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The Visual System. Light Enters the eye as electromagnetic radiation Enters the eye as electromagnetic radiation Travels in a wave that vary in amplitude.

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Presentation on theme: "The Visual System. Light Enters the eye as electromagnetic radiation Enters the eye as electromagnetic radiation Travels in a wave that vary in amplitude."— Presentation transcript:

1 The Visual System

2 Light Enters the eye as electromagnetic radiation Enters the eye as electromagnetic radiation Travels in a wave that vary in amplitude (height) and wavelength (between peaks) Travels in a wave that vary in amplitude (height) and wavelength (between peaks) Amplitude= brightness Amplitude= brightness Wavelength= color (hue) Wavelength= color (hue)

3 Humans see a mixture of several wavelengths Humans see a mixture of several wavelengths Varies purity Varies purity Small portion of the spectrum Small portion of the spectrum Animals- what do they see? Animals- what do they see?

4 Parts of the eye

5 Parts of the Eye Cornea (1) transparent covering/protection Cornea (1) transparent covering/protection Pupil and Iris (2) bright light/contracts, dim light/relax Pupil and Iris (2) bright light/contracts, dim light/relax Lens (3) focuses light on the retina, accommodation Lens (3) focuses light on the retina, accommodation Retina (4) neural tissue that absorbs light Retina (4) neural tissue that absorbs light Optic disk & Blind Spot (5) Optic disk & Blind Spot (5) Optic Nerve (6) Optic Nerve (6) Fovea (7) Fovea (7) Blind Spot Activity!! Blind Spot Activity!!

6 The Retina Millions of receptor cells Millions of receptor cells 10 % of light 10 % of light Rods- 100 to 125 million Rods- 100 to 125 million Cones- 5-6 million Cones- 5-6 million Expt- What Color is it?? Expt- What Color is it??

7 Light and Dark Adaptation

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9 From the Eye to the Brain

10 Processing in the Visual Cortex Feature Detectors Feature Detectors Simple Cells Simple Cells Complex cells Complex cells Ventral (what) pathway Ventral (what) pathway Dorsal (where) pathway Dorsal (where) pathway

11 Color Theory Psychological interpretation- Blends of three aspects or properties of light Psychological interpretation- Blends of three aspects or properties of light Three theories regarding color Three theories regarding color

12 Trichromatic Theory- Young and Von Helmholtz The eye does the mixing by varying the ratio of neural activity among these 3 types The eye does the mixing by varying the ratio of neural activity among these 3 types Color blindness Color blindness –Dichromats –Monochromats

13 Opponent Process Theory- Hering Color perception depends on receptors that make antagonistic responses to 3 pairs (red v. green) (yellow v. blue) (white v. black) Color perception depends on receptors that make antagonistic responses to 3 pairs (red v. green) (yellow v. blue) (white v. black) When excited they respond to one color and when inhibited they respond to the other When excited they respond to one color and when inhibited they respond to the other

14 Opponent Process Theory- Hering Complementary colors (p.101) Complementary colors (p.101)

15 Afterimage

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17 Reconciling Theory Both theories correct Both theories correct Perception of color is processed in stages Perception of color is processed in stages Beginning stages- trichromatic Beginning stages- trichromatic Later stages- opponent processing Later stages- opponent processing

18 Form Perception Perceptual Set - The influence of prior assumptions and expectations on perceptual interpretations Perceptual Set - The influence of prior assumptions and expectations on perceptual interpretations

19 Perceptual Set What do you see in the center picture: a male saxophonist or a woman’s face? Glancing first at one of the two unambiguous versions of the picture is likely to influence your interpretation. What do you see in the center picture: a male saxophonist or a woman’s face? Glancing first at one of the two unambiguous versions of the picture is likely to influence your interpretation.

20 Feature Analysis Bottom Up Processing & Top Down Processing Bottom Up Processing & Top Down Processing I cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. It dseno’t mataetr in what oerdr the ltteres in a word are, the olny iproamtnt tihng is taht the frsit and lsat ltter be in the rghit pclae.

21 Gestalt Principles (p105) Figure Ground Figure Ground Proximity Proximity Closure Closure Similarity Similarity Simplicity Simplicity Continuity Continuity

22 Phi Phenomenon The illusion of motion when fixed lights are turned on and off in a sequence The illusion of motion when fixed lights are turned on and off in a sequence Stare at the X in the middle and notice what happens. Is the Green Dot Moving? Stare at the X in the middle and notice what happens. Is the Green Dot Moving?

23 Relationship Between Perceived Size and Perceived Depth To perceive the size of objects accurately we must also perceive their distance accurately To perceive the size of objects accurately we must also perceive their distance accurately Many visual illusions occur because of a lack of sufficient depth cues Many visual illusions occur because of a lack of sufficient depth cues This figure shows that image size depends upon both object size and distance Retina Pupil Image A B A

24 Depth Perception Binocular depth cues Binocular depth cues –Retinal disparity- objects 25ft project images to different locations on the right & left retina

25 Monocular Depth Cues Linear Perspective Linear Perspective Motion Parallax Motion Parallax

26 Monocular Depth Cues Texture gradient Texture gradient Interposition Interposition

27 Monocular Depth Cues Relative Size Relative Size Height in a plane Height in a plane

28 Size Constancy People are the same size even though their image sizes differ People are the same size even though their image sizes differ The depth cues such as linear perspective and relative size help judge the size accurately The depth cues such as linear perspective and relative size help judge the size accurately

29 Size Distance Relationship

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32 Shape Constancy The understanding that an object’s shape remains the same even though the angle of view makes the shape appear changed The understanding that an object’s shape remains the same even though the angle of view makes the shape appear changed

33 Shape Constancy It is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward. It is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward. If we add texture, the texture gradient helps us see that it is actually a square If we add texture, the texture gradient helps us see that it is actually a square

34 Brightness Contrast Perceived lightness stays roughly constant as long as the context or surroundings stay the same. Perceived lightness stays roughly constant as long as the context or surroundings stay the same. When the context changes you may perceive the color as changing. When the context changes you may perceive the color as changing. Want to see more of these perceptions? Goto

35 Sensory Deprivation & Restored Vision Early visual experience can have a profound effect on perception. Blakemore & Cooper’s restricted environment with kittens. Early visual experience can have a profound effect on perception. Blakemore & Cooper’s restricted environment with kittens. Do the kittens ever fully regain normal sensitivity to horizontal or vertical lines? NO. Do the kittens ever fully regain normal sensitivity to horizontal or vertical lines? NO. The “Use it or lose it” phenomenon. The “Use it or lose it” phenomenon. From the time their eyes first opened, and until the age of 5 months, these kittens were removed from darkness each day to spend 5 hours alone in a black- and-white striped cylinder with a clear glass floor. A stiff collar prevented the kittens from seeing anything else, even their own bodies. Afterward, these kittens had difficulty perceiving horizontal forms, compared with other kittens exposed only to horizontal forms.

36 Sensory Deprivation & Restored Vision These experiments show that lacking stimulation, the cortical cells had not developed normal connections making them functionally blind to shape. These experiments show that lacking stimulation, the cortical cells had not developed normal connections making them functionally blind to shape. A sensory restriction does no permanent damage if it occurs later in life. This suggests that visual experiences during infancy are a critical period for normal sensory and perceptual development. Experience guides the organization of the brain’s neural connections. A sensory restriction does no permanent damage if it occurs later in life. This suggests that visual experiences during infancy are a critical period for normal sensory and perceptual development. Experience guides the organization of the brain’s neural connections. If deafness or blindness is corrected as an infant, it awakens the pertinent brain area. Nurture sculpts what nature has endowed. If deafness or blindness is corrected as an infant, it awakens the pertinent brain area. Nurture sculpts what nature has endowed.

37 Context The setting or environment in which we interpret sensory stimuli The setting or environment in which we interpret sensory stimuli Culture can also influence how we perceive information. Culture can also influence how we perceive information. –People actively construct their perceptions by drawing on their prior learning and cultural experiences. – People living in urban and industrialized environments where there are more right angles and straight lines will be more susceptible to the Muller-Lyer Illusion than people in non-carpentered natural environments.

38 Context & Culture What is above the woman’s head? In one study, nearly all the East Africans who were questioned said the woman was balancing a metal box or can on her head and that the family was sitting under a tree. Westerners, for whom corners and boxlike architecture are more common, were more likely to perceive the family as being indoors, with the woman sitting under a window. What is above the woman’s head? In one study, nearly all the East Africans who were questioned said the woman was balancing a metal box or can on her head and that the family was sitting under a tree. Westerners, for whom corners and boxlike architecture are more common, were more likely to perceive the family as being indoors, with the woman sitting under a window.

39 Illusions When we misperceive the true characteristics of an object or image. When we misperceive the true characteristics of an object or image. Help researchers understand how sensation and perception normally works Help researchers understand how sensation and perception normally works

40 Müller-Lyer Illusion Perceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away Perceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away Specifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case Specifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case

41 Müller-Lyer Illusion

42 Most people think segment AB equals BC. In reality AB is much longer than BC.

43 Müller-Lyer Illusion

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46 Ponzo Illusion Converging lines indicate that top line is farther away than bottom line Converging lines indicate that top line is farther away than bottom line

47 The interplay between perceived size and distance (a) The monocular cues for distance make the pursuing monster look larger than the pursued. It isn’t. (b) This visual trick, called the Ponzo illusion, is based on the same principle as the fleeing monsters. The two red bars cast identical-sized images on our retinas. But experience tells us that a more distant object can create the same-sized image as a nearer one only if it is actually larger. As a result, we perceive the bar that seems farther away as larger. The interplay between perceived size and distance (a) The monocular cues for distance make the pursuing monster look larger than the pursued. It isn’t. (b) This visual trick, called the Ponzo illusion, is based on the same principle as the fleeing monsters. The two red bars cast identical-sized images on our retinas. But experience tells us that a more distant object can create the same-sized image as a nearer one only if it is actually larger. As a result, we perceive the bar that seems farther away as larger.

48 Moon Illusion Moon appears larger when it is on the horizon than when it is directly overhead. Moon appears larger when it is on the horizon than when it is directly overhead. Objects on the horizon are perceived as farther away than those above us Objects on the horizon are perceived as farther away than those above us The moon appears to be behind those objects on the horizon. Since it is bigger than those object it is perceived as huge! (click on box below for explanation) The moon appears to be behind those objects on the horizon. Since it is bigger than those object it is perceived as huge! (click on box below for explanation) Click Below to View an Explanation: Moon Illusion

49 Ames Room Illusion: Secret Revealed We perceive the room to be as we are used to, a perfect square or rectangular. When in fact it is a trapezoid!

50 Poggendorff Illusion

51 Impossible Figures These grouping principles help us construct reality but perceptual contradictions can lead us astray These grouping principles help us construct reality but perceptual contradictions can lead us astray See how this and others like it are done

52 More Impossible Figures

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54 Escher’s Impossible Scenes

55 Chrysanthemum Is this 3-D?

56 Heads or Houses? Water or Monks?

57 Rocks or Horses? In or out of the picture?

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