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  1. Perception

  2. It’s not as Easy as it Looks

  3. Sensation and Perception • Sensation • The process through which the senses pick up visual, auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted • Perception • The process by which sensory information is actively organized and interpreted by the brain

  4. We see the world with our brain • How Light Enters the Eye

  5. Interpretation What do you see?

  6. Interpretation Now what do you see?

  7. Attention and Perception • Your perception of a rich visual environ-ment is an illusion! • You actually are only aware of the small part of the scene that you are attending to

  8. Attention and Perception • Change Blindness/Inattentive Blindness • you can’t notice changes in a scene unless you attend to the location of the change • Bet you can't do this

  9. Illusions • An illusion occurs when what you perceive is not what is really out there • Optical illusions occur when the physical stimulus itself is distorted – but interpreted correctly by the brain! • But sometimes the brain gets it wrong – and we see a visual illusion • Visual Illusions happen in your visual system – the physical stimulus is correct but misinterpreted by the brain.

  10. Optical and visual illusions Optical Illusion Visual Illusion

  11. Visual illusion

  12. Categories of visual illusion • Gregory identified FOUR categories of visual illusion. • Ambiguous figures • Paradoxical figures • Fictitious figures • Distortions

  13. Ambiguous figures • the same input leads to different outputs due to switches in attention. • For these figures we make two alternative hypotheses about what sort of object could result in that particular pattern of information on our retina. • We can only fulfil one of these hypotheses at a time, but it depends which one

  14. Ambiguous figures – 1 Necker Cube • In which direction is the cube facing?

  15. Ambiguous figures – 2 Rubin vase

  16. Ambiguous figures – 3

  17. Paradoxical figures • Figures we assume are “real” 3-D objects are impossible in the “real world”. • We appear to be unable to accept that they are simply lines drawn on a flat surface, in two dimensions • Our hypothesis appears to be that there are a number of depth cues in the drawings, so they must represent 3-D objects and we attempt to interpret the objects in three dimensions.

  18. Paradoxical figures - Impossible Staircase

  19. Fictitious figures • We see what is not there, not actually given in the stimulus array. • We appear to construct perceptual hypotheses based on our best guess about the whole visual array, which gives us a perception of an object that is not actually there!

  20. Fictitious figures - Kanizsa triangle

  21. Distortions • Here we make a perceptual mistake • We attempt to understand the data in terms of how we normally interpret the world but this misleads us and we make mistakes. • It seems our perception is greatly affected by the context in which an object is seen - we make a hypothesis based on what we normally experience in these circumstances and that hypothesis is mistaken.

  22. Distortions – 1 Muller-Lyle

  23. Explanation? • Gregory – we impose our knowledge of a 3-D world onto a 2-D image. • Day – ‘conflicting cues theory’ i.e. we have to make sense of 2 cues when judging the length of the lines – the actual length of the line and the overall length of the figure.

  24. Distortions – 2 Ponzo

  25. Distortions – 2 Ponzo • Ponzo

  26. Distortions – 3 Titchener • Another example of a distortion illusion is Titchener’s circles

  27. Explanation • Your brain usually tries to increase differences between things to make it easier to tell them apart. • In the left hand image to make it even easier for you to tell the large outer circles apart from the smaller middle circle, your brain makes the difference between them even larger. This makes the middle circle look even smaller. • In the right hand image to make it even easier for you to tell the small outer circles apart from the larger middle circle, your brain makes the difference between them even larger. This makes the middle circle look even bigger. • Comparing the middle circles, one looks larger than it really is while the other one looks smaller than it really is.

  28. You decide • On the next slides decide which type of illusion is being created!

  29. Penrose Triangle Ambiguous? Paradoxical? Fictitious? Distortion?

  30. Ambihelical Hexnut Ambiguous? Paradoxical? Fictitious? Distortion?

  31. ? Ambiguous? Paradoxical? Fictitious? Distortion?

  32. The Pool Ambiguous? Paradoxical? Fictitious? Distortion?

  33. Penrose Trident Ambiguous? Paradoxical? Fictitious? Distortion?

  34. ? Ambiguous? Paradoxical? Fictitious? Distortion?

  35. ?

  36. ? • Keep staring at the blue dot in the middle of the picture.

  37. ? • In which direction is the horse facing?

  38. Morinaga’s paradox

  39. Morinaga’s paradox • In reality both judgments, of vertical alignment and of the horizontal gaps, are illusions.   • The tips of the arrows are perfectly aligned vertically, and • the horizontal gaps between the three sets of arrowheads are all exactly the same. (This is a version of the Muller-Lyer illusion!)

  40. Variation with Ambihelical Hexnut Ambiguous? Paradoxical? Fictitious? Distortion?

  41. The Terrace Ambiguous? Paradoxical? Fictitious? Distortion?

  42. ? Ambiguous? Paradoxical? Fictitious? Distortion?

  43. Ehrenstein Illusion Ambiguous? Paradoxical? Fictitious? Distortion?

  44. ? Ambiguous? Paradoxical? Fictitious? Distortion?

  45. ? Ambiguous? Paradoxical? Fictitious? Distortion?

  46. Zöllner illusion Ambiguous? Paradoxical? Fictitious? Distortion?

  47. Poggendorff Illusion Ambiguous? Paradoxical? Fictitious? Distortion?

  48. Apparent Motion • Object disappears and reappears somewhere else • Visual system “interpolates” motion in between

  49. Is this a spiral ? Ambiguous? Paradoxical? Fictitious? Distortion?

  50. Frazer Spiral