Hearing and echolocation Human hearing Adaptations for hearing

Hearing and echolocation • Human hearing • Adaptations for hearing in bats – Outer ear – Middle ear – Inner ear – Auditory pathways

The human ear Next slide

Human cochlea

Hair cell damage

Frequency detection in the cochlea

Hearing is tuned to echolocation: How? CF bats are tuned to dominant frequency FM bats show broad frequency sensitivity

Ear pinna amplifies selected frequencies - Pinna acts as a horn - Larger pinna transmit lower frequencies better - Wavelength of the resonant frequency equals 4 x length of the ear canal

Middle ear adaptations Tympanum: oval window area = 53: 1 in Tadarida, 35: 1 in a cat Malleus: incus = 3 -5: 1 in bats, 1. 5: 1 in a cat

Ear tympanum speed Faster at high frequencies because it is much thinner

Inner ear (cochlea) adaptations Basilar membrane is longer and thicker at base A basilar membrane that is thicker at the base increases sensitivity to high frequencies

Rhinolophus ferrumequinum

The auditory pathway

Tonotopic map in the auditory system Auditory cortex Gray areas correspond to call frequencies Auditory cortex is expanded at frequencies associated with echolocation

Open space Tonotopic representation varies by species Blood feeder Inferior colliculus frequency maps Ground gleaner

Neuronal tuning in horseshoe bats Q 10 = best freq/ bandwidth at -10 d. B

Pteronotus parnellii

Information decoded from echos Range pulse-echo time delay Velocity pulse-echo frequency change Target size frequency of echo Location ear amplitude difference

Combination-sensitive neurons encode range and velocity in CF bats

Cortical maps vary by species