1. Attentional influences on hearing

Selective attention can strongly modulate auditory perception. For audition as a primarily undirected sense it is mainly spatial selective attention that is important for separating relevant sound sources from interfering background noise. We have found such effects of spatial selective attention on sound localization behavior in barn owls and rats (Johnen et al. 2001). Recent studies using psychophysical methods in rodents and humans focus on non-spatial selective attention, on focusing attention in time, and on the interaction between attention and scene segregation.

2. Neuronal adaptation in the auditory system

An important part of attentional focusing is the automatic orienting towards sensory stimuli of behavioral relevance. Novel acoustic stimuli are by themselves of presumed great importance compared to frequently occurring signals in the acoustic background. The stimulus-specific neuronal adaptation of responses to frequently occurring stimuli is one of the neural mechanisms presumably underlying novelty detection in the auditory system. We are investigating neuronal adaptation in the auditory cortex (von der Behrens et al. 2009) and in the auditory thalamus (Bäuerle et al., submitted) of small rodents. Parallel recording of neuronal responses and field potentials allow for a close comparison to investigations on mismatch negativity in humans. Possible neuronal mechanisms are investigated by manipulating the corticothalamic feedback loop.

3. Interactions between tones: perceptual effects and their neural basis

Many important signals such as animal communication sounds or human speech are actually segmented sequences of acoustic signals. The perception of these signals might not just be a step-by-step processing of separate parts, but might also depend on interactions between neighboring segments. We study such context-dependent sensory processing in a paradigm that combines different pre-tones with an FM-direction discrimination task. We found clear frequency-dependent interactions over time (up to 1 – 2 sec) and across a broad frequency-range (up to 2 oct). Interactions were not abolished by an interspersed noise burst and were also, in many listeners, dependent on the pitch of a missing fundamental. Non-invasive brain activity recording (MEG) revealed a strong involvement of higher auditory cortical areas.

4. 'Behavioral characterization and neural mechanisms of chronic tinnitus

Based on the well characterized acoustic startle response in gerbils (Gaese et al., 2009) we

The perception of frequency-modulated (FM) stimuli is investigated, as the ability to differentiate between FM-stimuli is strongly based on central auditory processing. As a prerequisite for the analysis of the underlying neuronal mechanisms we have investigated the ability to differentiate between upward and downward FM not only in humans (thesis S. Wehner) but also in rats (Gaese et al. 2006).