noc20-hs33-lec07

[Music] [Music] hello and welcome to the course introduction to brain and behavior I am dr. karma from IIT Kanpur this is the second week of the course and we will be talking about we begin to talk about some of the basic methods that are used in cognitive neuroscience in in today's day and how these methods help us answer some of the interesting questions and hypotheses about the functioning of the human brain now the genetic method in cognitive neuroscience or in any science for that matter is referred to as the scientific method I've talked about the scientific method in a course on cognitive psychology in basic advanced for basic cognitive processes in a lot of detail so I'll not go there again if if you want to really read a little bit about it now you should go and refer to those lectures but let me give you a very brief idea of what the scientific method would be now cognitive neuroscience as why we were making up the definition we saw that it would derive from cognitive psychology as in cognition and it would derive from the methods which will be used in neuroscience but the generic method is the same is the basic scientific method which has you know a few process a few steps and a basic generic you know cycle that is very very essential so if you remember the hypothetical deductive model that we talked about it basically begins with making observations once you've made some observations you can say for example okay so the basic method is an essential method is basically the hypothetical deductive method and it basically involves you know it begins with making an observation once you've made some observations you can create some hypothesis specific testable statements and then what you need to do is you need to conduct an experiment conduct devise a way to test these hypotheses once you devise this way you'll go out conduct this experiment collect data once you've had the data you you will analyze the data and analysis of the data will help you to accept or reject this hypothesis whatever the outcome be the data they've generated and the analysis that you've thought of done at the end you will derive some conclusions from it say for example I believe that my data helps me accept this hypothesis or a check this hypothesis that basically adds on to the existing body of knowledge and this is in a very short sense the idea of the whole process but predominantly let us now talk about the specific methods that cognitive neuroscience is basically banking upon so cognitive neuroscience is heavily banking upon the methods which it derives from cognitive psychology and we first talked about the behavioral methods now cognitive psychology if you I'm sure you would have some idea of it or if you don't let me give you an idea cognitive psychology predominantly looks at mental processes or at least classical or early cognitive psychology looks at mental processes mainly as an information processing endeavor so the idea is that the human brain must be performing these mental operations must be performing these mental computations in the same way as the computer does which is basically the information processing paradigm okay and this paradigm will need to have certain steps and they probably be a processing cycle which is obviously as I said resembling you know to borrow from the metaphor of computers that is that is typically how cognitive psychology is sort of begins around 1950s if you remember the lecture where we are talking about a brief history of neuroscience we've talked a little bit about that now what what do these steps include so simple things like acquisition of information storage or manipulation of information and then using that information to arrive at say for example what is the responses then I want to generate what is the specific responses that I will choose and I will execute okay as far as human beings are concerned it could be that we say for example receive information from the world through our senses we have you know five senses vision audition touch taste smell so we receiving this information from this outside world and then what is the next step we need to do something with this information we need to transform this information you know why are these neural impulses to a sort of a representation where we can you know manipulate this and then we can you know we decide what do we need to really do about this information what do what are we going to do and then eventually we need to come up with a response say for example I show you a picture of an of an apple and I ask you to name it so you need to go through this entire series of steps before you can actually name the Apple say for example you look at the picture you will visually analyze it you will sort of compare it with something in your memory you see okay I know what this fruit is I know the name now you basically then you know assemble towards assemble together the sounds that make up that name and then ask your articulator ask your local operators to create that name that is typically how this would work now the main crux of investigations in cognitive psychology is basically to figure out the intervening processes between receiving of information and generating of response this is typically what cognitive psychology has been most concerned with in the information processing paradigm typically it is believed that information we received from the outer environment undergoes an elaborate series of steps elaborate series of transformations or computations before we can generate or choose an appropriate response for whatever the stimulation is received cognitive psychologists typically design experiments to estimate the nature of these mental operations they keep coming up with the interesting hypothesis about this is how this process would be this is how that process would be and these mental processes about the nature of these mental processes and then they design intuitive experiments to test these hypotheses to accept or reject these hypotheses in this process what they do is they learn a little bit in about the nature of mental activity they learn a lot about how the mental activity meant different mental activities are linked with each other how are they organized in the brain and so on now let's talk a little bit about these mental representations or transformations it is believed in under the tradition of cognitive psychology it is believed that to be able to process stimuli from the external world which are physical stimuli and the mental space is a metaphysical world we need to perform this you know we need to perform this conversion of the physical stimulus to a form that the mental you know space can talk about it can manipulate it store it or you know work with it again I've talked a lot about this in the course on basic cognitive processes but let us say let us discuss for the sake of an example and if I show you a chair you say for example you know think about the chair if you were asked to you would have a representation of a chair you will have a concept of a chair that a chair is something you know that affords you to sit it it should have you know some height it should have some kind of a flat surface on which you can sit and then once you have this concept you can apply that concept to many many different kinds of chess many many different designs of chairs that are available sometimes even to objects that afford sitting but are not typically regarded as chairs in your daily life so there has to be some kind of way in which using which we can represent the stimuli in the outer world to our mental space so that is the first part and the choice of the kind of mental representation that you would have say for example whether you will have a visual representation which will have the shape and the color etc whether you have an audible you know sound based representation you could just have the sound chair in your head and on the basis of that you regenerate all the information that there is to be generated all say for example you could you have a different kind of a thing maybe if say for example people who are congenitally blind may usually will have a tactile sort of a representation of how things are a very good demonstration of the fact that there can be different kinds of representation for similar stimuli is basically given is discussed by Posner's experiment using the letter matching task and in this task basically the task of the participants is that they have to look at the screen on the screen represented with two letters adjacent to each other simultaneously and they have to see whether they these two match with each other or not if they match you press one key if they don't match you press another key the interesting part is the design of this experiment which has around five conditions it has physical identity condition which is the same letters in the same format it has a phonetic identity condition say for example one of the letters is in uppercase the other letter is in lowercase so it could be a capital C and you know a small C you have to sort of say that this matches similarly both letters are from the same category as vowels or consonants or it could be a different category condition in which both letters may be the same type size font size color of ink etcetera but are different letters okay so the parts man sort of have to you know judge on what criteria things are similar and you know make these judgments what happens was it was found that persons respond fastest to the physical identity condition because that's the shallowest and there's something most easy to compute and their slowest to really answer in terms of the same category condition when you have to evaluate whether both are vowels or both are consonants so typically why is there difference in you know in response times to these different kinds of conditions the idea is that these results show that participants may be able to derive different kinds of different levels of representations for the same kind of simile in the letters that are you know that are being used here cognitive psychologists have have been concerned a lot with the kinds of representations we derive out of different kind of stimuli and how we sort of convert one kind of representation to into another kind of representation depending upon what is the task at hand what is say for example if I have to draw a visual impression a visual representation would work best if I have to speak ordinary representation would work best so this is something that college psychologists have been sort of talking about and have been concerned about since a long time another thing that cognitive psychologists have been doing and is very very interesting is that they have been concerned about the reaction times they have been concerned about the time it takes to perform each mental operations I've briefly mentioned this in one of the earlier lectures in this course as well that the time that the brain takes or the time that individual takes in processing a particular or stimulus or in performing a particular mental operation is of extreme importance it tells us to some extent the degree of complexity involved in performing a particular task it also in some sense sort of tells us because these times are additive it tells us that whether a task has just one process or series of steps or series of processes so cognitive psychologists have believed for the longest time that the analysis of the time taken in these manual operations is very very important because it reveals a lot about the nature and the complexity of the mental operations that are involved so this is also something that sort of gets borrowed in in cognitive neuroscience and makes a lot of that in coming chapters so we have talked about the mental representations let us talk about the computations or transformations that might be needed now an important assumption in cognitive psychology is that the representations that we derive out of the stimuli a from the world will need to undergo several transformations or computations say for example if you're exposed to a particular stimulus that you know the that will lead you down a train of processing events which basically say for example let's take an example listening to the word Apple may you know make you recall your childhood if you've you know been to an apple orchard during a vacation in Shimla and that because it could make you nostalgic and you could decide okay I need to talk to my mother I need to make this call so just exposure to a stimulus can lead to several of these processing events that may eventually cause changes in your behavior or lead to particular consequences now these computations typically allow the perceptual representations to be transformed into action representations so here the picture of an Apple could be a perceptual representation or the or the sound of the word Apple could be a perceptual representation but once that perceptual representation is taken in it is processed it's linked with memory and it makes you recalls all the other things it leads to a sort of an action based representation for action representation which helps you sort of you know decide or make the call to your mother so that is something that happens all the time and that is something which we will talk about in great detail going further now all the impressions may be otherwise mental operations cannot be really thought of as just a series of simple step entirely a series of one comes after you know one and then two and then three it can also be thought of as a for example several operations in in a cascaded fashion sometimes in a parallel fashion as well so keep keep an eye out for that wheel and keep an ear out out for that and we'll sort of see how these processes are organized and linked to each other now let's talk a little bit about the nature of these computations now Sternberg in 1975 through his very famous little comparison task demonstrated that participants must be undergoing a series of primary mental operations in order to sort of perform you know very simple simple you know tasks that we anyways do in our daily lives so his task was the letter comparison task and the idea was that he would first make participants memorize a set of you know letters and then later he would present the participants on the computer screen with with separate letters and the idea was the person had to sort of match that whether this letter presented on the screen was part of that memorised set or not so this is basically what the batsman has to do now this process basically would involve at least four different things that the participant we need to do in order to make the connect response first when the batsman sees the letter on the computer screen they'll have to encode it they'll have to visually analyze it and encode it suppose the letter is M so I have to visually analyze and understand you cognize that okay this is the letter M then I have to do a comparison with the letters that I've already memorized so whether suppose the letters were a b c d and e or a b c d f so i compare em with you know these six letters and will try and come out with a decision whether this map this is part of that set or not and then once I've made the decision that yes this is part of that set or no this is not part of that set I will be able to make the decision I will be able to press the key that the experimenter has asked me to this is a very interesting experiment as a very simple but a very intuitively designed experiment what it shows us is also a very interesting thing Sternberg's results when he actually finds out that you know basically the response times that but actually take is directly proportional to the set size of the memory I said if I've just memorized one letter and there's one letter on the screen the time is the least if I've memorized to the time increases and it increases in fixed the number of in fixed amount of time for each item that I keep adding to this memory I said so in some sense what it sort of tells us is that this process of comparison of this with the stimuli that I have in my memory I said is a single sort of a process I am comparing em with each of a b c d e and f and that is basically what is you know taking up all sort of all of this processing time that I am showing so this is this is a little bit interesting but here is a demonstration of the fact that you have to sort of undergo a series of computations a series of steps in order to process you know a certain kind of information and perform these very simple tasks that you anyways do in your daily life now it's not that everything that the brain does is happens in a serial manner because in other tasks for example righteous Word superiority effect it is demonstrated that you know this task sort of happens in in a sort of a parallel manner the task is very simple the task is that the persons have to identify a set of target letters from three kinds of embeddings they could either be embedded in a series of X's you could either they could be embedded in a series of nonsense words or they could be embedded in a in actual word say for example if you have to look at if you have to identify the words well the letter R it could be embedded in xxx R X xx and I have to sort of see whether it is there or not it could be in a nonsense ring like say for example R and R is there I have to recognize it or it could be in a word like fork or frock where I have to recognize it it was founded participles do this task rather quickly but they do it fastest when the letter is embedded in a meaningful word why are they doing this they're probably doing this because when you're reading a word there are two levels of representations that are simultaneously activated there is a letter level representation that gives you the identify of identity of each of the letters and there's a word level representation which is also much faster and easier to remember if you remember that word in your mental lexicon you will be able to do it much much faster so the point here is that the processing of these mental steps is basically in in their sense is a not always serial or not always parallel now there are some of the constraints on on the information processing capacity of the plane and this is something which keeps emerging out of range of cognitive psychology experiments that have been performed and will come through come across a lot of these these different kind of experiments as well now the constraints on this information processing capacity of the human brain or of humans typically we can typically be of various kinds they could be a you know a specific to a system or the individual say for example there there could be individuals which have lower working memory capacity there could be individuals who have higher working memory capacity or generally just work memory capacity they could be it could be a general constraint that a task is very very difficult you know or that it will be difficult to do this in any in any case or it could be very task as we concerned that this that this processing in this task is difficult if it were in a different task it would be very fast or very quick let's take an example jsoup demonstrated this different kind of constraint the task specific constraint in a task that he devised which is called the Stroop task and the Stroop task is a very very interesting task let's quickly show you the task in this you have basically letters basically color words and the color words are basically written with inks of different colors say for example you can probably see red written in red in color green written green in color blue written in Blowing color or you can have a different version where you have red written in blue ink color green written in red in color blue written in green in color and so on so in in this case you and you and sort of mix these stimuli up and you can ask the participant to name it and what you will typically find is that when the the name of the word and the color of the ink they match parchments are fast when the name of the ink and the name of the word do not match the parts are slowest this is this is a fairly a fairly simple demonstration has a very robust effect because it stays on even after thousands of practice trials if they are afforded to the participants what is happening here again I'm sure you you'd be able to answer that that there are two levels of representations that are simultaneously getting activated in parallel name of the word is something that as soon as you see it it automatically activates it's a very fast very quick all-or-none kind of a process you cannot unreadable or you cannot stop in the middle of reading wood as soon as you see a word and you know the language and you are aware of that word you read it immediately so that is something that is activating very very quickly and that is something that is interacting with your main task which is naming the ink color so if both of these things are generating the same response say for example in simulator for semi on the Left if red color if the word red is written in red color ink I will be fast because both of my parrot it represent a shion's are leading to the same response but if I look at similar on the right where the the word green is written in reading color I have to say red but the I am also activating the the name of this word which is green this will sort of cause interference with each other and we slow the participant or so this is a very good example of what is referred to as a task specific constraint and this is something which has been demonstrated you know over and over again and participants have sort of you know shown this effect again and again and obviously this effect has been used in different other paradigms Israel so this is just an example of what is called a task specific constraint and it does a very important thing it tells us that while the human brain might be processing let us say for now be processing information in this information processing paradigm but it does not have unlimited capacity also it cannot handle an unlimited amount of information at the same time so this is something which is a very very important one of the things that we keep in mind going further so I've sort of given you a brief very very sort of a sketchy outline of the kind of methods that are used in cognitive psychology and the idea is that cognitive neuroscience as a field derives a lot of its methods from cognitive psychology and we will be talking about these methods more and more and again and again in the course of this semester thank you [Music] [Music] [Music]