can be derived from the ETA by linear deconvolution. The performance of the method is illustrated with simulated examples as well as data from an auditory evoked field (AEF) study. It is also outlined how to handle experiments with two or more different events. Intriguing applications beyond the scope of baseline correction arise from the fact that the ERR is invariably estimated for a time window longer than the mean interval between successive events. The method may help, for example, to better understand the relationship between transient and steady-state responses or to delineate the component structure of a specific ERR.