psych chapter 5 sensation and perception

synesthesia

a condition in which stimulation of one sense unintentionally evokes perceptions in another sense (ex: hearing colours, tasting shapes), it involves mixing of sensory modules

what do Maurer and Mondloch suggest about synesthesia in infants?

that all infants may be born synaesthetic because early neural pathways are undifferentiated, potentially causing cross-module perceptions 

how does functional MRI support synesthesia?

synesthetes with word-colour linkages show activity in visual cortex when hearing certain words, indicating cross-activation between sensory regions

what does diffusion tensor imaging show in synesthesia?

increased white matter connectivity, supporting the idea that synesthetes retain extra neural connections 

what are the 2 main theories explaining synesthesia?

1. failure of neural pruning - infants’ excessive connections weren’t removed 

2. deficit of neural inhibition - normal inhibitory processes fail to prevent overflow between modules  

sensation 

The process which sensory organs detect and translate environmental stimuli into nerve impulses 

perception

the active process of organizing and interpreting sensory input to give it meaning

transduction

the conversion of physical stimulus energy (light, sound, chemicals, pressure) into neural impulses

what is the sequence from sensation to perception?

1. stimulus received

2. transduction into nerve impulses

3. feature detectors analyze stimulus

4. stimulus features reconstructed into neural representation

5. compared with stored knowledge

6. recognized and interpreted

7. perception occurs

the binding problem

the question of how separate sensory features (colour, shape, smell, touch) are combined into a unified perception

psychopsychics 

the study of relationships between physical stimuli and sensory experiences

2 main concerns of psychophysics

1. absolute limits of sensitivity

2. sensitivity to differences between stimuli

absolute threshold

the lowest stimulus intensity detected correctly 50% of the time

subliminal stimulus

a stimulus below the absolute threshold that is sensed but not consciously perceived

difference threshold (JND)

the smallest detectable difference between 2 stimuli, detected 50% of the time

weber’s law

the JND is proportional to he magnitude of the original stimulus, expressed as a Weber fraction

• ex: for lifted weights, the Weber fraction is 1/50: a 50 g weight must be compared with at least 51 g to detect a difference

what does signal detection theory account for?

sensory judgements influenced by psychological factors (fatigue, expectations, consequences)

decision criterion

the standard a person uses to decide if a stimulus is present, can shift based on context

sensory adaptation

decreased sensitivity in sensory receptors to constant or unchanging stimulation

• adaptive because it enhances our ability to detect changes in the environment

what is the normal stimulus for vision?

electromagnetic energy (light waves)

what wavelengths can humans detect?

approximately 400-700 nm

what is the function of the cornea?

transparent protective structure that starts focusing incoming light

what controls pupil size?

muscle of the iris; dilates in low light, constricts in bright light

how does the lens focus?

• becomes thinner for distant objects

• thicker for nearby objects

myopia vs hyperopia

• myopia = nearsightedness - focal point is in front of the retina; eyeball is too long

• hyperopia = farsightedness - focal point is behind the retina; eyeball is too short

how does natural light protect against myopia and hyperopia?

increases dopamine and vitamin D, which support eye development

rods

• photoreceptor cells in the retina of the eye

• very sensitive to light, function in dim light

• do not detect colour

• 120 million (in each eye)

cones

• a type of photoreceptor cell in the eye that is responsible for colour vision and seeing fine details

• concentrated in fovea (a small depression/pit in the retina)

• 6 million (in each eye)

why is visual acuity (sharpness of vision) highest in the fovea?

each cone has its own dedicated bipolar cell (neurons in the retina that connect photoreceptor to retinal ganglion cells, forming a key part of the visual pathway)

why are the rods effective in dim light?

many rods share bipolar cells, allowing their signals to combine (weak signals from many individual rods combine → highly sensitive to light, essential for night vision)

what causes the blind spot?

optic nerve exits the eye wherer there are no photoreceptors

• we don’t notice the blind spot because because our brain fills in the missing information

photopigments

light-absorbing molecules that change shape when they absorb a photon, converting light energy into an electrical signal sent to the brain, found in photoreceptor cells

dark adaptation

increased sensitvity to light as photopigments regenerate

trichromatic theory

three cone types (red, green, blue) whose relative activation produces all colours

• evidence challenging it:

  • people with red-green colourblindness still perceive yellow

  • negative afterimages

opponent-process theory

three receptor systems that work in opponent pairs:

• red-green

• blue-yellow

• black-white 

dual process theory

combines trichromatic (at receptor level) and opponent-process (at neural processing level)

trichromat, dichromat, and monochromat

• trichromat - normal vision

• dichromat - one colour system is deficient

• monochromat - only black-white; total colour blindness

feature detectors

neurons in the visual cortex that respond selectively to specific features (colour, movement, depth)

parallel processing

stimulatenous analysis of multiple visual features (shape, colour, movement)

frequency

number of cycles per secod (Hz); determines pitch

amplitude

height of sound wave; determines loudness (measured in decibels)

• the absolute thresold for hearing is 0 dB

3 bones in the middle ear

hammer (malleus), anvil (incus), stirrup (stapes)

cochlea

fluid-filled, snail-shaped structure containing basilar membrane (stiff, vibrating structure, frequency analyzer) and organ of Corti (produces nerve impulses in response to sound vibrations)

hair cells

sound receptor cells that release neurotransmitters when bent by fluid waves (found in the organ of Corti)

frequency theory

nerve impulses match the frequency of sound waves - works up to 1000 Hz

place theory (Bekesy)

location on the basilar membrane where waves peak encodes pitch; supports higher frequencies

how do frequency and place theory fit together?

• frequency theory - low frequencies

• place theory - high frequencies

how do we localize sound?

by comparing timing and intensity differences between ears 

conduciton deafness

mechanical problems transmitting sound to cochlea; treatable with hearing aids

nerve deafness

damage to hair cells or auditory nerve; hearing aids ineffective

4 primary taste qualities

sweet, sour, salty, bitter (plus umami)

where are the taste buds located?

primarily along edges and back of the tongue

how does taste work?

chemicals dissolve in saliva → enter taste pores → activates taste receptors → neural signals combine to create flavour

olfactory receptors

approximately 40 million receptors in nasal cavity that bind odour molecules

how are odours coded?

different odours activate specific regions of the olfactory bulb (neural structure in the forebrain that processes information about smells)

pheromones

chemical signals that can influence behaviour (ex: menstrual synchrony)

4 basic skin sensations

pressure, pain, warmth, cold

free nerve endings

pain and temperature receptors beneath skin surface, lack a complex sensory structure or capsule

why do some areas have higher sensitivity?

more coritcal area in somatosensory cortex devoted to them

phantom limb phenomenon

sensations from a missing limb due to brain’s representation of the body

gate control theory of pain

pain perception results from spinal gates that open or close based on sensory input 

central control mechanism

mental factors (thoughts, expectations, emotion) influence pain perception

what role glial cells play in pathological pain?

they become activated by immune challenges or substances in the pain pathway, releasing cytokines that increase inflammation and amplify pain

what causes the ache all over feeling when you’re sick?

cytokine release from activated glial cells that promotes inflammation

how do endorphins reduce pain?

they inhibit the release of neurotransmitters involved in transmitting pain signals from the spinal cord

what conditions can acupuncture help with?

fibromyalgia, lower back pain, Parkinson’s disease, and migraines

kinesthesis

the sense that provides feedback on body position and mvoement, enabling coordinated motion

vestibular sense

the sense of balance/orientation, located in the inner ear’s vestibular apparatus

what do the semicircular canals (3 fluid filled tubes in the inner ear) detect?

• acceleration and deceleration of head movement

• detect rotational movements of the head to help maintain balance

why don’t the semicircular canals respond to constant movement?

The fluid and hair cells return to their resting state once constant speed is reached

what infomation do the vestibular sacs provide?

detect whether the body is upright or tilted

what principle does the Sonicguide use to help the blind navigate?

echolocation - high frequency sound waves bounce off objects and are converted into audible cues

why is the tongue used in the “seeing tongue” device? (for blind individuals)

it provides detailed tacticle input and is highly sensitive

how do retinal implants help restore vision?

they replace damaged photoreceptors or stimulate ganglion cells (final output neurons of the retina, transmit visual info from eye to brain via optic nerve) using light pulses processed from visual images

cortical implants

neuroprosthetics that connect directly to the cerebral cortex and provide localized stimulation depending on placement

cochlear implants

bypass damaged hair cells by directly stimulating the auditory nerve with electrodes, for people that have nerve deafness (can’t be helped with hearing aids)

what sensory function does the SmartHand restore?

touch, using 40 sensors connected to sensory nerves in the arm (prosthetic for people that have lost their hands)

name the monocular cues (using one eye) for depth perception

• light/shadow (3-D effect)

• linear perspective (perception that parallel lines converge or angle toward each other as they recede into the distance)

• interposition (objects closer to us may cut off parts of our view of more distant objects)

• height in plane

• texture gradient 

• clarity

• realtive size 

• motion parallax (when moving, nearby objects appear to move faster and in the opposite direction compared to distant objects)

binocular disparity

each eye sees a slightly different image; the brain uses this disparity to perceive depth

convergence

eye muslces turning inward to focus on near objects; the brain uses this for depth cues

primaru cue for perceiving movement

movement of an image across the retina

stroboscopic movement

illusory movement created by rapidly flashing lights in sequence, used in marquee lights and movies

illusions

erroneous perceptions or incorrect perceptual hypotheses

what causes most visual illusions?

perceptual constancies that usually help us perceuved accurately but can be tricked

how can illusions arise from monocular cues?

when cues are manipulated to create “impossible” scenes that don’t match our perceptual schemas

critical period

a time when specific experinces must occur for normal sensory/perceptual development

• if a critical period is missed, permanent deficits may occur that cannot be reversed

what did Blakemore and Cooper’s kitten experiment show?

early visual experiences shape brain development; lack of variety in visual input leads to lasting perceptual deficits

what happened to Virgil after cataract surgery?

he could see light and colour but couldn’t interpret visual information; early deprivation prevented normal perceptual development (missed critical period)

3 categories of factors that shape perception?

• biological: evolutionary processes in sensory systems

• environmental: environmental stimulation is needed during early critical periods for development of the sensory systems

• psychological: stimuli are given psychological meaning; we are especially attentive to stimuli that are relevant to our well-being