Psyc 100

Lecture 5: Sensation and Perception

Sensation: Act of using sensory systems to detect environmental stimuli

-        What stimuli can our body detect, and how?

Perception: Conscious recognition and identification of a sensory stimulus

-        How does brain make sense of the information our sense have detected?

Senory Receptor Cells

-        Specialized cells that convert a specific form of environmental stimuli into neural impulses

o   Sensory transduction: Process of converting stimuli into a neural impulse that our brain can read

Limits of the Senses

-        Thresholds: Our senses require a certain amount of sensory input to detect things

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-        Absolute Threshold: Smallest amount of stimulus that one can detect

o   Smell: A drop of perfume diffused throughout a six-room apartment

o   Taste: 5 mm of sugar in 9 litres of water

o   Touch: Insect’s wing falling on your cheek from a centimeter of height

o   Hearing: Tick of a watch 6 meters away in a quiet room

o   Sight: Candle flame 50 km away on a clear, dark night

-        Difference Threshold (just noticeable difference): Minimal difference needed to notice a difference between two stimuli

o   Sensory sensitivity depends on experience, expectations, and consequences for failure

-        Signal Detection Theory: Response to a signal depends on the ability to differentiate between the signal and noise, and on their response criteria

o   E.g. Explores how strong a signal must be for detection

Sensory Adaptation

-        Repeated stimulation of a sensory cell leads to reduced response

o   Ex. Tag in your shirt bothered you in the morning, but now it is unnoticeable.

Bottom-up processing

-        Perception where environmental stimuli are transformed to neural impulses that successfully move into more complex brain regions

o   Ex. Light from friend’s face is converted to neural impulses that travel into the brain to visual regions

Top-down Processing

-        Perception process led by cognitive processes, such as memory or expectations

o   Ex. When you look at your best friend, brain regions that store information about what faces look like can help perceive and recognize visual stimulus

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The Senses

-        Nervous system is composed of different sensory systems that transduce different stimuli into neural impulses

o   Smell, touch, taste, sound, sight, kinesthetic (body’s movement, posture), vestibula (head’s position and movement), and thermoception (temperature detection) and nociception (pain detection)

The Chemical Senses

-        Olfactory sense (smell), Gustatory sense (taste)

-        Smell

o   Odourants: Airborne chemicals that are detected as adours

o   Olfactory receptor neurons: Cells that convert chemical signals from odourants into neural impulses

-        Taste

o   Papillae: Bumps on tongue that contain clumps of taste buds

o   Taste buds: Clusters of sensory receptor cells that convert chemical signals from food into neural impulses

§  Includes sweet, sour, bitter, salt, and umami (taste of MSG) receptors

§  Babies like sweet more than sour, prefer odour of mother’s milk

Individual Differences in Taste and Smell

-        Females are more sensitive to odours than males

-        Taste is variable in individuals; some more sensitive to bitter than others

Smell and Taste Disorders

-        Ageusia: Inability to taste

-        Anosmia: Inability to detect odours

-        Hyposmia: Reduced ability to smell

-        Reflex epilepsy: Seizure occurs only after exposure to a specific odour

-        Migraine headaches: Specific odours can trigger migraines

Tactile or Cutaneous Senses

-        Tactile or somatosensory system: Combination of skin senses

o   Pressure

o   Touch

o   Temperature

o   Vibration

o   Pain

Different Somatosensory Receptors

-        Free nerve endings

o   Located near surface of the skin

o   Detects touch, pressure, pain, and temp

-        Meissner’s corpuscles

o   Located in fingertips, lips, and palms

o   Transduce information about sensitive touch

-        Merkel’s discs

o   Located near surface of the skin

o   Transduce information about light to moderate pressure against the skin

-        Ruffini’s end-organs

o   Deep in the skin

o   Register heavy pressure and movement of joints

-        Pacinian corpuscles

o   Deep in skin

o   Respond to vibrations and heavy pressure

Two Pathways of Pain

-        Fast pathway: Sharp, localized pain is felt quicker because it travels along myelinated neurons to the brain

-        Slow pathway: These inputs communicate with brain regions involved in processing emotions; pain we perceive via the slow pathway is more often burning pain than sharp pain

Development of Tactile Senses

-        Developed at birth

-        Ability to respond to different somatosensory stimuli is dependent on brain development and learning

Tactile Senses: Individual differences

-        Women have lower threshold for detecting pain than men

-        Neuroimaging studies have revealed that people’s brains react differently depending on their sensitivity to pain

Disorder of the Tactile Senses

-         Chronic pain is most common abnormality

-        No pain: Rare genetic condition resulting in inability to detect pain or temperature

-        Phantom limb sensations: tactile hallucinations of touch, pressure, and pain in body part that no longer exists

Auditory Sense

-        Sound waves: Vibrations of the air in the frequency of hearing

-        Frequency: Number of cycles per second in a wave: measured in Hz 

-        Amplitude: Magnitude (height of a wave): measured in dB

How the Ear Hears

-        Sound waves enter outer ear

-        Waves hit the eardrum

-        Waves pass into the middle ear

-        Stapes hits the oval window, causing a wave to form in the fluid of the cochlea

-        Fluid deflects the basilar membrane, bending its hair cells that transduce the sound wave into electrical activity

-        As hair cells move, neural impulses are created and sent to the brain

Identifying Frequency and Pitch

-        Frequency Theory: Different sound frequencies are converted into different rates of action potentials

o   High-frequency sounds produce a more rapid firing

-        Place Theory: Differences in sound frequency activate different regions of the basilar membrane

o   Brain equates the place activity occurred on the basilar membrane with a particular frequency

Sound Adaptation

-        Muscles around our ears can contract so less sound waves enter the ear

-        Ears become less sensitive to continuous noise

-        Our brains filter out sounds that are not important

-        Cocktail party effect: Brain picks up relevant sounds even in noisy environments

Sound Localization

-        General loudness: Louder sounds seem closer

-        Loudness in each ear: The ear closer to the sound hears a louder noise than the other

-        Timing: Sound waves will reach the ear closer to the source of the sound before they reach the ear farther away

Development of Hearing

-        Babies can hear before they are born

-        Ability to recognize and respond appropriately to sounds develops in first few months

-        Infants prefer speech to non-speech

Hearing Loss

-        Deafness: Loss of hearing

o   Can be genetic, infectious, physical, exposure to toxins, etc.

-        Tinnitus: Ringing in ear

o   Due to abnormalities in the ear

Visual Sense

-        How the eye works

o   Light enters eye

o   Iris adjusts pupil size to control amt of light

o   Iris also changes shape of the lens to focus

o   Lens focuses the light on the retina, a multi-layered sheet of nerve cells

o   Photoreceptors (sensory receptor cells for vision called rods and cones) are located in retina

o   Rods and cones transduce light waves into a neural impulse

The Retina

-        Rods

o   Detects light

o   Used for periphery and night vision

o   Not as acute as cones

o   Many more rods than cones

-        Cones

o   Used for central and colour vision

o   Very acute (very clear)

§  The fovea (centre of retina) contains all cones

o   Less than rods

Seeing in colour

-        Hue: Experience of colour based on the wavelength of light

-        Saturation: Purity of color: how bright or vivid it is

-        Brightness: How much light is reflected from the object  

Theories for how we see colour

-        Trichromatic theory: Three different snsors for colour and each type responds to a different range of wavelengths of light

-        Opponent process theory: Colour pairs work to inhibit one another in the perception of colour

Visual Pathway

-        Optic nerve contains the axons of 1 million ganglion cells that exist the eye via the blind spot and project to the thalamus

“What” Pathway

-        Helps determine identity

-        Visual agnosia: Damage to the “what” pathway; cannot recognize objects

-        Prosopagnosia: A form of visual agnosia in which people cannot recognize faces

“Where” Pathway

-        Locating objects in space

-        Hemi-neglect: damage to the “where” pathway: people ignore one side of their visual field

o   People with damage to the right side of “where” pathways neglect left side of their visual field

Gestalt (Top-Down Processing) Laws

-        Proximity: Objects physically close together are grouped together

o  

-        Similarity: Similar objects are grouped together

-        Continuity: Objects that continue a pattern are grouped together

-        Closure: We fill in small gaps in objects to perceive them as whole objects

-        Figure ground: Tendency to perceive one aspect as the figure and other as the background

Depth Perception

-        Binocular cues: Cues from both eyes

-        Retinal Disparity: different images of objects are cast on the retinas of each eye

-        Convergence: Tendency of eyes to move toward each other as we focus on objects up close

Monocular Cues

-        Relative height: We see objects that are higher in our visual plan e as further away than those that are lower

-        Texture gradient: We can see more details of textured surfaces when they are closer

-        Relative Height: When two objects we know are the same size, the smaller one we recognize as further

-        Linear perspective: parallel lines seem to converge in the distance

Perceptual Constancies: Shape and Size Constancy

-        Perceptual constancy: Our top-down tendency to view objects as unchanging, despite shifts in the environmental stimuli we receive

-        Size constancy: We perceive objects as the same size regardless of the distance from which it is viewed

-        Shape constancy: we see an object as the same shape no matter from what angel it is viewed

The Visual Sense: Sight

-        Development of sight

o   Newborns can see, but their vision will improve significantly by two months

o   At eight months, visual acuity is similar to adults

o   Experience with the visual world is necessary for normal visual system development

-        Visual Impairment

o   Strabismus: Lack of coordinated movement of both eyes

o   Amblyopia: Loss of visual abilities in a weaker eye

Other senses

-        Kinesthetic – receptor cells in your muscles tell the brain when we are moving and where our body parts are in space

-        Vestibular – located in the semicircular canals of our inner ears; the movement of fluid tells us if we are standing up or swaying from side to side

Lecture 7: Learning

Learning

-        Lasting change caused by experience

-        Associative Learning: Connections are formed between two or more stimuli; accounts for most learning

o   Conditioning: The association of events in the environment

o   Classical Conditioning: A form of associative learning between two previously unrelated stimuli that results in a learned response

§  Unconditioned stimulus (US): a stimulus that on its own elicits a response (food)

§  Unconditioned response: a physical response elicited by an unconditioned stimulus (does not need to be learned). i.e. salivation

§  Conditioned stimulus (CS): neutral stimulus that eventually elicits the same response as an unconditioned stimulus which it has been paired (bell)

§  Conditioned response (CR): physical response elicited by a conditioned stimulus; acquired through experience and is usually same as unconditioned response

§  Processes of Classical Conditioning

·       Acquisition: Initial learning of the stimulus-response relationship

o   The more pairings between CS and US, the more likely the association is learned

·       Extinction: Reduction of a conditioned response after repeated presenatations of conditioned stimulus alone

·       Spontaneous recovery: re-emergence of a conditioned response some time after extinction has occurred  

·       Stimulus generalization: What occurs when stimulis similar to the original conditioned stimulus trigger the same conditioned response (people scared of snakes are scared of all snakes, not just the first encountered one)

·       Stimulus discrimination: the ability to tell the difference between one stimulus and similar stimuli

·       Higher-order conditioning: What occurs when a previously conditioned stimulus functions as if it were an unconditioned stimulus for further conditioning (if pavlov started pairing music with the bell and music leads to salivating)

-        Non-associative learning: Learning that does not involve forming associations between stimuli; learning occurs following repeated exposure to a single stimulus or event

o   Habituation: Weaking of response to a stimulus after repeated presentation

o   Dishabituation: There is a recovery of attention to a novel stimulus following habituation

o   Sensitization: A strong stimulus results in an exaggerated response to the subsequent presentation of weaker stimuli

Phobias

-        Persistent, irrational, or obsessive fear of a specific object or situation that may arise as a result of fear conditioning

-        Systematic desensitization: process to remove phobias with gradual exposure

Operant Conditioning

-        Behavior is modified depending on its consequences (Form of associative learning)

-        Law of effect: Behaviours leading to rewards are more likely to occur again, while unpleasantness are less likely.

Behaviourism and Operant Conditioning

-        Systematic study and manipulation of observable behaviour

-        B.F. Skinner: Organisms operate on the environment

Reinforcement

-        Reinforcer: Experience that produces an increase in a certain behaviour

-        Positive reinforcement: Pleasant consequence following a behaviour to make it more likely to reoccur

-        Negative reinforcement: Removal of an unpleasant stimulus after a response to make it more likely to reoccur

o   Ex. Putting seatbelt on to remove the beeping, phobia is negatively reinforced when individual escapes anxiety by avoiding the object

-        Punishment: Experience that decreases certain behaviour

-        Positive Punishment: Presentating an unpleasant consequence following a behaviour

-        Negative Punishment: Removal of pleasant stimulus as a consequence to a behaviour to make it less likely to reoccur

Types of reinforcers

-        Primary reinforcers: A stimulus that has survival value

o   Food, water, termination of pain

-        Secondary reinforcers; neutral stimulus that becomes rewarding when associated with a primary reinforcer; learned

o   Money, grades, praise, approval

Types of Punishers

-        Primary punisher: a stimulus that is naturally aversive to an organism

o   Slapping, loud sounds, extreme temperatures

-        Secondary punishers: Stimulus that becomes aversive when associated with a primary

o   Disapproval, criticism, bad grades

Schedules of Reinforcement

-        Continuous: Reinforced every time it occurs

-        Intermittent: Behaviour only followed by reinforcement some times

o   Ratio schedule

§  Fixed ratio schedule: Reinforcement occurs after a fixed number of responses

§  Variable ratio schedule: Reinforcement occurs after an unpredictable, average number of responses

o   Interval schedule

§  Fixed interval schedule: Reinforcement occurs every time a fixed time has elapsed

§  Variable interval schedule: Reinforcement occurs after varying lengths of time

Operant Conditioning and New Behaviours

-        Shaping: Introducing new behaviour by reinforcing behaviour close to the desired behaviour

o   Ex. Teaching a dog to roll over

-        Behavior modification: systematic approach to change behaviour using principles of operant conditioning

Learned Helplessness

-        Situations in which repeated exposure to inescapable punishment eventually produces a failure to make escape attempts

Observational Learning

-        Observational learning: Occurs without overt training in response to watching models

-        Vicarious learning: Occurs when an individual observes the consequences to another’s actions then chooses to duplicate the behaviour or refrain from doing so

-        Mirror neurons: Neurons fired when an animal or human performs an action or when they see another perform the same action

Learning and Cognition

-        Implicit learning: Refers to acquisition of information without awareness

-        Spatial navigation learning: Involves formal associations among stimuli relevant to navigating in space

-        Latent learning: a form fo learning that is not expressed until there is a reward or incentive

-        Insight learning: a sudden realization of a solution to a problem or leap in understanding new concepts

Factors that facilitate learning

-        Timing: Multiple exposures separated by time facilitate learning facts

-        Context: Studying in several different locations increase slikelihood to form strong memories about the information

-        Awareness and attention: Can enhance learning

Stroop Effect

-        Delay in reaction time between neutral and contradicting stimuli