Sensation and Perception

Sensation - physical stimulation of the sensory receptors is processed by sensereceptors. Our brain interprets the info from out 5 senses which leads to perception.

Perception - Organisation and interpretation of sensory info by the brain. Info received from sense receptors is combined with the brain's interpretation of what that info means.

Sensation is the detection of a stimulus in the environment such as light or sound waves.

Perception is the brain interpreting and understanding these sensations.

Theories of perception differ.
Gregory's constructivist theory sees a difference between sensation and perception
Gibson's direct theory sees sensation and perception as the same.

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Visual illusions

Ponzo illusion - Misinterpreted depth cue.
Two separated horizontal lines of the same length, one above the other, surrounded by two lines converging, gives the appearance of depth.
People perceive the top horizontal line as longer than the one below because it appears to be more distant.

Müller-Lyer - Misinterpreted depth cue.
Two separate vertical lines of the same length, side by side, one with outgoing fins and the other with ingoing fins. Vertical line with outgoing fins perceived as longer than the other.

Rubin's vase - An ambiguous figure.
Image of two faces and a vase in the same picture. Both are correct so your brain can't decide which image is shown.

Ames Room - Misinterpreted depth cue.
Room looks normal but actually trapezoid shape. When two people stand either side on the back wall, one appears to be much bigger than the other even though both are same size.

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Visual cues, constancies and binocular depth cues

Visual cues- features of the environment that give us information about movement, distance etc.

Visual constancies - objects look the same despite seeing them from different angles and distances.

Binocular depth cues - needs both eyes to work

Retinal disparity - Each eye sees things differently as they are positioned on the face about 6cm apart. Retinal disparity is the difference between the left and right eye's view. The brain uses this information to work out depth and distances.

Convergence - The eyes become closer together when objects are close to us. Muscles in the eyes work harder when objects are close. This information is sent to the brain to give information about depth and distance.

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Monocular depth cues

Monocular depth cues - needs one eye to work

Height in plane - Objects that are higher up in the visual field appear further away.

Relative size - Smaller objects in the visual field appear further away.

Occlusion - Objects that are in front of others appear closer to us wjilstobjects behind other objects seem further away.

Linear perspective - When parallel line converge in the distance, the point at which they come together is perceived to be further away.

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Explaining visual illusions pt1

Size constancy - The brain perceives familiar objects as a constant size despite the size of the image they produce on out retina changing with distance.
Misinterpreted depth cues - Objects in the distance that appear smaller are scaled up by our brain so they look normal size. Sometimes the brain sees the distance when there isn't any which creates a visual illusion as in the following two examples:

Ponzo illusion Converging lines give the illusion of distance. The brain uses size constancy and mentally scales up the more distant line while mentally scalling down the closer line.

Müller-Lyer Outgoing fins are shaped like the inside corner of a room which is stretching away from us.
Ingoing fins are shaped like the outside of a building projecting out.
This gives the illusion of distance/nearness.
We mentally scale up the line that appears closer (outgoing fins) so it appears longer.

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Explaining visual illusions pt2

Ambiguous figures - A type of illusion where there are two possible interpretations of the same image, and the brain can't decide which one to choose.

Necker Cube The same image of a cube can be perceived as either pointing upwards to the right or downwards to the left.

Fiction - A type of visual illusion that causes the brain to see something that is not there.

Kanizsa triangle
Illusory contours to create the impression that a second triangle is overlapping the first one.

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Gibson's theory theory of perception

Gibson's theory suggests that the environment gives us all the info required for perception. Gregory's suggests that perception is to do with past experiences.

Direct perception - Sensation and perceptin are the same thing. The eyes detect everything we need to judge depth, distance and movement. We don't need past experience.
- When moving, the point we are moving towards is stationary, everything else rushes away from it. This monocular depth cue is detected by our eyes thich tells the brain that we are moving, so we know the speed and direction that we are travelling in.
Motion parallax- This is another moocular depth cue. Tells out brain the speed we are moving. Objects closer in our visual field move faster than those further away.

Gibson's view was that the ability to perceive is inborn - innate - we don't learn it. The eyes detect fine changes in light, texture, movement and depth so we can understand distance and depth.

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Evaluation for Gibson's theory

Real-world meaning: Strength. Theory has real-world meaning. Research basedon the experience of pilots in WWII. Therefore, makes it more relevant to explaining how we perceive the world on daily basis.

Struggles to explain illusions: Weakness. Gibson proposed that we will always be able to perceive accurately. However, illusions trick the brain into misperception. Therefore, there is more to perception than his theory suggests.

Support for the role of nature: Strength. Comes from Gibson and Walk's study. Very few infants crawled off a 'visual cliff'. This suggests that infants have an innate ability to perceive depth, which shows some perception to be innate.

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Gregory's constructivist theory of perception

Contrasts with Gibson's theory that sensation and perception are the same thing. Gregory's theory proposes that we use past experiences to make sense of the world around us.
Perception is a construction- the brain uses incoming sensory information plus info that we already know about the world, perception is therefore construction.
Inference - the brain uses sensory info that is available and then fills in the gaps. Past experience means we infer what should be there and draw a conclusion.
Visual cues - When making inferences, features of the environment give the brain info about depth, distance etc. Visual illusions occur because the brain has drawn the wrong conclusion from the cues given.
Past experience (role of nurture) - Gregory proposes that perception depends on experience. For example, learning to see a chair as a chair. The more we interact with the world, the more sophisticated our perception becomes.

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Evaluation for Gregory's theory

Support from research in different cultures: Strength. Has support from studies of cultural differences in perception. For example, Hudson's study showed experience affects how visual cues are interpreted. Therefore, their different experiences have affected their perception.

Visual illusions: Weakness. Gregory's use of visual illusions to support his theory. They are artificial 2D images that are deliberately designed to fool us. Therefore, his theory may not tell us much about how perception works in the real world.

How does perception get going: Weakness. Theory cannot explain how perception gets started. Research has shown that babies have some perceptual abilities at birth, such as they prefer human faces to random patterns. Therefore, not all perception is the result of experience.

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Hudson's study - Culture affecting perception

Perceptual set and culture - Perceptual set = tendency for out brain to notice some aspects of the environment than others. Culture = the social world that surrounds you

Aim: Aimed to find out whether people from different cultures/educational backgrounds perceived depth cues in 2D images differently.

Method: South Africans were shown 2D drawings - native black people (schooled & unschooled) and white Europeans (schooled & unschooled). Ppts had to say which animal the man was pointing the spear at. Depth cues suggest that the spear was actually pointed at the antelope not the elephant.

Results: Many believed that the spear was pointed at the elephant. Schooled ppts more likely to perceive depth than unschooled. White schooled ppts more likely to perceive depth than black schooled ppts.

Conclusion: People from different cultural/educational backgrounds use depth cues differently and have different perceptual sets. Supports Gregory's theory that depth cues are learnt.

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Evaluation for Hudson's study

Cross-cultural research: Weakness. Instructions may lack sense. The language barrier means translations of the method may have been unclear. Therefore, the validity of the results is affected.

Problems with the method: Weakness. Some of the ppts may have been confused by seeing drawings on paper. When more familiar materials were used they gave different answers. Therefore, representation affects results.

Poor design: Weakness. The study is from a long time ago and had some design issues. For example, the tester asked the questions out loud and may have unconsciously indicated the answer to give. Therefore, the conclusions may lack validity.

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McGinnies's study - Emotion affecting perception

Perceptual set and emotion - the tendency for our brain to notice things that are exciting, interesting or unusual. But also block things that make us anxious or we find threatening.

Aim: Wanted to see whether things that cause anxiety are less likely to be noticed than things that are emotionally neutral.

Method: 8 male & 8 female students were shown neutral and 'taboo' words. Ppts had to say each word out loud. The amount of emotional arousal was measured through their galvanic skin response (GSR).

Results: Ppts took longer to sat offensive words than neutral words. Taboo words produced bigger changes in the GSR than neutral words.

Conclusion: Shows that emotion affects perceptual set. Perceptual defence is used when the brain when dealing with words that caused offense or anxiety.

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Evaluation for McGinnies's study

Objective measurement: Strength. Used an objective measurement of emotion. A scientific method was used - GSR - to test biological anxiety responses. Produces results that are less open to bias than, for example, rating scales.

Embarrassment, not defence: Weakness. Delayed recognition may be more to do with embarrassment. Ppts may have hesitated in giving an answer as they were uncomfortable repeating rude words in the study. Suggests that awkwardness may have been an extraneous variable.

Results are contradictory: Weakness. Sometimes perceptual defence occurs and sometimes perceptual sensitisation. But we don't know why this happens. Makes it difficult to draw firm conclusions.

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Gilchrist and Nesberg's study - motivation

Perceptual set and motivation - The force that drives your behaviour can affect how you perceive things. Wanting something can increase its attractiveness.

Aim: Aimed to find out if food deprivation affects the perception of food pictures.

Method: Two groups of students - one that was deprived of food, the other a control group. Students were shown four slides of meals. Each slide was shown for 15 seconds. The picture was shown again, dimmer, and ppts had to adjust the lighting so it looked the same as before.

Results: Ppts perceived food as brighter is they were deprived of food. Control group didn't perceive food as brighter.

Conclusion: Being deprived of food increased perceptual sensitivity. Shows that hunger is a motivating factor affecting the way food is perceived.

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Evaluation of Gilchrist & Nesberg's study

Support from similar studies: Strength. Similar studies have found similar results. Sanford deprived ppts of food and showed them ambiguous figures. The longer the food deprivation the more likely they were to see food. Increases the validity of the study.

Ethical issues: Weakness. Studies in this area tend to be unethical. Because depriving ppts of food and water could cause them to feel uncomfortable. Is an issue as you should not do this in psychological research.

Not like everyday life: Weakness. Ppts were asked to judge pictures of food rather than real food. This makes it harder to apply the results to situations in the real world.

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Bruner & Minturn - Expectation affecting perceptio

Perceptual set and expectation - The belief about what is likely to happen based on past experiences can affect how much we attend to or notice things in the environment.

Aim: Aimed to find out whether an ambiguous figure was seen differently if the context of the figure was changed.

Method: An independent groups design was used where ppts were either presented with a sequence of letter of a sequence of numbers with the same ambiguous figure in the middle. The ambiguous figure could either be seen as the letter B or the number 13.

Results: Those who saw a sequence of letters were more likely to see the letter B than the number 13 and vice versa.

Conclusion: Shows that expectation of what the figure represented was affected by the context that the figure was in.

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Evaluation for Bruner & Minturn

Artificial task: Weakness. An ambiguous figure is designed to trick perception. Makes the results lack validity.

Independent groups design: Weakness. Maybe individual differences between groups. An issue as differences in perception between the groups may have been due to ppt variables rather than their expectations.

Real-life application: Strength. Can explain errors such as misidentifying an aircraft as an enemy plane because of expectations. Therefore helps to explain why people sometimes make serious mistakes on tasks in the real world.

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