How Hearing Works



How Hearing Works

Hearing has evolved in animals based on the acoustical information they need to determine their dynamic relationships with their surroundings.

Hearing adaptations reflect predator/prey relationships, community settings, and the strength or suitability of other perceptions. For example: you are likely to find more complex hearing adaptations in habitats that are less conducive to light transmission – underwater, underground, or in nocturnal settings because visuality in these settings is unpredictable. Outer ears reflect the mechanics of habitat as well. Birds and animals that swim will not have outer appendages called “ears” because they would produce dynamic drag (and noise).

Main Points:
Ears are adapted for survival based on an animal’s:

  • Position in food chain
  • Habitat

Forward-facing ears are found on predators
Highly movable ears are found on prey animals
Regardless of being predator or prey, habitat determines the different forms ‘ears’ take

Types of Ears:
External
Internal
Movable
Fixed
Purpose of Ears:
Evaluate relationship with the surroundings
Locate Prey
Identify Threats
Orient to surroundings
Establish connections to conspecifics
Anatomy of Ears:
Pinnae or Auricle – the outer ear shaped to focus the gathering of sound.
Concha “collecting cup.” Secondary reflections off the pinna and concha distort the incoming signal in time to assist us in localizing the source of sound.
Auditory meatus – the ear canal.
Ear drum – a diaphragm that converts pressure variations into mechanical motion
Ear bones – Incus, stapes, malleus – transfers the motion of the ear drum to the cochlea.
Cochlea – a stunning little organ that converts all of the signals from the vast surroundings into that neural impulses that animals use to create their “auditory scene.”
Terms:
Echolocation
– Bio-sonar used precisely by bats, dolphins, and porpoises. Used more generally by other animals (including humans).

Temporal and spatial distortion
– Sounds in a setting that reflect off of surfaces prior to being heard will be delayed from the sounds that arrive directly into the ears. The nature of the delay, as well as the characteristics of the delayed sound will give cues to the surfaces that caused the distortions – such as proximity, location, texture, and size.

Stereophonic or ‘binaural’ hearing
– Localization of sound sources by correlating time-of-arrival differences between two hearing inputs.

Diagram of a Human Ear

Diagrammatic View of the Ear

Guinea Pig Cochlea

B0000110 Cochlea of the inner ear

Whale Bulla
2005 whale bulla - ear bone

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