The Processing of Auditory Information

Our environment consist a whole variety of full complex sounds which our auditory system breaks down into simple waves allowing us to process them. By understanding how complex sounds are formed from simple waves it will help us understand how the auditory system breaks those complex sounds into the simple waves and this is what we are going to look at in this essay.

(Open University, 2019) Sounds waves that travel in air are longitudinal waves. This means that the particles of the sound vibrate in the parallel direction that the sound wave moves. (The Physics Classroom, 2019) This wave is produced by the motion or vibration of an object. Those sounds are picked by our auditory system which is responsible for sense of hearing.  This system is divided into two parts the peripheral auditory system which is the outer ear and the central auditory system which is everything inside our ear including cochlear nucleus and auditory cortex (S. Sincero, 2013).

The eternal part of the ear provides protection to the middle and inner ear. This is where the pathway of auditory sound starts. The sound waves are transformed to unidirectional wave which is then directed to auditory canal where they can be amplified. The sound then travels to the middle part of the ear where it reaches the tympanic membrane and cause vibrations. The vibrations are depended on the loudness of the sound. The louder the sound the bigger the vibration. (Kenhub,2020) Those vibrations pass further into the ear via different bones. Those bones are called Malleus, incus and the stapes that form a passage to oval window.

Through oval window the middle part of ear can communicate with the inner ear. The sound travels through the oval window and enters the cochlea in the inner ear Cochlea is responsible for transferring the pressure waves into nerve impulses by  mechanical stimulation of hair cells within corti. (J.Casale,2018 ) The electrical impulses are then transmitted by cochlear nerve to temporal lobe which is responsible for auditory information’s inside the brain. Here the nerve impulses are converted into meaningful sound. This whole process only last few second and allow us to hear the entire complex sounds around us.

There are different characteristics of sound wave that pass through our ear and there are three aspects to each wave: frequency, amplitude and the phase.

The frequency is the number of waves; higher number of frequency which are closer together will make higher pitch (Figure.1). This is measured in Hertz (Hz). The amplitude is the height of the wave reaching maximum from the resting position so the higher the amplitude the louder the sound will be (Figure.2). This is what helps us determine how loud or soft the sound is. The phase relates to when a waveform at different point so the air pressure decreases and increases at different point for each sound. Phase information is important in sound localisation.

Figure 1 ‘High and Low Frequency wave’

Figure 2 ‘High and Low Amplitude wave’

The sound signal can be coded by the auditory system by extracting the information’s about the frequency and the intensity of the sound inside the cochlea. The coding depends on the frequency of the stimulus the higher frequencies rely on place code and the lower frequency will use the temporal coding.

There are two ways the frequency of a sound can be coded in the auditory nerve: by place which depends on tonotopic organisation or by temporal code which depends on phase locking.

Place frequency theory relates to the individual hair cells on the basilar membrane of the cochlea which possess different frequencies. The frequencies cause the vibration in the specific parts of basilar membrane. The brain will detect the pitch and compare it to the position of the hair cells that transmitted the neural signal(Y.Williams,2016).The basilar membrane allow different frequencies due to the changing biochemical properties like the size and the stiffness. The high frequency sound will not reach the end of the basilar membrane and will be sensed at the membrane near middle ear. Where low frequency sound will travel all the way to the end of the membrane. It’s the organisation of tonotopic that is maintained in auditory system that allow the cells response to different frequencies.

The coding by temporal theory is the timing of neural firing which is caused by the vibrations on the basilar membrane. The stereocilia (tiny hairs) on the hair cells move from side to side in response to sound wave. The hair cells are activated when those stereocilia are bent in one direction. The nerve impulses will occur at particular time or phase in each cycle of the sound wave ad this process is called phase locking because the neural firing is depended to the frequency vibration of each position on basilar membrane (C. Plack , 2012).

Intensity of signals are also coded by the auditory system in two different ways. First one is Intensity coding by firing rate.  This is when the intensity is coded in the cochlear nerve by an increase is discharge rate if action potentials (Open University, 2019b). The basilar membrane will vibrate with greater amplitude as the stimulus gets more intense. As the stimulus increases the number of produced action potentials increases too. Those vibrations cause the membrane to be depolarised and hair cells to release glutamate. This causes the neurons to fire at increased rate onto the hair cells. Intensity is also coded by the number of neurons. The result of increased sound and the amplitude of vibration is the number of neurons frequency being activated. Neurons that have the frequency close to the input will fire more strongly compared to those neurons with frequency slightly removed from the incoming signal. (Open University, 2019c)

Sound localisation is very important as it allows locating the origin of the sound. It also helps us determine the sounds direction and distance. The location is calculated through cues. There are three auditory localisation cues, which are Interaural time difference (ITD),  Interaural level difference (ILD) and Head-related transfer function (HRTF). (A.Lorenzi, 2019).

ITD explains the time difference from when the sound wave arrives at each ear. It then allows estimating the position of the sound in the horizontal plane. ILD calculates the difference of the intensity of the sound in each ear. It all however depends on the frequency of the sound. If the frequencies are below the 1500 Hz the Interaural level difference does not exist and anything above 1500 Hz will make the ILD a useful cue. (A.Lorenzi, 2019).

It’s amazing how we can localise and identify the sound that is coming from the background. We can process the sound waves that are complex and break them into single sound wave that gives us sufficient information that allows us to identify different sound sources. All of that happens as soon as the sound waves enter the outer ear and passes all the way into inner ear. We can use the differences in intensity of the sound and difference in the time of arrival of sound to our ears that help us to localise the sound source in the horizontal plane. This technique is very important and can be very crucial for helping us in dangerous situations by saving us.

References

A.Lorenzi (2019) ‘LOCALISATION’ [Online] Available at http://www.cochlea.eu/en/sound/psychoacoustics/localisation (Accessed on 10.01.2020)

C. Plack (2012) ‘Hearing pitch – right place, wrong time?’ [Online] Available at https://thepsychologist.bps.org.uk/volume-25/edition-12/hearing-pitch-%E2%80%93-right-place-wrong-time (Accessed on 11.02.2020)

J. Casale (2018) ‘Physiology, Cochlear Function’ [online] Available at://www.ncbi.nlm.nih.gov/books/NBK531483/ (Accessed on 11.01.2020)

Kenhub (2020) ‘Auditory pathway’ [Online] Available at https://www.kenhub.com/en/library/anatomy/auditory-pathway (Accessed on 10.01.2020)

Open University (2019) ‘2.1 What is sound?’, ‘Block 4 Chapter 2’ [Online] Available at https://learn2.open.ac.uk/mod/oucontent/view.php?id=1513663§ion=2.1 (Accessed on 28/12/2019)

Open University (2019b) ‘4.1.3 Intensity coding by firing rate’, ‘Block 4 Chapter 4’ [Online] Available at https://learn2.open.ac.uk/mod/oucontent/view.php?id=1513665§ion=4.1.3 (Accessed on 11.02.2020)

Open University (2019c) ‘4.1.4 Intensity coding by number of neurons’, ‘Block 4 Chapter 4’ [Online] Available at https://learn2.open.ac.uk/mod/oucontent/view.php?id=1513665§ion=4.1.4 (Accessed on 11.02.2020)

S.Sincero (2013) ‘The Auditory System’ [Online] Available at https://explorable.com/auditory-system (Accessed on 28/12/2019)

The Physics Classroom (2019) ‘Sound as a Longitudinal Wave’ [Online] Available at https://www.physicsclassroom.com/class/sound/Lesson-1/Sound-as-a-Longitudinal-Wave (Accessed on 28/12/2019)

Y. Williams (2016) ‘Place Theory of Hearing: Definition & Explanation’ [online] available at https://study.com/academy/lesson/place-theory-of-hearing-definition-lesson-quiz.html (Accessed on 20.02.2020)

Image of ‘High and Low Frequency wave’ Figure 1 .adapted from

J.Brainard (2019) ‘Wave Frequency’ [online] available at https://sciencewaveproperties.weebly.com/frequency-of-transverse-and-longitudinal-waves.html (Accessed on 20.02.20)

Image of ‘High and Low Amplitude waves’ Figure 2. Adapted from

H.Davies (2005) ‘Noise and hearing loss in farming’ [online] available at https://www.researchgate.net/figure/Low-amplitude-quiet-sound-waves-compared-to-high-amplitude-loud-sound-waves_fig2_29734945 (Accessed on 20.02.20)

Part 2

a)

Paper 1

M.Billot, P.Jaglin, P.Rainville, P.Rigoard, P.Langlois, N.Cadinuad, A.Tchalla, C.Wood (2019) ‘Hypnosis Program Effectiveness in a 12-week Home Care Intervention To Manage Chronic Pain in Elderly Women’, Clinical Therapeutics [Online] Available at https://doi.org/10.1016/j.clinthera.2019.11.007 (Accessed on 15.01.2020)

Paper 2

M.Brugnoli, G.Pesce, E.Pasin, M.Basile, S.Tamburin, E.Polati (2018) ‘The role of clinical hypnosis and self-hypnosis to relief pain and anxiety in severe chronic diseases in palliative care: a 2-year long-term follow-up of treatment in a nonrandomized clinical trial’ [Online] Available at http://apm.amegroups.com/article/view/17664/18505 (Accessed on 13/02/2020)

b)

c)

i)

M.Brugnoli article looks at the patients with severe chronic diseases which suffer from pain and anxiety. The clinical trial was nonrandomized and 50 patients took part both women and men where 25 of them were in the hypnosis group and 25 of them were in the control group. The aim of the study was to see if hypnosis was effective over a long period of time 2 years it was compared to pharmacological therapy along to see the effect of hypnosis therapy. Patients taking part suffered from rheumatic, neurologic and oncologic diseases. The results has showed that the Visual Analog Scale (VAS) for pain for the hypnosis group has decreased over 2 years from 81.9±14.6  at baseline to 38.9±12.4 at 2 years follow up. As well as the Hamilton Anxiety Rating Scale has showed decrease in hypnosis group and no change in the control group. Overall the study was success and has  proven that the patients in the hypnosis group has showed significant decrease in pain and anxiety as well as decrease in pharmacological pain treatment over 2 years compared to control group. This could mean that hypnosis could be considered as an effective pain and anxiety control in chronic diseases for patients in palliative care.

M.Billot article also looked at the effectiveness of hypnosis therapy to manage pain however only in elderly women and over shorter period of time which was 12 weeks. The aim of this study was to see the effects of hypnosis therapy delivered in home care a little more basic compared to the M.Brugnoli study. This trial took place in France and only 15 women took participation in the study. All the women suffered from chronic pain for longer than 6 months. The result has showed that the pain perception and pain interference has decreased after the 3 hypnosis sessions in 12 weeks. This means that the hypnosis could provide chronic pain managing in older generation.

ii)

Looking at two articles the study done by M.Brugnoli seems more professional. It’s more complex it took more time but more results were given. They provided control group to show the effect of hypnosis. Therefore they were able to compare and contrast the effectiveness of the hypnosis therapy to the pharmacological therapy alone.  The group of participants were larger compared to the M.Billot and wider population was considered for the study. Where in M.Billot study only older women took part in the study so we would have to see if there’s the same effect on for example older men. Both articles are very recent therefore a very reliable source of information.

iii)

Both articles did look at different pain managements however both gave me the answer to the question I was looking at which was ‘Can hypnosis successfully relieve pain’. I think that hypnosis can relive pain and can be used in a lot of different pain types. It’s great that there are other methods except medicine that can help people with their pain. As both articles looked at different pain types it shows that hypnosis can help with any pain and in the long time help with the life quality. What was also interesting to see that not only the hypnosis helped with managing pain, it also improved the participant’s mood, anxiety levels, sleep pattern and relationship with other people. This shows that there are other benefits to hypnosis therapy that medicine would not be able to help in patients with chronic diseases as a lot of time medicine prescribed have a lot of side effects which do affects people’s lives. However because the first article only looked at the pain management in older women  there would have to be more research done to see if the effect is the same on men too. As well as both articles only included adults in their study it would be good to see if hypnosis therapy has the same effect on children or does it only work from certain age. What would also be interesting to see if there’s any hypnosis therapy for a shorter pain management like for example broken leg could this help people manage the pain without any medications. Looking at the results from both studies I can see that there are improvements in participant’s pain management and anxiety over period of time. There are however limitations to hypnosis therapy as each therapy is different and some might work for certain people and might not work for other so trying to find the right one might take some time therefore this type of pain relive could be a vey long process before it works.