our ears and brains have evolved to pick up those air vibrations and to interpret them as ^^sounds-caused-by-events-at-a-location^^
the air vibrations that hit our ears can vary in many ways, but always in the 2 dimensions of ^^intensity and time^^
Intensity: the amount of energy ^^transmitted by the wave^^, where this is evident as the pressure (^^sound pressure levels^^) exerted by the sound wave as it travels through the air
^^intensity and frequency^^ are ^^physical attributes^^ that can be measured, while ^^loudness and pitch^^ are ^^psychological attributes^^ that result from the perceptual processing by the ears, the auditory nerve and the brain
The Auditory System
External Ear: consists of the pinna and the ear canal
Middle Ear: consists of the eardrum (tympanum) and the ossicles (ear bones)
Inner Ear: made up of the cochlea and the auditory nerve
Cochlea: a coiled tube-like structure filled with fluid and an array of sensitive hair cells attached to a vibration-sensitive membrane
the ^^balance system or vestibular system^^ is also a part of the cochlea and consists of 3 circular tubes filled with fluid and hair cells which transduce the movements of the head into nerve impulses
operates in 3 phases: ^^reception, transduction, and perception^^
sound energy to be transmitted to the inner ear behind the eardrum
neural impulses travel to the auditory processing centers in the brain and are interpreted into ^^sound perceptions^^
on the inner side of each eardrum is a chain of 3 of the smallest bones in the body called the ^^ossicles^^ which ^^transforms the air vibrations into mechanical vibrations^^
the last of the ossicles vibrates onto a small membrane covering the end of a fluid-filled coiled canal called the ^^cochlea^^ which ^^transforms vibrations into electrical impulses^^ through the membranes and hair cells
hair cells have receptors nerve-endings which fire an ^^electrical impulse^^ when the hairs are moved
Perceptual Constancy: in hearing, perception can be constant despite the changing sensory information which allows us to separate out sound into perceptual “figure and ground”
“What” and “Where” Pathways: the visual system often takes priority when we need to work out where something is, with hearing only providing supplementary information
Psychophysics
Georg Ohm (1789-1854) and Herman von Helm Holtz (1821-1894) tried to identify the limits of perception in well-controlled lab environments
Applications: hearing aids, recording techniques and the acoustic design of concert halls and theaters
Limitations: reductionistic in character; assumed that in order to understand how we perceive complex sounds, one should begin with “simple” sounds
Auditory Scene Analysis
Bregman (1990) focused on how research on ^^auditory perception^^ should be about ^^finding out how parts of the acoustic wave are assigned to perceptual objects and events^^
combining aspects of both Gestalt psychology and ecological psychology, he created auditory scene analysis
Auditory Scene Analysis: the scene by which out auditory system “creates individual descriptions that are based on only these components of the sound which have arisen from the same environmental event”
the auditory system decides through innate and learned heuristics, which bits of acoustic energy belong together and this needs to be done simultaneously
Areas of Research
Localization
3 sources of information used by the auditory system to localize the origin of a sound: amplitude, time, and spectral information
Duplex Theory of Sound Localization: when a sound comes from the left of the person’s head, it hits the left eardrum earlier and with slightly more energy compared with the right eardrum
humans locate sound below 1.5 kHz by analyzing ^^temporal differences^^, while frequencies above 3 kHz are located by the comparing ^^amplitude differences^^
humans are better at locating sounds in the horizontal plane than in the vertical plane
we can locate sound source with an accuracy of above 5 degrees, and this can increase to within 2 degrees when the sound source is moving an dis broadband (like a white noise) rather than a single tone
when a sound is directly in front of us, above the midline of our hands, or directly behind us, there are amplitude and time differences between the 2 ears
the auditory system uses the changes made to the sound by the shape of the pinnae (i.e., the external ear), and to some extent the shape and reflecting properties of the head and shoulders
Guski (1990) printed out that auditory localization improves markedly with ^^free hand movement^^ (Fisherman & Freedman, 1968) the use of ^^natural sound sources^^, and with ^^sound-reflecting walls^^
he found that localization was better with the reflecting surface on the floor and worse when it was placed above the listener
Non-Speech Sounds
Van Derveer (1979) recorded naturally occurring sounds such as people walking up and downstairs, crumpling paper bags, whistling, jangling keys, and hammering nails. She found that listeners were able to identify each sound with a high degree of accuracy. Listeners tend to classify sounds according to the gross temporal patterning, or rhythm, as well as on the basis of the continuity of the sounds.
Top-Down Processing: Ballas and Howard (1987) suggested that we continually attempt to construct meanings for the sounds we hear and drew parallels with some of the processes found in speech perception
Speech Reception
When we listen to speech we do not notice the actual sounds being made, but instead process the meaning effortlessly if we are fluent in that language.
Categorical perception suggests that we have evolved more efficient ways of processing sounds by ignoring some information in the acoustic signal and use the influence of top-down processing to help us to become even more efficient.
Warren (1970) presented the sentence “the state governors met with their respective legislatures convening in the capital city'“ to listeners and replaced the middle “s” in “legislatures” with a 120 millisecond tone. Only 5% of listeners reported hearing the tone, but despite hearing it they could not identify where in the sentence they had heard it. This phonemic restoration effect is quite reliable.
Applications of Auditory Perception Research
Auditory Interfaces and Displays
in computer interface design, using sounds is especially useful in alerting us that something is happening outside our field of vision or attention
Auditory Icons: caricatures of everyday sounds, where the source of the sound is designed to correspond to an event in the interface
Opening a folder may be accompanied by the sound of a filing cabinet drawer opening, or putting a file in the trash or recycle bin is accompanied by a scrunching-up sound
Earcons: based on musical motifs such as a short melody, and they are designed to represent aspects of the interface
When a folder is opened a musical crescendo might be played and when it is closed a descending sequence of notes is played
Sonification
the use of synthesized sounds to help visualize quite complex data sets by using the data to control the sound output
Navigational Aids for People with Visual Impairments
some blind people are able to avoid colliding with obstacles through the echoes reflected from surfaces, but they are not aware that they are using hearing to do so
people describe the feeling the pressure “waves” on their faces when approaching objects rather than any change in sounds
a common arrangement is to have a laser range-finder scan the environment, with its output influencing a sound
other systems use a camera on a headset worn by the visually impaired person, with a small computer reading the visual scene and converting the image into an image made up of black and white pixels, which is then converted into high and low pitches
SAT NAV
used stereo sounds to help the visually impaired listener scan the environment to acoustically detect objects in their way
Warning Sounds
hearing is often described as an ^^orienting system^^, the purpose of which is to alert an animal to changes in the environment and make it aware of the direction of a possible attach or food source
acoustic alerts often work better than visual ones, as the receptor organs do not need to be focused on the source, and unlike light, sound is both transmitted in the dark and goes around corners
The sound properties of emergency vehicle alarms and sirens have been studied to optimize how we perceive them. Our perception of which direction a speeding emergency vehicle is coming from and where it is going can be influenced through the types of sounds the sirens produce
Machine Speech Recognition
automatic systems are used in call centers to navigate menus and even help identify irate customers who can be directed to a real customer service representative
analysis of ^^acoustic-phonetics^^ can give a depth of information, such as emotional meaning of the way somebody says something
Earwitnesses Testimonies
research there is tells us that we are fairly good at recognizing familiar voices, not very good at all with unfamiliar voices, and that for both types of voice we tend to overestimate our ability to identify the speaker correctly
earwitness reports were more vulnerable to misleading post-event information than eye witness memory for a car accident scenario
length and repetition of the utterance in the lineup can also help to improve recognition, possibly allowing the listener more opportunity to process the speech in a more careful manner