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This 6 page Bundle was uploaded by Tricia Mae Fortuna on Friday October 14, 2016. The Bundle belongs to 461 at Towson University taught by John W Webster in Fall 2016. Since its upload, it has received 32 views. For similar materials see Cognitive psychology in Psychology (PSYC) at Towson University.
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Date Created: 10/14/16
Cognitive Lecture: Perception Rev. F’15 1 Perception: Object Perception & Pattern Recognition Broader Issues in Perception o General Processes (occur in a variety of cognitive systems): Bottom-up – Data driven Top-down – Concept/Experience driven o Formal Theories of Perception: Direct Perception theories vs. Constructivist Basic differences How rich/detailed in the information reaching our receptors Degree (if any) of higher mental processes on perception Gibson’s “Ecological” direct perception theory (“bottom-up” process) o Purpose of perception is to allow an organism to function in its environment o Environment contains the necessary information to do this (locomotion being critical) o Depth Perception needed for survival; environment presents us information that helps us to adapt in it; mental things is added and not basic o Three components Optical flow – moving while visual system is registering that you are moving and tells you where you are in space. Stable things on your side looks like it moves fast Invariant features – texture/density gradients & linear perspective (things get closer together the further they are) – tells you where are things and its relativity Affordances (typically monocular cues – you can use just one eye) – let us know if an action in the physical environment is “___able”. (climbable, catchable, etc) o Visual cliff (Gibson & Walk 1960) o Problems Inaccurate perceptions – why do visual illusions work? We can use very degraded environmental information Constructivist theory (e.g., Gregory 1960s) – a top-down process o Goes back to Helmholtz in 19 cent. (unconscious inference) o Perception based on prior knowledge experiences in our environment – e.g., assume light from above personal knowledge (Bayesian inference) – what I’m used to We rely on perceptual hypotheses (inferences) because so much information from environment is lost (e.g., most light entering the eye never strikes the retina) or degraded We try to make sense of the environment Because of this we can be fooled – visual illusions o Problems Perceptual processes/phenomena are generally consistent across cultures Some perceptual processes seem innate (or are apparent very early in life) Cognitive Lecture: Perception Rev. F’15 2 Both mechanisms/theories are involved – probably at different levels of perception direct perception is consistent with dorsal stream functions – parietal lobe constructivist is consistent with ventral stream functions – underneath the brain (recognitions, etc.) Gestalt Psychology (e.g., Wertheimer late 19 cent.) – Tendency toward organization (Prägnanz) o Individual sensations cannot account for all mental experiences (apparent movement). “The whole is greater than the sum of its parts.” o Mind tends to perceptually organize patterns in certain ways. o Tendencies are innate and are due to the mind trying to make sense out of what we see. o “top-down” – but “innate tendencies” o The “Laws” of perception described the basic tendencies that we have to organize visual stimuli. o Emergence: although it looks like there’s no pattern, something will emerge (Dalmatian) o Figure-Ground: isolating an object from everything (born) o Closure: filling out the missing parts o Similarity: Pick out patterns where certain elements are similar in nature o Proximity: things that are close together seems to belong together Here are some formal examples of the Gestalt Laws. Proximity Figure Ground Similarity Figure—Ground Closure Cognitive Lecture: Perception Rev. F’15 3 What visual illusions can tell us about brain processes in perception o The brain (probably V2) likes edges because edges define an object (illusory contours – the “Kanisza Triangle”): o Brightness and darkness are relative – the brain makes the computation by local contrast, but our experiences interacting with objects (i.e., light and shadow) make us look at the image globally. Hypothesis testing Ambiguity is an example of “hypothesis testing” in perception Ecologically “Invariant” Features can mislead – Anamorphic Street Art sees it in a particular angle Cognitive Lecture: Perception Rev. F’15 4 Pattern/Object/ Recognition * = best theories as of today Pattern Recognition Explanations: o Template Matching o Feature Analysis and Identification* Object Recognition Explanations o Recognition by Components * o Prototypes* Template: A master pattern used to produce exact copies. Needs exact copy to work – we’re conditioned with this (acquired). Some examples Simple – stencil sheet for letters; sewing pattern. OCR (optical character recognition) – scanners – has images of letters and recognize these shapes (letters) o Recognition via a template: Exact representation of the form (duplicate) is stored in the brain External object/form matches the form stored in the brain. o Evaluation of Template Matching Advantage – Rapid identification of stimuli as long as the stimuli are not noisy Problem –Rigid – we have extraordinary flexibility of pattern recognition. Feature Analysis o Classic bottom-up description o Process occurs in stages 1st stage – object to be identified is analyzed as a collection of simpler discrete units. 2nd stage – units are assembled into a coherent whole – judgment/identification made Second stage units may be aggregated in to larger units How a feature analysis system might perceive the letter T o Support Experimental: Visual search Biological support: Hubel & Wiesel o Evaluation of feature analysis Positive – Massive amounts of research support Problems What is a “feature?” Can a feature analysis system, by itself, handle complex stimuli? e.g., context affects recognition Cognitive Lecture: Perception Rev. F’15 5 Object Recognition: Biederman’s GEON Theory o Visual system processes objects as collections of basic geometric forms (cubes, cylinders, etc.). o These 36 “geometric primitives” (shapes) are GEONS to make up an object Analogous to phonemes (basic sound units) Morphemes are the simplest units of meaning in language GEONS possess the same information regardless of variations in perspective. Assumes recognition is viewpoint invariant (VI) Edges (vertices) and concave lines help us recognize the GEONS Canonic Perspectives – e.g., of viewpoint dependent (VD) angle or orientation matters on our perspective o View of an object that best represents the object. o Many people have similar internal representations of common objects (Palmer, et al. (1981). o Reflects a top-down process o Unaware – but angle is chosen because it gives us the most information o If someone asked you to draw a cup and saucer, it would probably look like this o Recognition of objects is faster when object is in canonical perspective o Explanations Information: Perspective that provides the most information an object’s visual characteristics. Experience (Familiarity): Perspective represents the view of an object that is the “best” single representation of the object (Prototype?). o Prototypes: Both bottom-up and top-down elements. Similar to “concepts” o “prototype” – a model against which similar things can be compared. o Abstract, but based on knowledge/experience o Pattern recognition: match object with abstract prototype stored in memory Not as rigid as a template useful in explaining face recognition (and problems with) From Palmer, 1981) o Prototype Research o Typical procedure: 1: Construct a set of prototypes and distortions (e.g. Posner, et al.’s geometric figures, letters, random shapes and faces (Solso & McCarthy) 2: Participants see the distortions and perform some task with them (e.g., sort into “correct” piles). 3: Participants presented with some old distortions, new distortions, and the prototype. 4: Test to determine if prototype was acquired. Cognitive Lecture: Perception Rev. F’15 6 o Pseudomemory: a person has a distinct memory of something they haven’t seen or experienced before (false memory) o Prototype Explanations Central-Tendency: Prototype in our minds an average of the examples of an object Attribute-Frequency: Prototype a collection of the most salient (obvious or outstanding) features – i.e., it is the best example of the object.
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