Transcript
Chapter Summary: Chapter 5
How Does Perception Emerge from Sensation?
5.1 Sensory Information Is Translated into Meaningful Signals
Sensation is the detection of physical stimuli in the environment. Perception is our conscious experience of those stimuli. Bottom-up processing is based on features of a stimulus. Top-down processing is based on context and expectations. Transduction is the process of converting sensory stimuli into a pattern of neural activity. Transduction takes place at sensory receptors, specialized cells within each sense organ that respond to energy to activate neurons. Most sensory information goes to the thalamus and then specialized brain regions.
5.2 Detection Requires a Certain Amount of the Stimulus
Information from the environment needs to surpass some level before you can detect it. Absolute threshold is the minimum amount of stimulus intensity needed to activate a sensory receptor. Difference threshold is the amount of change required for detection by a sensory receptor. Signal detection theory is about the subjective nature of detecting a stimulus. Sensory adaptation occurs when sensory receptors stop responding to an unchanging stimulus.
5.3 The Brain Constructs Stable Representations
In perception, the brain integrates millions of diverse neural inputs to produce stable representations. This activity produces awareness, a conscious experience of the physical world. Sometimes those representations can produce unusual experiences, such as in synesthesia.
5.4 Think like a Psychologist: Does ESP Exist?
The ability to perceive information beyond ordinary sensory information is called extrasensory perception (ESP). Although psychologists continue to debate the existence of ESP, the available evidence is weak or nonexistent.
How Are We Able to See?
5.5 Sensory Receptors in the Eye Transmit Visual Information to the Brain
Light is focused by the lens onto the retina, which is at the back of the eye. The retina houses the photoreceptors: rods and cones. Rods and cones communicate with ganglion cells of the optic nerve. This nerve exits the eye at the blind spot and crosses into the brain at the optic chiasm. There, axons from each eye cross into opposite sides of the brain, so the left hemisphere processes information from the right visual field and vice versa. The information is processed in the thalamus and the primary visual cortex (in the occipital lobe). From the visual cortex, the ventral stream processes “what” information about objects, and the dorsal stream processes “where” information about locations.
5.6 The Color of Light Is Determined by Its Wavelength
The human eye detects electromagnetic radiation wavelengths of 400?700 nanometers. The retina contains three types of cones. Each type is responsive to a different wavelength (short, medium, or long), and this responsiveness enables us to perceive colors. Color blindness is caused by a malfunction in one or more of the cone types. Colors are differentiated by their hue, saturation, and lightness.
5.7 Perceiving Objects Requires Organization of Visual Information
Gestalt principles—such as proximity, similarity, continuity, and closure—account for the ways in which perceptual information is organized into wholes. Humans are especially good at recognizing faces. The fusiform gyrus is one of the brain regions most responsible for this ability.
5.8 Perception Is Guided by Cues in the Environment
Depth perception is critical for locating objects in space. To perceive depth using only a two-dimensional retinal image, the brain draws on binocular and monocular cues. Size perception depends on distance: Close objects produce large retinal images, whereas far objects produce small retinal images. Motion is detected by motion-sensitive neurons in the visual cortex. Object constancy refers to how the brain accurately perceives images even with minimal or changing stimulus cues. The four constancies are size, shape, color, and lightness.
How Are We Able to Hear?
5.9 Audition Results from Changes in Air Pressure
The amplitude and frequency of sound waves cause the perceptual experiences of loudness and pitch, respectively. Sound waves travel from the outer ear through the auditory canal to the eardrum. Vibrations from these waves stimulate the ossicles, bones of the inner ear. The vibrations of these bones stimulate the oval window, a membrane on the cochlea, a fluid-filled chamber in the inner ear. Pressure waves from the cochlear fluid stimulate the basilar membrane. This stimulation causes the ear’s sensory receptors, the hair cells, to bend. The bending of the hair cells activates neurons in the auditory nerve. These neurons send messages through the thalamus and to the primary auditory cortex (in the temporal lobe). Cochlear implants can help with hearing loss by directly stimulating the auditory nerve, overcoming the lack of hair cells in the inner ear.
5.10 Pitch Is Encoded by Frequency and Location
Low-frequency sound waves are sensed through temporal coding, as cochlear hair cells fire at a rate equivalent to the frequency of the waves. High-frequency sound waves are sensed through place coding—that is, by hair cells at different locations in the cochlea. For high-frequency sound waves, groups of hair cells must take turns firing.
5.11 Using Psychology in Your Life: Are Your Listening Habits Damaging Your Hearing?
Loud noises can permanently damage the sensitive hair cells that line the ear canals and transmit signals to the nerves involved in sound perception. Once those hair cells are damaged, they cannot be repaired.
How Are We Able to Taste?
5.12 There Are Five Basic Taste Sensations
Gustation, the sense of taste, is produced by taste buds. The taste buds are located in the papillae, structures on the tongue. The five types of taste buds yield the taste sensations: sweet, sour, salty, bitter, and umami (savory). Cultural factors help determine taste preferences.
How Are We Able to Smell?
5.13 Smell Detects Odorants
Olfaction occurs when odorants stimulate smell receptors, which are located in the olfactory epithelium in the nose and nasal cavity. Smell receptors send messages to neurons in the olfactory bulb, located below the frontal lobes. The signals are sent directly to other brain areas, including those that regulate memory and emotion. Pheromones are chemicals that do not produce odor but are processed by the smell receptors. Pheromones can motivate sexual behavior in nonhuman animals and may function similarly in humans.
How Are We Able to Feel Touch and Pain?
5.14 The Skin Contains Sensory Receptors for Touch and Pain
Touch is known as the haptic sense. Tactile stimulation activates touch receptors in skin, which respond to temperature, pressure, and pain. Touch information travels to the thalamus, which sends it to the primary somatosensory cortex (in the parietal lobe). The perception of pain prompts organisms to protect themselves from damage. Fast, myelinated fibers process sharp sudden pain. Slow, nonmyelinated fibers process dull chronic pain. According to the gate control theory, pain perception requires both the activation of pain receptors and spinal cord processing of the signal. The gate can be closed or occupied if other stimuli are processed simultaneously. Activities such as rubbing an area around the painful one, distracting oneself, or thinking happy thoughts can decrease the perception of pain.
