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 batsare tunedto dominantfrequency

FM batsshow broadfrequencysensitivity

Ear pinna amplifies selected

frequencies

- Pinna acts as a horn- Larger pinna transmit lowerfrequencies better- Wavelength of the resonantfrequency 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 islonger and thicker atbase

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

Gray areas correspond to call frequencies

Auditory cortex

Auditory cortex is expanded at frequencies associated with echolocation

Tonotopic representation

varies by species

Open space

Blood feeder Ground gleaner

Inferior colliculus frequency maps

Neuronal tuning in horseshoe bats

Q10 = best freq/ bandwidth at -10 dB

Pteronotus parnellii

Information decoded from echos

Rangepulse-echo time delay

Velocitypulse-echo frequency change

Target sizefrequency of echo

Locationear amplitude difference

Combination-sensitive neurons encode range and velocity in CF bats

Cortical maps vary by species