L07 - Sensations and Perceptions Flashcards
Who is Gustav Fechner?
He was interested in vision. Vision comes from psychophysics (the science of defining quantitative relationships between physical and physiological events). He was blind for staring at the sun too ling - eventualy got his vision back. He started the study of sensations and perceptions.
What is absolute threshold?
The level of stimulus intensity required to create a conscious experience
What is the signal detection theory?
Accounts for individual biases. This changes between people but it is the difference between people’s visions.
What is sensation?
The ability to detect a stimulus. Features of an environment that are used to create an understanding of the world.
What is perception?
The act of giving meaning to a detected stimulus. Combining of sensations arriving from the sensory system with prior knowledge.
What is transduction?
Conversion of one energy to another. Process where stimuli (i.e,) light (soundwaves maybe) are converted to neural electrochemical energy (action potential).
Perception; How do we assign meaning to income sensory information?
Bottom-up processing!
What is the difference between bottom-up processing and top-down processing?
Bottom-up processing states that it is a day to driven species - look for info, once we know, then we figure out what we see/hear… *Very unbiased approach
Ex. We recognize that the lines /-\ make A
Top-down processing is the idea that we have memory in mind - like a template - that we use as sensory information and we look to fill in this template. *Biased approach
Ex. There are a bunch of lines and dots and if I tell you that it is a dog, you will start to see the dog and believe it is a dog.
What is the Extromission theory of vision?
“Vision comes from eyes sending out beams”
The opposite of the Intromission theory.
First suggested in 4th century B.C. Plato - stating that the eyes send out vision beams which seize objects. 50% of Americans today still believe in the extromission theory.
What is the Intromission theory of vision?
“Vision comes from objects entering the eyes”
The visual perception of objects comes from some representation of the object entering the eyes.
How does light reflect in our eyes according to the Intromission theory of vision?
Sun emits photons
Photons emit light
Comes to Earth
Scattered around at the atmosphere
Ones that make it through bounces off objects or are absorbed
Light reflects in our eyes
Explain Light.
Light is an electromagnetic energy that exists both as particles (photons) and as waves. We can only detect a small band. (400-700nm)
Terms to know regarding light
Wavelength - perceived hue (the distance between 2 peaks - hue means colour)
Frequency - cycle rates
Amplitude - perceived intensity (increase of height in peaks)
What are Rods?
Photoreceptors
Dim light (“night vision”)
Sensitive to all wavelengths of light
Black and white vision
What are Cones?
Photoreceptors
Bright light (“daylight vision”)
Sensitive to blue/red/green wavelengths of light
“Color vision”
What do photoreceptors do?
Transduce* light into neural activity
Found in the back of the retina
Two types of photoreceptors (rods and cones (few cones – 5mill and lots of rods – 100mill))
Tetrachromats
Humming birds are tetrachromats
Can see UV wavelength
What is the blindspot?
The point where the optic nerve leaves the eye
The nerve is in the way so there cannot be any photoreceptors
The visual system usually fills in blindspot information from the surrounding area
What are Bipolar Cells?
Intermediate cells that determine the information flow from photoreceptors to ganglion cells
There are two types of bipolar cells
Diffuse bipolar cells
Midget bipolar cells
What are diffuse bipolar cells?
Found in the periphery
Respond to around 50 rods – increase sensitivity but reduced activity
Convergence of information – many RODS = one diffuse bipolar cell
What are midget bipolar cells? Hint - Cones
Found in the fovea (center)
Receive input from a single cone and pass on info to a single ganglion (1 midget bipolar, 1 CONE)
Where are ganglion cells located?
In the retinal ganglia - the final layer of the retina
contains m-cells and p-cells
What are m-cells? Hint; in the retinal ganglia
Large ganglion cells
Mostly respond to RODS cells via diffuse bipolar cells
What are p-cells? Hint; in the retinal ganglia
Small ganglion cells
Mostly respond to CONES via midget bipolar cells
What is the receptive field in the retinal ganglia?
The region on the retina in which visual stimuli influences neural firing rate
What is the difference between ON-center, OFF-surround cell and OFF-center, ON-surround cell in the receptive field in the retinal ganglia?
ON-center, OFF-surround cell
A ganglion cell that increases firing in response to INCREASE in light intensity in its receptive field center.
When light hits the center – firing rate at maximum
When light covers full receptive field – firing rate returns to baseline
OFF-center, ON-surround cell
A ganglion cell that increases firing in response to DECREASE in light intensity in its receptive field
Function; contrast in illumination help detect object edges, whether it is day time or night time or even indoors and outdoors.
Also thought to be involved in color processing
What is the Color detection theory?
Opponent process theory – based on retinal ganglia cells
P-cells fire rapidly to one wavelength and reduce to another forms pairs of colours
Red-green; p-cell
Blue-yellow; p-cell
Black-white; m-cell
Ex. the reduction of red firing = green
What is the trichromatic theory? Hint – based on photoreceptors.
Color vision occurs by comparing the activation of the three different CONES
What is the visual pathway?
Information from the retina leaves the eye via the optic nerve.
Information of the optic nerve travels to the optic chasm (cross over – right-left, left-right)
Lateral geniculate nucleus (LGN) of thalamus
Visual cortex/striate cortex/V1
There is more variation in V1 cell firing than retinal cells
What is ORIENTATION SELECTIVITY? Hint - simple and complex cells
Simple cells: Neuron fires vigorously when the line is orientated vertically, but reduces firing horizontally (left column of image).
Sensitive to orientation
Complex cells: Fire most when lines are in certain motion.
Fire much more when in certain motions (up, down, right, left)
What is the Visual cortical pathway; the WHAT stream vs. the WHERE stream
WHAT stream
Ventral stream
Temporal lobe
Object recognition
vs.
WHERE stream
Dorsal stream
Parietal lobe
Location of object in space
What is Visual Agnosia?
Inability to recognize OBJECTS
CAN see colors, shapes and faces
Damage to the VENTRAL pathway (what pathway)
TEMPORAL lobe
What is Prosopagnosia?
Inability to recognize FACES
Patients show emotional responses to very close relatives (partners, parents, children) suggest some unconscious emotional recognition is taking place when conscious recognition is not.
Damage to the VENTRAL pathway (what pathway)
TEMPORAL lobe
What is Akinetopia?
Inability to detect MOTION
Patients see life through a series of snapshots
Damage to DORSAL pathway (where pathway)
PARIETAL lobe
What are Gestalt Principles?
Gestalt psychology describes how people tend to organize visual elements into whole entities. Gestalt psychologists believe we are born with specific predisposed ways of organizing information so that it has utility
What is the principle of figure-ground?
A form, silhouette, or shape is naturally perceived as figure (object), while the surrounding area is perceived as ground (background)
What is the principle of proximity?
Occurs when elements are placed close together. They tend to be perceived as a group.
What is the principle of similarity?
Occurs when objects look similar to one another. People often perceive them as a group or pattern.
What is the principle of closure?
Occurs when an object is incomplete or a space is not completely enclosed. If enough of the shape is indicated, people perceive the whole by filling in the missing information.
What is the principle of continuation?
Occurs when the eye is compelled to move through one object and continue to another object
What is the principle of fate?
Occurs when objects that are moving together will be grouped together (as if they are going to end up in the same place).
What is the biological motion?
We use the motion to identify the nature of objects/beings
It helps us identify specific people and human intent
What are issues with the visual perception?
Blindsight and Agnosia
What is blindsight?
When patients have damage to visual cortex (V1 at the back typically only one cortex) results of strokes and brain trauma
Become blinded in that visual field – ex. right V1 damaged; lose vision in left visual field
If you present something in the blinded area (impaired visual field – in blind spot) of the patient, they somehow know and recognize the object shown without being able to see it
Suggests that information is still being transmitted from eyes to lower visual processing which is guiding our behavior. CONSCIOUS and UNCONSCIOUS vision
What is sensory substitution?
Paul Bach-y-Rita “We see with our brains, not our eyes”
Our brains are highly plastic
This means that (i.e.) blind patients can use tactile sensations from the tongue to translate to visual perception
Suggest that there is a hardwired perception of the world
What is Amplitude/Intensity when talking about sound?
The magnitude of displacement (increase or decrease) of a sound pressure wave. Perceived as loudness.
Always active
Greater amplitude, higher pitch, louder perceived
What is sound?
Vibrations in a medium (air/water) that cause pressure changes or “waves”
What is frequency when talking about sound?
For sound, the number of times per second that pattern of pressure changes repeats. Perceived as pitch.
What are the components of the outer ear?
Pinna and tympanic membrane
What is the Pinna?
Outer segment of the ear
Shaped to collect and funnel sound toward tympanic membrane
What is the tympanic membrane?
Eardrum
Transfers sound energy from the air to the ossicles
If you puncture an eardrum, it can heal itself (it is a piece of skin – it typically re-heals)
What are the components of the middle ear?
Only the ossicles
What are ossicles?
Amplify sound arriving at the eardrum to oval window (small membrane) of the cochlea
Made of three small bones
Malleus – connected to the tympanic membrane
Incus – connected to the malleus
Stapes – connected to the incus
What are the components of the inner ear?
Cochlea
Fluid-filled, coiled structure
Within the cochlea are two membranes which create three canals
Basiliar membrane
Where the hair cells (sound transduction) are located
Where transduction occurs
Tectorial membrane
Floats above and connects to hair cells
Why do we need hair cells in the ears?
They transduce mechanical movements from sound waves into neural activity
Fluid vibrations from sound causes the basilar membrane to move (ripple).
This movement causes the cilia of hair cells which are attached to the tectorial membrane to bend.
The bending of hair cells causes a neural signal to be sent down the auditory nerve.
What is the Place theory?
The brain uses the location of neural firing to understand sound
Higher frequencies cause the cells closest to the oval window to fire
Lowest frequency sound tend to excite cells that are much deeper in the cochlear
The only problem is that the budge of energy needs to hit all of the hair cells
What is the frequency theory?
The brain also uses information related to the rate of cell firing.
The more rapidly the cells fire, the higher the perception of pitch
What are the different auditory pathways?
Auditory information travels to medial geniculate nucleus of thalamus (major relay center for sensory information)
Auditory cortex in temporal lobe
Tonotopic organization (inside temporal lobe)
The spatial organization of the basilar membrane is maintained through the auditory pathway
If you have certain sounds that are perceived adjacent to each other alongside the cochlear, it will be similarly represented in your brain
What are Binaural cues?
where object/sound is coming from in our environment
Auditory cues that require comparisons from both ears
What is the Interaural time difference
Difference in arrival times at each ear (ex. Sound comes from the left, left ear will hear it first)
What is the Interaural level differences?
Differences in the intensity of sounds that reach each ear.
Your brain automatically does this to compute the time and intensity between ears to help find where the sound is coming from
What is the Phantom word exp.? Hint - What did you hear?
You can hear many words coming out of a sound that is always saying the same thing with only your imagination.
Although everyone listens to the same auditory stimulus (sensation) different perceptions of words are reported
Similar to vision what we “hear” is shaped by our prior knowledge
TOP-DOWN PROCESSING
What is touch?
Tactile sensations
Mechanical interactions, temperature and pain
Detection organ is the skin
What do Mechanoreceptors with touch?
Transduce mechanical stimulation (pressure) into touch sensation
What are Merkel receptors?
Application and removal of pressure (constant firing while pressure applied)
1 meissner corpuscle : 4 different meissner corpuscle : 3 different merkel receptors
More superficial receptors have much smaller receptor fields
What are Meissner Corpuscle?
Application and removal of pressure (fire only during the application and removal- changes in pressure)
1 meissner corpuscle : 4 different meissner corpuscle : 3 different merkel receptors
More superficial receptors have much smaller receptor fields
What are Ruffini cylinders?
Interpret sketch of skin
Much larger receptive fields
What are Pacinian corpuscles?
Vibration and texture
Much larger receptive fields
What do thermoreceptors do?
Sensory receptors that signal information about changes in skin temperature
Two distinct population; warmth and cold fibers
Also respond to chemical stimuli
When you eat capsaicin it feels hot
When you eat methanol it feels cold
Both in the epidermal and dermal layers
Respectively respond/increase firing rates depending on the temperature
What do nociceptors do?
Sensory receptor that transmits information about noxious (painful) stimulation that causes damage or potential damage to skin
Mix of signals transduced – mechanical, thermal, chemical
Pain comes from too much pressure or an increase in the heat/cold
Explain the somatosensory cortex.
Relayed via thalamus to contralateral parietal lobe
Somatotopic organization
Spatially mapped in the somatosensory cortex in correspondence to spatial events on the skin
Adjacent point on your skin are represented by adjacent points on somatosensory cortex
Left body info goes to right parietal lobe and vice versa
It is species specific
What did the rubber hand illusion experiment prove?
↳ Multi sensory perception can influence how we perceive our own body
↳ Shows how it can be overridden by visual information
↳ Shows powerful connection between what we see and what we feel
↳ fundamental change in the brain is taking place (brain is changing to accommodate the new rubber hand)
↳ Structural change: neuroplasticity
Brain can change in response to experience
Brain temporarily rewrites itself to adopt hand as its own
Brain responds to inanimate objets that you manipulate a lot like dropping cell phone: unsatisfying
Give an example of narrative.
Perception: act of giving meaning to a detected stimulus. Video about triangle and circle and a rectangle.
Automatically as singing characters, a plot, motives, goal directed behavior to shapes moving on a screen (rich narrative story making by our brain)
What is attribution of causality?
What kind of person is the small triangle?
Why did the circle go in the house?
Why did the big triangle break the house
NOTICE: If you are able to answer these questions after watching the video – you automatically assigned characters (triangles/circle), a setting (the rectangle/house) and a narrative (cause and effect) to inanimate, moving shapes.
Explain narrative.
Our brains have a natural tendency to find meaningful patterns and causality in our surrounding world.
Not linked to any singular sensory systems but rather a multimodal perception
We can not only combine prior knowledge to perceive what something is but we can also assign a deterministic cause for what we perceive
What is the default mode network?
Collection of region
Anterior medial prefrontal cortex, posterior cingulate cortex and angular gyrus
DMN is proposed to provide situation models; representation that link entities, actions and outcomes.
Cause and effect (make sense for narrative
Represents the internal world (i.e.) perception rather than external world (i.e.) sensory cortices.
What is narrative in the brain?
From perception to memory
Participants watch a movie in a fMRI scanner and then recall the story immediately afterward.
Synchrony in spatial brain activity across participants whilst watching the same movie (i.e. movie-movie).
Synchrony in spatial brain activity within participants between watching the movie and verbal recalling the movie (movie- recall).
The greatest synchrony of brain activity patterns occurred between participants during the recall session (recall-recall)
Perhaps we have hard wires ways of processing narrative (fit sensations in template)
Is this something innate? Natural tendency to have same stories in our brains that we tend to organize information? Culturally taught?
What is the resolution of cones? How many cones are there in each eye?
High resolution (one bipolar cell = one cone)
Around 5 million cones in each human eye
What are the three types of cones? What colours do they represent?
3 types of cones
S-cones; short-wavelength cones (blues)
M-cones; medium-wavelength (yellows and greens)
L-cones; long wavelength (reds)
Where are cones found? What are other details of cones?
Found in the FOVEA (center) of retina
Respond to QUALITY of light
Signal information about DETAIL
What is the resolutions of rods? How many rods are there in a human eye?
Low resolution (one bipolar cells; many rods)
Around 100 million rods in each human eye
Where are rods found? What are other details about rods?
Found in the PERIPHERY
Respond to the AMOUNT of light
Signal information about MOTION
