Biological bases of behavior notes

1.1 Heredity and Environment

Learning Objectives:
- 1.1-1: Describe the evolutionary psychologists’ use of natural selection to explain behavior tendencies
- 1.1-2: Describe how behavior genetics explain our individual differences
- 1.1-3: Explain how twin and adoption studies help us understand the effects and interactions of nature and nurture
- 1.1-4: Explain how heredity and environment work together
Nature vs. Nurture Issue:
- Psychology’s biggest issue: Are our human traits present at birth (nature) or do they develop through experience (nurture)?
- Nature: Our traits are a result of genetics.
- Nurture: Our traits are a result of our experience.
- Today’s science views traits and behaviors as arising from the interaction of nature and nurture.
Evolutionary Perspective:
- Evolutionary Psychology: The study of the evolution of behavior and the mind, using principles of natural selection.
- Charles Darwin is a key figure in this perspective.
- Natural Selection: The principle that inherited traits enabling an organism to survive and reproduce in a particular environment will most likely be passed on to succeeding generations.
- Behavior Genetics: The study of the relative power and limits of genetic and environmental influences on behavior.
Evolutionary Psychology: Understanding Human Nature
- Evolutionary psychologists use Darwin’s principle of natural selection to understand behavior and mental processes.
- Organisms’ varied offspring compete for survival.
- Mutation: a random error in gene replication that leads to a change.
- Certain biological and behavioral variations increase organisms’ reproductive and survival chances.
- Offspring that survive are more likely to pass on their genes.
- Eugenics: Based loosely on Charles Darwin’s theory, it seeks to eradicate genetic defects and improve the genetic makeup through selective human breeding.
Behavior Genetics: Environment and Heredity
- Behavior genetics explores the genetic and environmental roots of human differences.
- Environment: Nongenetic influence, from prenatal nutrition to our experiences of people and things around us.
- Heredity: The genetic transfer of characteristics from parents to offspring.
Genes: Our Life Code
- Genes: The biochemical units of heredity.
- Genome: The complete instructions for making an organism.
- Genetically speaking, humans and chimps are about 96% the same.
- There is no single gene that will predict intelligence, personality, or sexual orientation.
Twin and Adoption Studies:
- Identical (monozygotic) twins: Individuals who developed from a single fertilized egg that split in two, creating two genetically identical organisms.
  - Don’t always have the same number of copies of genes repeated in their genome.
- Fraternal (dizygotic) twins: Individuals who developed from separate fertilized eggs. They are genetically no closer than ordinary siblings but they shared a prenatal environment.
- Twin Studies: Allow researchers to examine the role of genes in the development of a trait or disorder. Comparisons between monozygotic twins and dizygotic twins are conducted to evaluate the degree of genetic and environmental influence on a specific trait.
- Studies have shown that environment shared by a family’s children has little impact on their personality, meaning that just because you are raised in the same environment does not mean you will have a similar personality as your parents/siblings.
Gene-Environment Interaction:
- Interaction: The interplay that occurs when the effect of one factor (such as the environment) depends on another factor (such as heredity).
  - Example: If you walk all summer barefoot your feet will become more callused. Your friend wears shoes and is tender-footed - biological adaptation-environmental changes.
- Epigenetics: The study of the molecular mechanisms by which environments can influence genetic expression.
  - Example: If a child is sleep deprived or nutritionally deprived they might not reach their biological/genetic height.

1.2 Overview of the Nervous System

Learning Objectives:
- 1.2-1: What are the functions of the nervous system’s main divisions, and what are the three main types of neurons?
Nervous System:
- Nervous System: The body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous system.
- Central Nervous System (CNS): The brain and spinal cord.
- Peripheral Nervous System (PNS): The sensory and motor neurons that connect the CNS to the rest of the body.
- Nerves: Bundles of axons that form neural cables connecting the CNS with muscles, glands, and sensory organs.
- Sensory (afferent) Neurons: Carry incoming information from the body’s tissues and sensory receptors to the brain and spinal cord.
- Motor (efferent) Neurons: Carry outgoing information from the brain and spinal cord to the muscles and glands.
- Interneurons: Within the brain and spinal cord, communicate internally and process information between the sensory inputs and motor outputs.
The Peripheral Nervous System:
- Somatic NS: Division of the PNS that controls the body’s skeletal muscles (AKA skeletal NS).
- Autonomic NS: Division of the PNS that controls the glands and the muscles of the internal organs.
  - Sympathetic NS: Division of the autonomic NS that arouses the body, mobilizing its energy.
  - Parasympathetic NS: Division of the autonomic NS that calms the body, conserving its energy.
Central Nervous System
- Brain: The brain controls most of the functions of the body, including awareness, movement, thinking, speech, and the 5 senses.
- Spinal Cord: The spinal cord is an extension of the brain and carries messages to and from the brain to the rest of the body.
- Reflex: Simple, automatic response to a sensory stimulus, such as the knee-jerk reflex.

1.3 Neuron and Neural Firing: Neural Communication and Endocrine System

Learning Objectives:
- 1.3-1: Neurons and transmission of information
- 1.3-3: Neurotransmitters’ impact on behavior and drugs’ impact on neurotransmission
- 1.3-4: Endocrine system and transmission of information
Neural Communication:
- Neuron: A nerve cell; the basic building block of the nervous system.
- Glial cells: A type of cell that provides physical and chemical support to neurons and maintains their environment; called the glue of the nervous system.
- Multiple sclerosis: A disorder in which the body's immune system attacks the myelin sheath, diminishes muscle control and can impair cognition.
- Myasthenia Gravis: A progressive autoimmune disease in which the body produces antibodies against acetylcholine receptors, hindering neural transmission at neuromuscular junctions. Symptoms include weakness in voluntary muscles (especially eyes, mouth, throat, and limbs).
Neural Impulse:
- Action Potential: A neural impulse; a brief electrical charge that travels down an axon.
- Threshold: Level of stimulation required to trigger a neural impulse.
- Refractory Period: In neural processing, a brief resting pause occurs after a neuron has fired; subsequently action potentials cannot occur until the axon returns to its resting state.
- All-or-Nothing Response: A neuron’s reaction of either firing or not firing.
How Neurons Communicate:
- Synapse: The junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap is called the synaptic gap or synaptic cleft.
- Neurotransmitters: Chemical messengers that cross the synaptic gap between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.
- Reuptake: A neurotransmitter’s reabsorption by the sending neuron.
Neurotransmitters:
- Acetylcholine:
  - Functions: Excites skeletal muscles; Inhibits heart action; Memory
  - Examples of Malfunction: Alzheimer's disease
- Dopamine:
  - Functions: Movement; learning: Attention; Motivation and reward
  - Examples of Malfunction: Parkinson's disease (too little); Schizophrenia (too much); Substance abuse
- Serotonin:
  - Functions: Sleep; Arousal; Mood; Eating; Pain perception
  - Examples of Malfunction: Depression; Obsessive Compulsive Disorder; Some eating disorders; Chronic pain
- Norepinephrine:
  - Functions: Sleep; Arousal; Mood; Endorphins: natural opioid-like neurotransmitters linked to pain control and to pleasure
  - Examples of Malfunction: Depression
- GABA:
  - Functions: Chief inhibitor; Regulates arousal
  - Examples of Malfunction: Some anxiety disorders; Some seizure disorders
- Glutamate:
  - Functions: Chief excitatory neurotransmitter; Many diverse functions
  - Examples of Malfunction: Neural death following head injuries
- Endorphins:
  - Functions: Suppression of pain; Some indication of a link to mood
- Substance P:
  - Functions: Carries pain signals; Some indication of a link to depresion
Drugs and Other Chemicals Alter Neurotransmission:
- Agonist: A molecule that increases a neurotransmitter’s action.
  - Morphine are agonists as they bind to the neurons to heighten pleasure or decrease pain.
- Antagonist: A molecule that inhibits or blocks a neurotransmitter’s action.
  - Haloperidol blocks the uptake of dopamine -- helps lessen the symptoms of schizophrenia.
Endocrine System:
- Endocrine System: The body’s “slow” chemical communication system; a set of glands and fat tissue that secrete hormones into the bloodstream.
- Hormones: Chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.
- The hypothalamus secretes hormones that stimulate or suppress the release of hormones in the pituitary gland.
- Adrenaline: A hormone and neurotransmitter secreted by the adrenal glands typically during stressful, exciting, or highly emotional situations
- Leptin: A hormone released b fat cells that works in concert with ghrelin to regulate appetite.
- Ghrelin: A hormone produced primarily by the gastrointestinal trac that helps to regulate appetite.
- Melatonin: A hormone released primarily by the brain’s pineal gland that regulates the body’s sleep-wake cycle.
- Oxytocin: A hormone produced by the hypothalamus and released by the pituitary gland. Known the “love hormone,” plays a key role in socializing, romantic relationships, and parent-child bonding

1.3b: The Neuron and Neural Firing: Substance Use Disorders and Psychoactive Drug

Learning Objectives:
- 1.3-5: Substance use disorders
- 1.3-6: Describe depressants and their effects
- 1.3-7: Describe stimulants and their effects
- 1.3-8: Describe hallucinogens and their effects
Tolerance and Addiction in Substance Use Disorder
- Psychoactive Drug: A chemical substance that alters the brain, causing changes in perceptions and moods
- Substance Use Disorder: A disorder characterized by continued substance use despite resulting life disruption
Depressants: drugs that reduce neural activity and slow body functions
- Alcohol:
  - Type: Depressant
  - Pleasurable Effects: Initial high followed by relaxation and disinhibition
  - Negative After Effects: Depression, memory loss, organ damage, impaired reactions
- Barbiturates (tranquilizers):
  - Type: Depressant
  - Pleasurable Effects: Reduce anxiety
  - Negative After Effects: Depress NS activity, can be prescribed to induce sleep or reduce anxiety, in large doses they can impair memory and judgment
- Opiates (Heroin):
  - Type: Depressant
  - Pleasurable Effects: Rush of euphoria, relief from pain
  - Negative After Effects: Depressed physiology, agonizing withdrawal
Stimulants: drugs that excite neural activity and speed up body functions
- Caffeine:
  - Type: Stimulant
  - Pleasurable Effects: Increased alertness and wakefulness
  - Negative After Effects: Anxiety, restlessness, and insomnia in high doses; uncomfortable withdrawal
- Nicotine:
  - Type: Stimulant
  - Pleasurable Effects: Arousal and relaxation, sense of well-being
  - Negative After Effects: Heart disease, cancer
- Cocaine:
  - Type: Stimulant
  - Pleasurable Effects: Rush of euphoria, confidence, energy
  - Negative After Effects: Cardiovascular stress, suspiciousness, depressive crash
- Methamphetamine:
  - Type: Stimulant
  - Pleasurable Effects: Euphoria, alertness, energy
  - Negative After Effects: Irritability, insomnia, hypertension, seizures
Hallucinogens: psychedelic drugs that distort perceptions and evoke sensory images in the absence of sensory input
- Ecstasy (MDMA):
  - Type: Stimulant; mild hallucinogen
  - Pleasurable Effects: Emotional elevation, disinhibition
  - Negative After Effects: Dehydration, overheating, depressed mood, impaired cognitive and immune functioning
- LSD:
  - Type: Hallucinogen
  - Pleasurable Effects: Visual “trip”
  - Negative After Effects: Risk of panic
- Marijuana (THC):
  - Type: Mild hallucinogen
  - Pleasurable Effects: Enhanced sensation, relief of pain, distortion of time, relaxation
  - Negative After Effects: Impaired learning and memory, increased risk of psychological disorders
- Near-death Experience: an altered state of consciousness reported after a close brush with death often similar to drug-induced hallucination
Tolerance and Addiction
- Tolerance: The diminishing effect with regular use of the same dose of drugs, requiring the user to take a larger and larger dose before experiencing the drug’s effect
- Addiction: Compulsive substance use that continues despite harmful consequences
  - Gambling, video games, and other behaviors can be considered addictive
- Withdraw: The discomfort and distress that follow discontinuing an addictive drug or behavior

1.4a: The Brain- Neuroplasticity and Tools of Discovery

Learning Objectives:
- 1.4-1: Explain why psychologists are concerned with human biology
- 1.4-2: Explain how biology and experience together enable neuroplasticity
- 1.4-3: Compare and contrast several techniques for studying the brain’s connections to behavior and mind
Biological Psychologist
- Biopsychosocial Approach: An integrated approach that incorporates biological, psychological, and social-cultural levels of analysis
- Levels of analysis: The differing complementary views, from biological to psychological to social-cultural, for analyzing any given phenomenon
- Phrenology: Franz Gall proposed the idea of phrenology, studying bumps on the skull which would reveal a person’s mental abilities and character traits
- Biological Psychologist: The scientific study of the links between biological (genetic, neural, hormonal) and psychological processes. AKA: behavioral neuroscientist, neuropsychologist, behavior geneticist, physiological psychologist, or biopsychologist
Power of Neuroplasticity
- Neuroplasticity: The brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience
Types of Neural Measures:
- Electroencephalogram (EEG):
  - How it works: Electrodes placed on the scalp measure electrical activity in neurons.
  - Example: Symptoms of depression and anxiety correlate with increased activity in the right frontal lobe, a brain area associated with behavioral withdrawal and negative emotion. (Thibodeau et al., 2006).
- Magnetoencephalography (MEG):
  - How it works: A head coil records magnetic fields from the brain's natural electrical currents.
  - Example: Soldiers with posttraumatic stress disorder (PTSD), compared with those who do not have PTSD, show stronger magnetic fields in the visual cortex when they view trauma-related images (Todd et al., 2015).
- Computed tomography (CT):
  - How it works: X-rays of the head generate images that may locate brain damage.
  - Example: Children's brain injuries, shown in CT scans, predict impairments in their intelligence and memory processing (Königs et al., 2017).
- Positron emission tomography (PET):
  - How it works: Tracks where a temporarily radioactive form of glucose goes while the brain of the person given it performs a given task.
  - Example: Monkeys with an anxious temperament have brains that use more glucose in regions related to fear, memory, and expectations of reward and punishment (Fox et al., 2015).
- Magnetic resonance imaging (MRI):
  - How it works: People sit or lie down in a chamber that uses magnetic fields and radio waves to provide a map of brain structure.
  - Example: People with a history of violence tend to have smaller frontal lobes, especially in regions that aid moral judgment and self-control (Glenn & Raine, 2014).
- Functional magnetic resonance imaging (fMRI):
  - How it works: Measures blood flow to brain regions by comparing continuous MRI scans.
  - Example: Years after surviving a near plane crash, passengers who viewed material related to their trauma showed greater activation in the brain’s fear, memory, and visual centers than when they watched footage related to the 9/11 terrorist attacks (Palombo et al., 2015).

1.4b: The Brain- Brain Regions and Structures

Learning Objectives:
- 1.4-4: Explain how the hindbrain, midbrain, and forebrain apply to behavior and mental process
- 1.4-5: Describe the structures of the brainstem, and explain the functions of the brainstem, thalamus, reticular formation, and cerebellum
- 1.4-6: Explain the limbic system’s structures and functions
- 1.4-7: Describe the four lobes that make up the cerebral cortex and explain the functions of the motor cortex, somatosensory cortex, and association area
The Brain:
- Hindbrain: Consists of the medulla, pons, and cerebellum; directs essential survival functions, such as breathing, sleeping, and wakefulness, as well as coordination and balance.
- Midbrain: Found atop the brainstem; connects the hindbrain with the forebrain, controls some motor movement, and transmits auditory and visual information.
- Forebrain: Consists of the cerebral cortex, thalamus, and hypothalamus, manages complex cognitive activities, sensory and associative functions, and voluntary motor activities.
Limbic System:
- Neural system located mostly in the forebrain-below the cerebral hemispheres-that includes the amygdala, hypothalamus, and pituitary gland.
The Lobes of the Brain:
- Motor Cortex: Involved in planning, controlling, and execution of voluntary movements.
- Somatosensory Cortex: Interprets tactile stimuli, such as touch, temperature, pain, and proprioception (awareness of body position).
- Visual Cortex
- Auditory Cortex
- Association Areas: Areas of the cerebral cortex that are not involved in primary motor functions, but rather are involved in higher mental functions such as learning, remembering, thinking, and speaking.

1.4c: The Brain- Damage Response and Brain Hemispheres

Learning Objectives:
- 1.4-8: Explain how a damaged brain can reorganize itself, and describe neurogenesis
- 1.4-9: Explain what a split brain reveals about the functions of our two brain hemispheres
Response to Damage:
- Neuroplasticity can occur after serious damage, especially in young children.
- Neuroplasticity can help those with vision or hearing loss.
  - Blindness and deafness make unused brain areas available for other uses (smell and sound).
  - Areas can also be strengthened.
- Neurogenesis: The formation of new neurons.
Divided Brain:
- Corpus Callosum: The large band of neural fibers connecting the two hemispheres and carrying messages between them.
- Split brain: A condition resulting from surgery that separates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum).
Left vs. Right:
- Right Hemisphere Traits:
  - Recognizing faces
  - Expressing emotions
  - Creating music
  - Reading emotions
  - Appreciating color
  - Using imagination
  - Being intuitive
  - Being creative
- Left Hemisphere Traits:
  - Language
  - Logic
  - Critical thinking
  - Numbers
  - Reasoning
- Neuroscientists know that the two sides of the brain collaborate to perform a broad variety of tasks and that the two hemispheres communicate through the corpus callosum.

1.5a: Sleep: Consciousness

Learning Objectives:
- 1.5-1: Explain the place of consciousness in psychology history
- 1.5-2: Explain dual processing being revealed by today’s cognitive neuroscience
Defining Consciousness:
- Consciousness: Our subjective awareness of ourselves and our environment.
  - Conscious awareness helps make sense of our life (sensation, emotion, choices, set goals, reflect on the past and present).
  - Helps focus our awareness.
Cognitive Neuroscience:
- Cognitive Neuroscience: The interdisciplinary study of the brain activity linked with cognitive (thinking, knowing, remembering, and communicating).
- Researchers have found that it is possible to map consciousness on brain scans - if you ask an athlete to think about a complex move the brain region responsible for that move will activate.
Dual Processing:
- Dual Processing: The principle that information is often simultaneously processed on separate conscious and unconscious tracks.
- Blindsight: A condition in which a person can respond to a visual stimulus without consciously experiencing it; possible because of dual processing.
- Parallel Processing: Processing multiple aspects of a stimulus or problem simultaneously.
- Sequential Processing: Processing one aspect of a stimulus or problem at a time; generally used to process new information or to solve difficult problems.

1.5b: Sleep: Sleep Stages and Theories

Learning Objectives:
- 1.5-3: Explain sleep as a state of consciousness
- 1.5-4 Explain how our biological rhythms influence our daily functioning
- 1.5-5: Explain the biological rhythm of our sleeping and dream stages
- 1.5-6: Explain how biological and environment interact in our sleep patterns
- 1.5-7: Explain sleep’s function
Sleep and Biological Rhythms:
- Circadian Rhythm: Our biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occurs on a 24-hour cycle.
- Jetlag: A temporary sleep problem that occurs when a person's circadian rhythm is out of sync with the time zone they are in
- Shiftwork: Shiftwork can disrupt circadian rhythms, which can lead to shortened sleep, excessive sleepiness, and other health concerns.
Sleep Stages:
- Sleep: A periodic, natural loss of consciousness resulting from a coma, general anesthesia, or hibernation.
- REM Sleep: Rapid eye movement sleep; recurring sleep stage during which vivid dreams commonly occur. Also known as paradoxical sleep because muscles are relaxed but other body systems are active (also called R sleep).
- Alpha Waves: The relatively slow brain waves of a relaxed, awake state.
- NREM Sleep: Non-rapid eye movement sleep; encompasses all sleep stages except for REM sleep.
- Hallucinations: False sensory experience.
- Hypnagogic Sensation: Bizarre experience, such as jerking or feeling of falling or floating weightlessly, while transitioning to sleep.
- Delta Waves: The large, slow brain waves associated with deep sleep.
Biology-Environment and Sleep Stages:
- Sleep is impacted by biology and the environment.
- Shiftwork, travel, and social media can impact sleep.
- Biological factors
  - Suprachiasmatic Nucleus: A pair of cell clusters in the hypothalamus that controls circadian rhythm. In response to light, the SCN adjusts melatonin production, thus modifying our feelings of sleepiness.
Why do we sleep?
- Sleep protects: Evolutionary perspective - safer to hunt/gather during the day and sleep at night.
- Sleep restores: Sleep gives your body a chance to repair, rewire, and reorganize. It helps the body to heal from infection and restores the immune system
- Sleep aids memory consolidation: Sleep helps restore and rebuild our fading memories of the day’s experience.
- Sleep feeds creative thinking
- Sleep supports growth: During slow-wave sleep, the pituitary gland releases human growth hormone
- Sleep conserves energy: Sleep preserves our energy for wake-time

1.5c: Sleep-Sleep Loss, Sleep Disorders, and Dreams

Learning Objectives:
- 1.5-8: Explain the effects of sleep loss
- 1.5-9: Explain the major sleep disorder
- 1.5-10: Describe the most common content of dreams, and explain the functions theorists have proposed for dreams
Sleep Deprivation:
- Brain:
  - Decreased ability to focus attention and process and store memories; increased risk of depression; decreased metabolic rate; increased cortisol; enhanced limbic brain responses to the mere sight of food; decreased cortical responses-reducing ability to resist temptation.
- Immune system:
  - Decreased production of immune cells; increased risk of viral infections, such as colds
- Fat cells:
  - Increased production; greater risk of obesity
- Joints:
  - Increased inflammation and arthritis
- Heart:
  - Increased risk of high blood pressure
- Stomach:
  - Increase in the hunger-arousing hormone, ghrelin; decrease in the hunger-suppressing hormone, leptin
- Muscles:
  - Reduced strength; slower reaction time and motor learning
Sleep Disorders
- REM Sleep Behavior Disorder
  - 1 in 100 adults for the general population
  - Acting out the content of dreams while asleep (vocal or motor
  - Accident risk
What and Why we dream:
- Dream: A sequence of images, emotions, and thoughts of passing through a sleeping person’s mind
- What we dream
  - 8 of 10 people have at least one negative event or emotion during dreams
  - Common Themes: being attacked, pursued, rejected, or experiencing misfortune
- Why we Dream
  - To file away memories: Information processing perspective proposes that dreams help sift, sort, and fix (consolidate) the day’s experiences in our memory.
  - To develop and preserve neural pathways: dreams provide a stimulating experience and experiences preserve and expand the brain’s neural pathways
  - Make sense of neural static: Dreams erupt from neural activation spreading upward from the brainstem
  - To reflect cognitive development: Dream content reflects dreamers' level of cognitive development--their knowledge and understanding--simulates our lives
- REM Rebound: The tendency for REM sleep to increase following REM sleep deprivation
Critical Consideration of Dream Theory
- Freud's wish-fulfillment:
  - Explanation: Dreams preserve sleep and provide a "psychic safety valve" - expressing otherwise unacceptable feelings; contain manifest (remembered) content and a deeper layer of latent content (a hidden meaning).
  - Critical Considerations: Lacks any scientific support; dreams may be interpreted in many different ways.
- Information-processing:
  - Explanation: Dreams help us sort out the day's events and consolidate our memories.
  - Critical Considerations: But why do we sometimes dream about things we have not experienced and about past events?
- Physiological function:
  - Explanation: Regular brain stimulation from REM sleep may help develop and preserve neural pathways.
  - Critical Considerations: This does not explain why we experience meaningful dreams.
- Activation-synthesis:
  - Explanation: REM sleep triggers neural activity that evokes random visual memories, which our sleeping brain weaves into stories.
  - Critical Considerations: But it's our brain weaving the stories, so this still tells us something about ourselves.
- Cognitive development:
  - Explanation: Dream content reflects dreamers' level of cognitive development - their knowledge and understanding. Dreams simulate our lives, including worst-case scenarios.
  - Critical Considerations: Does not propose an adaptive function of dreams.

1.6a: Sensation Basic Concepts

Learning Objectives:
- 1.6-1: Explain the three steps that are basic to all of our sensory systems
- 1.6-2: Explain the difference between absolute threshold and difference threshold
- 1.6-3: Explain the function of sensory adaptation
Basic Concepts of Sensation and Perception:
- Sensation: Input about the physical world obtained by our sensory receptors, and perception is the process by which the brain selects, organizes, and interprets these sensations.
- Sensory Receptors: Sensory nerve endings that respond to stimuli
- Perception: The way sensory information is organized, interpreted, and consciously experienced.
Basic Concepts of Sensation and Perception
- Bottom-up processing: Perceptions are built from sensory input and work up to the brain’s integration of sensory information
- Top-down processing: Interpret of sensations is influenced by our available knowledge, our experiences, and our thoughts
Transduction:
- Transduction: Conversion of one form of energy into another. In sensation, the transforming of physical energy, such as sights, sounds, and smells, into neural impulses the brain can interpret
- Psychophysics: The study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them
Thresholds:
- Absolute threshold: The minimum stimulation necessary to detect a particular stimulus 50% of the time.
- Signal detection theory: A theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise).
Thresholds
- Subliminal below one’s absolute threshold for conscious awareness.
- Priming the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.
Thresholds
- Difference threshold: The minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (jnd).
- Weber’s Law: The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)
Sensory Adaptation
- Sensory Adaptation: Diminished sensitivity as a consequence of constant stimulation.
- Synesthesia: A neuropsychological condition that causes the brain to route sensory information through multiple unrelated senses, resulting in simultaneous experiences

1.6b: Vision

Learning Objectives:
- 1.6-4: Explain the characteristics of the energy that we see as visible light and describe the structure in the eye that helps focus that energy
- 1.6-5: Describe how the rods and cones process information, and explain the path information travels from the eye to the brain
- 1.6-6: Explain how we perceive color in the world around us
- 1.6-7: Describe the location and explain the function of feature detectors
- 1.6-8: Explain how the brain uses parallel processing to construct visual perception
Energy and the Eye Structure
- Wavelength: Distance of one wave peak to the next light or sound wave to the next.
- Hue: Color determined by length of the wave.
- Intensity: Amount of energy in wavelengths (determined by height/amplitude of wave- higher=brighter).
Eye Structure:
- Accommodation is the process by which the eye changes its optical power to maintain a clear image or focus on an object as its distance varies
- A nearsighted person sees near objects clearly, while objects in the distance are blurred.
- Farsightedness is the result of the visual image being focused behind the retina rather than directly on it.
- Lens: The transparent structure behind the pupil that changes shape to help focus images on the retina.
- Retina: The light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information and sending the info to the brain.
- Cornea: Outer covering of the eye. Bends light to provide focus. Protects the eye.
- Pupil: The adjustable opening in the center of the eye through which light enters.
- Fovea: The central focal point in the retina, around which the eye’s cones cluster.
- Iris: A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening. The iris dilates/constricts in response to changing light intensity
- Blind Spot: The point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.
- Optic Nerve: The nerve that carries neural impulses from the eye to the brain.
Eye Structure - Information Processing:
1. Light entering eye triggers photochemical reaction in rods and cones at back of retina.
2. Chemical reaction in turn activates bipolar cells.
3. Bipolar cells then activate the ganglion cells, the axons of which converge to form the optic nerve. This nerve transmits information to the visual cortex (via the thalamus) in the brain.
- Cones
  - Number: 6 million
  - Location in retina: Center
  - Sensitivity in dim light: Low
  - Color sensitivity: High
  - Detail sensitivity: High
  - Function: daylight, well-lit, color sensations
- Rods
  - Number: 120 million
  - Location in retina: Periphery
  - Sensitivity in dim light: High
  - Color sensitivity: Low
  - Detail sensitivity: Low
  - Function: black, white, gray
Color Processing:
- Young-Helmholtz