Auditory enhancement effects: late auditory responses to a second tone are modulated by the length of the interstimulus interval
Heinemann, L. V., Kaiser, J., Rahm, B., and Altmann, C. F.
Institut für Medizinische Psychologie, Johann Wolfgang Goethe-University, Frankfurt am Main
Frequency modulation (FM) is an important sound feature of human speech as well as many animal vocalizations. To investigate the neuronal mechanisms that underlie the processing of FM sweeps, we recorded the magnetoencephalogram (MEG) in human subjects during the presentation of consecutive FM sweep-pairs. We aimed at examining repetition effects for FM sweeps and their modulation by different interstimulus-intervals (ISIs: 100-600ms). To this end, we presented FM sweep-pairs in four different conditions: a) two upward FM tones, b) two downward FM tones, c) an upward followed by a downward FM tone and d) a downward followed by an upward FM tone. Regional sources in the bilateral auditory cortex were used to model the evoked magnetic field. We observed an enhancement of MEG signal strength for same in contrast to different FM directions. This effect was maximal for short ISIs (100-300ms) and decreased at longer ISIs (~500ms).