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LECTURE COGNITION- THREE: PERCEPTION 1/14/2010 Perception: Processing sensory information such that it produces a meaningful understanding of the information. Visual Agnosia: A deficiency in the ability to recognize visual information despite being able to see. Its not that visual agnosics have a sensory impairmenttheir eyes are fine. They just cannot cognitively interpret the information they see. Visual agnosia is also specific to the visual domain. When presented with everyday objects such as brush, patients can identify them by means of using other senses such as touch. Associative Agnosia: a form of visual agnosia marked by a difficulty naming objects. These patients have trouble identifying objects that they see even though they have the visual ability to reproduce the objects by drawing them. When individuals with time spaces hear or see the names of various units of time such as days, weeks, and months, they experience seeing them in spatial patterns external to themselves. Time spaces: the perceptual experience of times units such as days of the week or months of the year as occupying spatial locations outside the body. Perception as a Function of the Environment Gibsons theory of ecological optics (perception involves directly absorbing the visual information present in the environment) focused on the idea that in real-world situations, the sensory organs receive a complex array of information that can be directly apprehended and used to guide action. Gibson articulated, Perception is the function of stimulation and stimulation is a function of the environment; hence perception is a function of the environment. He argued that perception is accomplished mostly by the sensory organs themselves. Gibson described this panorama of visual information available as we look out at the world from any given position as the ambient optical array (AOA). Gibson noted that from every different viewing point, a unique pattern of light enters the eyes because it is reflected from and emitted by a unique combination of surfaces. Ambient optical array (AOA): All the visual information that is present at a particular point of view. Texture Gradients: Gradual changes in the patter of a surface that is normally assumed to be uniform, which provides information about surface characteristics such as whether the surface is receding or curved. Gibson also noted that when two different textures intersect, they create a discontinuity in the pattern, which he called a topological breakage. A critical aspect of Gibsons paradigm was the he included observer and environment motion as a fundamental component of perception. He believed that as the mover moves, the entire optical array undergoes a change. This change in the way all surfaces project light on the retina is referred to as a transformation of the optic array. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Transformation: In the theory proposed by Gibson (1966), the change of optical information hitting the eye when the observer moves through the environment. The focus on movement led to the concept of the optic flow field-- which is the movement of objects or of the observer through the environment produces changes in what is seen. Pattern Recognition Theories of pattern recognition differed from Gibsons view in at least two ways: 1. They do not consider the complex array of light information reflecting from all surfaces and objects as Gibsons theory does; the focus is primarily on specific objects or patterns 2. They focus on how it is that we build internal representation of objects during the process of recognition, rather than focusing on how information is directly perceived. Pattern recognition: The ability to recognize an event as an instance of the particular category of event. You are able to recognize words in this sentence as words and not just meaningless squiggles. Recognizing a configuration involves contact between the emerging percept and memory. Percept: meaningful interpretation of sensory information. Memory trace: the trace that an experience leaves in the brain. In order to recognize the letter a, shout it appear on another occasion, your emerging perception of a mush somehow make contact with the memory trace of a. This process is called the Hoffding Function. Hoffding Function: When an experience makes contact with a memory trace, resulting in recognition. A) Template Matching: According to the template matching theory, we would compare each a with the prototypical a that we have in memory, and, if the match is good enough, then we would recognize the letter. Template: A model against which a stimulus is compared to determine whether it belongs to a particular category. Prototype: A model that possesses all the typical characteristics of its class Template matching theory: comparing a stimulus with templates; when they math, the stimulus is recognized as belonging to that category. Problems with the theory: Uhr observed, the problem is to specify how a template can match not only patterns that are identical to it, but also patterns that are similar enough to it. For this reason template models have often been criticized. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Hintzman (1986) proposed a multiple-trace memory model: Traces of each individual experience are recorded in memory. No matter how often a particular kind of even is experienced, a memory trace of the event is recorded each time. This approach distinguishes between primary and secondary memory. Primary memory refers to what people are experiencing at any point in time, whereas secondary memory refers to all of the memory traces created out of all the experiences that person had. Secondary memory can be activated by means of a probe from primary memory. When a probe goes out from primary to secondary memory, then memory traces are activated to the extent that they are similar to the probe. The activated memory traces are said to return an echo to primary memory. B) Feature Detection Feature detection theory: detecting patterns of the basis of their individual features. Pandemonium: A model of pattern recognition consisting of three levels: data, cognitive demons, and decision demons. At the bottom level are the data, or image, in which a pattern of features is represented. These features might be things like size, colour, shape, and so on. The next level consists of so-called cognitive demons. There are like little elves who examine the pattern of attributes in the image. Each demon is ready to detect a particular pattern. If a cognitive demon thinks that it detects the pattern it is ready for, then it shouts. Sitting on top of this hullabaloo is the decision demon, which selects the cognitive demon that is shouting loudest. This choice constitutes the pattern that is recognized. Cognitive demon: A feature detector that decides whether the stimulus matches its pattern Decision demon: a feature detector that determines which patter is being recognized. Contrast energy: The degree of contrast between letters in a word and the background they appear on leading to the relative ease with which a stimulus can be discriminated from the background against which it is displayed. Idea developed from Pelli, Farell, and Moore (2003). Letters with low contrast energy are weak signals that the visual system may squelch. Squelching: The tendency of the nervous system to inhibit the processing of unclear features C) Recognition by Components To explain how feature analysis could apply objects, Irving Biederman (1987) developed a theory called recognition by components (RBC). Recognition by components (RBC): A model of perception based on subdividing objects into a basic set of geometric shapes. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 According to Biederman, when an image of an object is painted on the retina, RBC assumes that a representation of the image is segmented, or parsed, into separate regions at points of deep concavity, particularly cusps where there are discontinuities in curvature. According to the RBC theory, every object can be reduced to a combination of a subset of 36 geons. Geons: the basic geometric shapes that comprise objects. Once objects are reduced to their constituent geons, the theory states that the resulting geons are compared with existing geons configurations stored in memory. When a reasonable match is made between input and memory, you recognize the object. A more detailed penguin was recognized more accurately than a less detailed one. What complexity and detail provide is more geons, and more geons lead to a better recognition. Recoverability: The degree to which geons can be made out in a degraded image of an object. Context and Knowledge The process of building a whole image from a set of basic features is often referred to as bottom-up or data-driven processing (results from the combination of individual pieces of sensory information). As observers, we all b ring prior knowledge, goals, and expectations to the act of perceiving, and, these observer factors can also influence perception. The influence of goals, expectations, and prior knowledge on perception is often referred to as top-down, or user drive processing. Context effects: the influence that the situation plays on the perception of a stimulus. Apparent-distance theory: An explanation for the moon illusion; it posits that the moon on the horizon appears larger because cues distance lead the observer to perceive it as being nearer than the zenith moon. A) Letters in Context A profound example of the effect of context on word and letter perception is the humbled word effect. Jumbled word effect: The ability to read words in sentences despite having mixed-up letters in the middle of some of the words. Word superiority effect: it is easier to identify a letter if it appears in a word, than if it appears alone. Context effects on letter perception have been extensively modelled using connectionist approaches to pattern recognition. Connectionists approaches made us of parallel distributed processing (PDP). Parallel distributed processing (PDP): A model of perception that proposes that different features are processed at the same time by different units connected together in a network. B) Colours in Context Purves and Lotto (2003) generated a theory of the context effects on colour perception that they call an empirical theory of colour vision. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Empirical theory of colour vision: The proposal that colour perception involves not only the processing of wavelengths of light but also the influence of prior experiences about how different lighting conditions affect the appearance of the colours of objects. C) Cross-modal Context A compelling example of the extent to which auditory information can be affected by visual processing comes from the so called McGurk Effect. McGurk Effect: the auditory experience of the syllable da when seeing a mouth silently saying ga while at the same time hearing a voice say ba. The Grand Illusion Instead of having a true and accurate visual representation of the world, suppose that we are actually processing only fragmentary parts of our visual field and representing only one or maybe two objects in detail at a time. A) Change Detection Change Blindness: the common failure of people to notice changes to an object or scene. On of the main points raised by change blindness is that our internal representation of the world is not as rich as we think. The illusion of a rich and detailed representation of the external world is said to be the grand illusion of perception Grand illusion of perception: The experience of a clear and detailed picture of the world in ones visual field. It seems that the grand illusion is the result of a considerable amount of top-down interpretation of very fragmentary visual information. Important changes that might occur while driving, for example, create motion signals that draw our attention so that we become aware of them. B) Feature Integration Theory Introduced by Anne Treisman, the feature integration theory states(FIT): before we can attend to objects in the world we must extract the features that make up these objects The theory is based on the assumption that when we initially view objects in our field of vision we first extract and represent their features (colour, orientation) across the entire visual field through a process called pre-attentive processing. FIT assumes that for an object to be perceived as a whole object, there has to be feature binding at specific locations. Feature binding is a accomplished by a stage of processing known as attentive processing. Feature binding: the combination of visual features by attention to form whole objects COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Attentive processing: combining features into a whole object through attention. If a feature pops out of a display, then that feature, a pop-out, is a good candidate for being a basic property out of which we construct perceived objects. C) The Constraints of the Visual System Blind spot: A region in the eye where the optic nerve leaves the retina; it does not contain any photoreceptors. Perceptual completion (filling-in): The experience that something is present in part of a visual scene when actually it is absent from that spot, but is present in the surrounding region. Perceiving Whole Objects: Gestalt psychology Gestalt psychology (koffka, Kohler): A branch of psychology that focuses on dealing with wholes rather than parts. One of the main demonstrations forwarded by the Gestalters was that a resulting percept is not simply a straightforward function of the elements in a visual field. Ex. Through bi-stable figures Bi-stable figures: Images from which two separate percept can be formed. Gaetano Kanizsa defined the word gestalt as follows: Gestalt ought to be translated as organized structure, as distinguished from aggregate, heap, or simply summation. When it is appropriately translated, the accent is on the concept of organization and of a whole that is orderly, rule-governed, non-random. Believed that perception is holistic (focusing on the whole configuration of an object) in nature rather than atomistic (focusing on the features or components of objects). Also, that there are fundamental organizational principles by which we group visual elements in order to perceive a whole. Organizational principles: the rules that explain the ways in which people are able to perceive whole objects or events from individual parts. A) Organizational Principles Katz (1951) reviews six basic principles of organization (grouping) that have emerged from the Gestalt movement: 1. Principle of experience: A principle stating that elements are grouped based on the prior experience and knowledge of the observer. Figure and ground segmentation: perceptual organization of a scene such that one element becomes the foreground (figure) and the other element becomes the background. Denotivity: the degree to which an object is meaningful and familiar to an individual. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 2. 3. 4. 5. 6. Principle of proximity: things that are near one another are grouped together Principle of closure: things that form closed shapes are grouped together Principle of good continuation: Things that form continuous lines are grouped together Principle of similarity: things that are similar are grouped together Principle of common fate: things that are moving in the same direction are grouped together. B) Limitations of Gestalt Perception In the real world, different factors are constantly interacting with each other and the Gestalt movement did not specify the way we will or will not group objects under these conditions. Kanizsa (1979) stated the Gestaltists error: The assumption that whole objects should always dominate over the elements of an image. Ceteris Paribus: when all is equal Dissociations of Perception Apperceptive Agnosia: A form of visual agnosia marked by a difficulty matching or categorizing objects Optic Ataxia: A neural deficit in which the patient can identify objects but is unable to accurately interact with them manually. Prosopagnosia: An impairment in the ability to recognize faces despite intact recognition of other objects Skin conductance response Capgras Syndrome: A condition marked by the belief that significant others have been replaced by imposters, doubles, robots, or aliens. Sensation stimulus detection (very mechanistic). Ex. Touch, hearing. Perception our own subjective interpretation of those sensations (very cold, loud) Our Five Senses: 1. visual (light) 2. Auditory (sound) 3. Touch (somatosensory) 4. Taste (gustatory) 5. Smell (olfactory) Vision is the strongest of our senses. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Old myths when it comes to vision: (1) seeing as a faithful record (2) vision is passive (3) The eye sees Visual information gets completely decomposed, then recomposed again by the brain. Two limiting factors with the human visual system: we only see very well in our focal vision, and where our attention is attracted depends where we look and what we see We have large blood vessels running through our eyes, but we dont see that they are in fact obstructing our vision. Our eyes are not stationary. This creates a smear, and despite this we still see a continuous picture. The images we get are actually quite distorted. - We can actually see without our eyes! When we dream we see vivid pictures, in the absence of visual input. The perception that were getting is all in the brain. Visual system assumes that the world is light from above, and objects are attached to surfaces (because thats what the usual case is). The moon illusion on a horizon (look in the book). Contextual effects top down theory Gestalt bi-stable figures This is what shows that our percepts are whole, they just emerge. Key principles: Emergence percepts as a whole Reification percept contains more information than sensation Multi-stability tendency for different percepts to alternate Invariance simple objects are recognized independently of orientation Grouping principles: Closure perceptually close objects Proximity things that are close together are grouped together Good continuation tend to group elements of smooth lines Similarity similar items are grouped together Common Fate Objects moving in the same direction will be grouped together Symmetry objects seen symmetrical around the center Principle of Experience: the fact that you tend to see things consistent with how youve seen it before. COGNITION- LECTURE THREE: PERCEPTION 1/14/2010 Visual Dissociations What is vision for? Ventral Pathway the what area of the brain leads to visual agnosia Dorsal Pathway the how and where area of the brain optic ataxia ... View Full Document

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