Auditory System: Sound

The Stimulus Input: Sound Waves Sound, like light, comes in waves, which are characterized by their frequency (pitch) and amplitude (decibels). The height of the wave gives us the amplitude of the sound. The frequency of the wave gives us the pitch of the sound. Sound is vibration. The vibrational energy of vibrating objects, such as guitar strings, transfer the surrounding medium-air as the vibrating objects push the molecules of the medium back and forth. In space, there is no air, so the sound wave would have no medium to push. Any explosion, for example, would be eerily without sound. Frequency --> number of cycles completed by a wave in a given amount of time determines pitch **Pitch --> sound’s highness or lowness measured as hertz (Hz) High pitched sounds Amplitude --> physical strength of a wave--the “volume” of a sound; measured in decibels Low pitched sounds

The Stimulus Input: Sound Waves Locating where sound is originating from requires two cues: --Which ear hears the sound first? the louder sound?

The Stimulus Input: Sound Waves 4,186 Hz Highest note on a piano 1,000 Hz Highest pitch of human voice 100 Hz Lowest pitch of human voice 27 Hz Lowest note on a piano

The Stimulus Input: Sound Waves Discovering PSY p. 94 Figure 3.7 Above are examples of Frequency & Amplitude/decibels Timbre – distinctive quality of a sound determined by the complexity of the wave and its different combinations of frequencies. (Figure C is more complex than Figures A or B)

Distinguishing Pitch Frequency theory -- basilar membrane vibrates at the same frequency as the sound wave The higher the frequency wave, the faster the firing of hair cells Theory used to explain how you hear low frequencies Place theory -- different frequencies cause larger vibrations at different locations along the basilar membrane Different pitches stimulate different areas on the basilar membrane The brain receives these messages and interprets them as different pitches Theory used to explain how you hear high frequencies Use both theories when you listen to sounds with both high and low frequencies

Auditory Masking Piccolo, soft Bassoon, loud Piccolo, loud Bassoon, soft Distance along basilar membrane (a) (b) Effect of bassoon on basilar membrane Vibration amplitude of basilar membrane Effect of piccolo on basilar membrane Low frequency sounds effectively mask high frequency sounds High frequency sounds cannot effectively mask low frequency sounds Hockenbury Powerpoint (schulman)

Visual Capture The most accessible example is a movie theater. Imagine being in a movie theater. Where does the sound originate? The sides of the room we are in, because we can picture in their minds the big speakers hanging on the sides of the movie theater. When we are watching a movie, we believe the sound comes from the front of the room. When the actors are talking on-screen, the sound appears to come from their mouths because of visual capture - the eyes overrule the ears. Hockenbury Powerpoint (schulman)

The Process Of Hearing (How Sound Waves Become Auditory Sensations) Auditory perception occurs when sound waves interact with the structures of the ear Audition (sense of hearing) results in sound waves being collected in the outer ear, amplified in the middle ear, and converted to neural messages in the inner ear. The middle ear transmits the eardrum’s vibrations through a “piston” made of 3 small bones (the hammer, anvil and stirrup) to the cochlea (snail shaped tube). The incoming vibrations cause the cochlea’s membrane (oval window) to vibrate, moving the fluid that fills the tube. This motion causes ripples in the basilar membrane (hair cells). The movement of cells triggers impulses in the adjacent nerve fibers which form the auditory nerve that connects via the thalamus to the temporal lobe.

Parts Of The Ear

Parts Of The Ear Revisited Hockenbury Powerpoint (schulman)

Anatomy Of The Cochlea: Another View Outer ear Middle ear Inner ear A sound causes the basilar membrane to wave up and down Basilar membrane Hair cells Tectorial Round window Eardrum Oval window Cochlea, partially uncoiled Stirrup Anvil Hammer Sound waves Auditory canal

Parts Of The Ear Pinna --> Sounds waves enter it and are funneled to the auditory canal Auditory Canal --> Connects the outer ear with the eardrum (tympanic membrane) Ear Drum --> Tissue barrier that transfers sound vibrations to the ossicles; can be damaged by objects in the ear or exceptionally loud noises Ossicles (hammer, anvil, stirrup) --> Three tiny bones that transfer sound waves from the ear drum to the cochlea; in old age, they may become brittle or damaged, resulting in conduction deafness Oval window --> Point on the surface of the cochlea which receives the sound vibration from the ossicles; as the oval window vibrates, the fluid in the cochlea vibrates, moving hair cells along the basilar membrane Cochlea --> A hearing organ where sound waves are changed into neural impulses Hair cells --> Receptor cells for hearing in the cochlea that change sound vibrations into neural impulses. When they move, they trigger action potential in the base of the hair cell (transduction). --Similar to the rods and cones within the eye --If these are damaged (due to prolonged loud noises), then you have nerve deafness which cannot be helped by a hearing aid. Auditory Nerve --> Stimulated by the hair cells in the basilar membrane of the cochlea, it carries sound information from the ears to the thalamus then to the auditory cortex in the temporal lobes of the brain

Position And Movement Vestibular sense: The sense of body orientation with respect to gravity The receptors for this information are tiny hairs in the semicircular canal of the inner ear

Types Of Hearing Loss (Deafness) Conduction Hearing Loss --> Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea. Surgery Sensorineural Hearing Loss --> Hearing loss caused by damage to the cochlea’s receptor cells (i.e. hair cells) or to the auditory nerve, also called nerve deafness. Hearing aid to amplify sound Cochlear Implant