Perceptual Organisation

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  • Perceptual Organisation
    • Gibson   Bottom Up Direct
      • Also known as the Ecological theory due to the claim that perception can be explained soley in terms of the environment. He maintained that the environment provides so much rich info there is no need for any higher/topdown processing.
        • The starting point for his theory was the notion that the pattern of light reaching the eye can be regarded as an optic array  containing all visual info available to the retina of the eye. It provides ambiguous info about the layout of objects in space. This info comes in many forms.
          • Perception involves 'picking up' info provided in a direct way with little or no processing involved. Gibsons also assumes there is a close relationship between perception & action which is very important. He proposed an optic flow (the point towards which we more towards seems motionless with the rest of the visual environment moving away from the point.
            • The optic flow only exists when the subject is in motion. He argued that important aspects of the optic array remain the same when the subject moves around their environment & these aspects are known as invariants.
              • Invarients include 'the pole' and 'horizon ratio' (the ratio of an objects height to the distance between its base & horizon stays the same regardless of its distance from the viewer). According to Gibson this helps us to estimate the size of any given object whether it is close or far away.
                • Gibson also states there is a process of resonance which he suggests we can pick up from the environment fairly automaticall & effortlessly if we are atuned to that info, similar to a radio is atuned to certain frequencys,
      • Research has focused on his assumption that we use optic flow patterns to tell us the direction in which we are moving.
        • The evidence generally supports the view that optic flow info is one source of info that we use to work out how to move towards a target.
          • Warren & Hannen: produced films consisting of patterns of moving dots to stimulate the optic flow that would be produced if someone were moving in a given direction. Observers used this info to make accurate judgements of the direction they were heading.
            • Van den Burg & Brenner: pointed out that we need only 1 eye to use optic flow info however judgements about direction were more accruate when p.s used 2 eyes, this happened due to binocular disparity (slight difference in image on retina of each eye allows observers to obtain additional info about depths of objects.
      • Evaluation points
        • Affordance & resonance are much more complex than Gibson first assumed. None of them happen as capidly & automatically as he claimed.
          • Most objects give rise to more than 1 affordance eg a hungry person would percieve affordance of edibility for an orange whereas an angry person might look at it & detect the affordance of a projectile.
            • Notion of affordance was an unsuccessful attempt at explaining the meaningfulness of perception, as we can ttch many other kinds of meaning to stimuli eg the pole star can been seen as ust a star or as the pole star, this is down to individual perceptions & use of own knowledge.
              • Affordance of an object can change over time eg a stone plate was used to write on with a chisel but would now be used as a paving stone.
        • Gibson exaggerated role of optic flow, binocular disparity plays an important part in the judgement.
        • Gregory theory contradicts.
          • Gibsons theory fails to explain why visual illusions decieve our ability to percieve accurately.
            • Perception is a mix of recieving rich information from the environment & adding our own experiences tothese perceptions.
    • Gregory   Top Down Indirect
      • Evidence to support the model.
        • Hemholtz: has argued that we use inferences to add meaning to sensory info & we are unaware that we are making them because they are unconcious.
        • Visual Illusions
          • Size constancy means that an object is percieved as having the same size whether looked at from a short or long distance away. This constancy contradicts with the size of the retinal iage.
            • Supported by Ponzo's Illusion: the long lines look like railway lines/edges of a road receding into the distance, as a result the top rectangle can be seen as further away from us than the bottom one.
              • If this were a 3D scene then the top rectangle would be longer than the bottom rectangle, it looks longer to us on the 2D image due to misapplied size constancy & using our schemas.
            • The Muller-Lyer Illusion has a similar explanation to Ponzo. According to Gregory the 'longer' line figure looks like the inside of a room thus the vertical line is further away than the fins, the other figure looks like the outside of a building thus the vertical line is closer to us than the fins.
              • The principle of size constancy tells us that the line that is 'furthest away' must be the longest, hence why this illusion works.
      • Also known as the Constructivist theory, is a top-down indirect theory based on the assumption that the info available to the eye is inadequate on its own to permit detailed & accurate perceptions of the world around us.
        • Top-down theories propose that info/knowledge stored in the brain works downwards, helping us to interpret the basic sensory input.
          • According to Gregory perceptions areconstructions from the fragmentary scraps of data signalled by the senses & drawn from the memory banks, themselves constructions from the snippets of the past.
            • We use the info supplied to the eyes as the basis for making inferences or forming hypotheses about the visual environment.
              • He empahsises the active nature of perception rather than merely passively recieving information & we actively attempt to make sense of what we are seeing & propose a 'best fit' as to what it might be.
                • We construct our perception from the sensory input from the retina & our expectations from previous knowledge in our schemas, so visual perception is a result of interaction between sensory input & hypotheses. Our past experiences effect how we percieve the object/situation.
                  • Gregory claims that this is not always a correct process which is why visual illusions occur.
      • Evaluation point.
        • Idea of Muller-Lyer being percieved as building is inaccurate as this illusion works with other shapes at each end of the line eg circles.
        • Studies carried out by constructivist theorists make us of artifical/unnatural  stimuli so may not be relevant to real life.
          • Studies carried out in a lab are reductionist to the amount of stimuli that can be used.
            • Visual Illusions are 2D images & :. not representative of real life, lacks ecological validity so results cannot be transferred.
        • If everyone constructs our own individual perceptions then why is it that we all tend to percieve the world in the same way.
        • Theory allows for individual difference. regory allows for alpha bias & emic constructs, everyone is different as they use their own personal schemas to percieve things.
          • Explains why cross-cultural studies into perception show that different cultures percieve differently eg Deregowski, Turnbull and Hudson.
        • Gibson theory contradicts it. Gibson was correct in saying that the environment provides detailed information eg texture gradient,.
          • Gregory's statement that we are only provided with scraps of data is untrue.
            • The theories need to be used together as they both explain different parts of the phenomena & both put forward valid arguements.
              • Perception is a mix of recieving rich information from the environment & adding our own experiences tothese perceptions.
  • Evaluation points
    • Affordance & resonance are much more complex than Gibson first assumed. None of them happen as capidly & automatically as he claimed.
      • Most objects give rise to more than 1 affordance eg a hungry person would percieve affordance of edibility for an orange whereas an angry person might look at it & detect the affordance of a projectile.
        • Notion of affordance was an unsuccessful attempt at explaining the meaningfulness of perception, as we can ttch many other kinds of meaning to stimuli eg the pole star can been seen as ust a star or as the pole star, this is down to individual perceptions & use of own knowledge.
          • Affordance of an object can change over time eg a stone plate was used to write on with a chisel but would now be used as a paving stone.
    • Gibson exaggerated role of optic flow, binocular disparity plays an important part in the judgement.
    • Gregory theory contradicts.
      • Gibsons theory fails to explain why visual illusions decieve our ability to percieve accurately.
    • Culture bais: people learn about objects within culture rather than them being afforded.

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