Medical physics

Stephan Heise


Stephan Heise
Institut für Physik
Carl von Ossietzky Universität Oldenburg
D-26111 Oldenburg

phone: +49 441 798-5472
fax: +49 441 798-195472
office: W2 0-084a

Neurosensory Science and Systems group


Measuring threshold fine structure. A method ("FINESS") for a quick and accurate assessment of the fine structure of the threshold in quiet has been developed. The FINESS method is based on a tracking procedure whose parameters were optimised for the measurement of threshold fine structure. Runs are repeated automatically in a flexible way, so that the overall measurement duration is about ten minutes per octave. (Heise et al., 2006; Heise et al., 2008)

Detecting and quantifying cochlear fine structure. An algorithm for quantifying cochlear fine structure in a given input curve has been developed ("FINESS-detector"). The quantification is based on the level and frequency difference of adjacent extreme values and takes into account several criteria for the existence of fine structure so as to avoid an inadequate fixed criterion. The FINESS-detector has been applied to the fine structure of the threshold in quiet as well as to the fine structure of distorion product otoacoustic emissions (DPOAEs). (Heise et al., 2008)

The impact of threshold fine structure on modulation perception. The fine structure of the threshold in quiet is found to affect the perception of amplitude modulations near the threshold in quiet. Detection thresholds for sinusoidal amplitude modulation at low levels are higher (worse) when the carrier of the signal falls in a region of high pure-tone sensitivity (a minimum of the fine structure of the threshold in quiet) than when it falls at a fine-structure maximum. This project explores possible mechanisms behind this phenomenon by measuring modulation detection thresholds as a function of modulation frequency and of carrier level for tonal carriers and for narrow-band noise carriers. A large part of the results can be explained by assuming a reduction in effective modulation depth by spontaneous otoacoustic emissions (SOAEs)—or more generally: cochlear resonances—that synchronise to the carrier at fine-structure minima. Beating between cochlear resonances and the stimulus ("monaural diplacusis") may hamper the detection task but this cannot account for the whole effect. (Heise et al., 2009; Heise et al., submitted)

Complex Modulations Project. This project examines how higher order AMs are processed (e.g. a 2nd order AM is an amplitude modulation whose amplitude is modulated, i.e. whose depth changes over time). First experiments have shown that 2nd order AM may interfere with 1st order AM. The goal is to find a model which can predict this processing correctly.


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