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Chapter 3

PSYC 221 Chapter 3: PSYC221 Chapter 3 Textbook Notes

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Queen's University
PSYC 221
Monica Castelhano

PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY WEEK 2 Chapter 3: Perception The Nature of Perception - We define perception as experiences resulting from stimulation of the senses - Perceptions can change based on added information - Perception can involve a process similar to reasoning or solving a problem o Ex: remembering that the object you see is actually an umbrella, not wood, because you remember seeing it yesterday - Arriving at a perception can involve a process o Can be described as being a “reasoning” process o Happens so fast that it appears to be automatic - Perception occurs in conjunction with action o Ex. Running and perceiving at the same time o We are usually moving, and even when we are sitting down watching TV, for example, our eyes are constantly moving as we shift our attention from one thing to another - Perception involves dynamic processes that accompany and support our actions - Without perception, it is unlikely that these feats – of acquiring knowledge, storing it, and retrieving it later – would happen Perception Starts at the Receptors: Bottom-Up Processing - First step of perception is stimulation of receptors by stimuli from the environment which is called bottom-up processing - All of our sensations, except for something like “seeing stars” begin with bottom up processing Bottom-Up Processing: Physiological - The sequence of events that happen after light reflected from a tree stimulates the visual receptors in the eye o Triggers a series of events where electrical signals are transmitted from the receptors toward the brain - The initial effect of these signals in the cortex has been determined by recording electrical signals from individual neurons - An image can be created by a number of simple features like oriented bars, and each feature can activate detectors in cortex for that specific orientation Bottom-Up Processing: Behavioural - Idea that neurons fire to individual features suggests that our perception of a tree is created by combining information provided by the firing of many feature detectors - Proposed by Irving Bierderman called recognition by components (RBC) o Perceive objects through elementary features, called geons o Proposed that an airplane has 9 geons - 1 - PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY - Can perceive objects even if portions of geons are obscured which is an example of principle of componential recovery o If you can recover an object’s geons, you can identify the object - In 3.5 (b), corners and intersections of flashlight are covered, so the geons cannot be identified o If we can’t see the individual geons, the object cannot be recognized - The basic unit of RBC – the geon – is simple o Because perceiving simple geometric objects can be related to patterns of stimulation on the retina Beyond Bottom-Up Processing - Perception depends on information in addition to that falling on the receptors, including knowledge that a person brings to the situation Perception Depends on Additional Information - Additional processing is involved when the geons are combined to create objects - Same geons can be combined to make different objects (Ex. Pail and cup above) - Able to recognize based on arrangement of geons, and give these objects names, such as pail or cup, because of knowledge we being to the situation o This idea of bringing prior knowledge is called top-down processing o Also involved in our ability to recognize objects based on a few geons only or when large portions of the object are hidden - 2 - PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY - “Multiple personalities of a blob” suggests that a blob can be perceived as different things depending on orientation and the context in which it is seen o Has the same geons in every photo o Perceive it as different objects because of our knowledge of the objects that are likely to be found in the different types of scenes - Also must consider physiology: o As signals travel from the brain, other signals in addition to those generated by the object’s features become apparent o Some signals, for example, provide info about the scene (Ex. Grass around tree) o Simultaneously, have signals associated with person’s knowledge and expectations travel from higher centers  influence incoming signals = feedback signals o CONCLUSION: Perception = signals representing object + signals representing other aspects of environment + feedback signals - This additional information is carried in additional physiological signals Perceiving Size: Taking Distance Into Account - Both images cover the same distance in your retina BUT you perceive them as being different sizes o Means that something in addition to size of animal’s image on your retina determines your perception of its size - Research has shown that two objects at different distances are perceived as their true size o Perceptual system takes the distance into account o Makes sense because in our everyday experience, a distant object can result in same sized image on retina as a smaller one (ex. A skyscraper and a vase) o System takes into account depth - May also take into account object size relative to other things in the environment - Can be demonstrated if you hold up 2 quarters, with one far away and one about half distance closer o When viewing with one eye, edges look like they are touching and the further one is smaller o Farther coin creates smaller image on retina, but when eyes open, more similar o Opening both eyes increases your perception of depth; perceptual system takes in relative distance and you can perceive sizes more accurately - 3 - PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY - Size constancy happens in everyday life where we tend to perceive objects as remaining the same size even as they move to different distances o ex. Someone who is 6 feet tall does not appear to shrink as they move across room Perceiving Odour: Taking Sniffing into Account - Would you rate the flower’s odour intensity differently following the first and second sniff? (where the first is a weak sniff, the second being strong) o Experiment found that people gave almost identical ratings for both sniffs o HENCE, this means that even though you may have more odour molecules to stimulate receptors, it does not influence odour intensity ratings - Participants were taking sniff strength into account o Similar to visual perception system that takes distance into account - Perception starts at receptors, but depends on additional sources of information as well Using Knowledge: Top-Down Processing - Top-down processing depends on a person’s prior knowledge or expectations o Recall the geons and the blob with multiple personalities - Sound signal for speech is generally continuous o Almost impossible to tell from sound record (of a sentence, for example) where each word begins and the last ends - Due to previous knowledge of a language, able to tell when one word ends and the next begins, called speech segmentation o Spanish speaker and English speaker receive identical sound stimuli but experience different perceptions ▪ HENCE, experience with language influences perception of it Helmholtz’s Theory of Unconscious Inference - Some of our perceptions are the result of unconscious assumptions that we make about the environment - Proposed to account for our ability to create perceptions from stimulus information that can be seen in more than one way - 4 - PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY - Includes the likelihood principle stating that we perceive the object that is most likely to have cause the pattern of stimuli we have received - We may also make these decisions based on experiences we have had with similar situations in the past - Perception ~ solving a problem o Determine which object has caused a particular pattern of stimulation o Solved by applying pattern of knowledge of the environment to infer what the object might be ▪ Process can be unconscious = unconscious inference - An example could be: as you get closer to an object you pass on your run, you are more likely to connect it with having seen it the day before o Not exactly this, but similar concept The Gestalt Laws of Organization - Concerned with perceptual organization – the way elements are grouped together to create larger objects - Proposed a number of laws of perceptual organization that indicate how elements in the environment are organized, or grouped together - Things that usually occur in the environment o When one object overlaps another in the environment, the overlapped (underneath) object usually continues unbroken beneath the object on top ▪ Still perceived as continuous - Law of Good Continuation: Points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tent to be seen in such a way as to follow the smoothest path o It predicts that what we perceive is based on what usually happens in the environment o Will accurately reflect what is happening in the environment if it follows these rules - 5 - PSYCHOLOGY 221: COGNITIVE PSYCHOLOGY - Similar to Helmholtz’s likelihood principle in the sense that perception corresponds to object most likely to have happened in the environment - The Law of Pragnaz or Law of Figure or Law of Simplicity o Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible o For example, we see the Olympic rings as five circles, not a combination of more complicated figures - Law of Similarity o Similar things appear to be grouped together o Ex. 4 rows of alternating black and white dots will appear to us as vertical rows, but all black circles could be rows, columns or diagonal - Meaningfulness of Familiarity o Things that form patterns that are familiar or meaningful are likely to be grouped together o Think of the photo with faces hidden in the forest (made of rocks etc) o Once you see the faces, it becomes hard NOT to see them in that way o Unlikely that the elements in an actual scene would be arranged in such a way The Gestalt “Laws” are “Heuristics” - Fall short of being laws because they don’t always accurately predict what’s in the environment - For example, if you are in the forest, and you see two shapes, one to the left and one to the right of a tree, as a single object due to: good continuation, extending smoothly from one side of the tree to another and the resemblance to an animal you hav
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