# Visual Cliff: A Test of Depth Perception

Visual Cliff: A Test of Depth Perception Babies seem to develop this ability at crawling age. Even newborn animals fear the perceived cliff. 1 Perceiving Depth From a 2D Image: Binocular Methods Binocular (using both eyes) cues exist because humans have two eyes in the front of our head. This gives us retinal disparity; the two

eyes have slightly different views, and the more different the views are, the closer the object must be. In an extreme example, your nose is so close that each eye sees a completely opposite half-view of it. How do we perceive depth from a 2D image?... by using monocular (needing only one eye) cues 2 Binocular Cues Retinal disparity: Images from the two eyes differ.

Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a finger sausage as shown in the inset. 3 Binocular Cues Convergence: Neuromuscular cues. When two eyes move inward (towards the nose) to see near objects and outward (away from the nose) to see faraway objects.

4 Monocular Cue: Interposition Interposition: When one object appears to block the view of another, we assume that the blocking object is in a position between our eyes and the blocked object. 5 Monocular Cue:

Relative Size We intuitively know to interpret familiar objects (of known size) as farther away when they appear smaller. 6 Monocular Cues: Linear Perspective and Interposition The flowers in the distance seem farther away because the rows

converge. Our brain reads this as a sign of distance. 7 Tricks Using Linear Perspective These two red lines meet the retina as being the same size

However, our perception of distance affects our perception of length. 8 Monocular Cues: Shading Effects Shading helps our perception of depth. Does the middle circle bulge out or

curve inward? How about now? 9 Monocular Cues Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower. 10 Monocular Cues: Relative Motion When we are moving,

we can tell which objects are farther away because it takes longer to pass them. A picture of a moon on a sign would zip behind us, but the actual moon is too far for us to pass. 11 Motion Perception Motion Perception: Objects traveling towards us grow in size and those

moving away shrink in size. The same is true when the observer moves to or from an object. 12 Apparent Motion Phi Phenomenon: When lights flash at a certain speed they tend to present illusions of motion. Neon signs use this principle to create motion perception. Two lights flashing

one the other. One light jumping from one point to after another: Illusion of motion. 13 Perceptual Constancy Our ability to see objects as appearing the same even under different lighting conditions, at different distances and angles, is called

perceptual constancy. Perceptual constancy is a top-down process. Examples: color and brightness constancy shape and size constancy 14 Color Constancy This ability to see a consistent color in changing illumination helps us see the three sides as all being yellow, because our brain compensates for shading. As a result, we interpret three

same-color blue dots, with shades that are not adjusted for shading, as being of three different colors. 15 Brightness Constancy On this screen, squares A and B are exactly the same shade of gray. You can see this when you connect them. So why does B look lighter? 16

Shape Constancy Shape constancy refers to the ability to perceive objects as having a constant shape despite receiving different sensory images. This helps us see the door as a rectangle as it opens. Because of this, we may think the red shapes on screen are also rectangles. 17 The Moon Illusion The moon appears larger on the

horizon than overhead. Why do we perceive the moon as a different size depending on its location? One possible theory is that our ancestors assumed overhead objects were closer than objects on the horizon. The moon, like one of these monsters, seems larger because we see it as farther away. 18

Size Constancy We have an ability to use distance-related context cues to help us see objects as the same size even if the image on the retina becomes smaller. The Ames room was invented by American ophthalmologist Adelbert Ames, Jr. in 1934. The Ames room was designed to manipulate distance cues to make two same-sized girls appear very different in size. 19

Sensory Deprivation Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars. Blakemore & Cooper (1970) 20 Schemas Schemas are concepts that organize and interpret unfamiliar information.

Children's schemas represent reality as well as their abilities to represent what they see. 21 Perception & Human Factors Human Factor Psychologists design machines that assist our natural perceptions. Courtesy of General Electric Photodisc/ Punchstock

The knobs for the stove burners on the right are easier to understand than those on the left. 22 Human Factors & Misperceptions Understanding human factors enables us to design equipment to prevent disasters. Two-thirds of airline crashes caused by human error are largely due to errors of perception. 23

Human Factors in Space To combat conditions of monotony, stress, and weightlessness when traveling to Mars, NASA engages Human Factor Psychologists. Transit Habituation (Transhab), NASA24

Hearing/Audition: Starting with Sound Length of the sound wave; perceived as high and low sounds (pitch) Height or intensity of sound wave; perceived as loud and soft (volume) Perceived as

sound quality or resonance 25 The Ear 26 Cochlea Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals. 27

Sound Waves Reach The Ear The outer ear collects sound and funnels it to the eardrum. In the middle ear, the sound waves hit the eardrum and move the hammer, anvil, and stirrup in ways that amplify the vibrations. The stirrup then sends these vibrations to the oval window of the cochlea. In the inner ear,

waves of fluid move from the oval window over the cochleas hair receptor cells. These cells send signals through the auditory nerves to the temporal lobe of the brain. 28 Preventing

Hearing Loss Exposure to sounds that are too loud to talk over can cause damage to the inner ear, especially the hair cells. Structures of the middle and inner ear can also be damaged by disease. Prevention methods include limiting exposure to noises

over 85 decibels and treating ear infections. 29 Sound Perception: Loudness Loudness refers to more intense sound vibrations. This causes a greater number of hair cells to send signals to the brain. Soft sounds only activate certain hair

cells; louder sounds move those hair cells AND their neighbors. 30 Theories of Audition Place Theory suggests that sound frequencies stimulate the basilar membrane at specific places resulting in perceived pitch. http://www.pc.rhul.ac.uk 31

Theories of Audition Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. Sound Frequency Auditory Nerve Action Potentials 100 Hz 200

32 Sound Perception: Pitch How does the inner ear turn sound frequency into neural frequency? Place theory At high sound frequencies, signals are generated at different locations in the cochlea, depending on pitch. The brain reads pitch by reading the location where the

signals are coming from. Frequency theory At low sound frequencies, hair cells send signals at whatever rate the sound is received. Volley Principle At ultra high frequencies, receptor cells fire in succession, combining signals to reach higher firing rates. 33 Localization of Sound

1. Intensity differences 2. Time differences Time differences as small as 1/100,000 of a second can cause us to localize sound. The head acts as a shadow or partial sound barrier. 34 Hearing Loss Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea. Sensorineural Hearing Loss: Hearing loss

caused by damage to the cochleas receptor cells or to the auditory nerve, also called nerve deafness. 35 Taste Our tongues have receptors for five different types of tastes, each of which may have had survival functions. Sweet: energy source

Sour: potentially toxic acid Umami: (savoriness) proteins to grow and repair tissue Bitter: potential poisons

Salty: sodium essential to physiological processes 36 Neurochemistry of Taste There are no regions of the tongue, just different types of taste receptor cells projecting hairs into each taste buds pore. These cells are easily triggered to

send messages to the temporal lobe of the brain. Burn your tongue? Receptors reproduce every week or two. But with age, taste buds become less numerous and less sensitive. Top-down processes still can override the neurochemistry; expectations do influence taste. 37 Smell Like taste, smell is a chemical sense. Odorants enter the nasal cavity to stimulate

5 million receptors to sense smell. Unlike taste, there are many different forms of smell. 38 Age, Gender, and Smell Ability to identify smell peaks during early adulthood, but steadily declines after that. Women are better at detecting odors than men. 39

Smell and Memories The brain region for smell (in red) is closely connected with the brain regions involved with memory (limbic system). That is why strong memories are made through the sense of smell. 40 Mixing the different senses together

Sensory interaction occurs when different senses influence each other. For example: a burst of sound makes a dim light source more visible. flavor is an experience not only of taste, but also of smell and texture. seeing text or lip movement, or even feeling the puff of air from consonants, affects what

words we hear. 456789 Synaesthesia is a condition when perception in one sense is triggered by a sensation in a DIFFERENT sense. Some people experience synaesthesia all the time, reporting that, the number 7 gives me a salty taste or rock music seems purple. 41

Touch The sense of touch is a mix of four distinct skin sensespressure, warmth, cold, and pain. 42 Skin Senses Only pressure has identifiable receptors. All other skin sensations are variations of pressure, warmth, cold and pain. Pressure

Burning hot Vibration Vibration Cold, warmth and pain 43 Pain Pain tells the body that something has gone wrong. Usually pain results from damage to

the skin and other tissues. A rare disease exists in which the afflicted person feels no pain. AP Photo/ Stephen Morton Ashley Blocker (right) feels neither pain nor extreme hot or cold. 44 Biopsychosocial Influences 45

Gate-Control Theory Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological gates that either block pain or allow it to be sensed. Gary Comer/ PhototakeUSA.com 46 Pain Control Pain can be controlled by a number of therapies including, drugs, surgery,

acupuncture, exercise, hypnosis, and even thought distraction. Todd Richards and Aric Vills, U.W. Hunter Hoffman, www.vrpain.com 47 Sensing Body Position and Movement Kinesthesis (movement feeling) refers to sensing the movement and position of individual body parts relative to each other.

How it works: sensors in the joints and muscles send signals that coordinate with signals from the skin, eyes, and ears Without kinesthesis, we would need to watch our limbs constantly to coordinate movement. 48 Sensing Body Position and Movement Vestibular sense refers to the ability to sense the position of the head and

body relative to gravity, including the sense of balance. How it works: fluid-filled chambers in the inner ear (vestibular sacs and semicircular canals) have hairlike receptors that send messages about the heads position to the cerebellum Vestibular sense serves as the human gyroscope, helping us to balance and stay upright. 49

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