Sensation & Perception Flashcards
Sensation def.
Can be considered transduction - the conversion of physical, electromagnetic, auditory, and other information to electrical signals in the nervous system
performed by receptors in the PNS
Perception def.
Processing of sensory information to make sense of its significance
Sensory receptors
Neurons that respond to stimuli and trigger electrical signals
-can encode multiple aspects of a stimulus
Ganglia
collections of neuron cell bodies found outside the CNS
-used to transmit information from the receptors to the CNS
Photoreceptors
respond to electromagnetic waves in the visible light spectrum
hair cells
respond to movement of fluid in the inner ear structures
-hearing, rotational and linear acceleration
nociceptors
respond to painful or noxious stimuli (somatosensation)
thermoreceptors
respond to changes in temperature
osmoreceptors
respond to the osmolarity of the blood
olfactory receptors
respond to volatile compounds
taste receptors
respond to dissolved compounds
Threshold
minimum amount of a stimulus required to render a change in perception
Absolute threshold
minimum stimulus energy needed to activate a sensory system
- threshold in sensation not perception
- how bright/loud/intense a stimulus must be before we sense it
Threshold of conscious perception
sensory signals can reach the CNS without perception occurring
-stimulus is to subtle or brief to be attended to
Difference threshold
also called the just-noticeable threshold
minimum difference in magnitude between two stimuli before one can perceive this difference
Weber’s law
Constant ratio between the change in stimulus magnitude needed to produce a jnd and the magnitude of the original stimulus
= change in stimulus / original stimulus magnitude
signal detection theory
How the perception of stimuli can be affected by nonsensory factors such as memory, motives and expectation
Response bias
tendency of subjects to respond systematically to a stimulus in a certain way due to nonsensory factors
-can be determined by the proportion of misses or false alarms in an experiment
Basic signal detection experiment components
catch trial: signal is presented
noise trial: signal is not presented
hits: correct perception of signal
misses: fails to perceive given signal
false alarms: perceives signal when none was given
correct negatives: correct identification of no signal
The eye detects light in the form of _____
photons
Sclera
“white” of the eye
- thick structural layer
- does not cover the front most part of the eye
Two sets of vessels supplying the eye
- choroidal vessels (b/w retina and sclera)
2. retinal vessels
Retina - form & function
innermost layer of the eye
- consists of neural elements and blood vessels
- develops as an outgrowth of brain tissue (part of CNS)
function: convert incoming photons of light into electrical signals
Cornea
clear, domelike window in the front of the eye
-gathers and focuses incoming light
Anterior chamber
Part that is in front of the iris
Posterior chamber
between the iris and the lens
-where aqueous humor is made by the ciliary body
Iris
Coloured part of the eye
- dilator pupillae: opens the pupil under sympathetic stimulation
- constrictor pupillae : constricts the pupil under parasympathetic stimulation
choroid
middle layer of the eye
-continuous with the iris as well as the ciliary body
Ciliary body
produces aqueous humor that bathes the front part of the eye
Canal of Schlemm
drains the aqueous humor
Lens
Helps control the refraction of incoming light
- located behind the iris
- shape is changed by contraction of the ciliary muscle which is under parasympathetic control
Accomodation
Process in which the ciliary muscle contracts, pulling on the suspensory ligaments which changes the shape of the lens
Vitreous
transparent gel that supports the retina
Duplexity/Duplicity theory of vision
retina contains two different kinds of photoreceptors (rods and cones)
Rods
- Work best in reduced lighting
- Only allow for sensation of light or dark as they only contain one pigment: rhodopsin
- low sensitivity to detail
*~120 million rods in the retina
Cones
- Work best in bright light (different cones absorb different wavelengths of light: short, medium, long)
- Used for colour vision
- High sensitivity to detail
Macula
central section of the retina with a high concentration of cones
Fovea
centermost point of the macula, contains ONLY cones
-visual acuity is best at the fovea
Blind spot
where the optic nerve leaves the eye
-no photoreceptors present
Bipolar cells
connect with rods and cones
synapse with ganglion cells
Ganglion cells
connect with bipolar cells
group together to form the optic nerve
- each one represents the combined activity of many rods and cones
- this results in a loss of detail as info from photoreceptors is combined
Amacrine and Horizontal cells
Receive input from multiple retinal cells in the same area before the info is passed to ganglion cells
- accentuate slight differences between visual information in each bipolar cell
- increase perception of contrasts
Visual pathways
both the physical connections between the eyes and the brain AND the flow of visual information along these connections
Optic chiasm
Where the fibers from the nasal half of each retina cross paths
- fibres carry information form the temporal visual field from each eye
- temporal fibres (carrying the information from the nasal visual field) do not cross the chiasma
==> because of this, all information from the left visual field of each eye projects to the right side of the brain and visa versa
Optic tracts
reorganized pathways leaving the optic chiasm
-travel to:
the lateral geniculate nucleus
Visual cortex (occipital lobe) via radiation in the temporal and parietal lobes
Lateral geniculate nucleus (LGN)
Located in the thalamus
Parallel processing
ability to simultaneously analyze and combine information regarding colour, shape, and motion
-then compare images to memories to determined what is being viewed
Parvocellular cells
Detect shape in the visual pathway
- have very high colour spatial resolution
- permit fine detail when an object is stationary
- poor temporal resolution = not for moving objects
Magnocellular cells
Detect motion in the visual pathway
- high temporal resolution
- low spatial resolution
- provide a blurry but moving image of the object
Vestibular Sense
rotational and linear acceleration
Pinna/Auricle
cartilaginous outer part of the ear
- first part of the ear that the sound passes through
- function is to channel sounds waves into the external auditory canal
External auditory canal
Canal of the outer ear
-directs sound waves to the tympanic membrane
Tympanic membrane
Vibrates in phase with the incoming sound waves
- frequency of the sound waves determines the rate at which the tympanic membrane vibrates (high frequency = high vibration)
- Louder sounds have greater intensity and therefor greater amplitude of vibration
*Divides the middle ear and the outer ear
Ossicles
three smallest bones in the body
- found in the middle ear
- malleus, incus, staples
Order of ossicle action
- Malleus acts on the => 2. Incus acts on the => 3. Stapes => presses on the oval window of the cochlea
Eustachian tube
Connects the middle ear to the nasal cavity
-helps equalize pressure between the middle ear and the environment
Inner ear
Located in a bony labyrinth
- contains the cochlea, vestibule and the semicircular canals
- structures are continuous with each other and filled by the membranous labyrinth which in turn is filled with a K+ rich fluid called endolymph
Endolymph
Potassium rich fluid that fills the membranous labyrinth
Cochlea: structure & function
Spiral shaped organ divided into 3 parts called scalae
- middle scalae houses the organ of Corti (resting on the basilar membrane)
- tectorial membrane (immobile) rests on top of the organ of Corti
Organ of Corti
comprised of thousands of hair cells that are bathed in endolymph
Perilymph
Transmits vibrations from the outside world and cushions the inner ear structures
-fills the other 2 scalae of the cochlea
Round window
Membrane covered role in the cochlea (lower down than the oval window) that allows the perilymph in the outer scalae to move
Basilar membrane movements
Sound entering the cochlea via the oval window causes vibrations in the perilymph which are transmitted to the basilar membrane
Which nerve carries stimulus to the CNS?
Auditory (vesibulocochlerar) nerve
Vestibule
Portion of the bony labyrinth that contains the utricle and the saccule
- sensitive to linear acceleration
- used as part of balancing apparatus
- determining orientation in 3D space
Hair cells of the utricle and saccule
Covered with otoliths
- as the body accelerates the otoliths resist the motion, causing the hair to bend
- the hair cells are then stimulated and send a message to the brain
Semicircular Canals
3 semicircular canals are sensitive to rotational acceleration
- arranged perpendicular to each other
- each end in a swelling called the ampula where the hair cells are located
*when the head rotates, endolymph resists this motion and cause the hairs to bend, sending signals to the brain
Auditory pathways (order)
- Most signals pass through the vestibularcochlear nerve to the brainstem
- Then it ascends to the medial geniculate nucleus of the thalamus
- Projects to the auditory cortex in the temporal lobe for sound processing
* * some info also sent to superior olive (localization) and the inferior colliculus (startle response)
Vestibulo-ocular reflex
Keeping the eyes fixed on a point which the head is turning
- startle response
- involves the inferior colliculus
Hair cell structure
Have long tufts of stereocilia on surface
Hair cell function
- Vibrations on the basilar membrane causes movement of endolymph and stereocilia to sway
- Swaying causes the opening of ion channels
- A receptor potential is created
Hair cells + tectorial membrane
Hair cells directly connected to the tectorial membrane are involved in amplifying incoming sounds
Tonotopical organization of cochlea
Basilar membrane thickness changes throughout the cochlea
- closest to oval window = highest frequency pitches
- furthest from oval window = lowest frequency pitches
Only 1 of the senses that does not pass via the thalamus
Smell
Smell is considered a ____ sense
Chemical sense
-responds to volatile or aerosolized chemicals
Olfactory chemoreceptors (nerves)
Located in the olfactory epithelium in the upper part of the nasal cavity
- highly varied
- chemicals must bind to specific receptors
Pheromones
Secreted by one person or animals and bind to the chemoreceptors of another, urging them to behave in a certain way
Olfactory pathway
- Odor molecules are inhaled into the nasal passages
- contact the olfactory nerves
- olfactory receptors are activated and they send signals to the olfactory bulb
- Signals are then relayed via the olfactory tract to higher regions of the brain (ie. limbic system)
5 basic tastes
Sweet, sour, bitter, salty, and umami (savoury)
Flavour
Complex interplay between smell and taste
-can be affected by non-chemical stimuli
Taste chemoreceptors
sensitive to dissolved chemicals
Taste buds
groups of cells that are receptors for taste
Papillae
small bumps on the tongue which contain the taste buds
Taste pathway
- Info travels from taste buds to the brainstem
- Ascends to the taste centre in the thalamus
- Travels from the thalamus to higher order brain regions
4 modalities of Somatosensation
- Pressure
- Vibration
- Pain
- Temperature
Brown-Séquard syndrome
If half the spinal cord is severed the patient loses pain and temperature sensation on the opposite side of the lesion and pressure/vibration sensation on the same side
*pain + temp use a different pathway then pressure +vibration
Pacinian corpuscules
respond to deep pressure and vibration
Meissner corpuscules
respond to light touch
Merkle cells (discs)
respond to deep pressure and texture
Ruffini endings
respond to stretch
Free nerve endings
respond to pain and temperature
Somatosensory signal destination
Somatosensory cortex in parietal lobe
Two point thresholds
minimum distance necessary between two points of stimulation on the skin such that the points will be felt as distinct
Physiological zero
Normal temperature of the skin
-objects feel cold if they are below and hot if they are above
Nociceptors
Involved in pain perception (most common receptor)
Gate theory of Pain
Special gating mechanism present that can turn pain signals on and off
Spinal cord can preferentially forward signals from other touch modalities, therefore reducing the pain sensation
Kinesthetic sense
Also known and proprioception
= ability to tell where one’s body is in space
Location of proprioception receptors
Mainly muscles and joints
Bottom up processing
object recognition by parallel processing and feature detection
-combining stimuli into a cohesive image before determining what the object is
also called data-drive processing
Top down processing
Driven by memories and expectation which allow the brain to recognize the whole object, then to recognize its components based on these expectations
-allow for quicker recognition
Perceptual organization
Ability to use both top down and bottom up processing in tandem with other sensory clues about an object to create a complete picture
Depth perception
monocular clues: relative size of the object, partial obscuring, convergence of parallel lines at a distance, position of object in visual field, and lights/shadows
binocular clues: slight differences in images projected on the 2 retinas and the angle required between the eyes to bring an object into focus
Form of an object
determined via parallel processing and feature detection
Constancy
idea that we can perceive certain characteristics of objects to remain the same, despite changes in the environment
Gestalt principles
ways for the brain to infer missing parts of a picture when it is incomplete
Law of proximity
elements close together tend to be perceived as a unit
Law of similarity
objects that are similar tend to be grouped together
Law of good continuation
elements that appear to follow the same pathway tend to be grouped together
-perceive continuous patterns over abrupt changes
Subjective contours
perceive contours and therefore shapes that are not actually present
Law of closure
A space that is surrounded by a contour it tends to perceived as a complete figure
-certain figures tend to be perceived as more complete than they actually are
Law of prägnanz
perceptual organization will always be as regular, simple, and symmetric as possible
-governs the other gestalt principles
