Vision. Definition. Sensing of objects by the light reflected off the objects into our eyes

Transcription

1 Vision

2 Vision Definition Sensing of objects by the light reflected off the objects into our eyes Only occurs when there is the interaction of the eyes and the brain (Perception)

3 What is light? Visible light Vision What triggers visual sensations Small part of the electromagnetic energy (described in terms of wavelength)

4 Vision Wavelength of visible light Determines the color, or hue Roy G. Biv Longest to shortest wavelength (how high or low the waves, determines the brightness)

5 The Visual System Process Eyes: Sense light reflected from objects, send info to the brain, visual perception takes place

6 Eyes Made up of the: Cornea (bends light rays so image can be focused on the retina-transparent covering)

7 Made up of the: Eyes Iris (More unique than fingertips) Muscles control the amount of light let in

8 Eyes Made up of the: Pupil (Dark opening) Changes depending on how much light needs to be let in

9 Made up of the: Lens (Flattens and bulges to look at an object..bulges to look at something close) Process is called visual accommodation Eyes

10 Made up of the: Eyes Retina (image appears upside down on it) Consists of cells called photoreceptors (sensitive to light)

11 Eyes Photoreceptors: Rods (120 million) Sensitive only to the intensity of light Allow us to see in black and white, and shades of grey Cones (6.5 million) Provide color vision

12 Eyes (Rods and Cones) Light Adaptation (cones) The process of adjusting to conditions of brighter lighting after being in darkness Example: Turning the lights on in the morning Dark Adaptation (rods and cones) The process of adjusting to conditions of lower lighting after being in brightness Example: Movie Theater

13 Eyes Light travels through several layers of neurons/cells in the retina: Rods Cones Bipolar cells Ganglion cells

14 Eyes Optic Nerve Made up of the axons of the Ganglion Cells Transmits sensory information from the eye to the brain

15 Fovea Eyes Most sensitive area of the retina (contains the cones, most sensitive area) Blind Spot Insensitive to visual stimulation Page: 98 activity

16 Eyes Size of pupil is affected by many factors: Lights Psychological factors Exerting mental effort Level of interest Car Salesman Arousal Scared Telling a lie

17 Pupil Size Used by psychologists to monitor effectiveness of therapy Example: Snake Phobia- as anxiety decreases, pupils dilate less when subjects are shown a snake

18 Eye Defects Presbyopia Old Eyes Eyes lose ability to flatten and bulge and actually swell and bloat Myopia Nearsightedness Hyperopia Farsightedness

19 Eye Movements Smooth Pursuit Movements Track objects Interesting Fact: Can t track a baseball all the way until it hits the bat- your eyes stop following it at 5 feet

20 Saccadic Movements Continuous small darting movements of the eyes that bring new portions of scenes into focus After movement, eyes fixate on target for about a quarter of a second Only pick up information during fixations 1,000 words a minute Eye Movements

21 Theories of Color Vision Opponent Process Theory (4 types of cones) Red-Green Blue-Yellow Black-White Explains Afterimages (lingering visual impression) If one cone color is stimulated the other cannot be working

22

23 Theories of Color Vision Color Vision Trichromatic Theory We receive 3 types of light because we have 3 types of cones (redyellow, green- yellow, and blue-violet) Ratio of each color to the other determines the exact color we see When all overlap we get white light

24 Theories of Color Vision Colorblindness Caused by defective cones in the retina Dichromates- people who are colorblind Monochromats- sensitive to only lightness and darkness (see no color, usually only shades of grey) Males are more likely than females to be colorblind (x and y chromosome) T or F all dogs are colorblind 1 out of 100,000 people are colorblind

25 Perceptual Constancies Size Constancy The ability to perceive the same object as being the same size even though the size of its image on your retina varies as a function of its distance Example: People (a six foot man doesn t get smaller he is just further away)

26 Perceptual Constancies Color Constancy The ability to perceive objects as retaining their color even though lighting conditions may alter their appearance Example: The color of your car at night and during the day

27 Perceptual Constancies Brightness Constancy The ability to perceive an object as being just as bright even though lighting conditions change its intensity

28 Perceptual Constancies Shape Constancy The ability to perceive an object as being the same shape although the retinal image varies in shape as it rotates

29 Gestalt Principles of Visual Form Perception Perception Figure-ground perception In order to perceive forms, meaningful shapes or patterns, we must distinguish a figure, an object from it s ground/it s surroundings

30 Figure Ground Perception Example: Words on this page are figures against the ground of the white paper Picture of a friend Figure- friend Background- building/sky

31 Visual Perception Proximity Stimuli that are close together are perceived as parts of the same form (they belong together) Nearness= Belongingness

32 Visual Perception Closure We fill in the gaps in the forms that we perceive

33 Similarity Visual Perception Stimuli that are similar to one another are perceived as parts of the same form (they go together) Example: teams wearing the same color uniform

34 Visual Perception Continuity Group stimuli into forms that follow continuous lines or patterns

35 Visual perception Contiguity The tendency to perceive two things that happen close together in time as being related Ventriloquist

36 Depth Perception Ability to judge the distance of others and objects Ability to see things 3-dimentionally How is this possible???

37 Depth Perception Binocular Cues Interaction of both eyes (helps us perceive depth) Two kinds Retinal disparity The degree of difference between the images of an object that are focused on the two retinas. The closer the object, greater the retinal disparity

38 Depth Perception Convergence Eyes turn inward to focus on nearby objects

39 Depth Perception Monocular Cues Requires only one eye to see depth Many kinds Linear Perspective Relative Size Texture Gradient Motion Parallax Overlap Aerial Perspective Accomodation

40 Visual (Perceptual) Illusions Definition: A misperception of physical reality usually caused by the misapplication of visual cues People think they see something when the reality is quite different X-ray example (paper in hand)

41 Visual Illusions Moon Illusion Appears larger when at the horizon than when it is overhead However, it is at the same distance Apparent distance hypothesis

42 Muller-Lyer Illusion

43 Visual Illusions Reversible Figures Ambiguous Sensory information that creates more than one form Example: 2 faces looking toward each other that is also a vase

44 Visual Illusions Impossible figures Objects that can be represented in 2- dimesonal pictures but can not exist in 3- dimensional space despite our perceptions Example: Artist-Escher: Hands drawing each other; waterfall that goes down and stays level at the same time

45 Illusions of Motion The Autokinetic Effect The tendency to perceive a stationary point of light in a dark room as moving Individuals even think that the light may spell words

46 Illusions of Motion Stroboscopic Motion The perception of motion is generated by a series of stationary images that are presented in rapid succession Movies We see 16 to 22 frames per second

47 Illusions of Motion Phi Phenomenon The perception of movement as a result of sequential presentation of visual stimuli Example: Scoreboards that show fireworks when the team scores

48 Factors that Influence Perception Perceptual Set or Perceptual Expectancy When people often misunderstand what is said to them because they ere expecting to hear something else People have a tendency to perceive things a certain way because their previous experiences or expectations influence them p. 125 Examples: Top-Down and Bottom-Up Processing

49 Factors that Influence Perception Top-Down Processing The use of pre-existing knowledge and patterns to organize the parts of the pattern, or individual features, into a unified whole What is the big picture? Man vs. Mouse

50 Factors that Influence Perception Bottom-Up Processing The analysis of the smaller features to build up to the complete picture