[MUSIC]. Okay. So how come stimulus, stimulus is so dis connected from the perception. Well because we take a long and winding road between stimulus and perception. The stimulus is, is something that happens either outside of us and in general we're going to talk about things that happen outside of us rather than inside our body. So we're talking about changes in light, changes in sound waves, changes in mechanical energy, touch, that kind of thing. Well, and the output is perception which depends on the cerebral cortex neocortex to be specific. So how do we get between here? Well we have to go through transduction. Somehow that energy, that light energy or that sound energy, has to be changed into neural energy. And neural energy, as we know, is electrical energy. So somehow we have to transduce, transform the stimulus into electricity. And that's a big step. That signal then has to go through its channels to reach the cerebral cortex. So it has to be transmitted, and the transmission pathway is another piece where things change. And most importantly, the transmission pathway is always going to involve the thalamus. Why? Because cer, cerebral cortex does not speak any other language it only speaks cerebral cortex and the only interpreter that can translate information into cerebral cortex is the thalamus. So, everything gets translated by the thalamus and then sent to the cerebral cortex. Finally, we have modulation. And, and you might think of modulation as something that's very fancy like how do you feel today and, and very cognitive. But in fact, modulation takes place at every level. It even takes place at the level of transduction. And one of those examples is the one that many people have experienced if you've ever had a sunburn, you realize that touching your skin where you've had a sunburn, or even worse, taking a hot shower when you've had a sun, sunburn is extremely painful. In a situation where if you didn't have the sunburn, it wouldn't be painful. So the perception has changed even though the stimulus is the same. Another example is I have a collection of photographs collected from magazines and, and newspapers showing different people getting vaccination shots. Good idea to get vaccination shots but the reaction to getting a shot, which is essentially all the same stimulus, is varied across a wide variety of, of people. Some people cry, some people look eh, some people are just completely nonplussed and look happy and, and that is an example of modulation at a higher level. Something were, what's the meaning of that, of that shot to the person? Another example of, of modulation at a higher level is how we think about food and whether something taste good. If you're really, really hungry, pretty much anything's going to taste great. If you're really, really thirsty, a drink of water is going to be like the best bottle of wine when you're not really thirsty. So, it's, it's a lot of context and that's due to modulation. So the final thing is, how do these, how do things go wrong in perception? Well, there are two basic places where they go wrong. One is in transduction, and in the case of vision and hearing, this is a big piece of it, just getting the signal in. So having the retina work and having the cochlea work, that's where the bulk of the problems exist. In the case of vision, there are also problems that occur in transmission due to strokes that's less true in, in hearing for reasons that we'll, we'll explore. But, what we're going to mostly do when we talk about vision and hearing is we're going to concentrate on transduction because that's where everyone loses their sight or their hearing or has a loss of sight and loss of hearing issues, is out here at the eye and the ear. [MUSIC].
