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PSY 305 Unit 2 Summary notes: PerceptionPerception refers to the way sensory information is organized, interpreted, and consciously experienced from the stimulation of the senses. Perception involves both bottom-up and top-down processing.Perception requires a connection between bottom-up and top-do...

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PSY 305 Unit 2 Summary notes: Perception

Perception refers to the way sensory information is organized, interpreted, and consciously experienced from the stimulation of the senses. Perception involves both bottom-up and top-down processing.

Perception requires a connection between bottom-up and top-down processing.

Processing visual information - only light enters our eyes but our brains are the ones that “see” things for us. A large portion of the brain is devoted to vision than all the senses put together.

Direct Perception theories -

Perception comes from the stimuli in the environment

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Bottom-up processing

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Parts (raw data) are identified, consolidate and then recognition occurs.

Constructive Perception theories -

People actively construct perceptions using information based on expectations.

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Top-down processing

Bottom-up processing refers to perceptions are built from sensory input. Visual processing based on incoming raw data. ● Eg. Light reflecting off the object enters our eyes and receives raw information such as a few round things, with specs of white all over the light brown surface, and NOT sugary donuts). Top-down processing refers to the interpretation of the sensations that are influenced by our available knowledge, our experiences, and our thoughts. ● E.g we try to make sense of the information received and realised that what you see are sugar donuts in a cardboard box. ● E.g the letter B or the number 13? Depending on the context.

● The context influences your expectations which consequently affects how you interpret the information received. Example (bottom-up & top-down processing) ● Surname OOI: The lecturer had never come across such a surname and the only way he could make sense of it was to relate it to Secret Agent 007 from the James Bond movie. As such, the lecturer made sense of an ambiguous information (bottom-up processing) using his existing knowledge (top-down processing). ● Aoorcrnig to a rseearch in Cmabrigde Uinertisity… You have no trouble reading the jumbled words because it is the context that helps make sense of ambiguous stimuli.

Perceptual error (misperceive) ● Our brain can sometimes be too efficient as it constantly strives to achieve cognitive economy. ● Consequently, our past experience and existing knowledge lead us to take short-cuts (heuristics) which sometimes results in inaccurate perceptions. As such perception errors take place.

How we interpret the visual signals and subsequently identify the ambiguous object depends on our past experience and existing knowledge. The difference in the way we perceived the picture is a result of the differences in our individual experiences and our existing knowledge. (e.g its a sugary donut, but other people might think its a bread or cookie)

Nature of perception and consider how intelligent our perceptual system is: ● the computer’s problem is that it doesn’t have the huge storehouse of information about the world that humans begin accumulating as soon as they are born. ● If a computer has never seen a toothbrush before, it identifies it as something with a similar shape. ● See also language: where the word “touch” can mean as Stay connected or physical touch. But AI won’t understand ● Human still out-perceive computers! ● Information for human perception: bottom-up & top-down processing

● Why perceptions is so difficult for computers to master? -

The stimulus on the receptors is ambiguous. - inverse projection problem: the task of determining the object responsible for a particular image on the retina. It involves starting with the retinal image and extending rays out from the eyes

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Objects can be hidden or blurred (e.g face being blurred out) - People tend to easily perceive etc book, phone as whole objects, even though they are partially hidden by other objects. Etc. the phone is half covered under a blanket. - People easily understands that the objects that were hidden partially continue to exist as a whole, and they are able to use their knowledge of the environment to determine what is likely to be present. - People have the ability to recognise objects that are not in sharp focus, such as faces.

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Objects look different from different viewpoints - People have the ability to recognise an object even when it is seen from different viewpoints (viewpoint invariance).

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Scenes contain high-level information - Requires some reasoning to figure out, as the computer doesn’t know the exact information about the object. - Etc. the computer recognises the objects are aeroplane and human walking. But it doesn’t know it is actually an old military plane that is no longer in service and the people walking towards the plane are not passengers boarding the plane.

Theories of Perception Bottom-up processing ● Gestalt Principles of Organisation Top-up processing ● Helmholtz’s Theory of Unconscious Inference (possibilities) ● Physical & Semantic Regularities (see more straight and horizontal lines)

● Bayesian Inference (combination between A and C… etc)

Gestalt Laws of Perceptual Organisation ● Gestalt approach to explaining perception: “the whole is greater than the sum of its parts.” ● The elements are grouped together to create larger objects. ● The basic assumption was that we tend to group elements in the environment to form larger parts based on the following law: -

Law of proximity

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Law of similarity - Similar things appear to be grouped together

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Law of closure

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Law of continuation/continuity - points that are connected that 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 also perceived as continuing behind the overlapping object.

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Law of good figure/simplicity/pragnanz - Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible. - e.g the Olympic symbol - is perceived as 5 circles, and not 9 shapes.

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Law of common fate

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Law of familiarity/meaningfulness

Helmholtz’s Theory of Unconscious Inference (object and face recognition) ● The image of stimulation is ambiguous. ● Ambiguity means that a particular pattern of stimulation on the retina can be caused by a large number of objects in the environment.

● E.g. for most people, the pattern on the retina results in the perception of a blue rectangle in front of a red rectangle (overlapping rectangles), and NOT caused by a six-sided red shape positioned behind the blue rectangle. WHY? ● Because Likelihood principle which states that we perceive the object that is most likely to have caused the pattern of stimuli we have received. ● Unconscious inference in which our perceptions are the result of unconscious assumptions or inferences that we make about the environment. E.g we infer that the rectangle covering another rectangle because of the experiences we have had with similar situations in the past. ● Helmholtz’s description of the process of perception resembles the process involved in solving a problem. The problem is solved by a process in which the perceptual systems uses the observer’s knowledge of the environment in order to infer what the object might be. ● The pattern on the retina happens rapidly and unconsciously. ● These unconscious assumptions, which are based on the likelihood principle, result in perceptions that seem “instantaneous”

Knowledge about the environment (Taking regularities of the environment into account): ● Frequently occurring characteristics such as blue is associated with open sky, landscapes are often green and smooth, are called regularities in the environment ● People make use of regularities in the environment to help them perceive. ● Physical regularities -

Regularly occurring physical properties of the environment

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E.g. more vertical and horizontal orientations in the environment than angled orientations.

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human-like environments ( buildings contain lots of horizontal and verticals), natural environments ( trees and plants are more likely to be verticals or horizontals than slanted)

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People can perceive horizontal and verticals more easily than other orientations (Appelle, 1972; Campbell et al., 1966; Orban et al., 1984) - oblique effect.

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Light-from-above assumption: we usually assume light is coming from above. E.g. the indentations caused by the people walking in the sand. If you turned the picture upside down, from indentations into rounded bumps. This shows that we assume light always shines from the top, illuminates an indentation causing a shadow, and the same light illuminating a bump caused a shadow.

● Semantic regularities -

Scene schema: our visualisations contain information based on our knowledge of different kinds of scenes.

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The knowledge of what a scene typically contains is called a scene schemas and the expectations created by scene schemas contribute to our ability to perceive objects and scenes. E.g when visualising a lion, people usually see not just the lion but also the lion within a setting such as in the zoo. E.g when perceiving a loaf of bread, it fits the kitchen scene faster than the mailbox which doesn’t fit the scene.

Bayesian Inference ● Our estimate of the probability of an outcome is determined by the prior probability (our initial belief/prior) and the extent to which the available evidence is consistent with the outcome (likelihood of the outcome)

● We come to most perceptual situations with prior probabilities based on our past experience. ● E.g Prior in our head, books are rectangular. Thus when you look at a book on your desk, your initial belief is that it is likely that the book is 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 that the book is rectangular, the likelihood is high and the perception “rectangular” is strengthened. ● It occurs automatically and rapidly. ● Bayesian inference restate Helmholtz’s idea - that we perceive what is most likely to have created the stimulation we have perceived - in terms of probabilities

Perceptual constancies ● Size Constancy (things are nearer, look larger but they could be at the same size)

(the retinal image of the two boxes are the same, but they don’t look the same size because of the additional cues around the environment, like linear perspective (converging lines), distance and height cues, which creates depth perception. So you might think that the box on the right is bigger) **the knowledge about this, then things further away look small but in actual size, we know that they're supposed to be depth perception exactly.

● Shape Constancy

(When the door is closed, it looks rectangular in shape, but when it starts to open, the shape appears to change based on the retinal image. However, despite the changing retinal image, we know that the door itself is not changing shape. And that is what shape constancy is about.)

● Colour Constancy

(the two grey circles are the exact same shade of grey. But it seems like one circle is darker than the other. This is because our perception of the grey circle is affected by surrounding cues such as its background) ● Brightness Constancy

( Similarly to brightness constancy, we know that objects do not change colour like they don't change in shape or size. The light waves reflecting off your red car under dim lighting may not be red, but you know that your red car hasn't changed colour all of a sudden. It just appears different under different lighting.)

When a person is far away from you, your brain upscale the image of that person. The brain is adjusting which may not be 100% accurate, e.g the person is shorter than you thought, this is because your brain inflated his height for you.

Scenes schemas - the knowledge of how a scene should look like, etc. how a cup should look like (Small and handy), or how a kitchen should look like. **To judge this environment, believe that it should be like that because normally it should look like that, so this challenges the way we usually perceived role that's why all of us are so surprised so tickled by it so the illusion.

Discuss the effects living in an upright world has on perceptual organization Perception Organisation: Figure-ground segregation...