Perception

• Sensations


  Human sense organs contain receptors that change information into electrical signals and relay information through sensory neurons to the appropriate places within the nervous system.
• Perception


  Cognitive process of interpreting or making sense of sensory information we receive. Experience builds our perception.
• Monocular depth cues


  Cues that tell us approx. how far something is using ONE eye.
• Binocular depth cues


  Cues that tell us precisely how far something is using BOTH eyes
• Height in the plane (Monocular)

  • When objects placed higher up appear or would be interpreted as further away.

  
• Relative size (Monocular)

  • The larger an object is, the closer it seems

  
• Occlusion (Monocular)


  • If an object covers another it appears closer

  
• Linear perspective (Monocular)


  • Depth cue which is the way straight lines seem to be pointing to a single point on the horizon

  
• Retinal disparity (Binocular)


  • The left and right fields of vision provide slightly different visual images when focusing on a single object

  
• Convergence (Binocular)


  • Our eyes focus differently when we see things that are closer compared to how they focus when things are further away. The brain detects the differences in how these muscles are working and use this as a cue to perceive distance.

  
• Visual illusions

  Happen when our visual perception is tricked into seeing something inaccurately due to the brain using inappropriate strategies for interpreting the sensory information it is receiving.
• Size constancy


  We keep our original perception of the size of an object even when seeing it differently.
• The Ponzo illusion

  • Example of a misinterpreted depth cue
  • The blue rectangles appear to be different sizes but they are the same size. The top rectangle appears to be further away. 

  
• The Ponzo illusion - EXPLANATION

  • Human beings have learned to interpret depth cues using  size constancy = a person/object who is viewed from far away appears to be smaller than their actual size
  • It is possible to ‘fool’ the brain into believing that differences in size occur when objects are placed at points which signal ‘far away’
  • The brain understands that parallel lines converge when viewed from afar but if two identically-sized objects are placed across those lines at different points, the brain sees the higher object as larger than the lower object 
• Muller-Lyer illusion


  • Example of size constancy (as well as being a misinterpreted depth cue)

  
• Muller-Lyer illusion - EXPLANATION

  • Human beings understand that objects/people appear to be growing larger as they move towards the viewer - they are not getting bigger as they approach
  • Size constancy occurs when an observer is familiar with an object or person, so that the object or person appears to have a constant size when viewed from various distances
• Rubin's vase - EXPLANATION

  • Ambiguity occurs when one image can be interpreted in two different ways
  • An ambiguous figure is one which may appear to show a specific image when viewed for the first time
  • It is only when the viewer shifts their perspective of the image that they are able to see that another image is also depicted as well as the first one
• The Necker Cube Diagram

  • Ambiguity

  
• The Necker Cube Diagram - EXPLANATION

  • Another type of ambiguous figure is one which can be perceived as pointing in different directions (e.g. upwards/downwards, right/left) depending on how it is viewed 
  • There are no visual cues as to its orientation, so it can be interpreted to have either the lower-left or the upper-right square as its front side.
• Gibson's Direct Theory of Perception

  • Gibson stated that sensation and perception are the same thing
  • Said that everything in our visual field gives us all the information we need to judge depth, distance and movement without needing past experiences
  • There are three parts of his theory = Optic flow patterns Motion parallax, Influence of nature
• Gibson's Direct Theory of Perception - Optic Flow Patterns

  • When moving towards a fixed point, it stays stationary while the rest of our view seems to rush by
  • If our brain does not see this optic flow, it struggles to recognise we are moving
• Gibson's Direct Theory of Perception - Motion Parallax


  • When moving, objects that are closer appear to be moving faster than those further away
• Gibson's Direct Theory of Perception - Influence of Nature

  • We do not need to learn to perceive world around us, these abilities are innate
• Gibson's Direct Theory of Perception - EVALUATION

  • Strength = Research provides good support for this theory. The visual cliff experiment shows we do not need to learn to perceive the world around us, they did not crawl off the edge. Supports Gibson's theory that it is innate.
  • Weakness = Perceptual errors not easily explained by this theory. Visual illusions show these errors. Evidence from illusions shows Gibson's theory is limited because it cannot explain this.
• Gregory's Constructivist Theory of Perception

  • We perceive based on past experiences
  • We make sense of world around us by building out perceptions based party on incoming information and using what we know about the world
• Gregory's Constructivist Theory of Perception - Inference


  • A lot of what we perceive in the world is incomplete and ambiguous
  • For this reason, out brain will "fill in the gaps" using inference. Brain uses information available to guess what our eyes are seeing
• Gregory's Constructivist Theory of Perception - Visual cues


  • The brain has help when making inferences in visual cues
  • Our perception is usually accurate but sometimes we interpret things wrong (e.g. visual illusions)
• Gregory's Constructivist Theory of Perception - EVALUATION


  • Strength = Research supporting (Seagall et al.) found that people in non-Western cultures don't fall for Muller-Lyer illusion.
  • Weakness = Research contradicting = visual cliff experiment, babies did not crawl over edge, showing some elements of perception are innate.
• Nature vs nurture

  • Gibson's = Nature, we are born with thoughts, feelings and behaviours. We perceive with what we are born with
  • Gregory's = Nurture, the environment shapes our thoughts, feelings and behaviours. We perceive based on experience.
• Comparing Gibson and Gregory's theories

  • Gibson = nature. Gregory = nurture.
  • Gibson = Sees sensation and perception as the same thing. Gregory = Sees sensation and perception as separate things.
  • Gibson = Difficulty in explaining cultural differences in perception. Gregory = Can explain cultural differences in perception
• Motivation effect on perception - Gilchrist/Nesburg - AIM

  To see if food deprivation would make food appear brighter
• Motivation effect on perception - Gilchrist/Nesburg - METHOD

  • Used 2 groups of people.
  • First group = 26 students who volunteered to go without food for 24 hours
  • Second group = Participants who ate as normal
  • Shown four slides of a meal for 15 seconds each
  • After each slide was shown, the participants were asked to adjust the lighting on a new photo so it looked the same as original
• Motivation effect on perception - Gilchrist/Nesburg - RESULTS

  Food deprived group adjusted lighting so it was brighter than before. The other participants adjusted it similar to the first photo.
• Motivation effect on perception - Gilchrist/Nesburg - CONCLUSION

  Hunger is a motivating factor that affects perception. Being deprived of basic needs makes us sensitive to food related pictures, making them appear brigher
• Motivation effect on perception - Gilchrist/Nesburg - EVALUATION


  • Weakness = Unethical to deprive participants of food. May have caused discomfort.
  • Weakness = Two different groups. Maybe the groups perceived differently regardless of being food deprived or not. This means that results may be inaccurate.
• Expectation effect on perception - Bruner/Minturn - AIM


  To see whether expectation is an important factor in perception
• Expectation effect on perception - Bruner/Minturn - METHOD


  • Showed participants an ambiguous figure (Looks like a B or 13)
  • First group shown figure in between A and C
  • Second group shown figure between 12 and 14
• Expectation effect on perception - Bruner/Minturn - RESULTS


  • Group that saw figure between A and C read it as a B
  • Group that saw the figure between 13 and 14 read it as 13
• Expectation effect on perception - Bruner/Minturn - CONCL


  Expectation is an important influence on perception
• Expectation effect on perception - Bruner/Minturn - EVALUATION


  • Has real life application. War of the Ghosts Study. Explains why participants changed story based on expectations. Increases credibility of theory
  • Was conducted a long time ago. We cannot say it would be the same now.