Chapter 4!

1. Chapter 4!

2. The Visual System:Essentials of sight

3. The Stimulus: Light • Light- a form of electromagnetic radiation that travels like a wave • Amplitude- the height within the wavelength • Mainly affects perception of brightness • Wavelength- distance between peaks • Affects the perception of color • Purity- how varied the mix is between the two • Influences the perception of the saturation (richness) of colors

4. Saturation • Refers to the whiteness that is in the color • Whiteness declines=saturation increases • Most objects don’t omit light; the reflect it

5. What is light? • Only including wavelengths that people can see • There are so many more, visual spectrum is only a small portion Insects- ultraviolet Fish/reptiles- infrared

6. The eye: A living optical instrument • Two main purposes: • Channel light into neural tissue that receives it (retina) • Houses the retina • Cornea- transparent “window” and the lens behind it form upside down image of objects then image is adjusted • Lens- transparent eye structure that focuses the light rays falling on the retina

7. Accommodation • Lens making adjustments that facilitate is called accommodation • Occurs when curvature of lens adjusts to alter visual focus • Nearsightedness • Close objects are clear; far objects blurry • Farsightedness • Far objects are seen clearly; close objects are blurry

8. pupil • Iris- the colored ring of muscle surrounding the pupil • Pupil- opening in the center of the iris that helps regulate the amount of light that passes through to the rear chamber of the eye

9. The Retina: the brain’s envoy in the eye • Retina- neural tissue lining the inside back surface of the eye- absorbs light- processes images- sends visual information to the brain • optic disk- fibers (axons) diving into a hole behind the retina • Blindspot- the hole that the optic disks creates in the retina

10. Visual receptors • Cones- specialized visual receptors that play a key role in daylight vision and color vision • Visual acuity- sharpness and precise detail • Fovea- tiny spot in the center of the retina that contains only cones- greatest visual acuity • Rods- specialized visual receptors that play a key role in night vision and peripheral vision- more sensitive

11. Dark and light adaptation • Dark adaptation • processes in which the eyes become more sensitive to light in low illumination • 30 minutes • Light adaptation • process in which light becomes less sensitive to light in high illuminations

12. Information processing in the retina • Optic nerve- collection of axons that connect the eye to the brain • Receptive field- retinal area that when it is stimulated affects the firing of that cell

13. Vision and the Brain • Light falls on the eye, but you see with your brain. • The retina does a lot of information processing for a sensory organ, visual input is meaningless until it is processed in the brain.

14. Visual Pathways to the Brain • Optic Chiasm- The point at which the axons from the inside half of each eye cross over then project to the opposite half of the brain. • Visual information gets to the brain by axons leaving the back of each eye form the optic nerves, then traveling to the optic chiasm. This insures that signals from both eyes go to both hemispheres of the brain. • After reaching the optic chiasm. They split into two pathways one leading to the thalamus. This is considered the main pathway where about 90% of axons from the retinas synapse in the lateral Genicualte nucleus (LGN) • Visuals signals are processed in the LGN and then distributed to areas in the occipital lobe making up the primary visual cortex.

15. Info. Processing in the Visual Cortex • Visual input ultimately arrives in the primary visual cortex located in the occipital lobe. • David Hubel and Torsten Wiesel identified three major types of visual cells in the cortex which were called simple cells, complex cells, an hypercomplex cells. • THe key point of all this is that the cells in the viual cortex seem to be highly specialized. They have been characterized as Feature Detectors. • Feature Detectors- Neurons that respond selectively to very specific fetures of more complex stimuli. • After visual input is processed in the primary visual cortex, it is often routed to other cortical areas.

16. Continued.. • After this they travel to one of two streams The ventral stream (what) or dorsal stream (where). • These are known as the what, where streams. • As signals move farther along in the visual processing system, neurons become even more specialized or fussy about what turns them on, and the stimuli that activate them become more and more complex. • “Grandmother cell” was to be humorous but it is the idea that certain cells react to the visual image of certain people.

17. Viewing the World in Color • The lights people see are mixtures of different wavelengths. Perceived color is primarily a function of the dominant wavelength in these mixtures. • Lights with the longest wavelengths appear red, whereas those with shortest appear violet. • Most of the diverse variations are the result of mixing a few basic colors, there are two kinds of color mixtures: subtractive and additive. • Subtractive- color mixing works by removing some wavelengths of light, leaving less light than was originally there. • Additive- color mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself

18. Viewing the World in Color • The lights people see are mixtures of different wavelengths. Perceived color is primarily a function of the dominant wavelength in these mixtures. • Lights with the longest wavelengths appear red, whereas those with shortest appear violet. • Most of the diverse variations are the result of mixing a few basic colors, there are two kinds of color mixtures: subtractive and additive. • Subtractive- color mixing works by removing some wavelengths of light, leaving less light than was originally there. • Additive- color mixing works by superimposing lights, putting more light in the mixture than exists in any one light by itself

19. Trichromatic Theory of Color Vision • the trichromatic theory of color vision was first stated by Thomas Young and later modified by Hermann von Helmholtz. • Trichromatic Theory- holds that the human eye has three types of receptors with differing sensitivities to different light wavelengths. • Helmholtz believed that the eye that had specialized receptors that were sensitive to the wavelengths associated with red, green, or blue. • Color Blindness- encompasses a variety of deficiencies in the ability to distinguish among colors. • Blindness is misleading because it is very rare to find someone to be completely blind of all colors they usually are dichromats meaning they see two of the three.

20. Continued... • Complementary colors- are pairs of colors that produce gray tones when mixed together. • The various pairs of complementary colors can be arranged in a color circle. • Afterimage- a visual image that persists after a stimulus is removed. • the color of the afterimage will be the complement of the color you originally started at. • Opponent process theory- holds that color perception depends on receptors that make antagonistic responses to three pairs of colors. • The antagonistic processes in this theory provide plausible explanations for complementary afterimages and the need for four names to describe colors.(red, blue, green, yellow) Activity one- blindfold

21. The Visual System: Perceptual Processes Exploring perceptual processes in vision

22. Perceiving Forms, Patterns, and Objects How does the brain make sense of forms, objects, depth, etc.? • The brain makes sense of it all through visual perceptions For example. A Reversible figure is made intentionally made to be ambiguous. It is usually a drawing that is compatible with two different interpretations that can shift back and forth.

23. Feature Analysis: Assembling Forms What is Feature Analysis? • It is the process of detecting specific elements in visual input and assembling them into a more complex form For example. • A person starts with the components od a form, such as lines, and then builds them into perceptions of objects, such as squares or triangles. (Form Perception)

24. Form Perception What is Form Perception? • Form Perception refers to our ability to visually perceive objects in the world in response to the patterns of light that they caste on our retinas Feature analysis assumes that form perception involves: • (1)Bottom-Up processing • (2) Top- Down processing

25. (1) Bottom-Up Processing What is Bottom-Up processing? • Bottom-Up processing is a progression of individual elements to the whole. For example. • We attend to or perceive elements by starting with the smaller, more fine details of that element and then building upward until we have a solid representation of it in our minds.

26. (2) Top- Down Processing What is Top- Down processing? • Top-Down processing is a progression from the whole to the elements. For example. • The is evidence that people can perceive a word before its individual letters, a phenomenon that has to reflect top-down processing

27. The Visual System: Perceptual Process

28. Perceptual Constancies in Vision • Is a tendency to experience a stable perception in the face of continually changing sensory input • Your brain is able to keep an object the same far away as up close • We are able to distinguish; size, color, shape, brightness, and location

29. The Power of Misleading Cues: Visual Illusions • visual illusion- involves an apparently inexplicable discrepancy between the appearance of a visual stimulus. • Involves a misinterpretation of perception • Common visual Illusions: Mueller-Lyer Illusion, the Ponzo Illusion, and Monster Illusion

30. Muller-Lyer Illusion • Two Lines appear different lengths • Reality they are same • Misperception of depth and size constancies lead to illusion.

31. Ponzo Illusion/ Monster Illusion • Horizontal lines same length • Seem different because of the vertical lines • Vertical lines slant towards each other • Monster Illusion • Same concept and both same size

32. Impossible Figures • Are objects that can be represented on a two dimensional drawing, but cannot be on a three dimensional drawing • First glance they look fine, but after close examination they don’t add up or actually work • One perception about hypothesis in vision is inconsistent while another would be consiten

33. Common Impossible Figures

34. What Do Illusions Reveal About Visual Perception? • Reveals about formulating hypothesis • Reveal about when hypothesis is wrong • Is completely subjective to what the person sees and only certain things can be objective.

35. The Auditory System: Hearing The ability to hear what is happening around you. Must be processed by the brain.

36. The Auditory System: Hearing • Triggered by any sound producing a sensory input in the form of sound waves. • Sound waves are the stimuli starting the hearing experience.

37. The Stimulus: Sound • Vibrating molecules produce sound. (Sound waves) • Sound is Characterized by the following: • Amplitude • Wave Length • Sound Purity

38. The Stimulus: Sound • Amplitude: the amount of energy in a sound wave. • Wave Length: the distance from one sound wave to the next. Measured from Crest to Crest • Sound Purity: measured in “Pitch”. It is also know as the tone of the sound.

39. Amplitude Graphs

40. Wave Length Graph

41. Human Hearing Capacities • Wavelengths of sound are described in terms of their frequency. • Frequency • is measured in cycles per second (Hertz) • Higher Frequency results in higher pitch • Lower Frequency results in lower pitch

42. Human Limits • Humans can hear sounds as low as 20 Hz and as high as 20,000 Hz. • The Human ear is most sensitive around 2000 Hz. • Humans are more sensitive to a single frequency rather than a complex mixture of many separate frequencies.

43. Frequency(Hertz) • Amplitude (Decibels)

44. Sensory Processing in the Ear • The ear is divided into three different sections that function by using different moving parts. • The External Ear-Vibration of air molecules • The Middle Ear-Vibration of movable bones • The Inner Ear- Waves in fluid

45. The external ear consists of the Pinna. The Pinna is basically a cone that collects the sounds. • Sound waves are picked up by the Pinna and funneled through the auditory canal into the eardrum which is a vibrating membrane. http://www.google.com/search?q=external+ear+pinna+and+ear+drum&hl=en&sa=X&tbm=isch&tbo=u&source=univ&ei=KDJPUbDrGsyLqQGt14H4Cw&ved=0CDsQsAQ&biw=1350&bih=679#imgrc=E3Ic_XBo-M-GKM%3A%3BIgia4g-zAQG3WM%3Bhttp%253A%252F%252Fwww.cochlea.org%252Fspe%252Fen%252Foreille-cochlee%252Fimages%252Fe_oreille_ext.gif%3Bhttp%253A%252F%252Fwww.cochlea.org%252Fen%252Fspe%252Fexternal-ear.html%3B380%3B362

46. Within the middle ear the vibrations of the eardrum are transmitted to vibrate 3 tiny bones in the ear (hammer, anvil and stirrup) together these bones are referred to as the Ossicles. • The Ossicles pick up small changes in air pressure.

47. The inner ear consists mainly of the Cochlea. The Cochlea is a fluid filled, coiled tunnel that contains receptors for hearing. The Cochlea is vibrated by the Ossicles and the signals are routed through the thalamus and auditory cortex.

48. Auditory Perception Theories of Hearing • There are TWO main theories of hearing and these are the Place Theory and Frequency Theory

49. Place Theory • Herman Von Helmholtz theorized that a specific sound frequency would vibrate in it’s own specific manor. This in turn would cause the basilar membrane to only vibrate in specific patterns. • This would be similar to plucking a specific guitar string makes a specific pitch.

50. In place theory it is said that perception of pitch corresponds to the vibration of different portions or places along the basilar membrane. • It is assumed in this theory that hair cells at various locations vibrate independently by different frequencies. Then that the brain detects the different frequency according to which area is most active.