PERCEPTION: STRIPPED

THE DIFFERENCE BETWEEN SENSATION AND PERCEPTION

SENSATION / PERCEPTIO N
  • physical process
  • collecting data via senses
/
  • psychological process
  • interpreting/making sense of data

Try to avoid using the words ‘see’ or ‘seeing’ when describing the difference between sensation and perception because the term can be used to mean both things i.e. ‘what the eyes see’ (sensation) and ‘seeing the world differently from others’ (perception).

PERCEPTUAL CONSTANCIES

Constancies let us perceive the environment as constant when sensations are changing.

  • Shape constancy lets us perceive an object’s shape as constant when sensations are changing e.g. when we walk around a chair its shape appears to change yet we know its overall shape stays the same.
  • Colour constancy lets us perceive an object’s colour as constant when sensations are changing e.g. we put an item of clothing under a different light - its colour appears to change yet we know that its actual colour stays the same.

Remember with both types of constancies it is the perception that is constant (while the sensation changes).

You may be asked for an example of shape constancy or colour constancy but, even if you are not, you may use one to help to explain what they are.

VISUAL ILLUSIONS

Illusions show very clearly how what we perceive can be different from what we sense.

SENSATION / EXAMPLE / PERCEPTION
Nothing is sensed. / / Something is perceived.
One thing is sensed. / / Two things are perceived.

There are no specific illusions that you need to know about for the exam, so you cannot be asked to name one or describe one. However, you may find it useful to have one or two specific illusions that you can talk about it. If they come up in the exam, it will be about how they show the difference between perception and sensation.

It is acceptable to draw an illusion in the exam if it is going to help you to (literally!) illustrate your point.

DEPTH CUES

Depth cues allow us to perceive a 3D world despite the sensations (on the back of our eyes) being 2D.

DEPTH CUE / LINEAR PERSPECTIVE / SUPER-IMPOSITION / HEIGHT IN PLANE / RELATIVE SIZE / TEXTURE GRADIENT
DESCRIPTION / Parallel lines appear to converge into the distance. / Nearer objects overlap objects which are further away. / The further an object is, the higher up in appears in a scene. / If an object is closer then it appears relatively larger than a similar sized object further away. / The nearer an object is, the more detail is visible.
EXAMPLE / / / / /

The most common way of testing depth cues in the exam is through giving you a picture or photo to look at where you then have to identify and explain the depth cues used in the image. Most depth cues will be in the picture but don’t assume that they all will be – look carefully. When applying the depth cues to the image be very precise about where they are (e.g. ‘the trees closer to us appear larger than the trees that are further away’). It is also important to use terms/phrases such as ‘closer’, ‘further away’, ‘in the distance’, ‘nearby’ to get across the idea of depth. Terms/phrases such as ‘front’, ‘back’, ‘behind’, ‘top of picture’, etc are not the same thing as they are not to do with distance/depth.

Make sure the depth cue you identify matches the one that you describe. For example, some candidates name one depth cue (e.g. ‘height in plane’) but then go on to talk about another one (e.g. things looking smaller in the distance – which would actually be ‘relative size’).

CONSTRUCTIVIST THEORY OF PERCEPTION

We construct our perception of the world based on past experiences.

The role of experience is important because it suggests we all perceive the world in a different way – depending on our own individual experiences.

Our experiences create a perceptual set. Perceptual set is a set of cognitive factors we hold in our minds to help us to perceive the world.

Perceptual set includes factors such as context, expectations and motivation.

Perceptual set relates to the idea of top-down processing.

Top-down processing is an important concept in Constructivist theory as it describes the way in which we interpret the world from the brain downwards. For example, the eyes send limited information to the brain and then the brain uses past experiences to ‘fill in the gaps’ and make sense of this information. This is why ‘Keep off the the Grass’ is often read as ‘Keep off the Grass’ – we are using our perceptual set to perceive the sentence rather than reading what it actually says!

A good description of Constructivist theory would link together the different terms. It is important to include as many of the terms as possible but make sure you know how they relate to each other to form the overall theory of how we perceive the world.

CRITICISMS OF CONSTRUCTIVIST THEORY

≠It is based heavily on artificial tasks using things like illusions.

≠Why do we keep falling for illusions rather than learning from past experiences?

≠Why do we appear to perceive the world in the same way as other people when we do not share the same experiences?

≠How do we explain new born babies’ ability to perceive the world (they have no experience)?

≠In general, the theory over-emphasises the need for experience and ignores the role of nature in perception.

You can pose questions like some of the criticisms above but make sure you try to address them as part of your evaluation.

Make sure that your evaluation points go beyond just description. If you say something like ‘Constructivist theory says we rely on past experiences to perceive the world’ then you are just describing the theory. If you are trying to say that the theory is wrong to say that we rely on past experiences then make sure you actually say this. You would then go on to say why experience cannot be that important e.g. using the example of new born babies being able to perceive depth, or the fact that we do not seem to learn from our experiences (e.g. falling for illusions), or the fact that our experiences are unique but our perceptions are not that different from each other.

CONSTRUCTIVIST THEORY VS NATIVIST THEORY

The main idea behind the Nativist theory of perception is bottom-up processing. This is the idea that we do not need to interpret what we sense to perceive it – most of the information we need enters through the senses and we instinctively know how we should perceive it.

CONSTRUCTIVIST / NATIVIST
■Top-down processing
■Perception driven by perceptual set
■Perception requires interpretation
■Perception is a product of past experiences
■Data holds limited information – that’s why the brain has to make sense of it / □Bottom-up processing (from eye to brain)
□Data driven perception
□Perception is immediate and direct
□Perception is a product of evolution
□Data holds all information needed for perception e.g. optic flow, affordances

It is not unusual for candidates to get top-down processing and bottom-up processing mixed up in the exam. Remember, top-down processing gets its name because the brain (which ‘sits’ above the eyes) drives what we see. However, it would be a mistake to say that we use our brain to see the world – the eyes are still the starting point but the brain does a lot of work ‘filling in the gaps’. Bottom-up processing suggests that the hard work is done at the ‘bottom’ of the process (using the eyes) and the brain just has to piece together information to form an image i.e. the brain does not play that big a role.

HABER & LEVIN’S (2001) EXPERIMENT INTO DEPTH PERCEPTION AND FAMILIARITY OF OBJECTS

Procedure / Findings
~Outdoor experiment
~Sample: 9 male college students
~A field was divided into 4 sections: (1) arrival area (2) real world objects of standard size (3) real world objects of varying size (4) cardboard cut outs
~Repeated measures design: participants were asked to estimate the distance of all objects in all 3 conditions. / *Participants’ estimates of distance were most accurate for the real world objects which were a standard size
*The estimates for the other real world objects and for the cut-outs of shapes were not so accurate
*Conclusion: it was easier to estimate the distance of familiar objects because the participants were relying on their past experiences. They expected objects such as milk bottles and doors to be certain sizes, and so could work out how far away they were based on their relative size.

Bear in mind the three common errors when describing this study:

(i)Candidates sometimes described as a field experiment. Although it took place in a field, it is more like a laboratory experiment because the setting was chosen because it offered some control (e.g. no buildings around).

(ii)Candidates quite often forget to say exactly what participants were trying to guess/estimate – that is the distance of objects.

(iii)Candidates are not very good at distinguishing between the different types of objects. The objects of known (standard) size are often just described as well known or familiar objects. Remember, the third section also had well known/familiar objects – it’s just that they were objects that did not have a standard size.

LIMITATIONS OF STUDY

(i)Sample too small – difficult to generalise from.

(ii)Biased sample – perception could be affected by the fact all participants were male, and all were well educated (students).

(iii)Task was artificial and setting was unfamiliar – so how realistic are results?

(iv)The findings may have been affected by the fact the participants were tested in groups of three – estimates may have been different if completed alone.

(v)What a ‘familiar object’ is subjective – depends on the individual’s own experiences.

Remember that limitations should read like evaluation. There is a difference between saying a sample is small (just description) and a sample is too small (which is evaluation) – or the experiment used all males (just description) and the experiment only used males (which is evaluation).

It is even better if you can expand on the evaluation points - for instance, if only males were used (1 mark) this may not represent women (1 mark) who may perceive distances differently because of their experiences or even because their brain functions differently (1 mark).

APPLICATIONS OF RESEARCH: ADVERTISING

If asked for one application of research into perception, you should take ‘advertising’ as your starting point and then talk about the different features e.g. use of context, use of expectations.

If asked for one way that research has been used in advertising then you should use ‘use of perceptual set’ as your starting point and then talk about the different features as an expansion of this.

EXAM STYLE QUESTIONS

  1. Explain how illusions show the difference between sensation and perception. (4)
  2. Name two types of perceptual constancies. (2)

Look at this photo.

Explain how two depth cues are used in this photo. (4)

  1. Describe the role of experience in perception. (4)
  2. Outline what is meant by perceptual set. (2)
  3. Evaluate the constructivist theory of perception. (3)
  4. Explain the difference between top-down processing and bottom-up processing. (4)
  5. Describe the findings of Haber & Levin’s experiment into depth perception. (3)
  6. Explain one limitation of Haber & Levin’s study. (3)
  7. Describe how research into perception can be used in advertising. (4)