Cognitive Science: An Introduction/Audition

Information
Audition is turning pressure waves in some fluid medium, such as air or water, into some internal representation.

Overview
The Human Auditory System (HAS) is the specific organization of the outer, middle and inner ear structures designed to transform sound waves from the environment into neural messages that are sent to the auditory cortex for speech comprehension. The HAS is directly involved with communication and the comprehension of speech. This begins with auditory perception through the various structures of the auditory system. The human auditory system is essential for routine cognitive processes such as speech comprehension, communication, memory, learning, equilibrium, and localization. While the HAS provides adaptive advantages such as information from the environmental and facilitating human cooperation, problematic issues include tinnitus and other auditory distractions that can degrade cognitive efficiency. Auditory information can be employed simultaneously with visual information to allow individuals to comprehend their surrounding environment.

Structure
The HAS is a complex system organized to ensure the transmission of sound vibrations into cognitively coherent input. Audition is the reception of acoustical energy, or sound waves, which cause vibration of the tympanic membrane, which is the main default mechanism of hearing. Vibrations are translated into auditory information with activates brain regions such as the frontal lobe and Wernicke’s, the areas of the brain responsible for speech and sound comprehension. The HAS is made up of three structures: the outer ear, the middle ear and the inner ear which are composed of various tissue and small bones that function together. The function of the outer and middle ear is to amplify auditory perception from our surrounding environments. Once the sound has been amplified, these waves pass through the inner ear. At this point, structures of the inner ear will convert the external auditory perception into vibrating impulses, which are then used to send information to the brain.

The Outer Ear
The outer ear consists of two parts: the pinna and the ear canal. It is defined as the visible structure of the ear with a purpose of collecting and transmitting auditory data. The pinna is responsible for the collection of sound, which can be defined as a SW with a frequency between 16 to 32 Hertz (Hz) and 16 000 to 20 000 Hz. The pinna and ear canal transfer external auditory data by processing sound from the bending of cilia of hair cells in the canal towards the tympanic membrane. The outer ear structures are responsible for capturing and transmitting sound to the middle ear.

The Middle Ear
The middle ear consists of two main parts: the tympanic membrane and the ossicular chain. The middle ear is also connected to the back of the olfactory system (the system responsible for smell) by the Eustachian tubes. Various structures that make up the middle ear include: the anterior ligament of the malleus, external auditory meatus, incus, malleus, manubrium, orbicular apophysis, posterior ligament of the malleus, round window, superior ligament of the malleus, stapedius, and tensor tympani. Further, the human middle ear contains three ossicles capable of handling higher auditory frequency transmission. The middle ear is composed of many smaller structures responsible for taking auditory input from the outer ear and amplifying it for additional processing, all taking place in the inner ear.

The Inner Ear
The inner ear is the structure capable of sound transduction and equilibrium. Complexity is increased compared to the outer and middle ear. Its structures include the cochlea, fluid-filled semi-circular canals, and the vestibule. The inner ear also shares a connection with the middle ear in correlation to the ossicle chain. The inner ear focuses on the analysis of sound wave frequencies and the mechanism of balance by examining the movement of fluid and hair fibres. Research findings on the precedent concept conclude that the evolution of the inner ear provides mankind with the ability of higher-frequency detections.

Sound Transducing Mechanism
The sound transducing mechanism (STM) specializes in the transduction of sound waves into impulses. During the phase of auditory perception, afferent pathways and static acoustic nerves transport neuronal impulses from the cochlea. The cochlea is used as a frequency analyzer for the brain stem, where these impulses will be processed by the central auditory pathways (CAP) of the brain. The efferent fibres of the inner ear bring impulses from the auditory cortex to the cochlea. This concludes that the STM is required for the communication of impulses to and from the brain, which occurs in the neuronal structures of the HAS.

The Neuronal Structure of the Human Auditory System
The HAS functions is to convert sound vibrations into neural impulses. The beginning of the neural process of the auditory system is in the midbrain, where specialized neurons are accumulated after auditory perception. In the process of auditory perception, hair cells become excited, activating neural impulses within the nervous system. Inner hair cells transduce vibrations of audible sound waves and frequencies. After sound waves trigger inner ear fibres the ion passages of the static acoustic nerve open and close allowing neuronal impulses and neurotransmitters to be released.

Memory and Learning
Memory is defined as the ability to encode new information, followed by the long-term storage of the knowledge learned. Human brains are capable of retrieving stored information to assist in cognitive tasks. This includes a part of short-term memory, also known as auditory working memory (AWM). AWM enables the ability to maintain and manipulate auditory data over a short time period after the stimulus is no longer perceptible. In the HAS, working memory is employed by transmitting auditory information to the AWM and auditory long-term memory (ALTM). Once the AWM system holds information from working memory, it can then be used in conjunction with visual working memory (VWM) and be transported to the central executive memory (CEM). Once held within the CEM, information can then be cognitively processed as one comprehensible unit and engage with higher-level cognitive tasks.

Vestibular Function, Equilibrium and Localization
The auditory system plays a major role in vestibular function, equilibrium, and localization for sensory division of the nervous system vertebrates. This division of vertebrates allows the vestibular and semi-circular canals to maintain balance. Another function provided by the HAS is that of localization - the ability to determine the location of a perceived sound. Localization begins when the pinna differentiates the timing of the audio received by both ears. The location of the sound is the cognitively perceived as a sense of direction. Sound travels at about 344 meters per second. Human ears are approximately 0.175 meters apart, hence two ears receive the same sound at different times - about half a millisecond timing difference. The difference between the arrival time is used to determine which direction the sound is coming from.

Hearing Loss
Complete or partial hearing loss is the third most common health defect in adults. Complete or partial hearing loss can result in cognitive confusion and mental decline due to social isolation [20]. Partial hearing loss in the HAS can result from many factors, notably the disruption of the equalization of pressure by the Eustachian tubes on both sides of the tympanic membrane.

A primary causes of hearing loss is the unremitting exposure of damage to the hair cells of the inner ear over time. Damage of the hair cell due to exposure is known as the “breakage of tip links.” Tip links are essential for connecting mechanical stimuli to the hair cell’s mechano-electrical transduction channel. The mechano-electrical transduction (MET) channel is responsible of the transformation of sound input from our environment into an electrical impulse and the subsequent cognitive input. Age-related hearing loss (ARHL) can simply be caused by the effects of long-term use of the HAS.

Tinnitus
A common issue in the human auditory system is the phenomena of tinnitus, the perception of noise that is caused by a physical condition in the ear. The chronic form form of tinnitus is known to affect 10-15% of individuals. There are two types; objective tinnitus (OT) and subjective tinnitus (ST). OT is caused by an abundance of blood flow causing vibrations that stimulate the cochlea. OT is defined as objective as the subjects are perceiving actual frequencies and vibrations from their circulatory system. ST, unlike OT, is not caused by an actual sound perception. ST is responsible for providing a sound perception to the subject affected, which is caused by the absence of sound perception and/or acoustic stimuli. ST has a lasting effect on sound perception for seconds to several minutes.

Echolocation
Echolocation is related to audition--it's using sounds created by the agent to determine spatial relationships in the world. The animal, say a bat or a dolphin, sends out high-pitched sounds. They reflect off of surfaces in the environment, and the agent's hearing interprets the information in terms of space. So echolocation can be thought of as using hearing to do what is often vision's job--understanding the structure of our physical world. But note that it cannot detect color, brightness, or other visual properties: only shape, distance, and texture.

Animal and Plant Auditory Systems
Some plants respond to sounds.


 * Examples of information other animals are capable of hearing that we aren't

Sensation in the human auditory system

 * Summary of information processing from outer to inner ear
 * Description of thresholds and significance of these
 * Low level coding that leads to some forms of "perception"

Perception in the human auditory system

 * Summary of our understanding of how this is put together in the brain
 * Examples of Atypical human perceptions

Artificial auditory systems

 * Examples