Biomedical subjects

Bernhard H Gaese

Publications and source records attributed to Bernhard H Gaese.

3 recordsLinked to original sources

PubMed2006

Discrimination of direction in fast frequency-modulated tones by rats.

Fast frequency modulations (FM) are an essential part of species-specific auditory signals in animals as well as in human speech. Major parameters characterizing non-periodic frequency modulations are the direction of frequency change in the FM sweep (upward/downward) and the sweep speed, i.e., the speed of frequency change. While it is well established that both parameters are represented in the mammalian central auditory pathway, their importance at the perceptual level in animals is unclear. We determined the ability of rats to discriminate between upward and downward modulated FM-tones as a function of sweep speed in a two-alternative-forced-choice-paradigm. Directional discrimination in logarithmic FM-sweeps was reduced with increasing sweep speed between 20 and 1,000 octaves/s following a psychometric function. Average threshold sweep speed for FM directional discrimination was 96 octaves/s. This upper limit of perceptual FM discrimination fits well the upper limit of preferred sweep speeds in auditory neurons and the upper limit of neuronal direction selectivity in the rat auditory cortex and midbrain, as it is found in the literature. Influences of additional stimulus parameters on FM discrimination were determined using an adaptive testing-procedure for efficient threshold estimation based on a maximum likelihood approach. Directional discrimination improved with extended FM sweep range between two and five octaves. Discrimination performance declined with increasing lower frequency boundary of FM sweeps, showing an especially strong deterioration when the boundary was raised from 2 to 4 kHz. This deterioration corresponds to a frequency-dependent decline in direction selectivity of FM-encoding neurons in the rat auditory cortex, as described in the literature. Taken together, by investigating directional discrimination of FM sweeps in the rat we found characteristics at the perceptual level that can be related to several aspects of FM encoding in the central auditory pathway.

Acoustic Stimulation↗

PubMed2003

Complexity and temporal dynamics of frequency coding in the awake rat auditory cortex.

Auditory cortical neurons are elements of a neuronal network that decomposes sounds into spectral and temporal information. In particular, their frequency selectivity has been investigated in great detail. Most studies used anaesthetized preparations and found mainly simple V-shaped tuning. The few data available from awake animals indicate that more complex forms of spectral receptive fields, i.e. frequency response areas, can be found there. We investigated frequency response areas in the awake rat primary auditory cortex using statistical evaluation and found complex forms of frequency response areas with several separate subregions in many neurons, besides classical V-shaped tuning. Response areas, as determined with narrow band noise, were very similar to those measured with pure tones. Their width was well correlated to the response strength to white noise stimulation. These results suggest that the excitatory subregions of frequency response areas were the neurons' predominant characteristic, relevant also for the processing of more complex types of stimuli. Investigating the spectrotemporal dynamics of frequency response areas revealed that approximately one-third of the neurons showed long-lasting excitatory or inhibitory components in addition to the typical ON-response. Inhibition was usually of longer duration and occurred mainly in frequency ranges outside the range of initial excitatory responses. These results indicate that auditory cortical neurons in awake animals can represent spectrotemporal information of rather different complexity.

Acoustic Stimulation↗

PubMed2002

Precognitive and cognitive elements in sound localization.

Sound localization behavior is of great importance for an animal's survival. To localize a sound, animals have to detect a sound source and assign a location to it. In this review we discuss recent results on the underlying mechanisms and on modulatory influences in the barn owl, an auditory specialist with very well developed capabilities to localize sound. Information processing in the barn owl auditory pathway underlying the computations of detection and localization is well understood. This analysis of the sensory information primarily determines the following orienting behavior towards the sound source. However, orienting behavior may be modulated by cognitive (top-down) influences such as attention. We show how advanced stimulation techniques can be used to determine the importance of different cues for sound localization in quasi-realistic stimulation situations, how attentional influences can improve the response to behaviorally relevant stimuli, and how attention can modulate related neural responses. Taken together, these data indicate how sound localization might function in the usually complex natural environment.

Journal Article↗