Key terminology Perception:
perception - the way the brain makes sense of the visual image detected by the brain.
retina - the light-sensitive layer at the back of the eye. It is made up of nerve cells called rods and cones.
rods - light-sensitive cells in the retina that respond even in dim light.
cones - light-sensitive cells in the retina that can detect colour.
optic nerve - bundle of nerves that leads out from the retina at the back of the eye. It carries information from the rods and cones to the brain.
blind spot – the area of the retina where the optic nerve leaves. It has no rods or cones so cannot detect light.
optic chiasma – the cross-shape where some of the information from the left and right eye crosses over to pass into the opposite side of the brain.
visual cortex – the area at the back of the brain that interprets visual information.
vision and perception are different – vision is the biological process of seeing and perception is the psychological process of making sense of the image.
- the light reflected from an object enters the eye and makes an image on the retina (at the back of the eye). It is here that nerve cells called rods (sensitive to bright light) and cones (detect colours) help us to perceive objects.
- the optic nerve carries the nerve impulses from the rods and cones to the brain.
- the blind spot is found in each eye. It is the area in the retina where there is no space for rods and cones therefore the area is ‘blind’ as there are no light-sensitive cells. We often don’t notice our blind spot because our two blind spots don’t overlap so if one eye can’t see something, the other one can.
- the optic chiasma is needed because information from each eye goes to both sides of the brain; some from the left eye goes to the left side of the brain and some to the right.
- the visual cortex allows us to understand shapes and distances and fills in the gap left by the blind spot in each eye.
Key terminology Depth cues:
depth cures – the visual ‘clues’ that we use to understand depth or distance.
monocular depth cues – information about distance that comes from one eye, such as superimposition, relative size, texture gradient, linear perspective and height in the plane.
binocular depth cues – information about distance that needs two eyes, such as stereopsis. size constancy – we perceive an object as the same size even when its distance from us changes. relative size – smaller objects are perceived as further away than larger ones.
texture gradient - an area with a detailed pattern perceived to be nearer than one with less detail.
height in the plane – objects closer to the horizon are perceived to be more distant than ones below or above the horizon.
superimposition-a partly hidden object must be further away than the object covering it.
linear perspective – parallel lines appear to converge (meet) in the distance.
stereopsis – a binocular depth cue. The greater the difference between the view seen by the left eye and the right eye, the closer the viewer is looking
we can judge depth in the real world (in 3D) and we can understand depth in pictures (2D) by the use of depth cues which are pieces of visual information that trigger or ‘cue’ our understanding of distance. monocular depth cues use one eye while binocular depth cues require the use of both eyes
when we look at an object that is close our brain scales it down so that it looks normal sized and when an object is further away we scale it up so it looks normal rather than tiny. This reminds us that the size of the object remains constant but helps us to make sense of our world. We perceive bigger objects as being closer than smaller objects (which we perceive as further away) by using the depth cue of relative size. We use the depth cue of texture gradient when looking at cobblestones or a sandy beach we see that close up the surface is very detailed while further away the texture is less clear. when we look at pictures that include the horizon, objects lower in the scene appear closer than those objects higher up which appear further away. This is the depth cue of height in the plane. superimposition reminds us that objects in front of (or partly covering) other objects are closer to us.
Gestalt laws – perceptual rules that organise stimuli.
figure-ground – a small, complex, symmetrical object (the figure) is seen as separate from a background (the ground).
similarity – figures sharing shape, size or colour are grouped together with other things that look the same.
proximity – objects which are close together are perceived to be related.
continuity – straight lines, curves and shapes are perceived to carry on being the same.
closure – lines or shapes are perceived as complete figures even if parts are missing.
Gestalt Revision Notes.
“the whole is worth more than the sum of its parts”. We organise these parts of what we can see (the stimulus information) to give us a more complex perception.
we look for patterns to help us make sense of our world.
we use the Gestalt law of figure-ground to see a more complex, symmetrical and smaller object from the ground.
we tend to group things that are similar in size colour or shape – this is the Gestalt law of similarity.
objects that are close together are seen as a group because of the Gestalt law of proximity.
Gestalt law of continuity says that we link things that follow a predictable pattern and see them as continuous even if they are not.
we tend to perceive objects as a whole – our brains ‘fill in the gaps’ – this is the Gestalt law of closure
Key terminology Illusions:
visual illusion – a conflict between reality and what we perceive.
fiction – an illusion caused when a figure is perceived even though it is not present in the stimulus.
illusory contour – a boundary (edge) that is perceived in a figure but is not present in the stimulus.
motion after-effect – an illusion caused by paying more attention to movement in one direction and perceiving movement in the opposite direction immediately afterwards.
colour after-effects – an illusion caused by focusing on a coloured stimulus and perceiving opposite colours immediately afterward.
ambiguous figure- a stimulus with two possible interpretations, in which it is possible to perceive only one of the alternatives at a time.
distortion illusion – where our perception is deceived by some aspect of the stimulus. This can affect the shape or size of an object.
Revision notes: illusions.
visual illusions occur when our perception conflicts or disagrees with reality; we are not seeing the world as it really is. We see an illusion when we misinterpret the stimulus, so the physical reality and our perception disagree.
- for ambiguous figures swapping between the two interpretations is quite difficult.
-some common geometrical illusions only work when seen on paper. If you see the object in real life and walk around it, the illusion goes away.
Gestalt theory of illusions:
For fictions such as the Kanizsa triangle when we see a figure as incomplete our perception makes a 'whole shaoe'. This is the figure of the figure-ground relationship.
When explaning distortions-the Muller-Lyer illusion- in perceiving the figure as a whole and tend to 'add' fins or circles to the central lines. When pointing out the fins drag out the line and make it look longer.
Gestalt theory explains ambigous figures by saying that we normally identify the figure or ground but in ambigous figures it could be either figure or ground because we cannot tell whether the black or the white area is the figure.
Gestalt theory provides a good explanation for ambiguous figures however it cannot explain any illusions other than the Muller-Lyer illusion.
Gestalt theory explains fictions well but in the case of the Kanizsa triangle Gestalt explanation says we would use closure to organise this figure which means we should see a six pointed star, but we don’t, we see two triangles
Gregory’s perspective theory of illusions:
remember size constancy and monocuular depth cues? we maintain the relative size of the objects regardless of their distance from us.
In the Hering illusion the radiating lines look like a linear perceptive cue so we constancy scaling as if the scene really had depth. The person who appers furthest away would be scaled up so they look bigger and the persn who appers closer would be scaled down, and look smaller.
The Ponzo illusion (the top bar looks bigger than the bottom bar)- if the railway tracks were used as cues to linear perspective, the top bar would seem futher away. As it is perceived to be more distant, it is saled up so it seems far bigger than the bottom bar.
The Muller-Lyer illusion can be explained using the ideas of linear perspective and constancy scaling.
Evaulating Gregory's theory.
Evaluating Gregory’s theory - it is a good explanation of distortions. If angled lines are used as depth cues, this explains many illusions.
However, Gregory’s theory cannot explain some versions of the Muller-Lyer illusion.
Gregory’s theory can explain some ambiguous figures when the two alternative figures are perceived using depth cues. e.g. On Leeper’s Lady the nose of the young woman looks further away than the wart on the old woman’s nose.
Depth cues can also explain some fictions as the background lines appear closer to the horizon and so further away.
Key terminology Schemas and perception:
schema -a framework of knowledge about an object, event or group of people that can affect our perception and help us to organise information and recall what we have seen.
perceptual set – the tendency to notice some things more than others. This is caused by experience, context or expectations.
independent variable – (IV) – the factor which is changed by the researcher in an experiment to make two or more conditions.
Dependent variable – (DV) – the factor which is measured in an experiment.
Revision notes:schemas and perception.
what we expect to see influences what we think we see.
Brewer and Treyens (1981) took participants into a room they were told was an office and asked them to wait. They were then moved to another room and asked what they could remember about the 1st room. They recalled more objects that fitted in with the context of an office. Nine of the 30 participants said they recalled books although there weren’t any. This study suggests that context can produce expectations and leads to the idea of schemas.
Palmer (1975) wanted to find out whether context would affect perception. He used a laboratory experiment and showed participants visual scenes such as one of a kitchen. They were then shown an object (a mail box, a drum, a loaf of bread) which they were asked to identify. There were 4 conditions in the experiment (the IVs – appropriate, inappropriate-similar, inappropriate-different and no context). It was a repeated measures design as all participants participated in all aspects of the experiment.
The number of correctly identified items was the dependent variable (DV). The participants correctly identified the most objects after seeing an appropriate context and the least after seeing an inappropriate context therefore Palmer concluded that expectations affect perception.
People have a perceptual set based on context which affects how accurately they recognise objects
Evaulating studies:Perception:Strengths and weakne
People have a perceptual set based on context which affects how accurately they recognise objects.
Strengths: controlled how long participants saw the object for.
clear instructions so they knew exactly what to do
data from two participants was not used as they had forgotten their glasses (poor vision could have affected the results)
Weaknesses - because the participants were told what they were doing it might have made them try harder in some conditions.
They might have been trying to please the experimenter.
As data from some participants couldn’t be used, this means there were fewer results.
Key terminology Bartlett (1932) Schemas/rememberin
serial reproduction – a task where a piece of information is passed from one participant to the next in a chain or ‘series’. Differences between each version are measured. (‘Chinese Whispers’)
repeated reproduction – a task where the participant is given a story or picture to remember. They then recall it several times after time delays. Differences between each version are measured.
Revision notes: Bartlett (1932)
Bartlett (1932) wanted to investigate how information changes with each reproduction and to find out why the information changes.
He deliberately chose ‘The War of the Ghosts’, a North American Indian folk tale from another culture and unknown to the participants.
The first participant read the story twice themselves (serial reproduction) then after 15-30 mins told the story to a second participant. Each participant repeated their story to the next person in a chain of participants.
For the repeated reproduction task each participant was tested separately after reading the story to themselves twice, 15 minutes later they gave their preproduction of it. Later reproductions were done at 20 hours, 8 days, 6 months and 10 years for different participants. Participants did not know the aim of the study.
Very, very few participants recalled the story accurately – Bartlett found the following pattern of errors – form (the order of events), details (names and numbers were lost), simplification (details are left out or made more familiar) and addition (inaccurate details were included).
Bartlett concluded that unfamiliar material changes when it is recalled. It becomes shorter,simpler and more stereotyped- this may be due to the effect of schema on memory.
Bartlett (1932) Strengths and weaknesses.
Strengths - Both the repeated and serial reproduction tasks were done many times to show that the changes to the story followed the same patterns.
Other stories were also used and showed similar results.
Weaknesses – By choosing unfamiliar material.
Bartlett could not be sure that the changes he found would happen with familiar information.
Bartlett did not always test the repeated reproduction participants after the same time intervals, so the changes over time cannot be compared fairly.
Key terminology Carmichael (1932) Do words affect
reconstructive memory- recalled material is not just a ‘copy’ of what we see or hear. Information is sorted and when it is remembered it is ‘rebuilt’, so can be affected by extra information and by ideas (like schemas) we might already have.
Revision notes: Carmichael (1932)
Carmichael, Hogan and Walter (1932) wanted to find out whether words shown with pictures would affect the way the pictures were remembered.
He used a laboratory experiment (with independent groups design) in which 95 participants were shown 12 pictures (the stimulus material).
The independent variable (IV) was which word they heard.
Between each picture the experimenter said, ‘The next picture resembles…’ followed by a picture from list 1 or list 2. The participants were then asked to draw the pictures they had seen and their drawings were compared to the original.
This was the dependent variable (DV).
The drawings produced by people who heard words from list one were very different to list 2.
The drawings looked like the words they heard. Carmichael et al. concluded that memory for pictures is reconstructed and the verbal context in which the drawings are learned affects recall because the memory of the word alters the way the picture is represented.
Carmichael (1932) Strenghts and weaknesses.
Strengths – by using a control group Carmichael et al. could be sure that people’s drawings weren’t always distorted in the same way
-by using 2 different lists they showed that the verbal labels affected people’s drawings.
-having 12 pictures and many participants gave them lots of evidence, so they could be sure their findings weren’t just a fluke.
-the findings are supported by recent evidence that verbal labels affect memory
Weaknesses – in real life things are not generally ambiguous as the stimulus figures shown.
-Prentice (1954) tested the effect of verbal labels on recognition rather than recall and found that verbal labels didn’t affect recognition, this means Carmichael’s findings did not apply widely.
Key terminology: Designing /Understanding experime
experiment – a research method which measures participants’ performance in two or more conditions.
experimental (participant) design – the way that participants are used in different conditions in an experiment. They may do all conditions or different participants may do each condition.
independent groups design – different participants are used in each condition in an experiment.
repeated measures design - the same participants are used in all the conditions in an experiment.
hypothesis – a testable statement of the difference between the conditions in an experiment. It describes how the independent variable will affect the dependent variable.
controls – ways to keep variable constant in all conditions of an experiment.
Revision notes:Designing/understanding experiments
An experiment is a way to find out whether one factor affects another.
Sometimes participants need to participate in all conditions of the experiment, other times they only participate in one.
Hypotheses are written to say what an experimenter expects will happen in an experiment.
They always operationalise the IV and DV and say how the IV will affect the DV.
The controls are what the experimenter does to keep variables the same in all conditions.
Key terminology Dealing with descriptive statistic
mode – an average that is the most common score or response in a set.
descriptive statistics – ways to summarise results from a study. They can show a typical or average score or how spread out the results are.
bar chart – a graph with separate bars. Usually there is one bar for each condition in an experiment.
median – an average that is the middle number in a set of scores where they are put in order from smallest to largest.
mean – an average that is calculated by adding up all of the scores in a set and dividing by the number of scores.
range – a way to show how spread out a set of results is by looking at the biggest and smallest scores.
Revision notes:Dealing with descriptive statistics
- averages tell us how most people responded. This gives us a general picture of the findings.
- different kinds of experiments produce different kinds of data and for each kind of data there is an average.
- bar charts are a way of displaying results - the conditions of the experiment (the IV) go along the x-axis and the total or average score goes on the y-axis. There would be as many bars as there are conditions in the experiment.
Key terminology Ethics in psychology experiments
ethical issues – potential psychological or physical risks for people in experim
informed consent – an individual’s right to know what will happen in an experiment, and its aims, before agreeing to participate.
right to withdraw – a participant’s right to leave a study at any time and they ability to do so.
ethical guidelines - advice to help psychologists solve ethical issuesents.
Revision notes: Ethics
wondering about what will happen in your experiment, being concerned about how good your answers were, making sure your participants are not harmed are all examples of ethical issues
one problem for experimenters is that ethics sometimes conflict with the need for controls.
When conducting experiments in psychology you need to ensure you meet all ethical guidelines before you begin your research. Participants must understand the nature of the study and agree to participate (this is fully-informed consent) and if they want to leave the study they can at any time and have the right to take their data with them (the right to withdraw)
The BPS (British Psychological Society) has a ‘Code of Conduct’ to help psychologists conduct their research in a way that will meet ethical guidelines.
Psychologists often give participants a summary about what will happen in a study although this is difficult in public places.
Revision notes:Evaluating experiments strengths.
Strengths of experiments: - in laboratory settings is easy to gain because you can tell participants exactly what is happening and they can give their fully-informed consent.
If they are told why they are doing the experiment this can cause problems because they might change their behaviour, which would alter the results.
when the participants come to the laboratory their right to withdraw can be explained.
the experimenter can control other factors that could change the DV.
By controlling other variables, the experimenter can be certain that differences in the DV have been caused by the different conditions.
the DV can be measured accurately.
Revision notes:Evaluating experiments weaknesses.
Weaknesses of experiments:
sometimes we need to avoid giving participants full information about a study. This is because knowing the aims of the study might alter the way they behave. This is called deception.
Not knowing the aims of the study may upset participants but sometimes researchers need to deliberately deceive participants.
When deception is used psychologists minimise harm by: avoiding deception unless it is absolutely necessary, avoiding other ethical problems such as embarrassment, explaining the real purpose as soon as possible and allowing participants to withdraw their results at the end.
Experiments should try to represent real life as much as possible.
Key terminology: Schemas and eyewitness memory
eyewitness – somebody who sees a crime or aspects of a crime and who helps the police to find out what has happened or to catch whoever was responsible.
Revision notes:Schemas/eyewitness memory.
Schemas are useful because they help us to predict what might happen but in the case of eyewitness memory we might think we see something based on our perception. e.g. stereotypes such as black people are violent and are likely to have committed the crime
Allport and Postman, 1945, the black man in the suit and the white man with the razor – people remembered the black man holding the razor in a threatening way.