Chap 2 Perceptionapproaches Gestalt BottomUp feature analysis template

Chap 2 Perception-approaches: Gestalt, Bottom-Up (feature analysis, template matching, prototypes), Top-Down and Pandemonium Balaji Niwlikar https: //www. careershodh. com/ 1

Introduction � Latin- perceptio, percipio. � Organization, identification, and interpretation of sensory information in order to represent and understand the environment. � Perception is the set of processes by which we recognize, organize, and make sense of the sensations we receive from environmental stimuli (Goodale, 2000 a Pomerantz, 2003). � visual perception, auditory perception (the two best studied forms), olfactory perception, haptic (touch) perception, and gustatory (taste) perception. � focuses on the processes of visual perception. https: //www. careershodh. com/ 2

Some Basic Concepts of Perception � � � � James Gibson (1966, 1979) provided a useful framework for studying perception. “classic” approach to defining perception The distal (far) object - the object in the external world (e. g. , a falling tree). Informational medium. - sound waves, reflected light, chemical molecules, or tactile information coming from the environment. Proximal (near) stimulation -(i. e. , the cells in your retina absorb the light waves). Perceptual object - created in you that reflects the properties of the external world. i. e perception. an image of a falling tree is created on your retina that reflects the falling tree that is in front of you. Perceptual modality = system for a particular sense, such as touch or smell. https: //www. careershodh. com/ 3

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Criticism to classic approach � Disagree that percepts are the same things as proximal stimuli. � Ex-- size constancy. -Extend your arm away from your body, and look at the back of your hand. Now, keeping the back of your hand facing you, slowly bring it toward you a few inches, then away from you. Does your hand seem to be changing size as it moves? Probably not, although the size of the hand in the retinal image is most certainly changing. � Y - perception involve classification and recognitionpattern recognition(recognition of a particular object, event, and so on, as belonging to a class(“shrubs” ) of objects, events, and so on. https: //www. careershodh. com/ 6

GESTALT APPROACHES TO PERCEPTION � Gestalt psychology, -concerned with how people apprehended whole objects, concepts, or units. � How we interpret stimulus arrays as consisting of objects and backgrounds? � Form perception. - cognitive process of segregation of the whole display � into objects ( figure) � and the background (ground). � The Figure-Ground Effect. -------------) � Illusory contours/subjective contours- Gregory (1972), believed that this relatively complex display is subject to a simplifying interpretation the perceiver makes without even being aware of making it. https: //www. careershodh. com/ 7

Gestalt principles of perceptual organization �-five major principles. 1. � � � the principle of proximity, or nearness. We tend to perceive this as a set of rows, rather than as a set of columns. This is because the elements within rows are closer than the elements within columns. Here, we group together things that are nearer to each other. https: //www. careershodh. com/ 8

� � the principle of similarity. – we perceive this display as formed in columns (rather than rows), grouping together those elements that are similar. https: //www. careershodh. com/ 9

� � � the principle of good continuation, we group together objects whose contours form a continuous straight or curved line. Thus we typically perceive as two intersecting curved lines and not as other logically possible elements. https: //www. careershodh. com/ 10

�the principle of closure, �when we looked at subjective contours. �we perceive this display as a rectangle, mentally filling in the gap to see a closed, complete, whole figure. https: //www. careershodh. com/ 11

�the principle of common fate� difficult to illustrate in a static drawing. The idea is that elements that move together will be grouped together, as depicted in Figure 3 -5(F). https: //www. careershodh. com/ 12

� Gestalt principles are subsumed under a more general law, the law of Prägnanz (Koffka, 1935). � This law states that of all the possible ways of interpreting a display, we will tend to select the organization that yields the simplest and most stable shape or form. https: //www. careershodh. com/ 13

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Bottom-Up Approaches � Bottom-up approaches � - perception starts with the stimuli whose appearance you take in through your eye. � You look out onto the cityscape, and perception happens when the light information is transported to your brain. � Data-driven (i. e. , stimulus-driven). � Direct perception� ecological perception� by Gibson • Information in our sensory receptors, including the sensory context, is all we need to perceive anything. • Based on our analysis of the stable relationships among features of objects and settings in the real world, we directly perceive our environment (Gibson, 1950, 1954/1994; Mace, 1986). • no need the aid of complex thought processes. https: //www. careershodh. com/ 15

Bottom-Up Approaches � Template � Models or � It suggest matching Theories previously stored patterns=templats. that we have stored in our minds countless sets of templates. � Templates are highly detailed models for patterns we potentially might recognize. � We recognize a pattern by comparing it with our set of templates. � We then choose the exact template that perfectly matches what we observe (Selfridge & Neisser, 1960). � Template matching theories is chunk-based theories suggest- expertise is attained by acquiring chunks of knowledge in LT memory that can later be accessed for fast recognition. https: //www. careershodh. com/ 16

Bottom-Up Approaches � Limitations of template-matching models � First, for such a model to provide a complete � explanation, we would need to have stored an impossibly large number of � templates. � Second, we are capable of recognizing new objects—DVDs, Palm Pilots, laptop computers, cellular phones. � A third problem is that people recognize many patterns as more or less the same thing, even when the stimulus patterns differ greatly � Ex -Handwriting of Shivani. https: //www. careershodh. com/ 17

Bottom-Up Approaches � � � � Featural Analysis Ex -able to recognize not only the whole door but also certain parts of it: such analysis of a whole into its parts underlies the basic processes used in perception. Instead of processing stimuli as whole units, we might instead break them down into their components, using our recognition of those parts to infer what the whole represents. The parts searched for and recognized are called features. Suggest --Recognition of a whole object depends on recognition of its features. Certain cells responded strongly to borders between light and dark and were called “edge detectors”—“horizontal-line detectors” and “vertical-line detectors, ” as well as other distinct detectors. (Hubel and Wiesel, 968)) https: //www. careershodh. com/ 18

Featural Analysis �Irving Biederman (1987)- Recognition-bycomponents (RBC) theory, that uses a type of featural analysis like some of the Gestalt principles of perceptual organization �‘when people view objects, they segment them into simple geometric components, called geons. �Geons =a total of 36 such primitive components, like phoneme https: //www. careershodh. com/ 19

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Featural Analysis. Pandemonium � � � � � Pandemonium A state of extreme confusion and disorder or chaos Selfridge (1959) A model for the perception of letters based on featural analysis. It consists different kinds of “demons= feature detectors. Demons at the bottom (first) level of processing scan the input, and demons at higher levels scan the output from lower-level demons. In response to what they find, the demons scream. The first kind of demons are image demons, which convert the proximal stimulus into representations that higher-level demons can assess. Each representation is scanned by several feature demons, each looking for a different particular feature (such as a curved or a vertical line). If a demon finds such a feature, that demon screams. https: //www. careershodh. com/ 21

Featural Analysis. Pandemonium � Feature demons communicate the level of confidence that the feature is present by screaming more softly or loudly. � Letter demons cannot look at the stimulus itself but can only listen to the feature demons. � Ex-. The A demon, -listens especially hard to the feature demons for “slanted line” and “vertical line. ” � Letter demons scream when the output from the feature demons convinces them their letter is in the representation—again, more loudly or softly, depending on the level of confidence. � A single decision demon listens to all this screaming and decides what letter is being presented. https: //www. careershodh. com/ 22

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Featural Analysis � � � Limitation of Featural analysis models no good definitions of what can be a feature and what cannot, except in very restricted domains, (perception of letters or the perception of line drawings of familiar objects). Consider the perception of a face. • Are there general features for eyes, nose, mouth? • Are there specific features for right nostril, left eyebrow, lower lip? • Just how many features can there be? • Do different kinds of objects have different sets of features? � � � Consider a vertical line. Although this feature is no doubt important for perceiving the letter A, how does it relate- to perceiving A beach ball? A wave crashing on shore? If there are different sets of features for different objects, how does the perceiver know which ones to use to perceive an object (remember, this must be decided before the perceiver knows what the object is). If the same set of features applies to all objects, the list of possible features would appear huge. How does the perceiver perceive objects so fast, then? https: //www. careershodh. com/ 24

Prototype matching. � Prototype � perception matching. in terms of matching an input to a stored representation of information, like template models. � In this case, however, the stored representation, instead of being a whole pattern that must be matched exactly or closely (as in template-matching), is a prototype= an idealized representation of some class of objects or events— � Ex --the letter M, a cup, a VCR, a collie, and so forth. � Perceptual processes - When a sensory device registers a new stimulus, the device compares it with previously stored prototypes. https: //www. careershodh. com/ 25

� An exact match is not required; in fact, only an approximate match is expected. � Allow for discrepancies between the input and the prototype, � More flexibility than template models. � An object is “perceived” when a match is found. � Prototype models take into account not only an object’s features or parts but also the relationships among them. � Posner and Keele (1968) demonstratedthat people can form prototypes surprisingly quickly. https: //www. careershodh. com/ 26

Top-Down Approaches � Top -down theories, � � theory-driven or conceptually driven/ constructive perception is driven by high-level cognitive processes, existing knowledge, and the prior expectations that influence perception (Clark, 2003). Both accuracy and the length of time needed to recognize objects vary with the context. (Biederman, Glass, & Stacy, 1973; Palmer, 1975). � https: //www. careershodh. com/ 27

Top-Down Approaches � � � 1. 2. 3. � processes, are those directed by expectations derived from context or past learning or both. constructive perception, the perceiver builds (constructs) a cognitive understanding (perception) of a stimulus. known as intelligent perception because it states that higher-order thinking plays an important role in perception. According to constructivists, during perception we quickly form and test various hypotheses regarding percepts. The percepts are based on three things: • what we sense (the sensory data), • what we know (knowledge stored in memory), and • what we can infer (using high-level cognitive processes). a context effect known as the configural-superiority effect (Bar, 2004; Pomerantz, 1981), by which objects presented in certain configurations are easier to recognize than the objects presented in isolation, even if the objects in the configurations are more complex than those in isolation. https: //www. careershodh. com/ 28

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Top-Down Approaches �Word Superiority Effect or the word advantage, �‘’Letters are apparently easier to perceive in a familiar context (a word) than in an unfamiliar context or in no context at all. ’’ https: //www. careershodh. com/ 30