Exam 1 Flashcards
What is the difference between sensation and perception?
Sensation: ability to detect a physical stimulus; i.e. touch on shoulder
Perception: act of giving meaning to detected stimulus; i.e. romantic touch or TSA touch
What is psychophysics and who came up with it?
Psychophysics: science of defining quantitative relationship between physical stimuli and psychological experience of these stimuli
Created by Gustav Fechner
What is another concept other than psychophysics that Gustav Fechner came up with?
Panpsychism: everything has a mind
What is psychometric function and how do we measure it?
Psychometric funtion: relationship between physical stimulus (x) and sensation intensity (y)
Measured using magnitude estimation
* participants assign estimated value to a physical stimulus
Why are most psychometric funtions not linear?
Observers are not perfect
What does Weber’s Law state?
The just noticeable difference (JND) is a constant fraction of the comparison stimulus
What does Fechner’s Law state?
The magnitude of perceived sensation increases proportionally to the logarithmic of stimulus intensity
Observer is less sensitive to high physical intensities than low physical intensities
What is the just noticeable difference/difference threshold?
Smallest difference detectable between two stimuli
What is the absolute threshold?
Minimum amount of physical sitmulus intensity necessary for person to detect 50% of the time
What are the different methods of testing used to find the absolute threshold?
- Method of constant stimuli
- Method of limits
- Method of adjustments
What is the procedure for method of constant stimuli?
- Present tones of different volumes in random order
- Participants report whether they could hear it or not
- Each volume level tested multiple times
Most accurate but time-consuming
What is the procedure for the method of limits?
- Present tones in ascending/descending order
- Participants report when they can hear it
- Multiple runs of ascending and descending tones
- Average = threshold
What is the procedure for method of adjustment?
Participants adjust volume until they can hear tone –> average = threshold
Who came up with the idea for signal detection theory and what does the theory state?
Created by Green and Swets
Observer’s goal is to detect signal amonst noise
What is the response criterion and how does it shift?
Response criterion: cutoff point for when you say “signal” vs. “noise”
Shifts depending on desired type of error
What is the difference between having a “liberal” response criterion vs. a “conservative” response criterion?
“Liberal” - will get every instance of phone ringing but lots of false alarms (right dom.)
“Conservative” - never mistake noise for phone ringning but lots of misses (left dom.)
How does the graph of someone with no sensitivity compare to someone with high sensitivity?
signal detection theory
No sensitivity - phone and noise lines almost overlap
High sensitivity - phone and noise lines are barely intersecting
What is the base rate of neurons?
Base rate: random firing of neurons with no stimulus present
What are the dendrites responsible for?
Receive information from other neurons
Where are action potentials generated?
Axon hillock
What is the axon responsible for?
Conduct action potentials away from the cell body
How was the action potential discovered and by who?
Isolate giant neuron from squid –> saw voltage increases because Na+ rushes into axon and pushes K+ out of the axon
Discovered by Hodgkin and Huxley
What are the stages of the action potential?
- Depolarization - voltage increases; cell “fires”
- Repolarization - voltage decreases
- Refractory period - cannot fire during this time
- Resting state
What happens at the synapse?
- Neurotransmitters released from presynaptic neuron
- Neurotransmitters bind to receptors on postsynaptic neuron
- Different neurotransmitters can either excite or inhibit the postsynaptic neuron
What are sensory receptors?
Transfers stimulus energy and turns it into electrical energy that neurons can use to communicate (transduction)
What is receptor specifity?
Most receptors are optimally tuned for a specific type/pattern of energy
What hogs the most energy in our body?
Blood vessels in the brain
What are glial cells?
Maintain integrity of the neurons and act as structural support for neurons
Which bypasses which: cranial nerves or peripheral nervous system?
Cranial nerves bypass peripheral nervous system
Do we have more glial cells or neurons in our brain and by how much?
3 x more glial cells than neurons
What is cranial nerve I? Sensory or motor nerve?
Olfactory - smell
Sensory
What is cranial nerve II? Sensory or motor?
Optic - vision
Sensory
Which cranial nerves are responsible for the muscles that move the eyes?
III (oculomotor), IV (trochlear), and VI (abducens)
Which cranial nerves are responsible for sensation and motor?
V (trigeminal), VII (facial), IX (glossopharyngeal), X (vagus)
Which cranial nerves are responsible for vestibular and auditory?
VIII (vestibulocochlear), XI (spinal accessory), XII (hypoglossal)
What is EEG? What are the pros and cons?
EEG: measures voltage fluctuations over time (brainwaves) from populations of neurons in the brain
Pros - relatively cheap and great temporal (time) resolutoin
Cons - poor spatial resolution because skull gets in the way of electricity and hard to tell what part of brain activity is coming from
What is an fMRI? What are the pros and cons?
fMRI: measures amount of oxygenated blood in a given brain region; blood-oxygen level-dependent (BOLD) signal
Pros - high spatial resolution
Cons - expensive and poor temporal resolution
What did the Brady et. al study from 2008 reveal?
memory study
Participants remembered 90% of images in recall test
What is refraction?
Direction of light waves can be altered when they pass through one medium to another
Where is light transduced into a signal in the eye?
Retina
What is the inner chamber of the eyeball called?
Vitreous chamber
What part of the eye is the first step in focusing light?
Cornea
Why is the anterior chamber of the eye filled with fluid?
Easier for the body to regulate the shape and pressure of the eye
What part of the eye controls the size of the pupil?
Iris
What does the lens of the eye do?
Focus light by bending itself
What are the two types of photoreceptors found within the retina?
Cones: specialized for color vision
Rods: specialized for night vision
What are the different types of light adaption?
- Pupil dilation
- Photopigment regeneration
- Neural circuitry
- Duplex retina
How is pupil dilation a form of light adaption?
Dilates in darkness to let more light in
How is photopigment regeneration a form of light adaption?
Photopigments used to transduce light into neural signals and if photopigments regenerate fast enough, we can perceive very bright stimuli
What occurs during bleaching?
Too many light photons overwhelm photoreceptors and use up all the photopigments
Sunglasses developed for this issue
How is neural circuitry a form of light adaption?
Retina detects contrast change via ganglion cells; inhibit and excite the retinal system
How is the duplex retina a form of light adaption?
Center of retina (fovea) is full of cones while periphery of retina is full of rods
What is the difference between the photopic system and scotopic system?
Photopic: full of cones that are good at discriminating colors during daylight
* high spatial acuity (detail)
Scoptopic: full of rods that function well at low light levels but poor at color discrimination
* low spatial acuity
What is the purpose of optical lens?
Focuses light via refraction
If we hold viewing distance and shrink an object, how does this affect the visual angle?
Shrinks visual angle
If we move an object closer to the eye, how does this affect the visual angle?
Increases visual angle
How does the eye focus on objects?
Accomodation: eye changes its focus by bending the lens
How do lens focus light onto the retina?
Via ciliary muscles
What happens when we focus on an object far away?
Ciliary relaxed, Zonules of Zinn tight, lens flat
What happens when we focus on an object close by?
Ciliary tight, Zonules of Zinn relaxed, lens bulge
How do we find the power of lens?
Diopter (D) = 1/F
F = distance in focal meters
What is emmetropia?
Perfect vision
* eye shaped normally
* focal point falls directly on retina
What is myopia?
Near sightedness
* eye is elongated (too long) –> focal point falls short of retina
* far away objects = blurry
* solution - concave lens
What is hyperopia?
Far sightedness
* eye is too short –> focal point falls beyond the retina
* close objects = blurry
* solution - convex lens
What is presbyopia?
“Old sight”
* lens becomes less flexible with age
* sometimes focal point falls short and sometimes falls beyond retina
What is astigmatism?
- Cornea = football shaped –> light refracted in abnormal manner
- multiple focal points
- images blurry at every distance
What are monochromats and how common are they?
Monochromats: see everything in shades of gray
Very rare form of color blindness
What are the two subtypes of monochromats?
- rod monochromat: no rods to distinguish color –> hypersensitive to light
- cone monochromat: only one type of cones
What is the Ishihara test?
Observers forced to do color discrimination in order to report the number value
After light hits the rods and cones in the retina, where is light processed next?
2 sites
Bipolar cells –> ganglion cells
What is the difference between midget bipolar cells and diffuse bipolar cells?
Midget bipolar cells: receive input from single photoreceptor; primarily found in central vision
Diffuse bipolar cells: receive input from multiple photoreceptor; primarily found in peripheral vision
What is the difference between on cells and off cells?
On cell: increases firing rate in response to photoreceptor sensing light; copies firing rate of photoreceptor in front of it
Off cell: decrease firing rate when photoreceptor senses light; increases rate when light is not present
What is the difference between on-center and off-center ganglion cells?
On-center: excitatory center (on) and inhibitory surround (off)
Off-center: inhibitory center (off) and excitatory surround (on)
What is the difference between P and M ganglion cells?
P ganglion cell: receives input from a single midget bipolar cell in central retina; outputs to parvocellular system
M ganglion cell: receives input from multiple diffuse bipolar cells in peripheral vision outputs to magnocellular system
How does spatial frequency affect grating cycles?
Less spatial frequency –> less grating cycles
If a grating cycle has a higher contrast, what happens to the ganglion cell?
Retinal ganglion cell will fire more
Which visual field does the temporal retina represent?
Opposite
Which visual field does the nasal retina represent?
Same space as visual field
What is the purpose of the lateral geniculate nucleus?
Relay station that copies information onward to the visual cortex
Preserves right vs. left information
What is the difference between the magnocellular system and the parvocellular system of the LGN?
Magnocellular: 2 layers of large cells that encode large moving objects; i.e. rabbit moves in corner of eye
Parvocellular: 4 layers of small cells that encode details of stationary objects; i.e. read a book
Information from the retina is represented by which visual cortex?
Contralateral (opposite)
Information from the retina is represented by which visual cortex?
Contralateral (opposite to stimulus)
What is cortical magnification?
Center of visual field has more V1 neurons representing it than the periphery
What is retinotopic organization?
V1 cortex is organized so that spatial information from the retina is retained
What is the purpose of the primary visual cortex?
Primary visual cortex: neurons in V1 accumulate information across several ganglion cells –> allows them to detect simple visual pictures like lines and edges
What animals have regions of visual cortex that are comparable to humans?
Macaque monkeys
How do neurons in V1 compare to neurons in V2 when it comes to border ownership?
V1 - not sensitive to border ownership
V2 - sensitive to border ownership
What is an illusory contour?
False edge that is perceived but is not represented in the physical stimulus; i.e. Kanizsa Triangle (chunk of three circles missing –> negative space forms triangle)
What is occlusion?
An object is covered by another object
What are the Gestalt principles for mid-level vision?
- Good continuation: 2 elements will tend to group together if they seem to fall on the same line
- Closure: a closed contour is preferred to an open one
- Similarity - group based on shape, size, color, etc.
- Proximity - if they’re close together
- Parallelism
- Symmetry
- Surroundedness - one object surrounded by another
- Size - one object smaller/larger than another
What is texture segmentation?
Parsing an image into regions of common texture properties
What is figure-ground segmentation?
Determining which item belongs to the foreground and which belongs to the background
What is the global superiority effect?
Properties of the whole object dominate local identities
What are ambigious figures and what is an example of one?
Ambigious figures: not sure from which perspective they should be interpreted
I.e. Necker cube
What is top-down perception?
Perception is driven by learning, context, or experience –> visual system is making educated guesses about the world –> susceptible to accidental viewpoints
What is the inverse optics problem?
Given retinal image, what is the state of the world?
What are the three basic challenges to object recognition?
- Multiple viewpoints
- Multiple classes of the same object (i.e. different breeds of dogs but they are all part of the “dog” group)
- Recognizing objects at different levels of specificity (beagle -> dog -> mammal -> animal)
What is the template matching model?
Visual system recognizes objects by matching neural representation of image with a stored representation of the same “shape in the brain
Struggles to explain how we would recognize multiple classes of the same object
What is the structural description model?
A description of an object in terms of its parts and the relationships between those parts
Image is made up of geons and those geons are pieced together to make different objects
Does not explain viewpoint specific effects
What is the difference between the dorsal pathway and the ventral pathway in the inferotemporal cortex?
Dorsal pathway: “where”; processes infromation about locations of objects and how to interact with them; crucial for visual attention
Ventral pathway: “what”; processes information about identity of objects; crucial for object recognition
What is the inferotemporal (IT) cortex important for?
Object recognition
What are “grandmother cells”?
Neurons in IT cortex that are tuned to very specific types of stimuli
What is visual agnosia?
Inabilitiy to recognize objects despite being able to see them; low and mid-level vision are intact but object recognition is impaired
Typically a result of brain damage to IT cortex
What is visual form agnosia?
Cannot discriminate simple objects (i.e. E vs. H)
Have a hard time perceiving coherent objects
What is associate agnosia?
Can perceive objects as a whole but cannot verbally name the objects
What is prosopagnosia?
Can perceive and name objects normally except for faces
What is the Thatcher Illusion and what is another name for it?
Thatcher Illusion/”Face Inversion” Effect: when the parts of an upside down face are rearragned, it’s hard to notice
What are the two types of ways objects can have color?
- Light sources - objects that generate electromagnetic energy in the visible spectrum (i.e. sun, lamps, TVs)
- Pigments - objects that reflect light from light sources
What is subtractive color mixing?
A mixture of pigments; the wavelengths of the two pigments act like filters when they combine
If an object appears to be white, what colors of the spectrum are reflected?
All colors
If an object appears black, what colors of the spectrum are reflected?
None
What is additive color mixing?
A mixture of lights; the wavelengths of the two lights add together to form a new color
When red and blue light is combined, what color is formed?
Magenta
When red and green light are combined, what color is formed?
Yellow
When blue and green light are combined, what color is formed?
Cyan
When red, green, and blue light are combined, what color is formed?
White
What is the principle of univariance?
A single photoreceptor cannot posssibly discriminate color
What color does each cone have a high response to ?
S - blue
M - green
L - red
In English, how many basic color terms are there?
11
What did the study of the Dani and Americans reveal?
color discrimination
Dani can discriminate colors just as well as Westerners, even though they use fewer color names in day-to-day life
What is top-down color perception?
The same physical colors can be perceived differently depending on scene context and prior experience
I.e. black and blue/white and gold dress
What are negative afterimages?
We adapt to the colors that are viewed for short periods of time so when these colors are removed, we see the opponent colors
What is color constancy?
Tendency of a surface to appear the same color under a wide range of light surfaces
