Auditory Cortex Activation by Infrasonic and Low-frequency Sound of Equalized Individual Loudness
Regular paper
Physikalisch-Technische Bundesanstalt
Wednesday 3 june, 2015, 14:00 - 14:20
0.9 Athens (118)
Abstract:
Categorical loudness scaling as standardized in ISO 16832 (2006) provides an
easy and fast procedure to determine the loudness over the whole dynamic range
of the auditory system. Within this method the loudness is rated by the subject
on a scale with named categories, such as soft, moderate, loud, etc. In clinical
audiology this method is widely used to assess the amount of recruitment in
hearing impaired listeners. We extended this method to infrasonic and low
frequencies in order to investigate the loudness perception for such
frequencies. 30 otologically normal subjects performed the categorical loudness
scaling procedure for monaural stimulation with pure tones between 8 and 125 Hz.
Stimuli were presented by means of a newly designed insert-earphone sound source
for infrasonic frequencies. The loudness functions showed a significant decrease
of the dynamic range towards lower frequencies. To investigate the hearing
mechanism for infrasonic frequencies more extensively, brain responses were
measured by means of Magnetoencephalography (MEG). We investigated the variation
of the M100 brain response stimulated by pure tones with decreasing frequencies
from 250 Hz down to 8 Hz for 16 otologically normal subjects. The stimuli were
ramped sine tones of equal individually perceived loudness determined by the
categorical loudness scaling method described above. Magnetic brain responses
were recorded by a Yokogawa MEG-system and averaged to obtain the M100 response.
Subsequently, the positions of the underlying magnetic field generators were
estimated offline, using a dipole fit routine. Stable responses were measured
for stimulation frequencies between 20 and 250 Hz. At 8 and 12 Hz the results
are difficult to interpret. This paper will present equal loudness contours
derived from the loudness scaling data and objective magnetic brain responses
for infrasonic and low frequencies.