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Communication Topic 10: Detecting Sound

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  1. CommunicationTopic 10: Detecting Sound Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

  2. DOT Point(s) • outline and compare the detection of vibrations by insects, fish and mammals • process information from secondary sources to outline the range of frequencies detected by humans as sound and compare this range with two other mammals, discussing possible reasons for the differences identified

  3. Introduction Mammals inhabit land, sea and air. Consequently, their uses of sound for communication are many and varied. Lets begin by thinking of noises that animals make to communicate. For example, barking, chirping, grunting, snorting, whistling etc. Can you think or any more?

  4. Introduction Now lets think about the reasons why animals would make such sounds. For example, co-ordination, distress, fear, warning, mating, navigation. Can you think of any more?

  5. Introduction Cicads produce sounds that are so loud (120 decibels) that is can be painful to the human ear. The main purpose of their songs is to find a mate. Cicads are a communal species so the sound can also be used to ward off predators. Because they often sing in a group it can also make it more difficult for a predator to locate individuals.

  6. Introduction Since many fish sounds are associated with reproduction, their noise is often used by researchers to measure the time and place of spawning. Dolphins are known to home in on sound-producing fish and dolphins’ whistles have been known to supress the chorus of some fish.

  7. Introduction Frogs croak for a variety of reasons, such as attracting a mate, marking territory and distress. Male birds have special calls for attracting mates as well as warding off other males and predators.

  8. Detecting Sound The Ear is one of the most complex organs of the human body and yet it can be traced back to a simple organ in prehistoric creatures. Even in modern jellyfish it is an organ of balance. Although this is a secondary function of the ear today.

  9. Insects • The tactile bristles on an insect’s cuticle and on its antennae respond to low frequency vibrations.

  10. Insects Many insects possess more specialised structures for hearing. • Orthopterans(crickets and katydids) have a tympanum (drum) or ear on each leg just below the knee. The tympanum is a cavity containing no fluid.

  11. Insects It is enclosed by an eardrum on the outer side and a pressure release valve on the other. • Nerve fibres are connected to the eardrum and pick up the vibrations directly. Female crickets are deaf to some frequencies and sometimes rely on the smell given off by the male as he raises his wing covers to make a call.

  12. Insects Both male and female cicadas possess organs for hearing despite the fact that it is only the males that sing. A pair of large, mirror-like membranes, the tympana, are connected to an auditory organ by a short tendon at the base of the abdomen. When a male cicada sings he crinkles his tympana to prevent deafening himself.

  13. Fish The hearing abilities of fish vary between species. • All fish have a lateral line sensory organ, a pronounced pair of sensory canals, which run the length of each side of the animal.

  14. Fish • Pressure waves in the surrounding water distort the sensory cells found in the canals, sending a message to the nerves. There is a significant link between the lateral line and the true organs of hearing. It has the same type of hair cells and nerves that are found in the inner ear of humans.

  15. Fish Some fish actually perceive sound waves by possessing an inner ear that has a sensory chamber composed of passages called the labyrinth. It contains an otolith (ear stone) and is lined with hair cells. Auditory nerves detect the differences in vibrations between the hair cells and the otolith. This is recorded as a nerve impulse, which is carried to the brain.

  16. Fish The swim bladder may also play a part in transmitting vibrations to the sensory chamber. In many freshwater fish, such as carp, the transmission may be enhanced by a series of small bones, the ossicles, which connect the swim bladder to the sensory chamber.

  17. FYI Amphibians For interest sake, some frogs have extremely large tympana (drums) on the sides of their heads. The size is related to the frequency and wavelength of their call. The tympana are connected to the lungs so that when the eardrum vibrates the lungs absorbs the vibration, thus preventing pain and injury.

  18. Mammals There are many similarities in the basic hearing processes in marine mammals and terrestrial mammals. We will use the human ear as a model for terrestrial ears. Although there are differences among the ears of different species, the basic processes of hearing are the same.

  19. Mammals The human ear is divided into three sections: • The outer ear which collects and directs sound • The middle ear filters and amplifies the acoustic energy to the inner ear • The inner ear transforms the acoustic energy to electrical signals that are processed by the brain. We’ll look at this in much greater detail later.

  20. Mammals Killer whales have an acute sense of hearing. Sound is received by the lower jawbone. This contains a flat-filled cavity which extends back to the auditory bulla (ear-bone complex). Sound waves are received and conducted through the lower jaw, the middle ear, inner ear and the auditory nerve to the well-developed auditory corex of the brain.

  21. Mammals Dolphins close their canals when diving. They detect vibrations through special organs in the head and some low-frequency sounds through the stomach.

  22. Frequencies Detected The frequency range of human hearing is limited to approximately 20-20 000 cycles per second (Hz). The ability to hear high-pitched sounds decays throughout life. -

  23. Frequencies Detected Mammals other than humans can detect sound frequencies lower than 20Hz and much higher than 20 000Hz. Dogs, for example, can easily detect sounds between 15Hz and 40 000Hz. They are able to hear a high-pitched dog whistle, which is inaudible to the human ears.

  24. Frequencies Detected The frequency of sounds produced by dolphins ranges from 0.25Hz to 150 000Hz and takes the form of whistles and clicks. Their hearing range is 150-150 000Hz.

  25. Frequencies Detected The high-frequency, shorter sound wave is used in dark and murky water to locate objects and find food. Dolphins use low-frequency sounds known as whistles for communication. Lower-frequency sounds travel further in water.

  26. Frequencies Detected Bats use a higher range of frequencies. Sounds produced are in the 10 000Hz-120 000Hz range. Their hearing extends from 1.0Hz to 120 000Hz.

  27. Frequencies Detected Bats are crepuscular (active in dim light- dawn/dusk) or nocturnal (active in darkness). As a result they rely strongly on echolocation for navigation and detection of prey. The higher-frequency sound wave, being short, produces more detailed messages for the bat about its surroundings.

  28. Frequencies Detected During the course of human evolution, the ability to modify the environment has resulted in less reliance on the sense of hearing for survival. Humans retain effective three-dimensional vision, which eliminated the need for echolocation.

  29. Activity -Students to Complete DOT Point 6.8 Range of frequencies detected by humans and two other mammals