Brief Introduction to Psychology - NPTEL PDF

BRIEF INTRODUCTION TO PSYCHOLOGY Prof. Braj Bhushan Humanities and Social Sciences IIT Kanpur  INDEX S. No Topic Page No. Week 1 1 Lecture 01 1 2 Lecture 02 56 3 Lecture 03...

BRIEF INTRODUCTION TO PSYCHOLOGY Prof. Braj Bhushan Humanities and Social Sciences IIT Kanpur  INDEX S. No Topic Page No. Week 1 1 Lecture 01 1 2 Lecture 02 56 3 Lecture 03 88 4 Lecture 04 128 5 Lecture 05 170 6 Lecture 06 225 Week 2 7 Lecture 07 278 8 Lecture 08 296 9 Lecture 09 333 10 Lecture 10 353 11 Lecture 11 388 12 Lecture 12 406 Week 3 13 Lecture 13 431 14 Lecture 14 457 15 Lecture 15 487 16 Lecture 16 519 17 Lecture 17 546 18 Lecture 18 581 Week 4 19 Lecture 19 615 20 Lecture 20 639 21 Lecture 21 668 22 Lecture 22 696 23 Lecture 23 714 24 Lecture 24 774  Indian Institute of Technology Kanpur National Programme on Technology Enhanced Learning (NPTEL) Course Title A Brief Introduction of Psychology Lecture – 01 Perception by Prof. Braj Bhushan Humanities & Social Sciences IIT Kanpur So welcome to this first lecture, initially before I take you into the details of some of the topics which might be very interesting to you from behavioural point of view just look at the line that you see on this screen. (Refer Slide Time: 00:34) What do you see right now, you can somehow guess that this is perhaps a curve line that someone has drawn, I extend it little more and then you realize that fine the line has now taken a more sharp turn towards the right and then I further now try to extend it, it is difficult to make a sense out of it and then I add these lines and you can very easily now make out who this person 1 is okay. This is the image that gets generated in your mind. When this image gets generated in your mind suddenly you recollect not only the name. But you recollect whole sequence of events attached to this very individual who is known as the father of the nation okay. You derive certain type of mental images of a certain type of representations like freedom, you you might even derive them a political map of a country called India, you might have now recollection of some philosophies that is now called as Gandhian philosophy, whole lot of things gets recollected okay. (Refer Slide Time: 01:47) So actually when you look at the real world we take certain inputs from the external environment, sometimes it might be that we might draw some inputs even from our internal mechanism and then we try to assign a meaning to it, in psychology this is what we call as the process of perception. Now the fact that I failed to decipher the line even though it was being extended couple of times till I got substantial cue to identify that I am looking at the line drawing that represents the father of the nation. I was searching for a possible cue so that I could assign a meaning to it, this process is what is called 2 as perception and the first topic that we would be taking as part of this very course is the topic called perception, the perceptual processes. We would know succinctly going into certain details the reason I am saying that I would be brief in my approach is the, primarily the fact that we have a limited number of hours available to us it is just a 10 hour course, so when you see these things or when you saw the line that you saw right now. To derive an image of what you are looking at you have learned certain things, certain things got recollected from your memory and then it did induce a sense of feeling within you okay, so these are the four prominent processes that we would be talking about as part of this course, so initially we will begin with the process of perception, then we will go to learning, then we will come to memory and finally we will be talking about emotional processes, the affective processes and that would complete our four topics that is designated for this very course. (Refer Slide Time: 03:39) (Refer Slide Time: 03:41) 3 Before we come to perception let us understand one thing, that the brain before it arrives at a conclusion, before it assigns a meaning to something it would require a trigger, it would require a sensation from outside okay, so any information that comes to the brain whether it is through the any external source or it is through the internal source this is called sensation and as you know that we are endowed with certain sensory organs okay. (Refer Slide Time: 04:41) 4 So these sensory organs whether it is eyes, ears, the somesthetic senses, tongue, okay all these senses they sense certain type of stimuli to the brain okay, so the internal or external is stimuli that evoke response in us okay is always important for a perception process to begin okay. So when the brain will start processing the signals that it receives from the environment okay it will then suddenly go ahead with the process of assigning meaning to it. (Refer Slide Time: 04:47) 5 Okay, so any perceptual process that we are looking at from the point of view of the sensory input coming through sense modalities will finally look for a possible meaning that would be considered as the most appropriate representation of what the brain has finally deciphered and this is what is called perception. What we will do as part of this very course is that initially our focus would be on the process of sensation so we would look at the basic sensory organs, the eyes, the nose, the ears, okay the somesthetic senses, the kinesthetic senses, the vestibular sense, the olfactory mechanism. And then we would know or try to get a feel that okay this is how the brain gets the information and this is how we understand what is there in the real world. (Refer Slide Time: 05:41) 6 For doing this I am taking this very example, here you see a boy who is primarily playing in the park. This boy is primarily trying to aim at the color disc that he is looking at, suddenly he finds a bird there and he starts following the bird because the chirping sound attracts him, he feels hungry and then he removes the rapper and eats the chocolate and then suddenly while eating he sees a rose in one of the corners of the park and he goes and smells it okay, these are the processes that all of us experience throughout our life. (Refer Slide Time: 06:26) 7 So when the physical energy of the stimuli, when it gets converted into the impulse and gets transmitted to the brain so that the brain can finally make a meaning out of it this is called as the process of transduction okay. So the physical energy getting converted into a, an impulse which the brain can process is the process of transduction, and this transduction is we can consider as the first step towards perceiving the external world. (Refer Slide Time: 06:59) 8 So we have as human beings five important sense organs vision, hearing, taste, smell, and touch and in addition to touch the skin also now provides you with the senses of heat, cold, pain, and pressure okay. Now look at this very video. (Refer Slide Time: 07:17) 9 Let us now understand that fine once we know that this is what our eyes can process how does the visual system work. (Refer Slide Time: 07:28) 10 To comprehend the visual mechanism clearly let us look at this video, here you see the electromagnetic radiations emitted by various objects, as you already know the visual spectrum extends from about 380 to 780 nanometers, the colors represent the visible spectrum. (Refer Slide Time: 07:51) 11 This is a color disc (Refer Slide Time: 08:03) 12 And this boy is aiming at it, we are trying to understand the visual mechanism so what did he see. (Refer Slide Time: 08:07) 13 To comprehend this let us look into his eyes. (Refer Slide Time: 08:10) 14 The light from the coloured disc entered the eyes through pupil, cornea, lens, and interiors of eyeball, it has now reached the retina. (Refer Slide Time: 08:32) 15 What you see now is a photo micrograph of the rod and the cone cells in the eyes. (Refer Slide Time: 08:40) 16 You are now looking at the ganglion cells that is the M and the P cells and the bipolar neurons, the light passes between the ganglion cells and the bipolar neurons, the bipolar neurons send the signal back to the ganglion cells, thereafter the optic nerve carries the signal. (Refer Slide Time: 08:59) 17 To the visual cortex. (Refer Slide Time: 09:02) 18 You now see the primary and the secondary visual cortex, that is visual area 1 mentioned here as V1 and areas 2, 3, 4, 5, 6, 7, and 8. (Refer Slide Time: 09:23) 19 Here you see the optic disc fovea and blood vessels. The visual sensation in this boy is completed now, he was aiming at the coloured disc so what did his brain see? The extension of the coloured disc that you see with dashes shows the visual field of the left and the right eyes respectively, the part of the coloured disc. (Refer Slide Time: 09:40) 20 That you see next to the eye balls show the respective projections on the retina of the left and the right eyes, the bright yellow light represents the movement of signal across the brain. (Refer Slide Time: 09:51) 21 Some of the optic nerves from both the eyes cross to the other side of the brain at optic chiasm, the neural conduction in the optic nerve reaches the lateral geniculate nuclei, the spread of colors on the left and the right sides show the inputs to the left and the right lateral geniculate nuclei respectively. (Refer Slide Time: 10:10) 22 Finally the input reaches the visual cortex. Once again the colors that you see in the part of the cortex represent the input that has reached the primary visual cortex on the medial surfaces of the left and the right hemispheres of the brain. It is worth looking that the full coloured disc that the boy was looking at (Refer Slide Time: 10:31) 23 has been processed differently by the two eyes and of course the two hemispheres of the brain, what is remarkable is that the parts of this information finally combined and we perceive it as a coloured disc. Now primarily what is important? (Refer Slide Time: 10:48) 24 For us to understand here is that the convex lens of our eyes it makes an inverted image fall in the retina okay, and the shape of the lens changes in order to bring light from near objects to a sharp focus on the retina and this very process okay of a know, bringing a sharp focus on the retina is what is called as accommodation, so what we have done we have talked about the transduction, we have right now talked about accommodation okay. (Refer Slide Time: 11:18) 25 Now the retina is a light-sensitive layer at the back of our eyeballs which contains two types of photoreceptors, the rod cells and the cone cells okay, and it is very interesting to understand that numerically our retina is (Refer Slide Time: 11:35) 26 Rod dominated okay, then the primary things that you saw in the video right now were the optic nerve which carries the visual information from retina to the brain, and the point where the optic nerve now makes an exit from the eye is called the blind spot because it does not have any photoreceptor. (Refer Slide Time: 11:53) 27 Now the rod in the cone cells they contain photosensitive pigments okay, and very interestingly the rod cells for example when it is not excited it is in the cis-rhodopsin configuration and when the light falls on it changes into the trans-rhodopsin configuration, and this concept we will again carry when we come to memory and when we would be talking about iconic memory. There we would be saying that right at the level of this sensory organ certain, certain amount of time very brief period of time. Some amount of information is retained okay, and at that time we would be referring to iconic memory but right now we are not going to memory, but I would just request you to remember this fact okay that the chemical configuration changes okay and to have a second round of excitation this trans-rhodopsin configuration will have to return back to it is cis configuration state okay. (Refer Slide Time: 12:53) 28 Now let us just compare the characteristics of the rod and the cone cells. In terms of number of course as I said that are pretty nice rod dominated so we have approximately 120 million rod cells compared to just 8 million of cone cells into some response. Rod cells are now of course now supposed to process the light in the dark condition and whereas cone cells also have the responsibility of identifying the colours, they are sensitive to colours. In terms of sensitivity to light rod cells of course are more sensitive compared to the cone cells. If you experience a dark situation so in terms of dark adaptation time the rod cell it takes approximately 30 minutes to adapt whereas the cone cells take approximately 10 minutes to adapt, whereas in the light condition both these cells they take approximately 1 minute for adaptation. (Refer Slide Time: 13:51) 29 And again now the optimum operation of the rod cells can be seen during darkness whereas cone cells maximum operations can be seen during bright light, and in terms of its location on the retina the rod cells are more dense just outside the fovea whereas cone cells are now distributed throughout the retina and it is more dense on the fovea, and in terms of neural connection to the bipolar neurons that you saw in the video the rod cells are know they are into pooled connected form format, whereas the cone cells they are 1 to 1connected. (Refer Slide Time: 14:31) 30 Now in the video that you saw for the visual mechanism you realize that we have a limitation in terms of our visible spectrum, it is not that the entire range of light can be seen by us, so is the limitation even with our auditory mechanism, look at this very video. (Refer Slide Time: 14:53) 31 To comprehend the auditory mechanism let us look at this video, this young boy is fascinated to the chirping sound of the little bird, he is crawling and approaching the bird, how does he hear the sound? Look at his pinna, his pinna collects the sound energy that is generated by the bird. (Refer Slide Time: 15:16) 32 This sound travels through the ear canal and strikes his tympanic membrane that is his eardrum, here sound energy is transformed into mechanical energy, the oscillation of the eardrum makes the malleus incus and steps move. Besides transmitting the energy these bones also amplify the sound, you can see the oscillation of steps in the middle ear. This now presses the oval window and the vibration enters cochlea, you now see the organ of corti, the wave in the cochlea has reached there. (Refer Slide Time: 15:51) 33 The organ of corti has numerous ear cells which act as receptors. (Refer Slide Time: 15:56) 34 The pressure on the waves stimulates these ear cells which in turn generate a receptor potential. (Refer Slide Time: 16:02) 35 This neural firing travels to the brain through the auditory pathway and the child senses that he is listening to this melodious sound of the bird. (Refer Slide Time: 16:13) 36 Having seen now how this child was actually listening to the chirping sound of the bird let us now come to the mechanism of olfaction okay. This boy now after now chasing the bird goes to a corner of the park and looks at the flower. Look at this very video. (Refer Slide Time: 16:35) 37 Let us look at this video to understand the olfactory mechanism. This young little boy is too fond of roses, he goes and sniffs the rose in his garden, how does he identify the smell of the rose? (Refer Slide Time: 16:48) 38 As you see here the vigorous intake of air by this boy has made the OBP release in his nose. (Refer Slide Time: 16:57) 39 The receptors at the olfactory epithelium specialize in a particular smell, this unique order reaches his olfactory bulb, you see the olfactory bulb, olfactory nerve, and meterio cells. (Refer Slide Time: 17:09) 40 You now see the olfactory receptor neurons that are blue, green, and red in color here. (Refer Slide Time: 17:16) 41 You can see the OBP release and the conduction of order signal in the olfactory receptor neurons. (Refer Slide Time: 17:21) 42 These order signals are now transmitted from the olfactory neuron (Refer Slide Time: 17:27) 43 To the meterio cells and finally the olfactory track carries the message to the brain. (Refer Slide Time: 17:33) 44 This is how this young boy got the smell of the rose. Now after having know how the smell of the flower now the boy feels hungry and he thinks of eating a chocolate, look at this very video which would explain the mechanism of taste. This young boy is enjoying a chocolate, how does he get the taste of it, look at his tongue. (Refer Slide Time: 18:03) 45 The tip of the tongue is sensitive to sweet and salty tastes, side to sour and the back to bitterness, you can see small bumps that contain the taste buds. (Refer Slide Time: 18:19) 46 These bumps are called papules, you can see a taste bud, the chemical components of the chocolate dissolve in the saliva and goes down to the services between the papule, this chemical interaction triggers the adjacent neurons. (Refer Slide Time: 18:34) 47 And these impulses travel to the parietal lobe and the limbic system of the brain of this boy, this is how he got the taste of the chocolate. (Refer Slide Time: 18:44) 48 Now if you combine all the videos that you have seen, you saw a video for the visual mechanism, you saw the video for the auditory mechanism; you saw the video for the olfactory mechanism, and finally the taste mechanism, so if you combine all these videos that you saw right now you can very easily sense that fine (Refer Slide Time: 19:03) 49 This is how we make a sense of the world okay. So till now we have discussed the five basic sense modalities, the visual and auditory systems are receptive systems since they are sensitive to our external stimuli whereas the somatosensory system also has an exteroceptive function to perform. (Refer Slide Time: 19:25) 50 So beside these 5 senses we have two important sensations, one is the kinesthesis senses, another is the vestibular senses, and both of them help us like anything in terms of living in this very world. (Refer Slide Time: 19:41) 51 Now kinesthesis is the feeling of motion of the body part involved in some form of a movement. Imagine the situation say for instance you are traveling, you are walking, you are running okay, now basically what you are doing is that you have a perception of your body parts how it moves okay, and that gives you a constant feedback in terms of synchronizing your movement so that you can perform the act that you are performing, whether it is say walking running whatever, whatever it is okay it is this very kinesthetic sense which gives you as complete feedback as to how your body parts are moving and this helps you perform the task meticulously. The other sense. (Refer Slide Time: 20:31) 52 That we are now coming to is the sense what is called as vestibular senses and these are the senses which are responsible for making us have the sense of the spatial orientation okay, spatial orientation would mean that it helps us know the position of our body in the space okay. Say for example if you are say trying to jump for instance okay, you have to understand very well at the relative position of your body in the space okay. So the sense of balance okay, during movement all types of movement is basically dependent on the vestibular senses. (Refer Slide Time: 21:21) 53 Let us now see this small video clips from the Beijing Olympics, these are some of the finest movements that human beings are capable of performing; all this requires extreme degree of coordination. Now that the video footage that you saw you had a gymnast who was moving without looking at the object that his hand was now resting the body weight upon, in the other case you saw know an athlete performing on the surface of the ice okay, and it was a perfectly synchronized movement even though the body weight was rested on one foot, two foot both the feets and then. Even while the whole body was now swinging very fast okay. Now these are the processes for which you require sound vestibular mechanism okay, so with this we come to an end to our discussion on the first topic where we focused exclusively on the sensory mechanism okay. Just to recapitulate we have discussed about the visual mechanism, we have talked about the auditory mechanism, we talked about the olfactory mechanism, we also talked about the taste mechanism, these four mechanisms and then we additionally we took into account the kinesthetic and the vestibular senses. So this is how the input comes to the brain, once this now following the process of transduction the information comes to the brain our brain then tries to assign an appropriate meaning to this 54 okay, if we succeed assigning an appropriate meaning to what we have sensed this is what is called as perception. Acknowledgement Ministry of Human Resource & Development Prof. Satyaki Roy Co-ordinator, NPTEL IIT Kanpur NPTEL Team Sanjay Pal Ashish Singh Badal Pradhan Tapobrata Das Ram Chandra Dilip Tripathi Manoj Shrivastava Padam Shukla Sanjay Mishra Shubham Rawat Shikha Gupta K. K. Mishra Aradhana Singh Sweta Ashutosh Gairola Dilip Katiyar Sharwan Hari Ram Bhadra Rao Puneet Kumar Bajpai Lalty Dutta Ajay Kanaujia Shivendra Kumar Tiwari an IIT Kanpur Production ©copyright reserved 55  Indian Institute of Technology Kanpur National Programme on Technology Enhanced Learning (NPTEL) Course Title A Brief Introduction to Psychology Lecture – 2 Perception by Prof. Braj Bhushan Humanities & Social Sciences IIT Kanpur We will now continue our discussion from this very process of a sensation. what we have done till now as part of our first lecture was that we just saw how these sense modalities they acquire the information, external information from the world and then how the signal gets processed in the brain, and then we discussed that well we all try to assign a meaning to what we have seen and depending on the meaning that we assigned to the object that we have perceived we have seen, in fact not even perceived we try to know look at the appropriateness of that meaning, if we are able to give an appropriate meaning fine perception has taken place. Sometimes we do commit error while doing that, okay. So in the process of sensation nothing went wrong but while assigning a meaning we do commit an error. And that is when we say that illusion has taken place, we will little later we will also come to illusion. But right now I will now go into little more detail of the perception phenomena but before that although I do not want you to go into detail of it, I would just like you to very quickly look at the screen and you see this is the in major connection of the visual system. And when you look at the major connections ultimately you realized that it is a tertiary and the Paralimbic system of the brain which gets activated at the end. And remember these are the areas of the brain which has to do with emotions, okay. Similarly if you look at the major connections of the auditory system right from the process at the level of inner ear where the eighth nerve starts conducting the information you realize its finally once again the sensory mechanism in terms of its a neural underpinning goes up to the tertiary and the Paralympic area. In terms of odour recognition, in terms of smell again we see that the limbic system gets into picture and if you look at the taste mechanism once again the later hypothalamus and the amygdala gets into action. What primarily you see here, again for even fine and kinesthesis that once again the tertiary in the paralimbic area gets activated, what is important to realize here is. That every time whenever we have this process of sensation taking place and the brain trying to assign a meaning to what we have sensed the areas of the brain which are actually supposed to take care of the emotional aspect, that gets activated. 56 (Refer Slide Time: 03:01) So whenever we sense from the external world the process of perception is not what you call free from emotion. So the moment we try to assign a meaning you remember last time we had discussed in the previous lecture that right at the level of sense modality we can store the information for a very, very brief period of time, okay. And I told you that remember this whenever we come to our discussion on memory at that time once again we will talk about sensory memory, and this was with reference to iconic memory. So memory gets activated here, now we are saying that fine emotion also gets activated and emotion would be the last topic that we would be talking about as part of this very course. Now that we have understood how sensation is conducted in the brain how the brain assigns a meaning to it, the key question is that is it that we process each and everything that comes to us? So do we see everything that is available in the visual spectrum, do we hear everything in the environment, do we smell everything, do we sense everything? So how, what, on what ground does the brain decide that this has to be processed and this has not to be, okay. Now there are many things with respect to perception, I am in a particular type of a environment, there are external stimuli around me. 57 (Refer Slide Time: 04:37) Which comes to my brain through my sense modalities, and at the same time I am at a particular type of a position in the given environment so the perspective that my particular sense of morality will take, for example if I am looking at the camera right now, okay, the perspective of the object which is available in my visual field, okay. Other type of no external stimuli and at the same time my own decision to know, act the way I want to at that point in time in the environment. So there are many, many factors that will now come into picture, what we are doing right now for the purpose of understanding the perception process what we are doing that in this very lecture we would be talking more about those external factors that has to do with the strength of the signal, okay. So we are looking at the external factors right now, we are not looking at the other aspects, other aspects we will come in the coming days. Now the most important thing when it comes to the external factors is the concept called threshold or limen. 58 (Refer Slide Time: 05:58) Three terms are to be remembered here, the absolute limen, the difference limen and the terminal limen. Now absolute limen means that this is the minimum intensity of the stimuli that you can detect a minimum fifty percent of the time. So whenever you have absence and the presence of the stimuli you should be able to detect it half of the time, okay. Now difference limen is basically nothing but it is the smallest difference between two stimuli. (Refer Slide Time: 06:32) That you can detect, and then comes the terminal limen where you realize that the threshold changes to the extent that you do not consider the sensation, the perception to be exactly what 59 you thought it initially was, the nature of the sensation changes, okay. Now let us understand this with an example. You just now on your computer monitor where you are watching this lecture right now, okay. Just minimize the volume make it come to zero, okay. And now you start increasing it, slide the slider now and then you realize that although physically the value changes it says 0123456 likewise know you know you get a indicator which tells you that the sound quality has changed, it has increased but somehow you are not able to listen to it, okay. So the first case when it was zero there was complete absence of this auditory signal, okay. You can do it, do the same with the visual signal, you turn your screen black and then you gradually start now adding brightness and contrast features and then you realize, okay that although physically things are changing psychologically you are not able to make out. So in the first case although the sound level is changing you are not able to detect it, you are not able to hear it. And then comes a time above which you can hear me, okay. So similarly if you change the brightness contrast feature, okay there it would be a point when you would be able to make out that, okay this is the object available on the screen right now, okay. So that very intensity of the stimulus where from absence to presence can be detected by you, okay. That is called absolute limen. Now although you are able to make out that I am saying something you are not able to detect the increase in the volume, first case was 0 means absence of the process to presence, now within presence you want to increase the volume. Now you again knows, use the slider and you see that physically the sound level is increasing but then you realize that the notable difference that you wanted to make that you wanted to increase the volume upto this level. That is somehow not reaching and then comes a point when you realize that yes now the sound quality has changed it has increased, and then if you know still continue moving it beyond 100 percent, 150 percent, 180 percent then you suddenly realize that this is no more a lecture it converts into noise. So that very threshold where the intensity of the sound becomes painful for you. The lecture converts into noise is terminal limen. So in terms of external attributes of the stimuli that we are sensing in order to assign a meaning to it, okay what is the intensity of that various stimuli? Absolute limen, difference limen, terminal limen has important role to play there, okay. Now along with this comes an interesting thing, okay. Right now we talked about it, that we have to make a distinction, no between the previous and the new state. 60 (Refer Slide Time: 10:18) Weber gave a law basically this is talked about know in the area of psychophysics, in Experimental Psychology you will come to read about it, here we would be very briefly looking at it, what it means and why it is so important for psychologists to understand Weber’s law? He says that the just noticeable difference in the stimulus. 61 (Refer Slide Time: 10:39) Is the proportion of the magnitude of the original stimulus, okay? So there is a smallest level of difference between two given points of a sensory stimulus, okay that can be detected. So if you are able to know realize that this is the magnitude of the original stimulus, and if the magnitude of the incoming stimulus is above this level only then that difference can be detected, the best example of it could be that you hold a torch in your hand, okay. And go in a bright daylight, whether your torch is switched on or off you are not able to make a sense out of it because the outside light is brighter than the light of the torch, okay. But the same phenomena if you repeat in dark situation you would very easily be able to detect, okay that your torch is on, the reason being that the magnitude of know the stimulus, okay the intensity of the light which is emitted by the torch, okay. In the first case is much less than the light already available in the environment. So during day time you do not detect that the torch is on whereas in the night you are able to detect it, okay. Take another example. 62 (Refer Slide Time: 12:01) If the headlight of your vehicle is on, okay. Now during day time once again you would not be able to make out whether the headlight is on or not, in the dark situation, okay. Whenever the outside light decreases, okay you would very easily be able to say that, okay that the headlight of my vehicle is on, okay. So now because the existing intensity, the intensity of the existing stimuli if that is strong enough then the intensity of the new stimuli has to be above that to be detected, okay that is what is called as just noticeable difference. I will give you two examples here, the first example is of the change in the brand name, okay. 63 (Refer Slide Time: 12:51) When IBM introduced Lexmark printer, okay, look at the change in the logo that you see of IBM here, in the first case you see only IBM. 64 (Refer Slide Time: 13:05) Now you see IBM lexmark4029 by Lexmark, just look at the font size also, okay. So earlier you had only IBM now you have addition of laser printer 4029 by Lexmark. 65 (Refer Slide Time: 13:18) Now there is a change, now suddenly IBM laser printer 4029 the font size decreases and Lexmark has replaced the remaining space. 66 (Refer Slide Time: 13:30) And then you see Lexmark goes on the top, laser printer 4029 comes at the bottom, and IBM is removed. Now this is an interesting application of just noticeable difference, now if you look at the first logo and the last logo you see a big difference, why? 67 (Refer Slide Time: 13:47) 68 (Refer Slide Time: 13:48) You saw the difference because there was the difference in the space, in the defined area of the logo, okay. Had stark difference but if you look from one phase to the other and gradually if you look at the four phases that means that while positioning this printer IBM wanted that in the memory of the users, okay. Lexmark printer should be attached to IBM and therefore it should not be considered that this is something new that has come to the market rather the existing brand name should suffice the positioning of Lexmark printer, okay. Now let us come to another example. 69 (Refer Slide Time: 14:35) This is a know example of Betty Crocker, now Betty Crocker over the years, okay, when they changed their brand ambassador, okay. 70 (Refer Slide Time: 14:46) Now look at this change no, right from1936 to 1996, okay. You see that a series of models were used for endorsing the product, okay. Now the lady in 1936 is far different from the lady that you see in 1996, okay. But if you look at the intermediate faces no, the model who endorsed the brand in1936 and the getup of the model who endorsed the brand in 1955, you see much of a similarity. Similarly between 55 and 64, 64 and 68, okay and then you realize that Betty Crocker basically what it was trying to do is that the models who were endorsing the brand, the difference in their physical appearance they tried their best to make it come below the just noticeable difference level, okay. Now if the previous and the new, these two models their physical appearance if it does not touch the just noticeable difference level. That means that you would consider that some makeup has been changed but by and large the person who endorses the brand remains the same, okay. These are the interesting applications of just noticeable difference, okay, in our real-life, okay. 71 (Refer Slide Time: 16:16) Now the change that is required for getting a stimulus perceived as different will always depend on the initial strength, that would mean that stronger is the stimulus in the first case for establishing your brand in the present, present example you require that the signal of or the strength of the incoming stimulus should be very, very strong. You must have seen these two ads of Madhya Pradesh Tourism, okay. 72 (Refer Slide Time: 16:43) Now let us look at the first ad. 73 (Refer Slide Time: 16:45) Hindustan Ka Dil Dekha Bandar dekha, haathi dekha. Barahsingha, aur cheetal dekha. Mowgli ke jungleon mein, Sher Khan ko dekha. Pachmarhi Satpura ka ajooba, Bhopal lake mein suraj dooba. Mandu ka jahaz mahal, Aur marble ka pahad dekha. Mahakaal mandir mein pooja, Photo khicha jaake Orcha. Gwalior ke kile mein bhatka, Khajuraho ne de diya jhatka. Dhim tana dhi re na nadir Purvajon ko milne jule, Jaa bahita mein Bhimbhetka. Train ki chik chuk sunte, Aa pahucha mein Sanchi stupa. Sanchi ki shanti mein, Khudke aandar jhaak ke dekha. Hindustan ka dil dekha. Hindustan ka dil dekha. The heart of incredible India, Madhya Pradesh. 74 (Refer Slide Time: 17:47) Now you have a very nice depiction, okay in a very, very artistic form, the major tourist destinations of Madhya Pradesh has been shown to you. This was one of the very, very popular ads of tourism and then much later in 2013 another ad for Madhya Pradesh tourism came into being. Now remember one thing the way the previous ad know which said know, Hindustan ka dil dekho. See the heart of India and the way the entire tourist destinations were depicted and the face of the women was taken into account to know express the emotional component that would be embedded in this whole phenomena was done certainly know something very, very exceptional. Now when in 2013 Madhya Pradesh tourism decided to replace this very ad by another ad, okay there was a necessity because the first signal had such strong strength. That the next ad had to be much more superior to that in terms of its signal, okay. I am, see basically talking about this very example to explain the importance of Weber’s law in psychology. Now look at this very ad. 75 (Refer Slide Time: 19:16) [other language][Song] 76 (Refer Slide Time: 20:47) What you see here okay is that the same tourist destinations which was depicted in the previous ad, okay are be once again being visibly shown to you, okay. But this visual representation is know in terms of using various colors, okay in different beautiful hues. Now the form is created of the say tourist destinations that was shown in the previous ad also but instead of showing you the image of the tourist destination. Now it is colors in different hues which are used to give you the mental image of that, okay. And this would you know primarily now show you that see the previous ad was so emphatic that the next ad had to know have very strong strength of the signal to be received, okay if it is going to replace the existing ad okay. So in terms of know real life situations this is how Weber’s Law plays a very, very important role, okay. 77 (Refer Slide Time: 21:56) So till now what we have discussed is that the incoming inputs from the environment, okay. 78 (Refer Slide Time: 22:05) They are assigned a meaning and once we succeed assigning a meaning to it we say that this is a perception, okay. Now to ensure that sense modality receives stimulation the stimulus must reach absolute threshold, okay. Therefore absolute threshold becomes the minimum intensity of the stimulus that the receiver can detect atleast fifty percent of the time. 79 (Refer Slide Time: 22:23) When we attach a meaning to what we have sensed we say that perception is taken place and whatever we experience is our perception, therefore the sensory cues that are received by the brain and the relevant past experience that one already has know, it is derived back to our working memory in order to provide a meaning to whatever we have sensed, okay. So this is how perception takes place but remember one thing. 80 (Refer Slide Time: 22:57) Perception need not always emulate reality, the raw information that is received by the brain is transformed or it is reworked in order to perceive. 81 (Refer Slide Time: 23:06) Hence a percept is an outcome of mental process such as form synthesis, such as feature differentiation, recollection of past experiences, and stimuli comparison. So these operations can either follow a top- down process or it can follow a bottom-up process. Let us understand this. 82 (Refer Slide Time: 23:31) The knowledge and memory pertaining to the stimuli and the language to understand and express it are crucial, expectations and belief and motivation are also important. All these constitute mental processes and are top-down processes, the environmental stimuli are processed by the sensory organs, this leads to sensation. These stimuli undergo perceptual organization based on their inherent characteristics; these are the bottom of processes. A synthesis of these two processes leads to identification or recognition of the stimuli. 83 (Refer Slide Time: 24:09) Let us now understand perceptual cycle proposed by Neisser. 84 (Refer Slide Time: 24:15) In 1976 U. Neisser proposed a model integrating the bottom-up and top-down processes into a cyclic process. This model focuses on perception, attention, and categorization. While perceiving an object one selectively attends to the available information, this is further modified by anticipatory schemata. So what we have understood now is that any percept that can be categorized, okay. 85 (Refer Slide Time: 24:45) For assigning a meaning has to be differentiated in terms of figure and background, okay. So while the pattern that becomes the focus of the attention becomes the figure, the backdrop against which the figure is seen, okay is considered as background. For instance if you are looking at me right now. So if I am the object then this green background against which you look at me becomes the background. Say if I write something on this green board and if you are looking at that very object although you stand in front of that green board, okay I become part of the background and the concept, the alphabets, the sentences written on the green board becomes the object. So figure and ground always remains interchangeable in nature, okay. And little later we will come to the concept of contour where we would be basically talking about the fact that more and more you are able to make a distinction between figure in the background, okay. More clarity you have in terms of perceiving object in the real world, okay. So we will end here and we will once again continue with the strength of the signal in our third lecture. 86  Acknowledgement Ministry of Human Resource & Development Prof. Satyaki Roy Co-ordinator, NPTEL IIT Kanpur NPTEL Team Sanjay Pal Ashish Singh Badal Pradhan Tapobrata Das Ram Chandra Dilip Tripathi Manoj Shrivastava Padam Shukla Sanjay Mishra Shubham Rawat Shikha Gupta K. K. Mishra Aradhana Singh Sweta Ashutosh Gairola Dilip Katiyar Sharwan Hari Ram Bhadra Rao Puneet Kumar Bajpai Lalty Dutta Ajay Kanaujia Shivendra Kumar Tiwari an IIT Kanpur Production ©copyright reserved 87  Indian Institute of Technology Kanpur National Programme on Technology Enhanced Learning (NPTEL) Course Title A Brief Introduction of Psychology Lecture – 03 Perception by Prof. Braj Bhushan Humanities & Social Sciences IIT Kanpur So let us now recapitulate whatever we have discussed till now, first lecture we focused on sensation, second lecture we looked at the concept of limen or threshold. We looked at absolute difference and terminal limen, then we talked about Weber’s Law and we took certain live examples I would say to understand how the concept of threshold and how the concept of you know intensity of the stimulus at the way it is described in Weber’s Law. How that makes an important type of contribution in terms of understanding our physical world. Then we ended the second lecture saying that always you, one has to know figure out, one has to extract the figure against the background, and this very idea of categorizing figure versus the background is an important phenomenon perception. We also said that figure and background could be interchangeable and we always look for contours, if we are able to establish it well and good. If we are not able to establish it we have confusion know, little later I think know towards the end we would also take some of the examples of reversible figures, reversible figure means. 88 (Refer Slide Time: 01:41) If you look at it from one point of view then you see the another type of an impression emerging out, for something half of the figure becomes the background and remaining half becomes the figure and then it keeps changing okay, and depending on what you consider as background the figure changes. But that we would see little later, right now we are again looking at the strength of the signal. Let us come to an interesting theory. 89 (Refer Slide Time: 02:09) Basically this very theory has its a root in communication and radar system. But in 1950’s, 60’s you know it drag the attention of psychologists because psychologists were interested in understating human behavior and they tried to understand the strength of the signal and its role in detection of this stimuli you, especially in conditions where the intensity of the signal is very weak okay, what was realized that Weber’s Law, fitness law, these laws were not sufficient enough to explain How human beings respond in situations when the signals are weak okay, and this led to what is called as theory of signal detection. 90 (Refer Slide Time: 03:03) Now look at the screen, you see a fighter aircraft, the radar system okay. 91 (Refer Slide Time: 03:15) And the radar of course has to be sensitive enough to receive the signal back from the flight and finally signal has to be detected by a human being. So when you look at the radar system everything seems very nice. 92 (Refer Slide Time: 03:34) 93 (Refer Slide Time: 03:36) But the problem with the human operator is that he or she has. 94 (Refer Slide Time: 03:39) To figure out the presence of the signal okay against some type of a noise, noise in psychology here is whatever is not your intended target is the noise okay. Let us understand this very theory by taking this example okay, you make a grid it is a two by two grid, so whether the signal is present or the signal is absent. 95 (Refer Slide Time: 04:08) That is category 1 and category 2 in terms of the human response the operator says yes or no, so yes versus no in terms of human response, presence versus absence in the case of signals. What are the possibilities? First when the signal is present and the person responds yes it is present okay, this is called hit condition okay. Second condition when the signal is absent and the respondent says that yes signal is present okay although signal is absent, this is called false alarm okay. 96 (Refer Slide Time: 04:48) The third situation, when the signal is not present okay and the respondent says that yes it is not present, this is correct rejection and the fourth situation where the signal is present but the person says the operator says that no it is not present, this is a miss condition, you have missed detecting the single okay. Now why this is so important from of course communication perspective okay, the radar system it makes sense no because the radar is supposed to detect the signal so that it can make distinction between the own aircraft versus enemy’s aircraft okay. But signal in itself does not make any sense. The human operator has to detect, the human operator has to say that fine I have identified the signal, which we are saying that this is a hit condition or the signal is not present and you say that fine signal is not present which is a correct rejection. These two conditions are fine, but think of two other conditions that is marked red here okay, that the signal is absent. 97 (Refer Slide Time: 05:59) And you say it is present, it is a false alarm. What would this mean? If you have a system for know combating the enemy aircrafts that is forcibly entering into your territory and you are the operator who based on the understanding of the radar signal gives the signal that fine the enemy aircraft has entered into our territory okay. The field guns will start firing at that very aircraft, you committed a mistake okay, when the signal was absent you said that yes there is a signal and therefore you raised a false alarm against which the support system started combat operation okay. And the second case is again far more dangerous where the signal is present but you say no it is not present okay, the enemy comfortably enters the your territory okay, there is a big price that the country pays for that. So you realize that the role of the human respondent is extremely important in terms of detecting the signal okay, and that is the reason why signal detection theory know is taken into account when we look at that perception mechanism. Now in terms of detection of this signal what is very, very important is the strength of the signal. 98 Remember in the second lecture also we were saying know that the strength of the signal has to play a role, and because the signal has to be detected therefore it is called that fine this is the discriminability index okay. (Refer Slide Time: 07:42) This is the strength of the signal okay, and the way you estimate it and accordingly that would shape your response. So the signal is discriminated depending on the separation and the spread of noise and signal and the noise curve okay. So we will take one experimental example here okay, and then we would move to graphical plotting of the response in this very situation what is called as the ROC curve. Now the percentage of hit and false alarms. 99 (Refer Slide Time: 08:15) Depends on the sensitivity of the operator to the signal, signal has strength, that we have discussed till now, and we have said that fine it is the strength of the signal which plays an important role, stronger the signal higher are the chances that we will detect it. But besides the strength of the signal what is also important is that I as an operator how sensitive I am okay, and that would be you know dependent on the cost-benefit analysis. 100 (Refer Slide Time: 08:43) What would be the cost-benefit analysis? I am rewarded okay, or I am punished for the response that I elicit okay. Therefore cost-benefit analysis will always play an important role. 101 (Refer Slide Time: 08:57) So in a given perceptual task one is always supposed to detect the signal, that is the stimuli against the non signal, that is the noise okay, and this means that the decision outcomes always comes amidst certain degree of uncertainty okay, you are not very certain, the strength of the signal plays an important role. 102 (Refer Slide Time: 09:17) Your sensitivity plays an important role, look let us look at know the one of the experimental demonstrations of this. We are taking a case that fine now the strength of the signal remains constant. In the first case what we were saying was that the strength of the signal changes and therefore it has an impact on the response. Now we are saying that strength of the signal is a made constant and it is the cost-benefit analysis that you make as an operator, fine. Now if the operator is rewarded for hits. 103 (Refer Slide Time: 09:50) But he is not punished for the false alarms okay, then the beta value that one sets is very, very low okay and this, what happens is it will maximize the number of hits. Because the operator is not worried about the false alarm, the reason, he is rewarded for the hit but he is also not punished for the false alarms. So even though I commit an error I do not get any adverse remark for it, and if I succeed fine, it is very good. So what I would do, I would relax my criteria okay. Earlier if I was using a very, very stringent filter to say that whether the signal was present or absent, now I do not do that okay. What is, what has happened to me, my relaxation of the criteria okay, which leads to maximizing of the hits, because I am not worried about the false alarm is primarily guided by this cost- analysis that I am making, that I am not paying a cost, but I am always deriving a benefit out of it so cost-benefit analysis comes into play here. Think of the other situation, D-prime has not changed now okay, so the strength of the signal has not changed. But I am not rewarded much for the hit. 104 (Refer Slide Time: 11:08) But I am punished for the false alarms okay. What would I do? Okay, my beta will be very high, so that the false alarms also becomes low, this of course would now result also into low hits. So if I am told that fine, whether you, you know go for a hit you correctly identify the signal okay, is important but it is not as important as if you commit an error while doing it. Take a situation, say in the court of law two attorneys are know, are going against a possible client who is likely to get death penalty okay. The cost involved is very, very high okay, and therefore what happens you suddenly realize that your beta is now very high because you do not want to create a false alarm, you do not want to argue saying that he is culprit because you know that if proven guilty the court will give him a death penalty. So you walk with extreme degree of caution okay, the previous example of the aircraft and the radar warning system that we were taking, if your signal by default know you press a button raising an alarm and in turns it no triggers airstrike okay, you would be very, very cautious okay, because false alarm the price that you pay for it is very high. 105 So you understand the situation now, case one when hits are rewarded and false alarms are not punished, in second case when hits are not rewarded but then for creating a false alarm you receive a punishment okay. Now if you graphically plot the result with false alarms on the. (Refer Slide Time: 13:17) x-axis and the hits on the y-axis okay, you get a curve, and this curve is called the ROC curve. The receiver operating characteristics curve okay. This curve represents the pattern of responding expected for a given dʹ at all values of criteria, so you can you change your criteria okay. The dʹ remains the same, and then you see that how depending on no the criteria that you have selected and the value of that criteria okay, the curves will change. 106 (Refer Slide Time: 13:51) Now when dʹ is 0, noise and signal plus noise curve are the same, and false alarms and hits will be the same okay, that is represented by the diagonal of, in the ROC graph okay. 107 (Refer Slide Time: 14:06) If the dʹ increases the ROC curve bows away from the diagonal. 108 (Refer Slide Time: 14:12) And you would realize the practical implication of it, of the fact that, that during the Second World War ROC curve was used for analyzing the radar signals know, and of course now we talk about it you know fondly in our discussion on signal detection in psychophysics. 109 (Refer Slide Time: 14:32) So you see the graphical representation here, the characterization, false alarms, hit and the miss that is defined by the theory of signal detection. 110 (Refer Slide Time: 14:43) And now look at this very video which explains the ROC curve. 111 (Refer Slide Time: 14:51) Look at this graph now, you have the proportion of the hits okay, and then you also have the proportion of the false alarms, and then of course now you have the chance level of response we are in now depending on the dʹ material set okay. Now you give your hits and the false alarms, so the detection of the signal okay, will actually no depend on your ability okay, to discriminate between the signal against the noise. The stimuli against the non stimuli, think of the other example okay. In real life situation where one has to detect signal amidst a noise, the best example in the present day would be the camouflage situation. 112 (Refer Slide Time: 15:38) When you try to know, make the signal of the stimuli weak enough so that the figure and the ground cannot be detected as two separate situations. 113 (Refer Slide Time: 15:51) You must have seen movies in real life several images no, where you have an individual no, who will put you know different colors on the face, would put some bushes on the hair, will add some bushes on the body also, the uniform that they wear they also have multiple colors okay, and then when you make a survey, when you look at the object from a distance okay, you are not able to detect know the background and the stimulus. So the object of is not very clearly perceived against the backdrop, that against which it is seen. So coming back to our key question that we initiated in our second lecture, do we process everything. 114 (Refer Slide Time: 16:39) What do you say now, what we have discussed till now, number one that it is the intensity okay of the signal that we receive in the involvement that would determine whether we would be processing it or not, number one. But number two what we have also seen is that, that characteristics of the criteria evolved by the user, the individual who responds is also important. So the intensity of their stimuli okay, and one, two what I decide, the criteria that I said for responding, both these things will have its importance when it comes to responding to the given situation. Now that we have understood that fine the intensity of the signal and the criteria that we set, both of them have a role to play and the fact that we are now saying that all images, all figures have to be extracted out of the ground. What is important once again we are coming to this concept, that you have to draw a line of difference no, the contours. Now basically contours are nothing. 115 (Refer Slide Time: 17:57) But these are change in the gradient okay, between the elements of a perception. So ambiguity in the contours lead to reversibility okay, and I said that little a little later we will see a few examples of reversible images. But in reality in most of the cases no, we have the edges and we have the contours okay, if you are able to establish this distinction then you would be very easily able to see a visual image against a background, and similarly you can hear a sound against the noise that you are hearing. Look at this very example. 116 (Refer Slide Time: 18:36) A famous example that you find in all text books, what do you see here? It is all no mix of black and white patches, it is extremely difficult to no decipher what is the object and what is the background, just concentrate at it, are you able to see? Now let me help you out, try to look at this very area, can you see the object now, the answer is yes okay. How you can now detect the object, because in this case this was the area that you were shown and very conveniently now you can look at these black and white patches and you can make out that you are looking at a dog okay against a familiar type of a background. Exactly similar type of thing works when it comes to human beings no. 117 (Refer Slide Time: 19:36) Now look at this very example, this is know a photograph published in a newspaper where an Indian Army soldier is shown in a camouflage and he is basically taking part in an exercise Sudarshan Shakthi in somewhere in Barmer district in Rajasthan okay. Now if you look no very clearly it is very no difficult if the same soldier is put on the ground and you look at the background there, making a distinction between the figure and the background becomes very difficult no. Now if you compare all this, the first case where know when we were trying to look at the flying aircraft and somebody sitting in front of the radar screen who is supposed to detect okay, the stimuli how difficult it would be, you saw the black and white patches where you were supposed to look at the dog against the similar background how difficult it was. And again here you see. 118 (Refer Slide Time: 20:36) Okay, it would be extremely difficult if you are not told what you are actually looking at okay, and that too we are looking at a very close shot. If know nothing of this information was given and you were looking at this very object from a distance it would have been extremely difficult to extract the image, the figure out of the background. Now coming back to the example. 119 (Refer Slide Time: 21:04) Of subjective contours, these were the cases where contours are still available no, the strength of the signal makes. 120 (Refer Slide Time: 21:13) That very difference no and of course your sensitivity, so one is your sensitivity other is the dʹ value, these two things would make difference, but cases. 121 (Refer Slide Time: 21:27) Where the contours are missing. 122 (Refer Slide Time: 21:30) What do we do? Okay and it has been observed that as human beings we create our subjective contours okay, and subjective contours play extremely important role, the reason being that what you actually see in the environment does not have that line of distinction. And because you have to read the figure against the background, so what would be the possible figure and what would be the possible background would depend primarily on the fact how you are subjectively trying to draw that line of distinction what is called as contours no. Look at this very video to understand subjective contours. 123 (Refer Slide Time: 22:15) Look at this image, what do you see? If I ask you, are you looking at a white triangle laid over you know three circles the answer would be yes for many of you, or know if you just you know perceive that no it is actually no three independent circles okay, with a piece cut out from each of them okay. But there is no triangle as such, so it could be very easily know interpreted as if you actually look at three independent black circles with a piece cut out of them okay, and there is no triangle as such. But even though the background is white okay, I am sure all of you would know when you look at this image you automatically draw a line to complete the triangle okay, to perceive that there is a white triangle know above this, this is subjective contour. 124 (Refer Slide Time: 23:09) We have already seen this image, let us look at it again, look at the three black circles in the triangle, you can see a sharp gradient change between the circles, triangle, and the background. Now move the triangle and superimpose it over the three triangles, you still see the triangle by filling creative subjective lines, you do not see three circles with piece cut out of them, well you were aware that the triangle was superimposed on the circles. 125 (Refer Slide Time: 23:41) Now see these three circles, they all have a piece cut out of them, although this time a triangle has not been superimposed you will still perceive a white triangle put over the black circles, this was an example to demonstrate the concept of subjective contours. Now that we have understood subjective contours in the next lecture we would be focusing on perception of form. How do we make out the forms that we see in the world, the shape, size, and all these things. 126  Acknowledgement Ministry of Human Resource & Development Prof. Satyaki Roy Co-ordinator, NPTEL IIT Kanpur NPTEL Team Sanjay Pal Ashish Singh Badal Pradhan Tapobrata Das Ram Chandra Dilip Tripathi Manoj Shrivastava Padam Shukla Sanjay Mishra Shubham Rawat Shikha Gupta K. K. Mishra Aradhana Singh Sweta Ashutosh Gairola Dilip Katiyar Sharwan Hari Ram Bhadra Rao Puneet Kumar Bajpai Lalty Dutta Ajay Kanaujia Shivendra Kumar Tiwari an IIT Kanpur Production ©copyright reserved 127  Indian Institute of Technology Kanpur National Programme on Technology Enhanced Learning (NPTEL) Course Title A Brief Introduction to Psychology Lecture – 4 Perception by Prof. Braj Bhushan Humanities & Social Sciences IIT Kanpur Till now we have talked about the, what to call extraction of image from the background, depending on one the properties of the external stimuli to the readiness of the person who is trying to perceive the object, and three what we were talking towards the end of the third lecture was, the idea of drawing the contours so that the image can very easily be extracted out from the background. (Refer Slide Time: 00:45) 128 So today we would be talking about form perception wherein we would try to emphasize on the organization of form. (Refer Slide Time: 00:53) How groups and patterns they emerge. 129 (Refer Slide Time: 00:58) And in this context we would be talking about the Gestalt principles. Gestalt basically means whole, complete. According to Kohler gestalt would be basically formed from ambiguous stimuli. So how you try to complete your perception based on whatever is available to you okay, that is that holistic part of the percept is the gestalt principal. The core principle is called the law of Prägnanz okay. And then there whole set of laws which are considered as part of gestalt principles. Now law of Prägnanz basically says that the simplest organization is one that demands minimum cognitive effort, okay. In German Prägnanz means clarity. So those cues in the external environment that does not you know require too much of mental effort from your side in order to decipher the figure from the background, okay. Those organizations basically would constitute a law of Prägnanz. So that basically means that as human beings we would also always like to minimize our cognitive engagement in terms of deciphering the image from the background. 130 (Refer Slide Time: 02:35) So simplest organisations would always require a minimal cognitive effort and therefore minimum time, minimum effort, best type of mental representation that you derive from the external environment, this is what would be considered as the principle of Prägnanz okay. So simpler and symmetrical forms, these are the two types of forms which are very easily perceived because it is too simple and because it is too symmetrical. Therefore you do not have to cognitively you know engage yourself in too much of know derivation of, extraction of cues, derivation of cues, arriving at a conclusion, combining them, and then finally deriving a meaning out of it. Hence simpler symmetrical forms will always be perceived very easily by human beings, this is what the law of Prägnanz says. Now look at this very circle on the screen. 131 (Refer Slide Time: 03:27) You have one circle, the second circle, third, the fourth, and the fifth, okay. Now all of them have come one by one and then they form a pattern out of it now. 132 (Refer Slide Time: 03:48) Now when you look at this very pattern you started from the first, came up to the whole no set of five rings. Now look at the third image there, okay. You could have sense it that way also no? So all types of no combinations where you realized there are small, small pieces cut out of the two converging rings there. But then we do not perceive things in such fragmented order, rather we always look at them as a whole, as a complete. You provide various colors to the rings and this is what we call as Olympic rings, okay. 133 (Refer Slide Time: 04:26) Now this is the logo of Rio Olympics which is schedule to be held next year, okay. And you do not see all these smaller elements, you do not detach them and perceive them separately rather you always perceive them together. So simpler symmetrical and this is what the law of Prägnanz says. 134 (Refer Slide Time: 04:53) Look at this very logo, you have three distinct components but they are too simple, okay and also form a symmetry, simpler symmetrical, okay. This is what the law of Prägnanz says and hence when you promote, okay tourism in Norway you suddenly feel Oh! The basic components which defines what Norway means, okay. 135 (Refer Slide Time: 05:19) Three elements put in a very simpler format, put in a very symmetrical order and this is what law of Prägnanz says, okay. Perception is very easy, deriving sense is very easy, remembering is very easy, okay. Cognitive effort is minimized, okay. And then you also have the best of the outcome that you want. Now law of Prägnanz is the core of the gestalt principles and then there are whole other sets of laws. 136 (Refer Slide Time: 05:44) We will talk about them one by one. The second law is the law of symmetry, law of symmetry basically says that similar objects that always tend to group together, okay. We first took in the case of Law of Prägnanz we took the example of circles, okay. So we will continue with earlier examples of circle, okay. And then again now go to the example which has a logo there, okay. Look at this very video. 137 (Refer Slide Time: 06:12) You find four circles here, and finally you have16 of them. So although they are independent circles we tend to perceive them as groups, the colorless circles form one group now while the rows of red circles form another one. Now let us make this situation a little more complex, okay. We had just know four circles finally leading to 16 circles and we had the red color ones and the colorless circles no. So this is how, we were trying to look at the formation of groups based on similarity. Now if you have some, much more complex situation. 138 (Refer Slide Time: 06:58) Once again you have a row of four colorless circles multiplying into four rows, just as the previous example the blue circles form a group when all of them become similar right now, okay. With their blue colors the ones which are bigger either horizontally, vertically, or diagonally they tend to form a group. 139 (Refer Slide Time: 07:27) So we basically look at know the difference, okay. And depending on know what you are actually trying to look at, okay. You will always search for a no certain reason based on which you can form a group so that you perceive it better. 140 (Refer Slide Time: 07:43) Look at this very logo, okay. It is a very commonly known logo to us, okay. And no actually when you see here you find law of similarity being used, okay. 141 (Refer Slide Time: 07:57) What we discussed was that similar objects they will tend to come together, okay. 142 (Refer Slide Time: 08:00) And here you have no three different you know representations, okay. All of them they tend to group together because they follow the law of similarity. The next law is the law of proximity, proximity means nearness. 143 (Refer Slide Time: 08:15) So objects which are nearer to each other they always tend to form a group. Once again we will continue with the example of circles, okay. And then again take an example of a logo. 144 (Refer Slide Time: 08:27) Initially you see four columns of green circles that are equidistant but when the two columns move closer to each other, okay they tend to move know on the two ends, they form two distinct groups, the first two columns from one group while the remaining two they form another group, okay. So this is the law of proximity, initially they were no seen as distinct columns, okay. Because know they were equidistant, okay. But the moment you have a separation now you see that know you have one column and the other column although color, and the size, the form remains the same, this is the law of proximity. 145 (Refer Slide Time: 09:09) Now look at this very logo, okay. Here you have you know structures which basically forms honeycomb but then they very easily because they are nearer to each other you can very easily consider that they form one group, okay. And you advertise for a particular event along with the sponsors the major sponsors of the event, okay. This is how law of proximity is beautifully utilized in the world of visual communication. 146 (Refer Slide Time: 09:40) Look at this very still image from Beijing Olympics, okay. Now here what you find is that there are a whole lot of arrangements and then you have a, when you look at this very image you look at things little differently. Now this very segment they tend to form one group, this very segment tend to form one group, this segment forms another group, okay. And this is how you have different, different types of representations here Where although the bigger screen carries whole lot of things when we look at it we combine separate parts together and then we try to sign a meaning to the external stimulus that we have been looking at, okay. Now law proximity the way it defines here is, that you have things which are closer to each other so one set of performance on the left-hand side who are closer to each other. And then there is a big distance between the other group so the left and right very easily gets divided. Those in the center of course they have a different color of the costume but then they are again separated from these two groups, okay. But then within themselves they are very close to each other, they are very nearer to each other and hence the law of proximity helps us consider that this is group 1, this is group 2, this is group 3. 147 They are all very, very symmetrical, okay. But then because of their nearness to one group compared to the other based on their proximity we consider them to be forming three separate groups. (Refer Slide Time: 11:28) We come to the next law that is law of closure. Law of closure basically says that if you have a discontinuous shape and when you perceive it we always tend to complete it, okay. And this completeness is based on whatever we are familiar with, let us take this very example again we are banking on the example of circle and then again we will move onto an example of logo. 148 (Refer Slide Time: 11:51) You see a circle right now, another one and yet another one, although you see 11 different circles but you perceive them as a ring, their individual identity is not taken into account, okay. So this is an important no, thing here that know when you look at the continuous things, okay. When you look at the patterns that emerge, okay ,that this continuous shapes is perceived as a complete, okay, if it represents something very, very familiar. 149 (Refer Slide Time: 12:26) You look at this no famous visual icon, now this is a logo of WWF. 150 (Refer Slide Time: 12:32) If you visit their site, okay. 151 (Refer Slide Time: 12:35) You see this image no, you see here no where I am moving the cursor right now, okay. You see WWF no you visit their site and you see exactly this very representation. 152 (Refer Slide Time: 12:47) Now when you actually see it, okay. You can very easily make out what you are looking at and you see it as Panda because the gaps that you see you try to know close it, you try to fill it, and therefore this is not know looked upon as a no some black field areas against a white background, but rather it is looked upon as an animal. 153 (Refer Slide Time: 13:08) We come to the next law that is the law of continuity, okay. Law of continuity basically says that continuous figures are always preferred. Now till now we were you know repeatedly taking examples of circles. Now let us take example of a straight lines and then we will look at one of the events from Beijing Olympics to understand law of continuity. 154 (Refer Slide Time: 13:31) The law of continuity says that continuous figures are preferred by us, okay. So something that runs in continuation. 155 (Refer Slide Time: 13:40) You can see a bold straight line entering from the left side of the screen. Now another one enters from the right side. Although they are two separate lines as you initially saw but when they join you see them as one straight line, when two more straight lines enter from top and bottom respectively you perceive an XY coordinate. When two of these lines become red, green, blue or yellow they are perceived as one continuous figure, when they are all black you perceive them as XY coordinate. Let us look at another example of law of continuity. 156 (Refer Slide Time: 14:21) Here you see dark black circles appearing on the screen, these circles are perceived as collective unit because they share a common feature of direction. Now initially you know you look at it as a straight line, okay. And the moment this know the other line the curve one know comes there you perceive it differently, you see as if it represents some type of direction. 157 (Refer Slide Time: 14:48) If you visit you know Indigo airline, okay. This is one of the airlines that you must have certainly seen here, okay. When you look at their logo, okay actually you see what know you saw here, okay. Now when you look here no look at your screen this very part where I am moving the cursor, okay. You actually see this law of continuity, okay. This image although this is a collection of dot something that you saw. Right now in this animation, okay but the moment you see here know it gives the direction and it know makes you feel that fine you are actually looking at something, a visual representation of Airline. 158 Now let us look at this video. (Refer Slide Time: 15:33) Do you see here the law of continuation working? 159 (Refer Slide Time: 16:05) The next Gestalt principle is the law of symmetry, we have been talking about symmetrical objects know right from we began with our discussion on Prägnanz. Now law of symmetry says that symmetrical objects they will always be collectively perceived, let us take the example of these squares and then we will also move to an example taking again a logo into account. 160 (Refer Slide Time: 16:30) Look at the sky blue square and the blue square dropping out of it, this overlap helps you see another square. Let us look at these squares without any color, we will perceive them as two squares. 161 (Refer Slide Time: 14:46) When the top and the bottom parts are removed we clearly see a small square, but when they are brought back we perceive two big squares overlaying each other, this demonstrates that in spite of distance symmetrical objects are collectively perceived. 162 (Refer Slide Time: 17:04) This is the logo of CSC which basically shows you how beautifully the law of symmetry can be used to represent visually represent one of the forms. The next law of gestalt principle is the law of common fate. 163 (Refer Slide Time: 17:23) The law of common fate says that objects which share common features they are grouped together. So objects in our perceptual field, okay, that function or move together in similar manner they will always, always be perceived together, okay. Now what is the importance of this very law, basically it helps us perceive things around us in terms of whether they are related or not, okay. 164 (Refer Slide Time: 17:51) You must have seen these beautiful images in our Republic day parade, look at this very video which basically tells you when different aircrafts which you basically know that these are different, different aircraft's but when they make a formation. 165 (Refer Slide Time: 18:09) They are then perceived together because they perform similar function, they move together and therefore even though they are separate aircrafts they are not viewed so. 166 [OTHER LANGUAGE][0:18:19] to [0:19:49] Song 167 (Refer Slide Time: 19:50) Now given the fact that based on the quality of the stimuli, based on our individual preparedness and preferences, and also based on the laws that govern our perceptual principles we provide meaning to what we have sensed from the world. Now based on what we have sensed from the world and depending on the appropriateness of the meaning that we have provided, we many a times tend to select certain inputs and retain them in our conscious experience for little longer period of time. So what we do, we tend to divide things into what would be in our focus and what we would know keep it on the margin, this is what is called as attention because we have a limited duration assigned for this very course so we will not go into details of attention, but I must tell you that the recommended book if you go through that, you will find a whole know in-depth description of the process related to attention. 168  Acknowledgement Ministry of Human Resource & Development Prof. Satyaki Roy Co-ordinator, NPTEL IIT Kanpur NPTEL Team Sanjay Pal Ashish Singh Badal Pradhan Tapobrata Das Ram Chandra Dilip Tripathi Manoj Shrivastava Padam Shukla Sanjay Mishra Shubham Rawat Shikha Gupta K. K. Mishra Aradhana Singh Sweta Ashutosh Gairola Dilip Katiyar Sharwan Hari Ram Bhadra Rao Puneet Kumar Bajpai Lalty Dutta Ajay Kanaujia Shivendra Kumar Tiwari an IIT Kanpur Production ©copyright reserved 169  Indian Institute of Technology Kanpur National Programme on Technology Enhanced Learning (NPTEL) Course Title A Brief Introduction of Psychology Lecture – 05 Perception by Prof. Braj Bhushan Humanities & Social Sciences IIT Kanpur Now let us talk about form perception. (Refer Slide Time: 00:16) Now form perception basically is dependent upon recognition of figure from the background okay. 170 (Refer Slide Time: 00:23) And this basically would mean that certain type of constancies will work, size, shape, and brightness okay, that would mean we would come through it in a few seconds from now that depending on the situation the size of the object might change, the shape of the object might change, the brightness the contrast effect might change, but then we have a tendency as human being to maintain mentally a degree of constancy in terms of shape, size, and brightness and that helps us perceive situation much better. Now in terms of depth, in terms of height okay. 171 (Refer Slide Time: 01:10) We always have the monocular and the binocular cues okay, inputs coming from only one eye is the monocular cue and input that comes from both the eyes they constitute the binocular cues, now my monocular cues. 172 (Refer Slide Time: 01:24) They basically depends on the linear perspective, clarity, interposition, the pattern of shadow, texture okay, and the relative movement. What we would do now is that all these six important ingredients of monocular cues we will talk about them one by one trying to take possibly the best example. 173 (Refer Slide Time: 01:50) So let us come to linear perspective. When parallel lines that converge at infinity they help us understand the relative distance of two parts of an object or they even help us understand the whole landscape. 174 (Refer Slide Time: 02:05) Okay look at now this very image, now imagine the point where no the dots converge, the straight lines converge okay, that you are standing at that very point and you are looking at the urban landscape okay, this is what is meant by linear perspective. 175 (Refer Slide Time: 02:23) So what actually happens you have the convergence of the lines okay. 176 (Refer Slide Time: 02:27) And this convergence of the lines helps you understand your position and the position of the objects in your landscape, and accordingly these monocular cues they help you understand the shape, the size, and of course depending on brightness and contrast you even can make out the distance of the object from yourself. 177 (Refer Slide Time: 02:48) Now look at this very image, now this is a usual railway track that we have been seeing right from our childhood days. Now what happens when you look at the two parallel bars, the two tracks, you stand in the center then you realize that they are wide apart, they are separated apart, but then when you look at it no at a distance you gradually realize as if the distance between the parallel bars they somehow tend to converge, they tend to come closer to each other okay. 178 (Refer Slide Time: 03:20) 179 (Refer Slide Time: 03:20) 180 (Refer Slide Time: 03:21) Now based on the monocular cues what we have been saying is that. 181 (Refer Slide Time: 03:24) When you look at the object where you are okay, and whether. 182 (Refer Slide Time: 03:28) The parallel lines they converge or not. 183 (Refer Slide Time: 03:31) That decides okay what you are looking at and how you perceive the world around you, the first was the example of the urban landscape. 184 (Refer Slide Time: 03:37) The second is the example of again a modern infrastructure that is the railway tracks. 185 (Refer Slide Time: 03:42) Now we come to clarity, if you are looking at an external environment and the more and more clearer things are you always tend to realize that those things are near to you okay, things which are very far off from you will now compromise on the degree of clarity. 186 (Refer Slide Time: 04:07) Look at this very image no and you compare both of them. The first case where you see the structure and you see the structure with much, much more clarity and you can sense that the object is much more nearer to you, the structure is much more nearer to you. In the other case of course okay you realize that the clarity is compromised with and with the compromising the clarity you realize that the image on the right tells you that the structure is nearer to you, the image on the left tells you that the image, that the structure is far off from you. So in terms of monocular cues how clearer is the image that is generated, that would tell you okay how far are how nearer you are to the object, the third is the interposition. 187 (Refer Slide Time: 05:00) Interposition is when you have two or more objects okay, in the same usual field and one object obstructs the view of the other one. Now the object which now looks very. 188 (Refer Slide Time: 05:15) Nearer to you would be the one which will block the clearer perception of the object at the back. Now look at these two circles, if I ask you how distant you are from these two circles okay it is very difficult for you, you will perhaps say that I am at a equi-distance okay. 189 (Refer Slide Time: 05:36) Now look at the movement pattern, now if I ask you which is nearer to you, you can very easily say that the one which is a smaller is nearer to me, why is it nearer to you, because monocular cue tells you that this color disc which is nearer to you is the one which blocks a part of the disc which is at the back, that means unless this very object will be no nearer to me it cannot no work as interference in a clearer perception of the object at the back okay. So this is interposition no the position of the object which is nearer to you is the also the one which blocks clear, clearer perception of the object at the back. 190 (Refer Slide Time: 06:20) Same is the situation here no 191 (Refer Slide Time: 06:23) Now we come to the shadow pattern, shadow now you know wherever you have light you will always have a shadow if an object is put there, so luminance and contrast they help us understand the depth okay and because it helps us understand the depth so if you inverse the phenomena you can say that this also helps us understand the height of the object, now look at this very video. 192 (Refer Slide Time: 06:51) This is know the aerial image of IIT Kanpur. Now this video no did show you the aerial image of various structures of IIT Kanpur campus. 193 (Refer Slide Time: 07:26) Okay and right now when y