Auditory unit responses to single-pulse and twin-pulse microwave stimuli

Area of Science:

• Neuroscience
• Bioacoustics
• Electromagnetics

Background:

• The mechanism of microwave hearing, also known as the microwave auditory effect, remains incompletely understood.
• Previous hypotheses suggested resonant frequencies of the human head might play a role in microwave perception.

Purpose of the Study:

• To investigate the physiological basis of microwave hearing in cats.
• To determine the relationship between microwave pulse characteristics and neural responses in the auditory system.
• To evaluate the contribution of head resonance to microwave auditory perception.

Main Methods:

• Electrophysiological recordings were made from units in the cat cochlear nucleus.
• Responses to single and twin microwave pulses of varying durations and interpulse delays were analyzed.
• Threshold specific absorption rate (SAR) and specific absorption (SA) were inferred.
• Unit characteristic frequencies (CFs) were measured.

Main Results:

• Inferred threshold SAR was < 6 mW/g and threshold SA was < 0.5 microJ/g.
• Observed unit responses across a wide range of CFs (931 Hz to 25.5 kHz) are inconsistent with head resonance as the primary mechanism.
• Response amplitude patterns exhibited periodicity related to 1/CF, correlating with pulse frequency content and auditory system processing.
• For pulses shorter than approximately 0.24/CF, response amplitude showed a direct proportionality to pulse energy.

Conclusions:

• Microwave hearing in cats is not primarily mediated by head resonance.
• The auditory system's signal processing and the frequency content of microwave pulses significantly influence neural responses.
• Pulse energy is a critical determinant of response amplitude for short microwave pulses.