Chapter 5: Sensation and Perception

Chapter 5: Sensation and Perception

5.1: Your Senses Detect Physical Stimuli, and Your Brain Processes Perception

• Sensation: The sense organs’ detection of external physical stimuli and the transmission of information about this stimulus to the brain

• Perception: The processing, organization, and interpretation of sensory information in the brain; these processes result in an internal neural representation of the physical stimulus

• Sensory receptors: Sensory organs that detect physical stimulation from the external world and change that stimulation into the information that can be processed by the brain

• Transduction: A process by which sensory receptors change physical stimuli into signals that are eventually sent to the brain.

• Primary somatosensory cortex = touch

• Primary olfactory cortex = smell

• Primary gustatory cortex = taste

• Primary auditory cortex = hearing

• Primary visual cortex = vision

5.2: There Must Be a Certain Amount of Stimulus for You to Detect It

• Absolute Threshold: The smallest amount of physical stimulation required to detect a sensory input half of the time it is present.

• Difference Threshold: The minimum difference in physical stimulation required to detect a difference between sensory inputs.

  • Weber’s law

  • Just-noticeable difference (JND: how much difference does there have to be in sensory in information for it to be detected as different)

• Sensory Adaptation: a decrease in sensitivity to a constant level of stimulation

5.3: Sensory Receptors in Your Eyes Detect Light

• Light waves pass through the cornea, the thick, transparent outer layer 

• The light then passes through the pupil, the small opening that looks like a dark circle

• The iris, a circular muscle, gives eyes their color and controls the pupil’s size to determine how much light enters the eye

• Behind the pupil, muscles change the shape of the lens, the adjustable, transparent structure behind the pupil; this structure focuses light on the retina, resulting in a crisp visual image

• Rods and Cones

  • Retina: The thin inner surface of the back of the eyeball; this surface contains the sensory receptors

  • Rods: Sensory receptors in the retina that detect light waves and transduce them into signals that are processed in the brain as vision. Rods respond best to low levels of illumination and therefore do not support color vision or detection of fine detail

  • Cones: Sensory receptors in the retina that detect light waves and transduce them into signals that are processed in the brain as vision. Cones respond best to higher levels of illumination, and therefore they are responsible for letting us see color and fine detail.

    • Each retina holds approximately 120 million rods and 6 million cones. Near the center of the retina is a small region called the fovea where cones are densely packed

• Information about what the eye has sensed is delivered to the ganglion cells

• The axons of each ganglion cell are gathered into a bundle. This bundle is called the optic nerve.

• There are blind spots in your left and right visual fields, where the optic nerve exits the retina.

• Half of the axons in the optic nerves cross to the other side of the brain. The rest of the axons stay on the same side of the brain.

• The information passes through the thalamus and travels to the primary visual cortex in the occipital lobe.

5.4: You Percieve Color Based on Physical Aspects of Light

• For humans, visible light consists of electromagnetic waves ranging in length from about 400 to 700 nanometers.

  • The amplitude is the height of the light wave from base to peak; people experience this quality as brightness

  • The wavelength of the lightwave is the distance from peak to peak. This distance determines your perception of hue.

• Hue refers to the distinctive characteristics of a particular color in the spectrum.

• Thrichromatic theory: There are three types of cone receptor cells in the retina that are responsible for the color perception. Each type responds optimally to different but overlapping ranges of wavelengths. (S,M,&L Receptors)

  • S Cones: the most sensitive to short wavelengths of light. This sensitivity results in perception of blue.

  • M Cones: the most sensitive to medium wavelengths of light. This sensitivity results in perception of green.

  • L Cones: the most sensitive to long wavelengths of light. This sensitivity results in perception of red.

• Opponent-process theory: The idea that ganglion cells in the retina receive excitatory input from one type of cone and inhibitory input from another type of cone, creating the perception that some colors are opposites.

5.5: You Percieve Objects by Organizing Visual Information

• The founders of Gestalt psychology postulated a series of laws to explain how our brains group the perceived features of a visual scene into organized wholes.

• An object is a figure that is distinct from the background. The background is referred to as the ground

• Grouping: The visual system’s organization of features and regions to create the perception of a whole, unified object.

  • Proximity: Close figures are grouped as an object.

  • Similarity: Similar figures are grouped in an object.

  • Continuity: Intersecting lines are interpreted as continuous.

  • Closure: Figures with gaps are interpreted.

  • Illusory contours: Contours are perceived even when they do not exist.

• Bottom-up processing: The perception of objects is due to analysis of environmental stimulus input by sensory receptors; this analysis influences the more complex, conceptual processing of that information in the brain.

• Top-down processing: The perception of objects is due to the complex analysis of prior experiences and expectations within the brain; this analysis influences how sensory receptors process stimulus input from the environment

5.6: When You Percieve Depth, You Can Locate Objects in Space

• Binocular depth cues: Cues of depth perception that arise because people have two eyes

  • Binocular disparity: We use both eyes to perceive depth through binocular disparity, where each retina has a slightly different view of the world

• Monocular depth cues: Cues of depth perception that are available to each eye alone.

• Motion aftereffects may occur when you gaze at a moving image for a long time and then look at a stationary scene

• The waterfall effect is a momentary impression that the new scene is moving in the opposite direction from the moving image

  • Motion afftereffects are strong evidence that motion-sensitive neurons exist in the brain

5.7: Cues in Your Brain and in the World Allow You to Percieve Motion

• Stroboscopic motion: Movies are made up of still images, each of which is slightly different from the one before it. When the series is presented fast enough, we perceive the illusion of motion pictures.

  • The perceptual illusion is called stroboscopic motion

5.8: You Understand That Objects Remain Constant Even When Cues Change

• Object constancy: Correctly perceiving objects as staying the same in their size, shape, color, and lightness, across viewing conditions that yield different physical input to the eyes

5.9: Receptors in Your Ears Detect Sound Waves

• The process of hearing begins when sound waves arrive at the shell-shaped structure of your outer ear

  •  The shell shape of the outer ear increases the ear’s ability to capture sound waves and then funnel the waves down the auditory canal

• Eardrum: A thin membrane that marks the beginning of the middle ear; sound waves cause the eardrum to vibrate

• Cochela: A coiled, bony, fluid-filled tube in the inner ear that houses the sensory receptors.

  • Running through the center of the cochela is the thin basilar membrane

• Hair cells: Sensory receptors located in the cochela that detect sound waves and transduce them into signals that ultimately are processed in the brain as sound.

5.10: Using Psychology in Your Life: How Can You Avoid Damage to Your Hearing from Listening to Loud Music with Earbuds?

• Noise-induced hearing loss affects more than 5 million young people nearly 13 percent of American children between the ages of 6 and 19

• Simple rules to follow in order to protect noise-induced hearing loss:

  • Use the 60/60 rule

  • Walk away from loud noise

  • Ringing ears are sending a warning

5.11: You Percieve Sound Based on Physical Aspects of Sound Waves

• The height of sound waves is called the amplitude 

  • Amplitude determines our perception of loudness

• The distance between peaks of sound waves is the wavelength

  • The time between the peaks in wavelength is called the frequency

  • The frequency of the waves determines the pitch of the sound, from high to low

  • It is measured in vibration per sound, called hertz

• Temporal coding: The perception of lower-pitched sounds is a result of the rate at which hair cells are stimulated by sound waves of lower frequencies

• Place coding: The perception of higher-pitched sounds depends on the point on the balisar membrane where hair cells are stimulated by sound waves of varying higher frequencies.

• Localization: The ear estimates the location of sound based first on when the sound arrives and second on the amplitude, or intensity, of the sound wave.

• Vestibular sense: Allows us to maintain balance

  • The vestibular sense uses information from receptors in structures of the inner ear called the semicircular canals

5.12: Receptors in Your Taste Buds Detect Chemical Molecules

• The sense of taste, which is also called gustation

• Taste buds: Structures, located in the papillae on the tongue, that contain sensory receptors

• Papillae: Structures on the tongue that contain groupings of taste buds.

  • The taste information is sent to other brain regions through a set of nerves, primarily the facial nerve

  • After processing by the thalamus, the information is further processed in the primary gustatory cortex

• Five main tastes: Sweet, sour, salty, bitter, and umami 

• Supertasters are highly aware of flavors and textures and are more likely than others to feel pain when eating very spicy foods 

• The texture of food affects taste preferences

• Cultural influences on food preferences begin in the womb

5.13: Your Olfactory Receptors Detect Odorants

• The sense of smell, which is also called olfaction, is the dog’s main way of perceiving the world

• Dogs have 40 times more olfactory receptors than humans do

• Dogs are 100,000 to 1 million times more sensitive to odors than humans are

• Humans have evolved to rely much more on vision

• Olfactory epithelium: A thin layer of tissue, deep within the nasal cavity, containing the olfactory receptors; these sensory receptors produce information that is processed by the brain as smell

  • Chemical molecules are called odorants

•  Olfactory bulb: A brain structure above the olfactory epithelium in the nasal cavity; from this structure, the olfactory nerve carries information about smell to parts of the brain, including the primary olfactory cortex

  • Smell signals bypass the thalamus

• There are thousands of olfactory receptors in the olfactory epithelium, but there are only about 350 types

  • Each receptor responds to different odorants

• Information about whether a smell is pleasant or unpleasant is processed in the brain’s prefrontal cortex

• The smell’s intensity is processed in the amygdala, a brain area involved in emotion and memory

5.14: Receptors in Your Skin Detect Temprature and Pressure

• Warm receptors: Sensory receptors in the skin that detect the temperature of stimuli and transduce it into information processed in the brain as warmth.

• Cold receptors: Sensory receptors in the skin that detect the temperature of stimuli and transduce it into information processed in the brain as cold.

• Pressure receptors: Sensory receptors in the skin that detect tactile stimulation and transduce it into information processed in the brain as different types of pressure on the skin

• Touch information travels first through the thalamus and then to the primary somatosensory cortex, which processes the information

• The sensation of touch above the neck is sent to the brain directly via cranial nerves

• The sensation of touch below the neck is sent to the spinal cord, and then spinal nerves transmit the information to the primary somatosensory cortex in the brain

• Penfield discovered that electrical stimulation of the primary somatosensory cortex could evoke the perception of touch in different regions of the body

  • For the most sensitive regions of the body, such as the lips and fingers, a great deal of the cortex is dedicated to processing touch

• Our kinesthetic sense tells us how our body and limbs are positioned in space

  • Kinesthetic sensations come from receptors in muscles, tendons, and joins

5.15: You Detect Pain in Your Skin and Throughout Your Body

• Fast fibers: Sensory receptors in the skin, muscles, organs, and membranes around both bones and joints; these myelinated fibers quickly convey intense sensory input to the brain, where it is perceived as sharp, immediate pain.

• Slow fibers: Sensory receptors in the skin, muscles, organs, and membranes around both bones and joints; these unmyelinated fibers slowly convey intense sensory input to the brain, where it is perceived as chronic, dull, steady pain

• Gate control theory: We experience pain when pain receptors are activated and a neural “gate” in the spinal cord allows the signals through to the brain

  • These ideas were radical that they depict pain as a perceptual experience within the brain rather than simply a response to a nerve stimulation

• Distraction can reduce your perception of pain

  • Listening to music is an extremely effective way to reduce postoperative pain, perhaps because it helps patients relax