Sensation and perception Flashcards
define sensation
simple stimulation of a sense organ
basic registration of light, sound, pressure, smell or taste as parts of the body interact with the physical world
Define perception
organisation, identification & interpretation of a sensation in order to form a mental representation
How do sensory receptors communicate with the brain?
transduction
Define transduction
- when receptors convert physical signals from the environment into neural signals that are sent to the central nervous sytem
What energy is the eye uniquely sensitive to?
light
What energy is the skin uniquely sensitive to?
mechanical pressure
What is the illusion of perception?
- we can only see a small portion of the electromagnetic frequencies > those that generate visible light
- we can seem them because we have visual receptors for those frequencies
What is sensory adaptation?
sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current (unchanging) conditions
What causes sensory adaptation?
- our sensory systems respond more strongly to changes in stimuli than to constant stimulation
- changes in stimuli often signal a need for action
- sensory signals that don’t change usually don’t require any action & are discarded by body
What is psychophysics?
methods that systematically relate the physical characteristics of a stimulus to an observer’s perception
What is the simplest quantitative measurement in psychophysics?
absolute threshold: the minimum intensity needed to just barely detect a stimulus in 50% of the trials
What is a threshold in psychology?
A boundary btw 2 psychological states
(eg. unawareness and awareness)
What does the absolute threshold assess?
- sensitivity: how responsive we are to faint stimuli
- acuity: how well we can distinguish 2 very similar stimuli
What is the Just Noticeable Difference (JND)?
- the minimal changes in a stimulation that can barely be detected
- not a fixed quantity: depends on sense being measured
State Weber’s law
- For any sense domain, the change in a stimulus that’s just noticeable is a constant proportion despite variation in intensities
- for any sensory domain the ratio btw JND and standard stimulus is a constant value
What is signal detection theory?
The response to a stimulus depends on
1. a person’s sensitivity to the stimulus in the presence of noise
2. person’s decision criterion
What is light?
waves of energy that vary in height and wavelength
What are the 3 physical dimensions light waves vary on?
- Length: hue of wave & what we perceive as color
- amplitude: how high peaks are, what we perceive as brightness
- purity: if light is emitting just 1 wavelength or a mix of wavelengths, affects color perception
In what order does the eye detect light?
Cornea > iris > retina >
What is the cornea?
- first outer layer of eye
- bends light wave and sends it through the pupil
What is the iris?
- colored part of the eye
- translucent donut shaped muscle that controls the size of the pupil & hence the amount of light that enters the eye
- behind the iris, a muscle controls shape of lens to bend light & focus it onto retina
What is the retina?
- layer of light sensitive tissue lining the back of the eyeballs
- interface btw light outside of body and the world of vision in the central nervous system
- muscle changes the shape of the lens to focus on objects at diff. distances
What is the process of visual accommodation?
- process whereby the eye maintains a clear image on the retina
What happens when the eyeball is too long?
images are focused in the front of the retina > myopia (nearsightedness)
What happens when the eyeball is too short?
images are focused behind the retina > hyperopia (farsightedness)
What are the 2 types of photoreceptor cells in the retina?
- cones
- rods
What are cones?
- detect colors
- operate under normal daylight conditions
- allow us to focus on fine details
What are rods?
- become active only under low light conditions /night vision
- more sensitive photoreceptors than cones but provide no info about color & sense > only shades of gray
- 120M distributed evenly across retina except middle
What is the area of the retina where there are no rods ?
Fovea: area where vision is clearest
- absence of rods means less sharpness of vision in low light but enhanced sensitivity to faint light in the rest of retina
- cones are densely packed in fovea
What are the 3 layers of the retina?
- Photoreceptor cells (rods, cones): innermost layer
- Bipolar cells: collect electrical signals from rods and cones and transmit them to outermost layer of retina
- Retinal ganglion cells: organise signals and send them to the brain
What forms the optic nerve?
- bundled Retinal ganglion cells form optic nerve
- optic nerve has no rods or cones > no mechanism for sensing light
What is a blind spot?
location in visual field that produces no sensation on the retina
Why don’t we notice blind spots?
Because our perceptual system automatically fills in using knowledge (color, texture) around blind spot
How does the optic nerve carry neural impulses to the brain?
- streams of action potentials containing info encoded by retina, travel along optic nerve
- info first goes to Lateral geniculate nucleus (thalamus)
- from LGN visual signals travel to Area V1 at back of brain
What is Area V1?
- part of occipital lobe that contains primary visual cortex
- contains neurons each tuned to respond to edges oriented a particular way in a particular location in space
Who discovered that the perception of color is created by the brain?
Isaac Newton 1670
What are the 3 types of cones?
- L-cones: sensitive to long wavelengths
- M-cones: sensitive to medium wavelengths
- S-cones: sensitive to short wavelengths
What do disorders where cone(s) is missing cause?
color vision deficiency or color blindness
What is the color opponent system?
- pairs of cone types work in opposition: L-cone against M-cone and S-cone against M-cone
What is the visual receptive field?
region of visual field to which each neuron responds
What are the 2 visual streams?
- ventral stream
- dorsal stream
What’s the ventral stream?
- travels across occipital lobe into lower levels of the temporal lobes & includes brain areas that represent an object’s shape & identity
> represents “what” an object is
What is the dorsal stream?
travels up from occipital lobe to parietal lobes & includes brain areas that identify where an object is & how it’s moving
How are the ventral & dorsal streams functionally distinct?
- one stream may be damaged & the other intact but the 2 streams must still work together during visual perception
> to integrate perception for identification (ventral)
> to integrate perception for action (dorsal)
What is visual form agnosia?
inability to recognize objects by sight
What is the binding problem?
how brain links features together so that we see unified objects in our visual world, rather than free floating/mismatched items
What is the theory linked to the binding problem?
Binding neurons: neurons in ventral visual stream that receive coincidental input from other neurons involved in representing diff. features of an object
How are individual features bound into a whole?
specialised feature detectors in diff. parts of the visual system analyse each of the multiple features of a visible objects: orientation, color, shape
What is parallel processing?
brain’s capacity to perform multiple activities at the same time
What is an illusory conjunction?
perceptual mistake whereby the brain incorrectly combines features from multiple objects
Why do illusory conjunctions occur?
Feature integration theory (Treisman)
- focused attention isn’t required to detect the features that make up a stimulus. but it’s required to bind those individual features together
- occur when it’s hard for people to pay full attention to features that need to be combined
Define attention
active & conscious processing of particular information
What are 2 theories on recognising objects?
- diff. regions of ventral stream responds preferentially to diff. objects (faces, scenes…)
- distributed representation: the pattern of activity across multiple brain regions that identifies any viewed object, incl. faces
What is machine learning?
computers learning from very large data sets to identify patterns
What is perceptual constancy?
even as aspects of sensory signals change, perception remains constant
Where in the brain are object’s visual properties analysed?
- ventral visual stream
What is perceptual organisation?
- group features that belong together into one object
- segregate features that belong to different objects
- perceptual system automatically delivers us the interpretation that’s simplest & most meaningful/consistent w/ our experience and expectations
What is gestalt perceptual grouping?
- simplicity: when confronted with 2 or more possible interpretations of an objects shape we tend to select the simplest interpretation
- closure: we tend to fill in missing elements of a visual scene
- continuity: edges/contours that have same orientation have good continuation & get grouped together
- similarity: regions similar in color/shape/texture are perceived as belonging to the same object
- proximity: objects that are close together tend to be grouped together
- common fate: elements of visual image that move together are perceived as part of single moving object
What are the 3 dimensions of objects?
length
width
depth
How many dimensions does retinal image contain?
2: length and width
What are the 2 types of depth cues?
- Monocular: aspects of a scene that yield info about depth when viewed with only one eye
- Binocular: difference in retinal images of the 2 eyes that provides info about depth
What are the 3 monocular depth cues?
- Linear: phenomenon where parallel lines seem to converge as they recede into distance
- Texture gradient: how textures look more detailed close up but more uniform & smooth when farther away
- Interposition: when one object partly blocks another, you can infer that the blocking object is closer than the blocked object
What does relative height of an image depend on?
field of vision:
- objects closer to you tend to be lower in visual field
- faraway objects are higher up in visual field
How do binocular depth cues work?
- eyes are slightly separated: each registers a slightly different view of the world
- brain computes the diff. btw 2 retinal images & uses this to perceive how far away objects are
Who invented the Stereoscope?
Sir Charles Wheatsone 1939W
What is a forced perspective illusion?
- when you view 2 objects that project the same retinal image size, the object you perceive as farther away will be perceived as larger
- only work from one vantage point
eg. Ames room
How does the visual system sense motion?
- it must encode info about space and time
- as an object moves across stationary observer’s visual field, it first stimulates one location on retina then soon after stimulates another location on retina
- neural circuits in brain can detect change in position over time & respond to specific speeds and direction of motion
What does the perception of motion depend on?
relative activity in opposing sets of motion detector cells
- if there’s no motion > activity in 2 set of cells is equal
- if one set of motion detector cells is fatigued due to adaptation to motion in one direction, stop is perceived as movement in opposite direction
What is apparent motion?
perception of movement as a result of alternating signals appearing in rapid succession in different locations
What is biological motion perception?
- our ability to perceive biological motion critical for identifying individuals & various socially relevant features
- occurs in posterior superior temporal sulcus
What is the visual system sensitive too?
spatial acuity: ability to distinguish btw 2 stimuli that are very close in space
What is the auditory system sensitive to?
Temporal acuity: ability to distinguish 2 stimuli that are close together in time
Define multisensory
Stimulating multiple senses at the same time
What is change blindness?
when people fail to detect changes to visual details of a scene
- importance of attention for detecting changes & binding features together
what is inattentional blindness?
failure to perceive objects that are not the focus of attention
What is synesthesia?
when one attribute of a stimulus leads to the conscious experience of an additional attribute
What are sound waves?
Changes in air pressure unfolding over time
hearing= transforming changes in air pressure into meaningful sound objects (or sources)
What is a pure tone?
a simple sound wave that consists of regularly alternating regions of higher & lower air pressure radiating outwards in all directions
What are the 3 dimensions of a sound wave
- frequency: repetition rate
- amplitude: intensity
- complexity: mix of frequencies
What is the frequency?
- depends on how often the peak in air pressure passes the ear (Hz)
- perceived as pitch > how high/low a sound is
What is amplitude?
- intensity of sound relative to the threshold for human hearing
- perceived as loudness
What is complexity?
- influences perception of timbre (quality of sound that allows you to distinguish 2 sources with the same pitch)
What are the 3 parts of the human ear?
- outer ear
- middle ear
- inner ear
What is the outer ear?
- collects sound waves and funnels them towards middle ear
- consists of visible part outside (pinna), auditory canal and eardrum
- eardrum= airtight flap of skin that vibrates in response to sound waves gathered by pinna & channeled into the canal
What is the middle ear
- transmits vibrations to the inner ear
- tiny air-filled chamber behind eardrum
- contains 3 smallest bones in the body (ossicles)
- ossicles fit together into a lever that mechanically transmits & amplifies vibrations from eardrum
What is the inner ear?
embedded in skull, where sound waves are transduced into neural impulses
What is the cochlea?
- in the inner ear
- fluid filled tube that contains cells that transduce sound vibrations into neural impulses
- divided along its length by basilar membrane
What is the basilar membrane?
structure in the inner ear that moves up and down in time with vibrations relayed from ossicles, transmitted through oval window
How does the basilar membrane move up and down due to sound?
In a travelling wave
How does auditory transduction work?
- inside cochlear, basilar membrane undulates in response to wave energy in cochlear fluid
- diff. locations in membrane sensitive to diff. frequency components
- movement of basilar membrane causes hair cells at those locations to bend
- bending generate action potential in attached auditory nerve axons which together form the auditory nerve that emerges from cochlea
What are inner hair cells?
specialised auditory receptor neurons embedded in the basilar membrane
How do auditory neural impulses get to the brain?
- auditory nerve carries action potential to the thalamus and ultimately to Area A1, the primary auditory cortex in temporal lobe
What is Area A1?
- primary auditory cortex
- folded into temporal lobe beneath lateral fissure in each hemisphere
- lower frequencies towards front of brain
- higher frequencies towards the back
What is a place code?
- diff frequencies stimulate neural signals at specific places along the basilar membrane
- brain use info about the relative activity of hair cells across whole basilar membrane, to help determine the pitch you hear
What is a temporal code?
- the brain uses the timing of the action potentials in the auditory nerve to help determine the pitch you hear
What are the 2 cues to location in hearing?
monoaural (one ear)
binaural (2 ears)
How do we determine where a sound is coming from?
- pinnas: intricate folds alter sound, emphasizing some frequency components over others, depending on where the sound is coming from
- speed of sound is slower than speed of light >this time difference is effective for indicating the location of lower frequency components
- higher frequency components are more intense in the ear closer to sound because listener’s head blocks higher frequencies
How do Gestalt rules apply to sound?
- sounds that are similar in frequency, loudness, pitch, timbre, or location are grouped into one sources
- sounds that occur close together in time are grouped
- sounds that start together and stop together are perceived as coming from the same source
What are the 2 types of hearing loss?
- conductive hearing loss: eardrums/ossicles are damaged to the point they can’t conduct sound waves effectively to cochlea
> medication, surgery, hearing aid - Sensorineural hearing loss: damage to the cochlea, hair cells or auditory nerve (aging)/ sensitivity and acuity decreases
What is a cochlear implant?
- electronic device that replaces the function of hair cells
- sound picked up by mic is transformed into electric signals by processor
- signal is transmitted to implant receiver, which activates the electrodes in cochlea
What is haptic perception?
active exploration of the environment by touching and grasping objects with our hands
What is a tactile receptive field?
small patch of skin that relates info about pressure, pain, texture, pattern or vibration to a receptor
What are 3 important principles regarding neural representation of the body’s surface?
- left half of body is rep. in right half of brain and vice versa
- diff locations on body send sensory signals to diff locations in somatosensory cortex; more of tactile brain devoted to parts of skin surface
- “what” and “where” pathways: what system provides info about properties of surfaces & objects and where system provides info about location in external space that’s being touched or bodypart stimulated
How is pain sensed?
- pain indicates damage/potential damage to the body
- fast-acting A delta fibres: transmit initial sharp pain
- C fibres: transmit longer lasting dull/persistent pain
What coordinates the pain-withdrawal reflex?
Spinal cord
Which 2 areas do neural signals for pain travel to?
- Somatosensory cortex: identifies where pain is occurring and what sort of pain it is
- motivational and emotional centres: hypothalamus, amygdala, frontal lobe; unpleasant & motivates us to escape from/relieve the pain
What is referred pain?
- when sensory info from internal and external areas converge on the same nerve cells in spinal cord
eg. when pain originates internally, we can feel it on the surface of the body
What is the gate-control theory?
signals arriving from pain receptors in body can be stopped by interneurons in the spinal cord, via feedback from skin or the brain
eg. rubbing stubbed toe activates neurons that close pain gate
Where does the brain’s feedback to the spinal cord come from?
Region in midbrain called Periaqueductal grey (PAG)
What is proprioception?
Your sense of bodily position
- perception of position and movement of limbs, torso, hands in space depends on stimulation of receptors in muscles, tendons and joints of body
- info about which way is up and about head movement (for balance) originates in the inner ear
How do we maintain our balance?
- vestibular system: 3 fluid-filled semicircular canals and adjacent organs located next to cochlea in each inner ear
- canals are studded with hair cells that detect movement of fluid when head moves
- bending of hairs generates activity in vestibular nerve that’s conveyed to brain
- this detected motion allows us to maintain balance + vision (mismatch btw info from visual cues & vestibular feedback causes motion sickness)
What is the perceptual experience of flavor?
the combination of smell and taste
How does olfactory info enter the brain?
- enters the frontal lobe, amygdala, hippocampus & other forebrain structures directly
- relationship btw smell and emotions and memories
What are odorant molecules?
chemicals
What is an olfactory receptor neuron (ORN)?
- contained in olfactory epithelium along top of nasal cavity
- receptor cells that transduce odorant molecules into neural impulses
- each ORN has receptors that bind some odorants but not to others
- 350M diff ORN types
Where do olfactory receptor neurons that are sensitive to the same odorant send their axons?
olfactory bulb
What is the final stage of olfactory bulb processing?
- in the axons that form the olfactory nerve
- olfactory bulb sends outputs to various centres in brain (incl. emotional & memory centres)
What are pheromones?
- biochemical odorants emitted by other members of an animal’s species that can affect its behavior or physiology
- play a key role in reproductive & social behavior in insects and some mammals
What is the main responsibility of the chemical sense of taste?
- identifying things that are bad for you (poisonous/lethal)
What are the 5 main taste receptors?
- salt
- sour
- bitter
- sweet
- umami (savory)
What are papillae?
- small bumps on surface of tongue
- contain taste buds: organs of taste transduction
How many taste receptor cells does each taste bud contain?
50-100
What are the tips of taste buds?
microvilli > react with tastant molecules in food
What is the 6th basic taste?
fat: sensation people experience in response to fatty acids > oleogustus
Which brain areas are sensitive to odors from food?
- primary olfactory cortex
- primary gustatory cortex (taste)
- mouth region of primary somatosensory cortex
