Unit 3:

1. Unit 3: PERCEPTUAL PROCESS

2. What is Perception? • Perception is a means where information obtained from the environment by means of sensory organs, is transformed into experiences of objects, events, sounds, taste, etc. • Perception is an important factor in human behaviour • Perception ….A process by which individual organize and interpret their sensory impressions in order to give meaning to the environment. • Perception can be defined as the process of receiving, selecting, organizing, interpreting, checking, and reacting to sensory stimuli or data.

3. What is Perception? • Perception is a process whereby, sensory stimulus in the environment is converted to mental representation (repeat). • Refers to the way the world looks (eyes), sounds (ears), feels (skin), taste (tongue) or smell (nose). • The first step in processing information around us.

4. Process in Perceptions • Stimulus received from the environment provide the raw data for experience  create an internal representation of objects in our surrounding. • Sensation( a process of transduction), where the process of converting the energy of light or sound (stimulus) into neural transmission • i.e. The sensory information is then transformed, elaborated and combined with memories to create what we actually experience or PERCEIVE.

5. The perceptual process The steps in this process are arranged in a circle to emphasize  the process is dynamic and continually changing. Blue arrows point to stimuli Greento processing Red to perceptual response. Arrows A, B, and C indicate three important relationships that researchers measure. 6 7 5 8 4 3 1 2

6. The Perceptual Process • Environmental stimuli - All available stimuli for an observer • Attended stimuli - Stimuli that are the point of focus for the observer • Stimulus on the receptors - “Image” of stimulus on receptor cells • Transduction - Change from environmental energy to electrical energy in the nervous system • Neural processing - Interconnected neurons that propagate the electrical signal from receptor cells throughout the brain

7. Figure 1.2 (a) We take the woods as the starting point for our description of the perceptual process. Everything in the woods is the environmental stimulus. (b) Ellen focuses on the moth, which becomes the attended stimulus.

8. Figure 1.3 (a) An image of the moth is formed on Ellen’s retina. (b) Transduction occurs when the receptors create electrical energy in response to the light. (c) This electrical energy is processed through networks of neurons.

9. Con’t…The Perceptual Process • Perception - Conscious sensory experience • Recognition - Ability to place objects in categories that provide meaning • Action - Motor activities that occur in reference to the perceived and recognized object

10. Figure 1.4 (a) Ellen has conscious perception of the moth. (b) She recognizes the moth. (c) She takes action by walking toward the tree to get a better view.

11. The Perceptual Process Figure 1.1 The perceptual process. The steps in this process are arranged in a circle to emphasize the fact that the process is dynamic and continually changing. Blue point to stimuli; green to processing; red to perceptual responses. Arrows A, B, and C indicate three important relationships that researchers measure.

12. Two Interacting Aspects of Perception • Bottom-up processing • Processing based on incoming stimuli from the environment • Also called data-based processing • Top-down processing • Processing based on the perceiver’s previous knowledge • Also called knowledge-based processing

13. Figure 1.6 Perception is determined by an interaction between bottom-up processing, which starts with the image of the receptors, and top-down processing, which brings the observer’s knowledge into play. In this example, (a) the image of the moth on Ellen’s retina initiates bottom-up processing, and (b) her prior knowledge of moths contributes to top-down processing.

14. WHY does perceptions vary from person to person • This could be due to: • Personal Variation • Physical Variations • Combinations of personal & physical variations • different people perceive different things about the same situation. • We assign different meanings to what we perceive  and the meanings might change for a certain person. • One might change one's perspective or simply make things mean something else.

15. VISUAL SYSTEM -The Eye visual perception

16. Visual Perception • The eyes play a vital role in transmitting information surrounding objects to our brain. • The human eyes consists of about 7 million cones and 125 millions rods • Rods & cones function as receptors that would accept information

17. The Eye Lens – focuses light on the retina Ciliary muscles alter the shape of the lens as needed Accommodation – the process of adjusting the lens to bring images into focus Figure 6.4

18. The Basic sensory equipment involved in human vision

19. Visual Perception • Retina: The layer of the eye covered with the rods and cones that initiate the process of visual sensation and perception • Parts of the retina: rods and cones, bipolar cells, and ganglion cells. • The retina is in a sense “inside-out” • Light passes through several cell layers before reaching its receptors • LIGHT retinal ganglion cells  bipolar cells receptors cells • Lateral communication • Horizontal cells • Amacrine cells

20. Visual Perception (con’t.) • Rods and Cones: These form the back layer of neurons on the retina and are the first neurons stimulated by light • Bipolar Cells: Patterns of neural firing from the rods and cones are forwarded to the second layer of neurons, the bipolar cells • Ganglion cells: Collected messages from the bipolar cells are passed along to the third layer of neurons, the ganglion cells. • Fovea: The highly sensitive region of the retina responsible for precise, focused vision, composed largely of cones

21. How do the eyes transmit visual information to the brain? • Each eye transmits visual information to the occipital lobes of both hemispheres of the brain, to the region known as the visual cortex The Visual Pathway

22. How accurate is our visual system? • Vision - carries out complex activities • Our visual system can create an accurate, richly detailed, 3 dimensional perception • Through a tiny , distorted, upside-down, 2 dimensional retinal images projected upon the visual receptors lining the back of our eyes.

23. Eye Position and Binocular Disparity • Convergence • eyes must turn slightly inward when objects are close • Binocular disparity • difference between images on the two retinas • Both are greater when objects are close • provides brain with 3-D image and distance information

24. The Visual System • Functions of the Visual System: • Answers two questions • What is it? (recognition) • Where is it? (location) • Transforms a distorted and upside-down 2-D retinal image into the 3-D world we perceive.

25. The Visual System • Does the visual system create an exact copy of the external world? • No! • The visual system creates a perception of reality.

28. Visual Illusions

29. Visual Illusions

30. Visual Illusions

31. Visual Illusions

32. Visual Illusions

33. Depth Perception

34. What is Depth Perception? • Depth perception is the visual ability to perceive the world in three dimensions (3D). • Depth perception is a visual illusion. • The ability to judge how far away an object is as well as how far away objects are from each other. • Depth perception refers to the phenomenon describing the ability to perceive the environment in three-dimensional form and to determine the spatial distance among objects. • This phenomenon ascertains our ability to judge the inter-distance among two objects in space.

35. Why is depth perception important? • Depth perception is crucially important for our survival and hence interacting with the world. • Using depth perception as a significant factor we may be able to provide response back to the environmental stimuli. • Without it, we may become unable to navigate around. • Depth perception enables us to estimate the distance of an object from us. • Depth perception enables us to locate the position of an object in space  hence we may become able to either reach at it or avoid it.

36. The Perception of 3-D space • Perceiving 2-D objects is fairly simple because 2-D visual  images are already constructed at the level of the retina. • Furthermore, our visual system is composed of numerous areas containing Topographical Maps of visual space. • The 3-D perception that we experience everyday results from our visual system’s use of depth perception: • Depth perception can be divided into 3 cues:- • Oculomotor Cues • Binocular Cues • Monocular Cues

37. Depth Perception • Space/depth perception can be divided into 3 cues:- • Oculomotor Cues - Cues based on our ability to sense the position of our eyes and the muscle tension in our eyes muscles. Created by convergence (inward movement of the eyes when we focus on nearby objects) & accomodation (change in the shape of the lens when we focus on objects at different distances) • Binocular Cues -   cues that are based on the receipt of sensory information in three dimensions from both eyes. • Monocular Cues - cues that can be represented in just two dimensions and observed with just one eye.

38. a. Oculomotor Cues • Oculomotor Cues is influence by 2 elements:-(depend on the distance of the 0bject observed), • Convergence- Convergence can serve as a cue for depth because the convergence of the eyes depends on the distance of the objects we fixate. • The inward movement of the eyes that occurs when we look at nearby objects. • Accommodation - serve as a depth cue because the shape of the lens depends on the distance of the objects we focus on. • The change in the shape of the lens that occurs when we focus on objects at various distances

39. b. Binocular Cues: Retinal Disparity • Binocular Cues – using both eyes to look at an object • As binocular creatures, our two eyes look onto the world from slightly different position, providing slightly different views of the world. • Binocular Disparity grants us important information about depth relationships between objects. • Some neurons in the visual cortex are able to detect retinal disparity and act as depth detectors.

40. Monocular Cues for Depth • Eventhough Binocular disparity is a powerful cuefor depth perception  but we can perceive depth beyond our binocular field of vision, i.e. and even with one eye closed. • Monocular Cues is cues for depth perception that come from the image obtained from one single eye. • Monocular Depth Cues - mostlypictorial cues that we use to create an impression of depth on a flat canvas. • 4 elements that influence monocular cues:- • Interposition • Linear Perspectives • Relative Size Texture Gradients • Light & Shadow

41. Monocular Cues: Interposition • When the boundary of an object is interrupted by the presence of another object, we use this pattern of blocking as a cue to determine the object as more distant from us. • The near object is perceived as interposed between the far object and us.

42. Monocular Cues: Linear Perspective • Distant objects necessarily produce a smaller retinal image than nearby objects of the same size. • This provides the basis for the cue of Linear Perspective.

43. Monocular Cues: Relative Size • That distant objects produce a smaller retinal image than nearby objects of the same size also provides the basis for the cue of Relative Size: i.e. • the larger of two identical objects tends to be perceived as closer that the smaller one

44. Framing Effect and Size Illusion • An object that seems to fill a bounding outline looks larger • than the same object within a larger outline. Size Consistency

45. Monocular Cues: Texture Gradients • Uniformly textured surfaces produce Texture Gradients thatprovide depth information: • as the surface recedes, the textureelements’ size decreases and their density increases.

46. Monocular Cues: Light and Shadow • The distribution of light and shadow on a objects is also a powerful monocular cue for depth provided by the biologically correct assumption that light comes from above.

47. The Perception of Movement Where is it going?

48. Retinal Motion • Our perception of movement arises from the motion of images across the retina as detected by visual neurons that either simply sensitive to motion or specifically selective to the direction of motion of visual stimuli. • These neurons are well-suited to act as motion detectors.

49. Apparent Movement • Motion can be perceived even when there is no motion of an image across the retina. • Appropriately timed change in position is sufficient for the visual system to make something appear as moving.

50. Illusion of Motion • We not only detect motion, we also interpret it. Specifically, • the perceptual system must solve the Correspondence • Problem: determining which elements of the current view • corresponds with which elements in the previous view.