MARB 403 Lecture 2

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Water is 800 times as dense as air

Sensory Organs

Filters between environment and brain

We hear 20 Hz to 20 kHz

Umwelt

everything we can detect

perception capabilities

Cetacean Senses

• Vision (sight; very good)
• Chemoreception
  • Olfaction (smell; bad)
  • Gustation (taste; meh)
• Tactility (touch; very good)
• Audition (hearing; very good)
• Magnetoreception (orientation/navigation; exists, but understudied)

Vision

Cetacean lens is spherical No ciliary muscles; cannot change shape for focusing

To compensate, they can change the shape of their eye to see in air

Circles of confusion

when an infinitesimal dot on an object is not in focus, the focal point is slightly in front of or behind retina

thus its image is spread as a (small) circle on the retina

Cetaceans have a slit pupil ("∞"-shaped), which creates two pupils when constricted

Two pupils means they might have binocular vision in one eye!

Brain is separated enough to move and focus eyes independently

Classical binocular vision from both eyes working in unison:

• forward-slightly-downward direction
• perhaps backward-slightly-upward direction

Color vision not well determined, but very good vision in dark

Chemoreception

Diffusion is pretty slow in water (15 times slower)

Very poor sense of smell:

• mysticetes have poor sense of smell
• odontocetes have no sense of smell

Taste buds tend to be at the root/base of the tongue

• bitter (quinine) and sour (citric acid) are well-developed
• salinity (salt) is meh
• sugar (sucrose) is bad

Olfactory part of brain is developed, but attached to tongue receptors (so their taste is rewired to smell)

Tactility

Overall highly acute, especially in following areas:

• 2.5cm around blowhole; any water will automatically shut it
• 2.5cm to 5cm around eye
• Lower jaw (sound and touch)
• Genitals and belly

Dolphins can "tickle" each other with their echolocation beam, but it's considered impolite to do so

Magnetoreception

May be responsible for mass strandings

Some humans and pigeons have very good magnetic detection

Sound and Hearing

Lecture Slides

Sound is our perception of vibrations in the air

Periodic

• Condensation (compression): high pressure pushes out
• Refraction (rarefaction): low pressure pulls in

Velocity of sound depends on compressibility of medium:

• Greater density and greater compressibility = slower speed

Sound in water is 4.5 times faster than in air
(Air: 340.29 m/s) × 4.5 = 1531.305 m/s

Wavelength is proportional to velocity and inversely proportional to frequency

Therefore, sound discrimination must have ears far apart (that's probably why dolphin brains are so stretched sideways—to get ears apart)

1000 Hz = 1 kHz

• wavelength in air = 0.34 m.
• wavelength in water = 1.5 m.

Dolphins use 100 kHz for echolocation: wavelength = 1531.305 m/s &divides; 100,000 /s = 0.015 m = 1.5 cm

This is their "pixel" size

Low frequencies go farther (very far) than high frequencies

Morphology / Physiologity

"No external ear... that would be a drag"

Reduced ear canal

3 ear bones similar to terrestrial mammals

• hang from ligaments
• more inlined (no amplification)
• not fused to skull

Time delay, loudness, and phase discrimination help us determine the direction of origin of sound

Auditory bullae

• Linked to jaw with fatty pad (insulation)
• tympanoperiotic complex
  • periotic bone - cochlea inside
  • Tympanic bone - 3 ossicles inside

Cochlea between vestibular and tympanic canals

• Longer basilar membrane
• More auditory ganglion cells
• Higher density of cochlear cells

Sound Production

Sound Production structures in Tursiops truncatus

Nasal plug muscle with two sides: one for clicks, one for whistles (even at same time)

three sets of paired sacs:

1. premaxillary sac below the plug
2. tubular sac above plug
3. vestibular sac near blowhole

nasal plug vibrates up to 800 clicks per second

sacs inflate and can force air back and forth across nasal plug

pure tone whistle is vibration over nasal plug

sound bounces off skull and through melon

echoes received through lower jaw

Note: Blowhole wind speed: Dolphins inhale and exhale at 200mph

Sound Basics

sound: compression and expansion of molecules in a medium (in the ocean, that medium is sea water.

frequency ($f$)

number of cycles per second [/s] or [Hz]

describes resolution and range

wavelength ($\lambda$)

distance between equal phases [m]

speed of sound ($c$)

changes with temperature, salinity, pressure

for our purposes, $c=1530\ {\text{m/s}}$

In echolocation, increased frequency (and thus decreased wavelength) improves resolution.

Parameters of Sound

energy ($I$)

intensity of signal; amplitude

$I={\tfrac {p^{2}}{p\,c}}$

pressure ($p$)

impedance ($Z$)

$Z=p\,c$

decibels [dB]

units of sound, always a ratio relative to 1µPa (micropascal)

Types of Vocalization

clicks

rapid onset and decay

pulses of sounds

broad-band (lo to hi freq)

click-trains

rapidly occurring clicks

flicker-fusion (ours for sight and sound is about 20 per second; dolphins can differentiate up to 800 clicks per second)

used in echolocation

used in communication (usually with some inflection or structure to them)

whistle

vibration of air

longer duration

sweeps through frequencies

non-pulsed

harmonics as by-product

fine line between click-trains and whistles since

Looking at Sound

• 

  Audiogram for select cetaceans

• 

  Echolocation

• 

  Burst Pulse

• 

  Whistle

audiogram

intensity vs. frequency

indicates what can be heard by animals

spectrogram

frequency vs. time

info contains: frequency bandwidth, duration of sound, and intensity (3rd dimension)

slice gives amplitude vs. frequency

waveform

amplitude vs. time

Scientist of the Day

Heinrich Hertz (1857-1894), Physicist

"I do not think that the wireless waves I think I have discovered will have any practical application."