Psychology 2e Chapter 3 Sensation and Perception.

Psychology 2e Chapter 3 Sensation and Perception

Module 7 Sensation

Learning Objectives 7.1 Discuss the differences between sensation and perception. 7.2 Explain the process of sensation. 7.3 Discuss the concepts of threshold and adaptation. 7.4 Identify physical energy forms for which humans and nonhumans have sensory receptors. 7.5 Explain how the visual sensory system works. 7.6 Explain how the auditory sensory system works. 7.7 Outline other sensory systems, such as olfaction, gustation, and somesthesis.

Sensation and Perception
Learning Objective 7.1: Discuss the differences between sensation and perception. Sensation: Sensory processes taking in information as raw data or meaningless pieces of information about the external world. Perception: The process of bringing meaning to sensations, by way of collecting, organizing, interpreting raw data.

The Process of Sensation
Learning Objective 7.2: Explain the process of sensation. Sensation: the activation of special neuron receptor sites in the sense organs, triggering conversion of various forms of outside stimuli into neural signals in the brain Transduction: the process of converting outside stimuli, such as light, into neural activity Sensory receptors: specialized forms of neurons stimulated by different kinds of energy such as light, vibrations, and pressure

Sensory Thresholds (1 of 2)
Learning Objective 7.3: Discuss the concepts of threshold and adaptation. Sensory thresholds: The point at which sensations begin and end Weber's law of just noticeable differences (jnd or the difference threshold) The smallest difference between two stimuli (detectable 50% of the time) is always constant. Absolute threshold: the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present

Sensory Thresholds (2 of 2)
Learning Objective 7.3: Discuss the concepts of threshold and adaptation. Subliminal stimuli: stimuli that are below the level of conscious awareness Just strong enough to activate the sensory receptors, but not strong enough for people to be consciously aware of them Subliminal perception: the process by which subliminal stimuli act upon the unconscious mind, influencing the behavior

Table 7.1: Examples of Absolute Thresholds

Signal Detection Theory
Learning Objective 7.3: Discuss the concepts of threshold and adaptation. Signal Detection Theory: Factors expectation and motivation into our sensory processes States motivation, biases, and expectations influence our detection of a stimulus Reactions to a stimulus can be categorized as: hit, miss, false alarm, correct rejection

Figure 7.1: Signal Detection Theory
The presence or absence of a signal is followed by a response or non-response depending on our ability to detect it Expectation influences the detection of a stimulus Factors other than volume of a sound, or brightness of a light influence the ability to detect stimuli

Habituation and Sensory Adaptation (1 of 2)
Learning Objective 7.3: Discuss the concepts of threshold and adaptation. Habituation: Lower centers of the brain filtering sensory stimulation ignore or prevent conscious attention to stimuli that do not change; sensory receptors respond to stimulation but no signal is sent to the cortex Sensory adaptation: the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging

Habituation and Sensory Adaptation (2 of 2)
Learning Objective 7.3: Discuss the concepts of threshold and adaptation. Microsaccades: constant movement of the eyes; tiny little vibrations that people do not notice consciously Prevent sensory adaptation to visual stimuli

Capabilities, Limitations of Sensory Processes
Learning Objective 7.4: Identify physical energy forms for which humans and nonhumans have sensory receptors. Sensation occurs when: special receptor sites on neurons in the sense organs are activated various forms of outside stimuli are transduced into neural signals in the brain Eye receptors are triggered by electromagnetic energy in the form of visible light Ear receptors are triggered by molecules of vibrating air Touch receptors are triggered by pressure or temperature

Figure 7.2 Some Forms of Energy We Can Sense

The Science of Seeing Learning Objective 7.5: Explain how the visual sensory system works. Light has the properties of both waves and particles Photons: Tiny packets of waves with specific wavelengths Aspects of our brain’s perception of light: Brightness Color Saturation

Light and the Eye (1 of 2) Learning Objective 7.5: Explain how the visual sensory system works. Brightness is determined by the amplitude of the wave – how high or low the wave actually is. higher the wave, brighter the light lower the wave, dimmer the light Visible spectrum is the portion of the whole spectrum of light that is visible to the human eye.

Light and the Eye (2 of 2) Learning Objective 7.5: Explain how the visual sensory system works. Color, or hue, is determined by the length of the wave Long wavelengths are found at the red end of the visible spectrum. Shorter wavelengths are found at the blue end of the visible spectrum. Saturation: the purity of the color people perceive Highly saturated red contains only red wavelengths; less saturated red contains a mixture of wavelengths. Mixing in black or gray lessens the saturation.

Optical Illusion A single point of light from a source travels through the structure of the eye and ends up on the retina as a single point. Refraction: the tendency of the light to bend as it passes through. substances of different densities Optical illusion is caused due to refraction of light. While looking sideways at a drinking straw in a glass of water, it appears that the straw bends, or is broken, at the surface of the water.

Figure 7.3: Structure of the Eye
Light enters the eye through the cornea and pupil. The iris controls the size of the pupil. From the pupil, light passes through the lens to the retina. The light is transformed into nerve impulses in the retina. The nerve impulses travel to the brain along the optic nerve.

Structure of the Eye (1 of 10)
Learning Objective 7.5: Explain how the visual sensory system works. Cornea: is a clear, protective membrane that covers the surface of the eye focuses most of the light coming into the eye has a fixed curvature Vision-improving techniques that can change the curvature (of the cornea) and the focus in the eye: photoreactive keratectomy (PRK) laser-assisted in situ keratomileusis (LASIK)

Learning Objective 7.5: Explain how the visual sensory system works. Aqueous humor: a watery fluid that continually replenishes and supplies nourishment to the eye Pupil: the hole through which the light from the visual image enters the interior of the eye

Learning Objective 7.5: Explain how the visual sensory system works. Iris: round muscle (the colored part of the eye) in which the pupil is located Can change the size of the pupil, letting more or less light into the eye Helps focus the image Lens: another clear structure behind the iris, suspended by muscles Finishes the focusing process begun by the cornea

Learning Objective 7.5: Explain how the visual sensory system works. Visual accommodation: the change in the thickness of the lens as the eye focuses on objects that are far away or close Presbyopia: a disorder in which people lose their ability for visual accommodation and therefore, their ability to focus as the lens hardens through aging

Learning Objective 7.5: Explain how the visual sensory system works. Aqueous humor: is a clear, jelly-like fluid that fills the open space beyond lens nourishes the eye, gives it shape helps keep the tissue-paper thin layers of the retina pressed firmly against the back wall of the eye

Learning Objective 7.5: Explain how the visual sensory system works. Retina: is the final stop for light within the eye is a light sensitive area at the back of the eye absorbs and processes light information has three layers: ganglion cells bipolar cells, and the photoreceptor neurons commonly called the rods and cones

Learning Objective 7.5: Explain how the visual sensory system works. Rods and Cones: are responsible for different aspects of vision are special receptor cells (photoreceptors) that respond to the various wavelengths of light receive the photons of light and transduces them into neural signals for the brain send neural signals first to the bipolar cells, and then to the retinal ganglion cells

Learning Objective 7.5: Explain how the visual sensory system works. Rods: responsible for peripheral vision, or noncolor sensitivity to low levels of light found all over the retina except fovea concentrated in the periphery sensitive to changes in brightness see in black and white and shades of gray

Learning Objective 7.5: Explain how the visual sensory system works. Cones: responsible for color vision and sharpness of vision concentrated at the fovea may have a private line to the optic nerve are the receptors with the greatest visual acuity require a lot more light to function than rods do work best in bright light sensitive to different wavelengths of light

Learning Objective 7.5: Explain how the visual sensory system works Blind spot: area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve; insensitive to light

Figure 7.4: Nearsightedness and Farsightedness
Nearsightedness, or myopia: The shape of the eye causes the focal point to fall short of the retina. Farsightedness, or hyperopia: The focus point is behind the retina.

Figure 7.5 The Blind Spot Demonstration
Hold the image in front of you. Close your right eye and stare at the picture of the dog with your left eye. Slowly bring the image closer to your face. The picture of the cat will disappear at some point because the light from the picture of the cat is falling on your blind spot. If you cannot seem to find your blind spot, try moving the image more slowly.

How the Eye Works Learning Objective 7.5: Explain how the visual sensory system works. Dark adaptation: the recovery of the eye’s sensitivity to visual stimuli in darkness after exposure to bright lights Light adaptation: the recovery of the eye’s sensitivity to visual stimuli in light after exposure to darkness

Perception of Color (1 of 2)
Learning Objective 7.5: Explain how the visual sensory system works. Trichromatic theory: theory of color vision that proposes three types of cones: red, blue, and green different shades of colors correspond to different amounts of light received by the three types of cones the combination of cones and the rate at which they fire their message to the brain’s vision centers determine the color that will be seen

Perception of Color (2 of 2)
Learning Objective 7.5: Explain how the visual sensory system works. Opponent-process theory: theory of color vision that proposes visual neurons are stimulated by light of one color and inhibited by light of another color. Afterimages: images that occur when a visual sensation persists for a brief time even after the original stimulus is removed Lateral geniculate nucleus (L G N) of thalamus

Figure 7.6 Color Afterimage
Stare at the white dot in the center of this oddly colored flag for about 30 seconds. Now look at a white piece of paper or a white wall. Notice that the colors are now the normal, expected colors of the American flag. They are also the primary colors that are opposites of the colors in the picture and provide evidence for the opponent-process theory of color vision.

Color Blindness Learning Objective 7.5: Explain how the visual sensory system works. Color blindness: also termed as color-deficient vision or dichromatic vision caused by defective cones in the retina of the eye caused by having one cone that does not work properly

Figure 7.7 The Ishihara Color Test
In the circle on the left, the number 8 is visible only to those with normal color vision. In the circle on the right, people with normal vision will see the number 96, while those with red-green color blindness will see nothing but a circle of dots.

Sound Waves and the Ear (1 of 2)
Learning Objective 7.6: Explain how the auditory sensory system works. Sound waves: vibrations of the molecules of air expanding, contracting, and traveling in waves Properties of sound waves: Wavelength: interpreted as frequency or pitch (high, medium, or low) Amplitude: interpreted as volume (how soft or loud a sound is) Purity: interpreted as timbre (a richness in the tone of the sound)

Sound Waves and the Ear (2 of 2)
Learning Objective 7.6: Explain how the auditory sensory system works. Hertz (H z): cycles or waves per second; a measurement of frequency

Figure 7.8 : Sound Waves and Decibels
The higher the wave, the louder the sound; the lower the wave, the softer the sound. If the waves are close together in time (high frequency), the pitch will be perceived as a high pitch. Waves that are farther apart (low frequency) will be perceived as having a lower pitch. A decibel is a unit of measure for loudness. Decibels of various stimuli. A decibel is a unit of measure for loudness. Two sound waves. The higher the wave, the louder the sound; the lower the wave, the softer the sound. If the waves are close together in time (high frequency), the pitch will be perceived as a high pitch. Waves that are farther apart (low frequency) will be perceived as having a lower pitch.

Structure of the Ear (1 of 4)
Learning Objective 7.6: Explain how the auditory sensory system works. Pinna, or the outer ear: visible part of the ear; funnels the sound waves from outside into structure of the ear; also an entrance to the auditory canal Auditory canal: short tunnel that runs from the pinna to the eardrum (tympanic membrane)

Learning Objective 7.6: Explain how the auditory sensory system works. Eardrum: thin section of skin that tightly covers the opening into the middle part of the ear When sound waves hit the eardrum, it vibrates and causes three tiny bones in the middle ear to vibrate. hammer anvil stirrup

Learning Objective 7.6: Explain how the visual sensory system works. Cochlea: snail-shaped structure of the inner ear that is filled with fluid Basilar membrane: a membrane running through the middle of the cochlea Organ of Corti: rests in the basilar membrane Contains receptor cells for sense of hearing Auditory nerve: bundle of axons from the hair cells in the inner ear Receives neural message from the organ of Corti

Learning Objective 7.6: Explain how the auditory sensory system works. Sound waves enter through the ear canal causing the eardrum to vibrate. The eardrum causes each of the three bones of the middle ear to vibrate, amplifying the sound. The stirrup, the last of the three middle ear bones, transmits its vibration to the fluid in the inner ear. The inner ear vibrates as the oval window vibrates. Basilar membrane contains the hair-like cells that send signals via the auditory nerve to the thalamus. Thalamus relays information to the auditory cortex.

Figure 7.9: The Structure of the Ear

Perceiving Pitch (1 of 2) Pitch: how high or low a sound is
Learning Objective 7.6: Explain how the auditory sensory system works. Pitch: how high or low a sound is Primary theories on how the brain receives information about pitch Place Theory Frequency Theory Volley Principle

Perceiving Pitch (2 of 2) Learning Objective 7.6: Explain how the auditory sensory system works. Place theory: different pitches are experienced by the stimulation of hair cells in different locations on the organ of Corti Frequency theory: pitch is related to the speed of vibrations in the basilar membrane Volley principle: groups of auditory neurons take turns firing in a process called volleying; accounts for pitches from about 400 Hz up to about 4000 Hz

Types of Hearing Impairments (1 of 2)
Learning Objective 7.6: Explain how the auditory sensory system works. Conduction hearing impairment, or conductive hearing loss can result from: Damaged eardrum: prevents sound waves from being carried into the middle ear properly Damage to the bones of the middle ear: sounds cannot be conducted from the eardrum to the cochlea

Types of Hearing Impairments (2 of 2)
Learning Objective 7.6: Explain how the auditory sensory system works. Nerve hearing impairment, or sensorineural hearing loss can result from: Damage in the inner ear Damage in the auditory pathways and cortical areas of the brain Tinnitus: ringing in one’s ears caused by infections or loud noises

Treating Nerve Hearing Impairment
Learning Objective 7.6: Explain how the auditory sensory system works. Cochlear implant: a microphone implanted just behind the ear that picks up sound from the surrounding environment A speech processor selects and arranges the sounds picked up by the microphone. The implant is a transmitter and a receiver, converting signals into electrical impulses. Collected by the electrode array in the cochlea and then sent to the brain

Figure 7.10 Cochlear Implant
In a cochlear implant, a microphone picks up sound from the surrounding environment. A speech processor selects and arranges the sound picked up by the microphone. The implant itself is a transmitter and receiver, converting the signals from the speech processor into electrical impulses that are collected by the electrode array in the cochlea and then sent to the brain.

Gustation: How We Taste the World (1 of 2)
Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Sense of taste is a combination of taste and smell Taste buds: clusters of taste receptor cells located on the tongue, the roof of the mouth, the cheeks, under the tongue, and in the throat Gustation The sensation of taste

Gustation: How We Taste the World (2 of 2)
Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Five Basic Tastes Sweet Sour Salty Bitter “Brothy,” or umami

Different sizes of Papillae on the surface of the tongue
Taste buds line the walls of papillae Each taste bud has about 20 receptors Taste is a chemical sense that works with the molecules of foods When molecules fit into the receptors, a signal is fired to the brain In turn, the brain interprets the taste sensation

The Sense of Scents: Olfaction (1 of 2)
Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Olfaction/Olfactory Sense: the ability to smell odors the part of the olfactory system that turns odors into signals is at the top of the nasal passages Olfactory Receptor Cells: nerve fibers inside the nasal cavity that carry information about smell directly to the olfactory bulb Cilia tiny hairlike cells are the receptors for the sense of smell

The Sense of Scents: Olfaction (2 of 2)
Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Olfactory bulbs the special place for the sense of smell in the brain located right on top of the sinus cavity on each side of the brain directly beneath the frontal lobes Epithelium a membrane within the nasal cavities, contains the olfactory receptor neurons sensitive to the chemical signals of smell

Figure 7.11: The Olfactory Receptors
Olfactory receptors send neural signals to olfactory bulbs. Olfactory bulbs send olfactory information to higher cortical areas.

Figure 7.12: Cross Section of the Skin and its Receptors
The skin is composed of several types of cells that process pain, pressure, and temperature.

Somesthetic Senses (1 of 9)
Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Somesthetic senses: the body senses consisting of (i) skin senses, (ii) the kinesthetic sense, and (iii) the vestibular senses “Soma”: body “Esthetic”: feeling

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Skin Senses Skin receptors receive information about touch, pressure, temperature, pain; transmit it to nervous system Some sensory receptors respond to only one kind of sensation Pacinian corpuscles respond to changes in pressure Nerve endings that wrap around the ends of the hair follicles respond to pain and touch Free nerve endings beneath the uppermost layer of the skin respond to temperature, pressure, and pain

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Pain acts as a warning system Pain Disorders Inability to feel pain congenital analgesia congenital insensitivity to pain with anhidrosis Phantom limb pain: when a person who has had an arm or leg removed “feels” pain in the missing limb

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Gate-control theory: pain signals must pass through a “gate” located in the spinal cord Gate represents the relative balance in neural activity of cells in the spinal cord receiving information from the body and sending it to the brain

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. How pain signals travel along spinal cord: Substance P is a neuromodulator released by the stimulation of the pain receptor cells that activate other neurons. Neurons send messages through spinal gates. From the spinal cord, the message goes to the brain, activating cells in the thalamus, somatosensory cortex, areas of the frontal lobes, and the limbic system. The brain interprets the pain information.

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Kinesthetic sense kinein means “to move” aesthesis means “sensation” Sense of the location of body parts in relation to the ground and each other Special receptors are located in the muscles, tendons, and joints Proprioceptive receptors (proprioceptors) cause joint movement or muscles stretching/contracting

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Vestibular senses: the sensations of movement, balance, and body position structures for this sense are located in the innermost chamber of the ear Kinds of vestibular organs the otolith organs the semicircular canals

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. the otolith organs tiny sacs found just above the cochlea contain a gelatin-like fluid within which tiny crystals are suspended crystals cause fluid to vibrate, setting off receptors on the inner surface of the sac the semicircular canals three circular tubes filled with fluid stimulate receptors when rotated

Learning Objective 7.7: Outline other sensory systems, such as olfaction, gustation, and somesthesis. Sensory conflict theory: an explanation of motion sickness in which the information from the eyes conflicts with the information from the vestibular senses Results in dizziness, nausea, and other physical discomforts

Module 8 Perception

Learning Objectives 8.1 Explain the nature of attention. 8.2 Discuss the importance of perceptual constancies. 8.3 Describe the Gestalt principles of perception. 8.4 Distinguish between binocular and monocular depth cues. 8.5 Describe the various types of perceptual illusions. 8.6 Outline how experiences and expectations influence perception.

Perception Learning Objective 8.1: Explain the nature of attention. Perception: the method by which the sensations experienced at any given moment are interpreted and organized in some meaningful fashion Powers of attention: helps in focussing on certain stimuli in the environment while ignoring the rest Paying attention is the first step in the process of perception

Perceptual Constancies (1 of 2)
Learning Objective 8.2: Discuss the importance of perceptual constancies. Constancy: the tendency to interpret an object as being constant Forms of Perceptual Constancies Size Constancy Shape Constancy Brightness Constancy

Perceptual Constancies (2 of 2)
Learning Objective 8.2: Discuss the importance of perceptual constancies. Size Constancy the tendency to interpret an object as always being the same size, regardless of its distance from the viewer Shape Constancy the tendency to interpret the shape of an object as constant, even when it changes on the retina Brightness Constancy the tendency to perceive the apparent brightness of an object as the same even when the light conditions change

Figure 8.1: Shape Constancy
The opening door is actually many different shapes, yet we still see it as basically a rectangular door. Though a triangle and a circle cast differently shaped images on our retina, we experience them as a triangle and a circle because of shape constancy.

Gestalt Principles (1 of 3)
Learning Objective 8.3: Describe the Gestalt principles of perception. Gestalt Principles focus on human perception and the brain’s tendency to group objects and perceive whole shapes Principles of Perceptions Figure-Ground Relationships and Reversible Figures Principles of Grouping: Proximity; Similarity; Closure; Continuity; Contiguity; Common region

Learning Objective 8.3: Describe the Gestalt principles of perception. Figure-Ground Relationships the tendency to perceive objects or figures as existing on a background Reversible Figures visual illusions in which the figure and ground can be reversed Proximity the tendency to perceive objects that are close to one another as part of the same grouping

Learning Objective 8.3: Describe the Gestalt principles of perception. Similarity the tendency to perceive things that look similar as being part of the same group Closure the tendency to complete figures that are incomplete Contiguity the tendency to perceive two things that happen close together in time as being related

Figure 8.2: The Necker Cube
A reversible figure: The visual presentation of the cube seems to keep reversing its planes and edges.

Figure 8.3: Figure–Ground Illusion
Figure-Ground relationship: Is it a wine goblet? Or two faces looking at each other? The figure and the ground seem to “switch” each time you look at the picture.

Figure 8.4: Gestalt Principles of Grouping
Proximity: By changing the proximity of certain dots, we experience the dots as vertical columns or horizontal rows. Similarity: The similarity of color makes you perceive these dots as black squares and color squares. Closure: Even though the lines are broken, we still see these figures as a circle and a square. Continuity: We are much more likely to see the figure as being made up of two lines, A to B and C to D, than to see it as made up of A to D and C to B or A to C and B to D. Common Region: The colored backgrounds define a visible common region, and the tendency is to perceive three different groups.

Depth Perception Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Depth perception: the ability to perceive the world in three dimensions helps in judging how far away are the objects seems to be present in infants at a very young age

Figure 8.5: The Visual Cliff Experiment
In the visual cliff experiment, the table has both a shallow and a “deep” side, with glass covering the entire table. When an infant looks down at the deep-appearing side, the squares in the design on the floor look smaller than the ones on the shallow side, forming a visual cue for depth. The infant seems to be very reluctant to cross over the deep-appearing side of the table, gesturing to be picked up, instead.

Types of Cues for Perceiving Depth
Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Monocular Cues Linear perspective Relative size Overlap Aerial perspective Texture gradient Motion parallax Accommodation Binocular Cues Convergence Binocular disparity

Monocular Cues (1 of 3) Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Monocular Cues (pictorial depth cues): cues for perceiving depth based on one eye only Linear perspective: the tendency for parallel lines to appear to converge on each other Relative size: perception that occurs when objects that a person expects to be of a certain size appear to be small and are, therefore, assumed to be much farther away

Monocular Cues (2 of 3) Monocular Cues (continued)
Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Monocular Cues (continued) Overlap/ Interposition: the assumption that an object that appears to be blocking another object is in front of the second object and closer to the viewer Aerial (atmospheric) perspective: the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater Texture gradient: the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

Monocular Cues (3 of 3) Monocular Cues (continued)
Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Monocular Cues (continued) Motion parallax: the perception of motion of objects in which close objects appear to move faster than the objects that are farther away Accommodation/muscular cue: the brain uses the information about visual accommodation (the tendency of the lens to change its shape, or thickness, in response to objects near or far away) as a cue for distance

Figure 8.6: Examples of Pictorial Depth Cues
(a) Linear Perspective: Both the lines of the trees and the sides of the road appear to come together or converge in the distance. (b) Texture gradient: Causes the viewer to assume that as the texture of the pebbles gets finer, the pebbles are getting farther away. (c) Aerial perspective: Notice that the road and farmhouse in the foreground are in sharp focus while the mountain ranges are hazy and indistinct. (d) Relative size: Notice that the flowers in the distance appear much smaller than those in the foreground.

Binocular Cues (1 of 2) Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Binocular cues: cues for perceiving depth based on both eyes Convergence: the rotation of the two eyes in their sockets to focus on a single object, resulting in greater convergence for closer objects and lesser convergence if objects are distant

Binocular Cues (2 of 2) Binocular Cues (continued)
Learning Objective 8.4: Distinguish between binocular and monocular depth cues. Binocular Cues (continued) Binocular disparity: because the eyes are a few inches apart, they don’t see exactly the same image; If the two images are very different, the object must be pretty close. If they are almost identical, the object is far enough away to make the retinal disparity very small

Figure 8.7: Binocular Cues to Depth Perception
A) Convergence: When objects are far away, the eye muscles are more relaxed; when objects are close, the eye muscles move together, or converge. B) Binocular disparity: In A, the object is far enough away that the difference is small. In B, while the object is closer, there is a greater difference between what each eye sees. The brain interprets this difference as the distance of the object.

Perceptual Illusions Learning Objective 8.5: Describe the various types of perceptual illusions. Illusion: a visual stimulus that "fools" the eye, or a distorted perception of something that is really there Unlike hallucinations, an illusion originates in reality rather than the brain

Perceptual Illusions: Müller-Lyer Illusion
Learning Objective 8.5: Describe the various types of perceptual illusions. Müller-Lyer Illusion: illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different Explanation: When a person is outside a building, the corner of the building appears close When a person is inside a building, the corner of the building seems to move away

Perceptual Illusions: The Moon Illusion
Learning Objective 8.5: Describe the various types of perceptual illusions. The Moon Illusion: the moon on the horizon appears to be larger than the moon in the sky Explanation: Apparent Distance Hypothesis Misapplication of the principle of size constancy

Perceptual Illusions: Illusion of Motion
Learning Objective 8.5: Describe the various types of perceptual illusions. Illusion of Motion: an object is perceived to be moving when it is actually still Autokinetic effect: a small, stationary light in a darkened room will appear to move or drift because there are no surrounding cues to indicate that the light is not moving Stroboscopic motion: a rapid series of still pictures seem to be in motion phi phenomenon: lights turned on in sequence appear to move

Figure 8.8: Rotating Snakes
Seeing the “snakes” rotate is due at least in part to movements of eyes. The explanations for this type of motion illusion include: factors dependent on the image’s luminance and/or the color arrangement, and slight differences in the time it takes the brain to process this information

Figure 8.9: Reinterpretation of Enigma
Many people will see the rings start to “sparkle” or the rings rotating. Tiny eye movements called microsaccades are directly linked to the perception of motion in Enigma.

Factors that Influence Perception (1 of 3)
Learning Objective 8.6: Outline how experiences and expectations influence perception. Perceptual expectancy: people’s tendency to perceive things a certain way because their previous experiences or expectations influence them Ambiguous figures: an experiment that illustrates the way perceptual set influences identification of various ambiguous figures Inattentional blindness: when we are paying attention to a stimulus we are perceptually “blind” to other stimuli that are present

Learning Objective 8.6: Outline how experiences and expectations influence perception. Top-down processing: the use of preexisting knowledge to organize individual features into a unified whole Bottom-up processing: the analysis of the smaller features to build up to a complete perception

Learning Objective 8.6: Outline how experiences and expectations influence perception. Ames Room Illusion Ambiguous Figures: Influenced by past experiences and expectancies, the viewer perceives the room as a rectangle, but in reality it is a trapezoid with angled walls and floor.

Figure 8.9: Perceptual Set
Look at the drawing. What do you see? Then look at the two pictures on the next slide Interpret the drawing

Figure 8.9: Perceptual Set
Would you have interpreted the first drawing differently if you had viewed these two images first? This is because the tendency to perceive things a certain way is influenced by the previous experiences or expectations.

Figure 8.10: The Devil’s Trident
At first glance, the Devil’s Trident seems to be an ordinary three-pronged figure. But a closer look reveals that the three prongs cannot be real as drawn. Follow the lines of the top prong to see what goes wrong.

Neuroscience of Magic (1 of 3)
Learning Objective 8.6: Outline how experiences and expectations influence perception. Visual illusions and cognitive illusions are among several types of illusions that serve as a basis for various magic tricks Visual illusions: occur when our individual perception does not match a physical stimulus and are caused by organizational or processing biases in the brain

Learning Objective 8.6: Outline how experiences and expectations influence perception. Take a pencil or pen, grasp it in the middle, and shake or wiggle it up and down. The pen or pencil will appear to bend or be made of rubber. Magicians use this to “blend” solid objects. End-Stopped Neurons Special neurons in the visual cortex are sensitive to motion and edges. These neurons respond differently if an object is bouncing, causing perception of blending.

Learning Objective 8.6: Outline how experiences and expectations influence perception. Magicians use persistence of vision effect to "make an object disappear" Show the audience the target object Remove it very quickly from the visual field The audience see the object due to after-discharge (a response in vision neurons that creates an afterimage lasting for up to 100 milliseconds after a stimulus is removed)

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