Editing Stimulus modality (section)

==Sound modality==

[[File:HumanEar.jpg|thumb|Diagram of the human ear.]]

===Description===
The stimulus modality for [[hearing]] is sound. Sound is created through changes in the pressure of the air. As an object vibrates, it compresses the surrounding molecules of air as it moves towards a given point and expands the molecules as it moves away from the point. Periodicity in sound waves is measured in [[hertz]]. Humans, on average, are able to detect sounds as pitched when they contain periodic or quasi-periodic variations that fall between the range of 30 to 20000 hertz.<ref name=Carlson />

===Perception===
When there are vibrations in the air, the [[eardrum]] is stimulated. The eardrum collects these vibrations and sends them to receptor cells. The [[ossicles]] which are connected to the eardrum pass the vibrations to the fluid-filled [[cochlea]]. Once the vibrations reach the cochlea, the [[stirrup]] (part of the ossicles) puts pressure on the [[oval window]]. This opening allows the vibrations to move through the liquid in the cochlea where the receptive organ is able to sense it.<ref name=Carlson />

===Pitch, loudness and timbre===
There are many different qualities in sound stimuli including [[loudness]], [[pitch (music)|pitch]] and [[timbre]].<ref name=Carlson />

The human ear is able to detect differences in pitch through the movement of auditory hair cells found on the [[basilar membrane]]. High frequency sounds will stimulate the auditory hair cells at the base of the basilar membrane while medium frequency sounds cause vibrations of auditory hair cells located at the middle of the basilar membrane. For frequencies that are lower than 200&nbsp;Hz, the tip of the basilar membrane vibrates in sync with the sound waves. In turn, neurons are fired at the same rate as the vibrations. The brain is able to measure the vibrations and is then aware of any low frequency pitches.<ref name=Carlson />

When a louder sound is heard, more hair cells are stimulated and the intensity of firing of [[axons]] in the [[cochlear nerve]] is increased. However, because the rate of firing also defines low pitch the brain has an alternate way of encoding for loudness of low frequency sounds. The number of hair cells that are stimulated is thought to communicate loudness in low pitch frequencies.<ref name=Carlson />

Aside from pitch and loudness, another quality that distinguishes sound stimuli is timbre. Timbre allows us to hear the difference between two instruments that are playing at the same frequency and loudness, for example. When two simple tones are put together they create a complex tone. The simple tones of an instrument are called [[harmonics]] or [[overtones]]. Timbre is created by putting the harmonics together with the [[fundamental frequency]] (a sound's basic pitch). When a complex sound is heard, it causes different parts in the basilar membrane to become simultaneously stimulated and flex. In this way, different timbres can be distinguished.<ref name=Carlson />

===Sound stimuli and human fetuses===
A number of studies have shown that a human fetus will respond to sound stimuli coming from the outside world.<ref name=Sontang>{{Cite journal | last1 = Sontag | first1 = L. W. | title = Changes in the Rate of the Human Fetal Heart in Response to Vibratory Stimuli | doi = 10.1001/archpedi.1936.01970150087006 | journal = Archives of Pediatrics & Adolescent Medicine | volume = 51 | issue = 3 | pages = 583–589 | year = 1936 }}</ref><ref name=Forbes>{{Cite journal | last1 = Forbes | first1 = H. S. | last2 = Forbes | first2 = H. B. | doi = 10.1037/h0071872 | title = Fetal sense reaction: Hearing | journal = Journal of Comparative Psychology | volume = 7 | issue = 5 | pages = 353–355 | year = 1927 }}</ref> In a series of 214 tests conducted on 7 pregnant women, a reliable increase in fetal movement was detected in the minute directly following the application of a sound stimulus to the abdomen of the mother with a frequency of 120 per second.<ref name=Sontang />

===Tests===
[[Hearing tests]] are administered to ensure optimal function of the ear and to observe whether or not sound stimuli is entering the ear drum and reaching the brain as should be. The most common hearing tests require the spoken response to words or [[Pitch (music)|tones]]. Some hearing tests include the whispered speech test, [[pure tone audiometry]], the tuning fork test, speech reception and word recognition tests, [[otoacoustic emission]]s (OAE) test and [[auditory brainstem response]] (ABR) test.<ref name="hearing test">{{cite web|author=Healthwise Staff|title=Hearing Tests|url=http://www.webmd.com/a-to-z-guides/hearing-tests?|publisher=WebMD|accessdate=29 July 2012}}</ref>

During a whispered speech test, the participant is asked to cover the opening of one ear with a finger. The tester will then step back 1 to 2 feet behind the participant and say a series of words in a soft whisper. The participant is then asked to repeat what is heard. If the participant is unable to distinguish the word, the tester will speak progressively louder until the participant is able to understand what is being said. The other ear is then tested.<ref name="hearing test" />

In [[pure tone audiometry]], an [[audiometer]] is used to play a series of tones using headphones. The participants listen to the tones which will vary in pitch and loudness. The test will play with the volume controls and the participant is asked to signal when he or she can no longer hear the tone being played. The testing is completed after listening to a range of pitches. Each ear is tested individually.<ref name="hearing test" />

During the tuning fork test, the tester will have the [[tuning fork]] vibrate so that it makes a sound. The tuning fork is placed in a specific place around the participant and hearing is observed. In some instances, individuals will show trouble hearing in places such as behind the ear.<ref name="hearing test" />

Speech recognition and word recognition tests measure how well an individual can hear normal day-to-day conversation. The participant is told to repeat conversation being spoken at different volumes. The spondee threshold test is a related test that detects the loudness at which the participant is able to repeat half of a list of two syllable words or [[spondee (grammar)|spondees]].<ref name="hearing test" />

[[Otoacoustic emission]]s test (OAE) and [[auditory brainstem response]] (ABR) testing measures the brain's response to sounds. The OAE measures hearing of newborns by placing an emitting sound into the baby's ear through a probe. A microphone placed in the baby's [[ear canal]] will pick up the inner ear's response to sound stimulation and allows for observation. The ABR, also known as the [[Brainstem auditory evoked potentials|brainstem auditory evoked response]] (BAER) test or auditory brainstem evoked potential (ABEP) test measure the brain's response to clicking sounds sent through headphones. [[Electrodes]] on the scalp and earlobes record a graph of the response.<ref name="hearing test" />