 Hi, and welcome back to this video course on biological psychology in this video video 3.5. We're going to take a look at hearing Hearing is the sensation of sound of course, right? And we also hearing is also called audition right like most senses There is a sort of a Latinized word audition and just a plain English word hearing So what is sound sound is waves of pressure in the air, right? So it is really literally like some some parts of the air are a little bit more compact than other parts of the air And these are waves that that sort of traverse through the air then and that's what we sense with our ears So waves pressure waves in the air The frequency of these waves determines the pitch so whether something sounds high pitched or low pitched So a high frequency is a high sound So if there if there is a very fast vibration in the air We perceive that as being high pitched compared to when there is a slow vibration in the air and The amplitude of the waves determines the intensity so high amplitude is a high intensity So it is loud. So if we have a high amplitude wave We will perceive that as being loud and if there's there's a slow amplitude wave We would perceive that as being less loud now so here on the right you see schematic of of essentially How loud things are in decibels and decibels is a logarithmic scale meaning that each increase in decibels is an exponential increase in the amount of in the amount of Energy that's actually in the sound and you see that we can hear across a very wide range of of decibels, right? So a whisper would be like 30 decibels apparently according to this graph and Like a car would be 80 right so there's 50 decibels so 50 exponential increases In energy now what I think is important to see in this graph is that our risk of hearing loss here is defined It's about 110 decibels And if you go to a concert, it is already 120 decibels, right? So It is much much higher above the risk of hearing loss So that is why I think or not why I think that is why hearing loss is such a huge problem Right. It's one of the most common disabilities of sorts, right? Because it is so easy for a hearing to become damaged by by things that are not even to our to us Don't even feel as being that loud, right? So a very large proportion of the population suffers from some degree of hearing loss I'm sure I suffer also from some degree of hearing loss because I've listened to a lot of loud music in in my life I'm here. I hear perfectly fine. It's not really a disability But I'm sure I would hear even better if I had never never done that So how do we translate how does the how does do these waves of pressure in the air translate to Translate to us hearing something. Well, the way it works is as follows. So it starts we pressure waves enter our Auditory canal here and they just go through there, right? Then they go to the tympanic membrane and the tympanic membrane is kind of a membrane That's inside your ear and it starts to vibrate when it when it is pressured by these pressure waves Then through this pretty complex contraption also calls kind of connected Connected bone like pieces in your ear These vibrations go through the overall window, which is another membrane But this is a membrane that is on your inner ear, right? So through a connection of all these things that vibrate and touch each other in and transfer vibrations at some point This oval window in our inner ear become starts to vibrate and because of that the cochlear fluid Inside our ear inside our inner ear also starts to vibrate So there's a whole cascade of things that vibrate and make each other vibrate and turn right and very complicated Unnecessarily complicated you would say way, right, but that's the way that evolution Designed quote-unquote designed our ears Now and then inside our inner ear we have hair cells now and hair cells are McKenna receptors So they are receptors. They become active. They start to sell sent nerve impulses due to chemical Stimulations are really is tearing and moving and the way it works is that you see that here in this picture Is that each hair cell which is this yellow thing has a stereocilia so cells, right? So the the hair cell itself is not a hair rather What's a hair is the thing that's on it, right? It's connected to it and these hair cells they connect the hair these hairs connect the hair cell to the Tectorial membrane which is another thing in your ear above it, right? Here you see it a little bit zoomed out Here you see it a little bit zoomed in Now then when the fluid in your inner ear starts to vibrate These hair cells also start to vibrate, right? So what happens there's a bit of friction that causes essentially the these like the Tectorial membrane and it's then part of your inner ear with the with the hair cells to go a little bit like this and That causes these these hairs the stereocilia to bend and stretch right to go Oh, whoop whoop whoop and that is then transferred into nerve impulses Right so and this is stretching and bending of these stereocilia. That's what triggers the action potentials in the hair cell now So how do we distinguish high and low frequencies? Well, there are two dominant theories One is that high and low frequencies stimulate different hair cells, right? So our inner ear has a lot of hair cells and they go kind of like in this this snail like better and the place theory of pitch perception simply holds that one set of these of these hair cells is Responsive to high pitch and another set of these hair cells is responsive to low pitch and this is the place theory of Perception because the place in your inner ear would determine whether you perceive something as high or low pitch and this is sometimes contrasted with the so-called temporal theory of pitch perception which holds that Different hair cells or what sorry that the same hair cells respond to different frequencies But they simply respond for example by firing at different rates to different frequencies, right? So there would be one hair cell that would respond for example very by rapidly firing to a high pitch and Firing less rapidly to a low pitch All right, so that would be in that case There is a temporal theory of pitch perception because the temporal aspect of how the neurons fire would determine whether we Perceive something as being lower high pitched now in reality There the reality is a mixture of both right so high pitch Causes high a high pitch sound cause different Neurons to fire different hair cells to fire, but it also causes a subset of the same hair cells to fire at different rates So the reality is a mixture of the place theory and the temporal theory of pitch perception as in many cases I would say in psychology Many theories are partly right now Hearing is processed in the auditory cortex So if you've seen the video on visual perception then we had the visual cortex, right? That process is visual information and the auditory code cortex processes auditory information Now the auditory cortex is part of the temporal lobe. So it's kind of The it's kind of hidden down here. Here you see here you see kind of it's kind of tucked away in there So if you want to see it, you have to get like a thing and open up your your cortex a little bit, right? It's kind of don't try that at home type of situation Now also in the lecture on visual perception I talked about the concept of topography that some aspect of the topography of your senses is often preserved now in the case of vision That was retinal topography. So the fact that different parts of your retina stimulate different neurons Right now, I should say the fact that neighboring parts of your retina If our process essentially by neighboring neurons in your brain In the auditory cortex the topography that that is preserved is the topography of pitch and it's called tonotopic Now what this means is that similar frequencies are processed by neurons that are very close to each other in your auditory cortex Right. So neurons that are near each other process sounds that are similar in pitch With that, let's move on to the next video video 3.6 in which we're going to talk about touch