Directional sensitivity of auditory processing
Auditory mate localisation is central to the lifestyle of many animals and requires precise directional hearing. When the incident angle of sound approaches 0° azimuth, interaural time and intensity differences gradually vanish. This poses a demanding challenge to animals especially when interaural distances are small. To cope with these limitations imposed by the laws of acoustics, crickets employ a frequency tuned peripheral hearing system. This enhances auditory directionality but the actual precision of directional hearing and phonotactic steering has never been studied systematically.
We analysed the directionality of phonotaxis in female G. bimaculatus walking on an open-loop trackball system by measuring their steering accuracy towards male calling song presented at frontal angles of incidence. Within the range of ±30°, females reliably discriminated the side of acoustic stimulation, even when the sound source deviated by only 1° from the animal’s length axis. Moreover, for angles of sound incidence between 1° and 6° the females precisely walked towards the sound source. Measuring the tympanic membrane oscillations of the front leg ears with a laser vibrometer revealed between 0° and 30° a linear increasing function of interaural amplitude differences with a slope of 0.4 dB/°. Auditory nerve recordings closely reflected these bilateral differences in afferent response latency and intensity that provide the physiological basis for precise auditory steering. Article available here
Our experiments demonstrate that an insect hearing system based on a frequency-tuned pressure difference receiver achieves a directional sensitivity which easily rivals best directional hearing in mammals and birds. We now analyze if the high acuity of cricket auditory steering is based on phase-shifts between sound waves entering the peripheral auditory system.
Group Members
Dr Berthold Hedwig (Group Leader)
bh202@cam.ac.uk
Dr Fabienne Dupuy
Research: Auditory motor interface
fyd20@cam.ac.uk
Dr Kostas Kostarakos
Research: Auditory brain neurons
kk437@cam.ac.uk
Dr Stefan Schoeneich
Research:Song pattern generation
ss817@cam.ac.uk
Kelly Seagraves
Research: Directional sensitivity
ks584@cam.ac.uk
Part II Zoology Project Students
Tanya Gunnarsdottir
Gemma Longson