How the auditory nervous system processes the intensity of pure tone sounds
Introduction
The human brain is a complex structure being the central part of the nervous system carrying out more complex and sophisticated functions of the human body. Every and each organ of the body is connected with the brain, the brain surrounded by a composite structure of skull bones. This is the ordinary capsule provided by nature to the brain so that it can be kept safe and sound as it occupies the position of a king in the human body.
In the same way the human ear has no exemption in regard of connectivity to the brain. The connections connecting various parts of body with the body are called nerves. These my be undestood as a complicted network string like threads spreading through out the body to convey different messages to and from brain to various organs of the body. The live example of the nervous system be used as synonym with the electric system of a country.
The anatomy of human ear is composed of varioius parts of the ear but here the scope of this study is how the auditory nervous system procesess the intensity of pure tone sounds.accordong to Watson C (1995) the human nervous system that sees, hears,feels, moves, remembers and dreams. These are the different functions carried out by the separate individual organs of the human body. The human brain by itself is an organ but this organ occupies a central position of the body and it has different connections through out the body.
As described above that the human is also greately connected with the brain solving the audition problems of humans. Ear is a part of body which is not distant from brain. Conversely it is near to brain. The nerve has also been explained earlier. Now what is the auditory nervous system. As its name indicates it is the nerve helping in audition of the human beings. All auditory communication becomes possible by the function of this nerve.
A researcher named Sincero S (2013) the auditory nervous system is a complex structure that is mainly accountable for perceiving sounds. More simply this system is responsible for the sense of hearing. This system has further divided into peripheral auditory system and the central auditory system.As far as its division is concerned, it has been done so for the sake of anatomy of the ear. While as regard function of the auditory system it is a specilized sort of organ specially responsible for hearing in the human body.
Amanda M. (2016) stated that cochlea is the inner ear. According to the research study of Amanda, the auditory nerve (spiral Ganglion Neurons) is seated in the cochlea. There are two types of auditory nerve fobers. These fibers are tuned to respond to certain specific ranges of frequency.Moreover, these fibers are responsible for conveying the intensity of sound to the brain. This is the reason that damages to cochlea result in certain types of hearing loss.
Pure Tone Audiometry
One of the researchers named Kurtz J. (2018) described pure tone audiometry as a behavioral test carried ot for the measurement of auditory responsiveness. In this test pure tone hearing responsiveness is graphed on an audiogram by the use of pure tone thresholds (PPTs) indicating the softest sound able to be heared by a person at least 50% of the time.
Cochlear Nerve and the Auditory Cortex
The reserch study of Friedland D (2006) stated that tympanic tympanic membrane or ossicles has a great role in transmitting sound to the cochlea.Tramo MJ et al (2002) stated that many neurons in auditory cortex are excited by pure tone stimulation only when the tone's frequency lies within a narrow range of the audible spectrum.Furthermore, the research study finded out that fine-grained frequency resolution at the perceptual level relies on neuronal frequency selectivity in auditory cortex.The more finer frequency leads to more soft and finner tuned neurons in auditory cortex.
Processing of Pure Tone Sounds
The research study of Strainer JC. et al (1997) stressed the point that pur tone sounds activted less pixels as compared to stepped tones or in other words it can be interpreted as higher intensity sounds activate more pixels and vice versa.The auditory cortex composed of neurons involved in decoding the cochleotopic and tonotopic spatial representation of a stimulus.And this is known as the primary auditory cortex (AI). The other one is called secondary auditory cortex (AII) having an important role in sound localisation and analysis of sounds. The elt region of the ear helps to integrate hearing with other sensory systems.
These are systems which are capable of extracting meaningful information from the surrounding advantageous for survival. A stimulus dimension across which sounds are relatively consistently perceived is intensity or sound level.The bandwidth of the sound depends upon the intensity of the sound. The bandwith increses with the intensity of sound. Similarly the auditory cortex plays an important role in this regard.Proper signals are sent to the brain through the cochlea neural network. So the brain helps in recognition of the sound.Furthermore, sources of sound at distant places have less intensity as compared to sources nearer the ear but all this depends upon the intensity of the sound. All this activity is carried out in the auditory cortex leading signals to the brain.
Recent experiments indicate that primary auditory cortex is necessary for the normally-high perceptual acuity exhibited by humans in pure-tone frequency discrimination. The present study assessed whether the auditory cortex plays a similar role in the intensity domain and contrasted its contribution to sensory versus discriminative aspects of intensity processing. We measured intensity thresholds for pure-tone detection and pure-tone loudness discrimination in a population of healthy adults and a middle-aged man with complete or near-complete lesions of the auditory cortex bilaterally. Detection thresholds in his left and right ears were 16 and 7 dB HL, respectively, within clinically-defined normal limits. In contrast, the intensity threshold for monaural loudness discrimination at 1 kHz was 6.5 ± 2.1 dB in the left ear and 6.5 ± 1.9 dB in the right ear at 40 dB sensation level, well above the means of the control population (left ear: 1.6 ± 0.22 dB; right ear: 1.7 ± 0.19 dB).
Summary
The results indicate that auditory cortex lowers just-noticeable differences for loudness discrimination. Activation in the primary auditory cortex depends on intensity of the auditory stimulus.
References
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