The gross structure of auditory system was familiar from high school. However, this week provided loads of new and interesting information and details of the structure of auditory system. The fact that outer hair cells mainly work just as amplifiers and that there is attenuating muscles inside the middle ear was surprising. Also the details of how the action potential forms from the audial stimuli due to the bending of inner hair cells increased our understanding.
This week we were also taught how the localisation of sound source is accomplished by the audial system. There are two methods that are used; inter-aural time difference and inter-aural intensity difference. In the inter-aural time difference the information of the time difference that the sound reaches each ear is used to localize the source of sound. If the sound is continuous the audial system detects the time difference via phase-locking. This means that the audial system recognises the difference of the phase the sound is when it reaches the ear. If the sound frequency is high enough phase-locking doesn’t work anymore. This is because the wavelength is smaller than the distance of the ears. In this kind of situation inter-aural intensity difference is the only way to localize the sound. In separating vertical differences in the location of sound inter-aural time difference doesn’t change. Thus, to localize the sound the shape of auricle and the way it reflects the sound waves is used.
One of the most interesting new fact was the concept of attenuation reflex. For example, we did not know about the tensor tympani and stapedius muscles. It is always intriguing to learn all the sophisticated systems the human body has to protect itself from injuries and traumas. The idea of evolution is here interesting that individuals who have had this kind of reflex have been able to pass this forward and those that were exposed to high frequencies without this reflex might have died as they were no longer able to hear after the high frequency noise. In addition, it would be extremely interesting to know if every individual has this kind of reflex or are there any differences in these kind of protective systems.
If we have an artistic view towards auditory system, we might want to know more about the role of our hearing system in perception of music among other random sounds we usually listen to. It would be scientifically fun to evaluate the perception of music from a physiological perspective rather than studying its cultural-specific elements. Generally, music is defined by manipulation of sound, the fact that how the auditory system encodes and maintain acoustic information forms our perception of music. One of the effective and determining dimensions that can be used by our auditory system to analyze a musical piece is pitch. Fo (common fundamental frequency of a harmonic spectra). Pitch of a sound helps us to determine whether a sound waveform is periodic and if so, with what period?! Peripheral auditory system is where both frequency and time domain information are present. Sound is broken down into its frequency contents by tonotopic mapping established in cochlea. This map of frequency is retained to some degree within the auditory system, including primary auditory cortex. In the time domain, information is present in the phase-locked action potentials of neurons, while each successive stage of auditory pathway reduces the precision of phase-locking. Although recent evidence shows that cortical neurons can be tuned to pitch, things about pitch mechanisms remain controversial and they are still being developed and studied. In a nutshell, regarding the perception of music, knowing that what pitches are representing and the relationship between pitches are very important,however, recognising the exact intervals by which the pitch changes is not easy. Depending on the stimuli, some unknown or learned pitch framework might be used by listeners to encode intervals in contexts of music. What we know for sure is that temporal lobe structures play an important role in pitch perception, Still we need more details about neural mechanisms.
The excursion this week was extremely well-organised and the company was fascinating. It was fun to see how the Nextism nTMS machine was used and how it actually worked. We think that the hosts were able to explain the functioning of the machine very well. There would have not been any better way to get well-acquainted with TMS. It was also fun to hear about the market and company, and see how the business model works. We realised that even though you have an almost perfect and one of a kind machine the product just does not sell itself and keeping up the business and being able to run it requires effort. In addition, it was peculiar that there is not much competition in this line of business.
Väinö, Maria, Ruhoollah