Week 4 - Perception PDF - PSY-260

PSY-260 Week 4 – Perception Dr. Marina Loucaides FIGURE 3.1 (a) Initially Emma thinks she sees a large piece of driftwood far down the beach. (b) Eventually when closer, she realizes she is looking at an umbrella. (c) On her way down the beach, she passes some coiled rope. She guesses that it...

PSY-260 Week 4 – Perception Dr. Marina Loucaides FIGURE 3.1 (a) Initially Emma thinks she sees a large piece of driftwood far down the beach. (b) Eventually when closer, she realizes she is looking at an umbrella. (c) On her way down the beach, she passes some coiled rope. She guesses that it might be continuous. Picks it up and explores it. What is perception? Experience resulting from stimulation of the senses. Basic concepts: – can change based on added information. – Involves a process like reasoning or problem solving. – occur in conjunction with actions. Possible that true human perceptual processes are unique to humans. Attempts to create artificial forms of perception (machines) have been met with limited success and each time have had problems that could not be solved. FIGURE 3.2 It is easy to tell that there are a number of different buildings. The middle two modern buildings are in front of two other rows of glass buildings. The trees grow between and behind the older buildings near the riverside. These perceptions are easy for humans but would be quite difficult for a computer vision system. FIGURE 3.3 Even computer vision programs that can recognize objects fairly accurately make mistakes, such as confusing objects that share features. In this example, the lens cover and the top of the teapot are erroneously classified as a “tennis ball”. FIGURE 3.4 A computer or a person can determine whether the two straight-on views in (a) and (b) are the same person, but the person outperforms the computer for faces at an angle, as in (c). So… Why is this the case? What do we do that computers don’t, or what do we possess that computers haven’t? Why can’t machines perceive like humans? (1) Inverse Projection Problem Task of determining the object responsible for a particular image on the retina. Involves starting with the retinal image, then extending outward to the source of that image. FIGURE 3.5 The retinal image created by the rectangular page could have been created by several different objects (a rectangular page, a tilted trapezoid, a much larger rectangle, objects located at different distances) A particular image on the retina can be created by many different objects in the environment Thus, somehow, we need to figure out what exactly has been presented to us. This is why we say that the image on the retina is ambiguous.  Why can’t machines perceive like humans? (2) Objects can be hidden or blurred People can often identify objects that are obscured and therefore incomplete, or in some cases objects that are blurry. People easily understand that the part of an object that is covered continues to exist, and they can use their knowledge of the environment to determine what is likely to be present. FIGURE 3.7 FIGURE 3.6 Who are these people? – our previous exposure to those faces and Can you locate the hidden pencil and the author’s pencil? previous knowledge help us to recognise them Why can’t machines perceive like humans? (3) Objects look different from different viewpoints Viewpoint invariance Images of objects are continually changing, depending on the angle from which they are viewed. Humans continue to perceive an object as the same from different angles, this isn’t so obvious to a computer. FIGURE 3.8 Your ability to recognize each of these views as being of the same chair is an example of viewpoint invariance. Information Used in Human Perception The human perceptual system uses two types of information: 1. Environmental energy stimulating the receptors. 2. Knowledge and expectations the observer brings to the situation. FIGURE 3.10 Perception is always a combination of both top- down and bottom-up processing. Bottom-up: refers to what comes from the environment Top-down: refers to what the individual brings. The Complexity of Perception Bottom-up processing – Perception may start with the senses – Incoming raw data – Stimulates the receptors. – The receptors “translate” the environmental energy into neural signals that are transmitted, via the thalamus towards cortical brain areas that will further process and store it Top-down processing – Processing starts in the brain – Person’s knowledge, experience, and expectations. https://www.youtube.com/watch?v=TLHlfPTRekA  Perceiving Objects FIGURE 3.12 FIGURE 3.11 Which horizontal line is the longest? What do you perceive the central stimulus to be? The context makes a difference!!! Depending on what you take as the context, it can be either seen as the letter S or the number 5.  Perceiving People Calbi et al. (2017): the dynamic emotional context of short video fragments affected how participants rated the emotional expression of a neutral face. “fear context”: neutral faces were judged to express a more negative emotion “happy context”: neutral faces were judged to have a more positive expression. Context spontaneously and unconsciously influences our perception. Perception of language Top-down processing influences our perception of language based on our individual experience with the language. Speech segmentation – Ability to tell when one-word ends, and another begins. Transitional probabilities – Knowing which sound will likely follow another in a word. The continuous sound signal enters the ears and triggers signals that are sent toward the speech areas of the brain (bottom-up processing); if a listener understands the language, that knowledge (top-down processing) creates the perception of individual words. Perception of pain Pain occurs when receptors in the skin are stimulated. – Direct pathway from skin to brain (Direct pathway model) This is a bottom-up process because it depends on stimulation of the receptors. Pain is also influenced by what a person expects, top-down processing how the person directs their attention and distracting stimuli present. Studies have shown that a significant proportion of patients with pathological pain get real relief from taking a placebo, a pill that they believe contains painkillers but that, in fact, contains no active ingredients. Or direct attention to something else (e.g., games) to take care of wounds. https://www.youtube.com/watch?v=eakyDiXX6Uc Summary up to this point Context affects our perception e.g., of a face or the length of a line Expectation and attention can influence our perception, e.g, a person’s experience of pain Perception is created by signals from the environment (bottom-up processing) and by what the individual brings to it (top-down processing). Perception depends on multiple sources of information à it is a complex process. Both “bottom-up” and “top-down” include the word “processing,” which implies that the perceptual system is doing something with this information. Helmholtz’s Unconscious Inference Figure 3.14 The display in: (a) is usually interpreted as being; (b) a blue rectangle in front of a red rectangle. (c) A blue rectangle and an appropriately positioned six- sided red figure.  Helmholtz’s Unconscious Inference Top-down theory Some perceptions are the results of unconscious assumptions we make about the environment – We use our previous knowledge to inform our perceptions. We infer much of what we know about the world Likelihood principle – We perceive the world in the way that is “most likely” based on our past experiences. The process of perceiving what is most likely à have caused the pattern on the retina to be explained rapidly and unconsciously. These unconscious assumptions, which are based on the likelihood principle, result in perceptions that seem “automatic,” even though they are the outcome of a rapid process. Perceptual Organization “Old” view—Structuralism (Wundt) – Perception involves adding up sensations. “New” view—Gestalt principles – Rejected the idea that perceptions are formed by simply “adding up” sensations. – The whole is more than the sum of its parts (gestalt = “whole”) – The mind groups patterns according to intrinsic laws of perceptual organization. – Gestalt psychologists proposed a number of principles of perceptual organization to explain the way that elements are grouped together to create larger objects. Gestalt Principles of Perceptual Organization Figure-Ground Principle FIGURE 3.15 Some black and white shapes that become perceptually organized into a Dalmatian.  Figure-Ground Principle We perceive something by grouping elements in such a way that a distinction is made between what is in the foreground (the figure or the object) and what is the background. Figure-Ground Principle What is the background for you in this example?  Good Continuation Principle Lines tend to be seen as following the smoothest path “Points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path. Objects that are overlapped by other objects are perceived as continuing behind the overlapping object.“ Figure 3.16 a) Rope on the beach. b) Good continuation helps us perceive the rope as a single strand. c) She was not surprised  Law of Pragnaz Principle Principle of simplicity or good figure “The perceptual field and objects within it will take on the simplest and most encompassing structure permitted by the given conditions” Every stimulus pattern is seen so the resulting structure is as simple as possible. Figure 3.17 The Olympic symbol is perceived as five circles (a), not as the nine shapes in (b).  Principle of Similarity “Similar things appear to be grouped together. Besides similarity of colour, grouping can also occur because of similarity of size, shape, or orientation.” Figure 3.18 (a) This pattern of dots is perceived as horizontal rows, vertical columns, or both. (b) This pattern of dots is perceived as vertical columns.  Photograph taken at the exact moment that the front of the white water, aligned with the white area on the woman’s clothing. Similarity of color causes grouping: Different colored areas of the dress are perceptually grouped with the same colors in the scene. Also, the front edge of the water creates grouping by good continuation across the woman’s dress. Gestalt Principles of Perceptual Organization Perception is determined by specific organizing principles Role of experience is minor compared to these intrinsic, “built in” principles in our “system”. Experience can influence perception but is not the key driver. Experience plays a minor role in perception vs Helmholtz’s likelihood principle (explanation of image in retina) Modern perceptual psychologists see our experience with the environment as a central component of the process of perception. Taking regularities of the environment into account Characteristics of the environment that occur frequently and therefore strongly influence what we expect to see Blue is associated with open sky, landscapes are often green and smooth, and verticals and horizontals are often associated with buildings. We can distinguish two types of regularities: physical regularities and semantic regularities. Physical Regularities Common physical properties of the environment. Oblique effect (angled) – We perceive verticals and horizontals more easily than other orientations. Light-from-above assumption – We assume light comes from above because this is common in our environment. – We perceive shadows as specific information about depth and distance. FIGURE 3.19 In these two scenes from nature, horizontal and vertical orientations are more common than oblique orientations. FIGURE 3.20 (a) A wall with textured surfaces that jut out. (b) The same picture turned upside down. Semantic Regularities The meaning of a given scene is related to what happens within that scene. Semantic regularities are the characteristics associated with functions carried out in different types of scenes. Scene schema: – It is knowledge of what a given scene ordinarily contains. – In the jewelry case at Tiffany’s, would you expect to see a plate of fish and chips or diamond rings? Scene Schema Study FIGURE 3.21 Stimuli used in Palmer’s (1975) experiment. The scene at the left is presented first, and the observer is then asked to identify one of the objects on the right. Up to here: 1. Helmholtz’s idea that we resolve the ambiguity of the retinal image by inferring what is most likely, given the situation 2. The idea that regularities in the environment provide information we can use to resolve ambiguities. 3. Bayesian Inference Bayesian Inference One’s estimate of the probability of a given outcome is influenced by two factors: – The prior probability - which is our initial belief about the probability of an outcome – The likelihood of a given outcome - the extent to which the available evidence is consistent with the outcome  Bayesian Inference Example 1 Figure 3.22 Hypothetical probabilities to illustrate Bayesian inference. (a) Mary’s beliefs about the relative frequency of having a cold, lung disease, and heartburn. These beliefs are her priors. (b) Further data indicate that colds and lung disease are associated with coughing, but heartburn is not. These data contribute to the likelihood. (c) Taking the priors and likelihood together results in the conclusion that Charles’s cough is probably due to a cold. Four Conceptions of Object Perception Top-down processing (1) Helmholtz’s Unconscious inference (2) Environmental regularities (3) Bayesian inference All have in common the idea that we use data about the environment, gathered through our past experiences in perceiving, to determine what is out there. Bottom-up processing (4) Gestalt principles Emphasized the idea that the principles of organization are built in. They acknowledged that perception is affected by experience, but argued that built-in principles can override experience, thereby assigning bottom-up processing a more central role in perception.  So, experience doesn’t count? Modern cognitive psychologists à the laws of organization could have been created by experience. Years of experience in seeing objects that are partially covered by other objects. When two visible parts of an object have the same colour (principle of similarity) and are “lined up” (principle of good continuation), they belong to the same object and extend behind whatever is blocking it. Gestalt principlesà they describe the operating characteristics of the human perceptual system, which happen to be determined at least partially by experience. Neurons, Knowledge, and the Environment Some neurons respond best to things that occur regularly in the environment. Neurons become tuned to respond best to what we commonly experience. – Horizontals and verticals compared to oblique Experience-dependent plasticity - mechanism through which the structure of the brain is changed by experience and learning. – Evolutionary process à People used to live in forests where the images they perceived were mostly horizontal and vertical – more neurons to perceive these images – passed down to future generations – Kittens experiment with oblique images FIGURE 3.27 (A): Stimulus examples shown at vertical/horizontal (cardinal) and oblique orientations. (C): fMRI activity maps. Black lines indicate the Parahippocampal Place Area (PPA) border. The coloured areas indicate higher activity when cardinal stimuli are presented than when oblique stimuli are presented. What we know up to this point? Perception is the outcome of an interaction between: 1. Bottom-up information: receptors to brain 2. Top-down information: knowledge about the environment or expectations related to the situation. Next, we will discuss yet another factor that influences perception: Action.  Movement facilitates perception FIGURE 3.28 Three views of Michelangelo’s famous sculpture of David. Moving around an object can reveal its true shape and identity. Seeing an object from different viewpoints provides added information that results in more accurate perception, and this may hold even more for objects that are less common. The Interaction of Perception and Action Constant coordination occurs in the brain as we perceive stimuli while also taking action towards them. Figure 3.29 Picking up a cup of coffee: (a) perceiving and recognizing the cup (b) reaching for it avoiding the flowers (c) you position your fingers to grasp the cup, taking into account the perception of the cup’s handle (d) then you lift the cup with just the right amount of force, taking into account your estimate of how heavy it is based on your perception of its fullness All these for just to pick up a cup! And it happens almost automatically with almost no effort at all! Movement Facilitates Perception Our movement adds complexity to perception compared to if we remain static but moving around a stimulus offers us more views to create accurate perceptions. Three views of a “horse.” Moving around an object can reveal its true shape.  Perception and Action: What and Where? What pathway: – Determining the identity of an object – Ventral pathway (lower part of the brain) Where pathway: – Determining the location of an object – Dorsal pathway (upper part of the brain) FIGURE 3.31 The monkey cortex, showing the what, or perception, pathway from the occipital lobe to the temporal lobe and the where, or action, pathway from the occipital lobe to the parietal lobe. Perception and Action: What and Where? The two types of discrimination tasks used by Ungerleider and Mishkin. (a) Object discrimination (What): Pick the correct shape. Lesioning the temporal lobe (purple-shaded area) makes this task difficult. (b) Landmark discrimination (Where): Pick the food closer to the cylinder. Lesioning the parietal lobe makes this task difficult. It has been suggested that these pathways can operate quite independently from each other. For example, that you do not necessarily have to recognize the cup to reach for it and to pick it up Perception and Action: What and Where? Milner and Goodale (1995)– Studied a 34-year-old woman with damage to the temporal lobe Visual agnosia - she no longer could recognize everyday objects, familiar faces and geometrical shapes, despite being able to identify an object’s colour or visual texture. She had no difficulty guiding her hand movements to reach for something and to pick it up. Perception and Action: What and Where? FIGURE 3.32 (a) D.F.’s orientation task. D.F.’s task was to rotate the card to match FIGURE 3.33 each orientation. (a) D.F.’s “mailing” task. D.F.’s task was to “mail” the card through the slot. (b) Correct matches are indicated by vertical lines. (b) Correct orientations are indicated by vertical lines. Perception and Action: What and Where? Milner and Goodale (1995) Perception pathway: – From visual cortex to temporal lobe – Corresponds to the what pathway – In this study was damaged and hence the difficulty to complete the task Action pathway – From visual cortex to parietal lobe – Also called the how pathway. – Corresponds to the where pathway Evidence that there is one mechanism for judging orientation and another for coordinating vision and action. The research shows that perception and action are largely processed in two separate pathways in the brain. Back to the cup of coffee 1. Identify the coffee cup (perception or what pathway). 2. Once the coffee cup is perceived, we reach for the cup (action or where pathway), considering its location 3. We avoid the flowers and orange juice, we position our fingers to grasp the cup (action pathway), considering our perception of the cup’s handle (perception pathway), 4. We lift the cup with just the right amount of force (action pathway), considering our estimate of how heavy it is based on our perception of the fullness of the cup (perception pathway). A Hearing example Hearing someone call your name and then turning to see who it is activates two separate pathways in the auditory system One that enables you to hear and identify the sound (the auditory what pathway) Another that helps you locate where the sound is coming from (the auditory where pathway) Bayesian Inference Example 2 Prior probability - books are rectangular The likelihood that the book is rectangular is provided by additional evidence such as the book’s retinal image, combined with your perception of the book’s distance and the angle at which you are viewing the book. If this additional evidence is consistent with your prior probability that the book is rectangular, the likelihood is high and the perception “rectangular” is strengthened. Further testing by changing your viewing angle and distance can further strengthen the conclusion that the shape is a rectangle. You aren’t necessarily conscious of this testing process—it occurs automatically and rapidly. While the retinal image is still the starting point for perceiving the shape of the book, adding the person’s prior beliefs reduces the possible shapes that could be causing that image.