Psych 4110: Exam 1 Flashcards
sensation
the ability to detect a stimulus
perception
the act of giving meaning to a detected stimulus
Gustav Fechner
created psychophysics
what is psychophysics?
the science of defining quantitative relationships between physical stimuli and the psychological experience of those stimuli
magnitude estimation
the strategy of having participants assign an estimated value to a physical stimulus
Fechner’s Law
the observer is less sensitive at high physical intensities than at low physical intensities
absolute threshold
the minimum amount of physical stimulus intensity necessary for a person to detect 50% of the time
absolute threshold in the real world- examples
Vision: stars at night, a candle flame 30 miles away on a dark, clear night
Hearing: a ticking watch 20 feet away, with no other noise
Vestibular: a tilt of less than half a minute on a clock face
Taste: a teaspoon of sugar in 2 gallons of water
Smell: a drop of perfume in three rooms
Tough: the wing of a fly falling on your cheek from a height of 3 inches
method of constant stimuli
present tones of different volumes (dB) in a random order
method of limits
present tones in an ascending or descending order
method of adjustment
the participant adjusts the volume until they can hear the tone
signal detection theory
-Green and Swets (1996) have a revolutionary idea about perception
The observer’s goal is to detect a signal amongst a noise
-Signal: what you are trying to detect
-Noise: internal and external factors that make the signal hard to detect
-Some people might have a better sensitivity than others
-A person can shift their response criterion, depending on the desired type of error
-We must set a response criterion
-Signal detection theory is everywhere
sensory receptors
transforms stimulus energy into electrical energy that neurons can use to communicate
your brain uses…
the most energy out of any organ, 20% of total energy
glial cells
-there are 3x more glial cells than neurons in your brain
-maintains the integrity of the neurons
-act as structural support for neurons
central nervous system
brain and spinal cord
peripheral nervous system
periphery nerves, none in the head
the cranial nerves…
bypass the peripheral nervous system and connect directly to the brain
behavioral experiments
-measure response time and accuracy to sensory stimuli
-most modern behavioral/psychophysical experiments are computer-based
eye tracker
specialized camera uses infrared light to measure eye movements
electroencephalography (EEG)
-several electrodes are placed on the scalp
-measure electrical activity from populations of neurons in the brain
-the electrodes measure voltage fluctuations over time (brainwaves)
functional magnetic resonance imaging (fMRI)
-measure the amount of oxygenated blood in a given brain region
-blood-oxygen level- dependent (BOLD) signal
single unit recording
-recording action potentials from a single neuron via a micro electrode
-invasive: this requires opening the skull and pushing an electrode through brain tissue
-prohibited in humans (only mice and monkeys)
other methods to measure perception
-computer simulations
magnetoencephalggram (MEG)
-functional near-infrared spectroscopy (fNIRS)
photon
particle of light
light is a…
waveform that is generated
some basic principles of light
-only a small portion of the electromagnetic spectrum is visible to humans
-the color of light depends upon it’s wavelength
-the color of objects is due to wavelengths that are reflected, not absorbed
-the direction of light waves can be altered when they pass from one medium to another (called refraction)
how does the eye perceive light?
-enters the CORNEA (transparent membrane)
-through the ANTERIOR CHAMBER (pouch of fluid, aqueous humor)
-IRIS (circular muscles that control the size of the pupil)
-PUPIL (hole in front of the eye)
-LENS (focuses the light by bending itself)
-VITREOUS CHAMBER (inner chamber of the eyeball, vitreous humor (fluid that fills the eye and maintains shape of eye))
-RETINA (light is transducer into a neural signal)
-OPTIC NERVE (where neural signal leaves your eye)
light adaptation
process in which your visual system adjusts to the overall light levels, takes 20-25 minutes
how do we achieve such a broad range of light adaptation?
- pupil dilation
- photopigment regeneration
- neural circuity
- duplex retina
pupil dilation
you can physically adjust the amount of light entering the eye
photopigment regeneration
-photopigments used to transduce light into a neural signal
-once they are used, they take time to regenerate
-if they can regenerate fast enough, we can perceive very bright stimuli
bleaching
if too many light photons overwhelm the photoreceptors, they will use up all the photopigments
neural circuitry
-the retina is set up to detect contrast changes via retinal ganglion cells
-basically, bright lights will simultaneously inhibit and excite the retinal system
duplex retina
-the center of your retina (fovea) is full of cones, whereas the periphery of your retina is full of rods
-rods detect dim light, and cones detect bright light
Properties of Photopic System (central vision, retina)
-photoreceptor: 4-5 million cones
-location on retina: mostly fovea
-spatial acuity: high
-light sensitivity: low
-color vision: trichromatic
Properties of Scotopic System (peripheral vision)
-photoreceptor: 90 million rods
-location on retina: outside fovea
-spatial acuity: low
-light sensitivity: high
-color vision: none
scotopic
full of rods that are poor at color discrimination
photopic
full of cones which are good at color discrimination
refraction
the phenomenon whereby light changes direction (or bends) as it passes from one medium to another
optical lense
-a device that focuses light via refraction
-magnifying glass, contacts, etc.
wedge prism goggles
a type of goggles that distorts the retinal image, makes everything look upside down
prism adaptation
when participants wear prism goggles, they learn how to adapt their motor movements to accommodate the distorted image
Martin et al. (1995)
-participants viewed the world through goggles that shifted images to the left
-tried to throw a ping-pong ball at a target object
how could you measure the size of the retinal image?
simple trigonometry
visual angle principle #1
if we hold viewing distance constant, shrinking an object will shrink the visual angle
visual angle principle #2
if we move an object closer to the eye, the visual angle will increase
a rule of thumb
if you hold your arm out, your thumbnail is about 1-2 degree angle
accommodation
-the process by which the eye changes its focus by bending the lens
-the lens focuses light on the retina via the ciliary muscles
when lens is flat
-focusing on far away object
-zonules of zinn are tight
-pulling lens out
when lens is bulged
-focusing on near objects
-zonules of zinn are loose
measuring the power of lens
diopter (D) = 1/focal distance in meters (F)
refractive error
-a very common disorder in which the image of the world is not properly focused on the retina
-results: the retinal image is blurry and out-of-focus
-solution: corrective lenses
-cause: four different causes
focal point
where the “focused image” falls in relation to the retina
emmetropia
perfect vision
-the eyeball is shaped normally
-the focal point falls directly on the retina
-this causes the image to be perfectly focused
myopia
near sightedness
-the eyeball is elongated in depth
-the focal point falls short of the retina
result: far-away objects appear out of focus
aid: concave lenses that distort vision so focal point goes farther back
hyperopia
far sightedness
-the eyeball is shortened in depth
-the focal point falls beyond the retina
result: close-up objects appear out of focus
aid: convex lenses
presbyopia
“old sight”
-the lens becomes less flexible with age
-sometimes the focal point falls short and sometimes falls beyond the retina
result: close-up and far-away objects appear out of focus
astigmatism
-the cornea is misshaped causing light to be refracted in an abnormal manner
-this leads to multiple focal points
-not a lens problem
result: images are blurry at every distance
what is color blindness?
-some people are born without certain types of photoreceptors
result: certain colors that are easily discriminable to most are undiscriminable to these patients
-affects an estimated 8% of men and 0.5% of women
monochromats
-these individuals see everything in shades of gray
-very rare form of color blindness
-two subtypes: rod and cone monochromats
-missing 3 cone receptors, only have rods
dichromats
-have only 2 of the 3 types of cones necessary to perceive color
-this makes colors difficult to discriminate
-3 basic types depending on which cone type (S,M, or L) is missing
M cone missing
-most common
-deuteranopia (blue and yellow)
L cone missing
protanopia (blue and yellow)
S cone missing
tritanopia (red to pink to blue)
Ishihara Test
-we cannot tell what someone’s phenomenological experience of color is
-but we can tell whether someone can discriminate two different colors or not
-observers are forced to do a color discrimination in order to report a number value
on cells
increase firing rates in response to a photoreceptor sensing light
off cells
decrease firing rates in response to a photoreceptor sensing light
ganglion cells
-each ganglion cell is connected to several bipolar cells
-on-center: excitatory center (on) and inhibitory surround (off)
-off-center: inhibitory center (off) and excitatory surround (on)
-on-center and off-center ganglion cells respond to different light patterns
spatial frequencies
-the number of grating cycles in a given unit of space
-these are commonly studied with Gabor patches
contrast
-how different the bars are from each other in color or luminance
-independent of spatial frequency
contrast general rule
the higher the contrast, the more a retinal ganglion cell will fire (when the spatial grating aligns with the tuning properties of the cell)
ganglion cells in the retina
the retina is covered in ganglion cells, it’s so crowded that their receptive fields overlap each other
lateral geniculate nucleus (LGN)
-a relay station that copies information onward to visual cortex
-complex organizational structure that preserves left vs. right information
-magnocellular: two layers of large cells that encode large moving objects
-parvocellular: four layers of small cells that encode details of stationary objects
cortical magnification
-the center of the visual field has more V1 neurons representing it than the periphery of the visual field
-fovea accounts for .01% of the retinal image, it consists of ~10% of neurons in V1 cortex
retinotopic organization
-V1 cortex is organized so that spatial information from the retina is retained
-In V1, the fovea to 2.5 degrees are near each other
-likewise, 2.5 degrees and 5 degrees are near one another
neurons in V1
-respond to simple line orientations
-accumulates information across several ganglion cells
primary visual cortex (V1)
-the neurons in primary visual cortex accumulate information across several retinal ganglion cells
-this allows them to detect simple visual features (lines and edges)
extrastriate cortex
-the regions that border V1
-Examples: V2, V3, V4, MT
-progressively tuned for more complex features
macaque monkeys
have regions of visual cortex that are comparable to humans (homologue to human visual system)
neurons in V1 do not care about
border ownership
border ownership
-when one object is in front of another, there will be a visual border formed between the object and the background
-that border is “owned” by the object… it is a property of the object not the background
neurons in secondary visual cortex (V2) are sensitive to…
border ownership
low-level vision
recognizing simple features
mid-level vision
grouping simple features into an object
object recognition
matching an object to memory
Gestalt means what in German
pattern or configuration
Gestalt psychology
-“the whole is greater than the sum of its parts”
-made up a set of Gestalt Principles
-These “grouping rules” are useful when thinking about mid-level vision
illusory contours
a false edge that is perceived but is not present in the physical stimulus
occlusion
when an object is covered up by another object
GP: good continuation
two elements will tend to group together if they seem to fall on the same line
GP: closure
a closed contour is preferred to an open contour
texture segmentation
parsing an image into regions of common texture properties
GP: parallelism
parallel contours tend to group together
GP: symmetry
symmetrical regions are more likely to be grouped
figure-ground segmentation
the process of determining which item belongs to the foreground and which item belongs to the background
global superiority effect
many experiments suggest that the properties of the whole object dominate local identities
common problems for mid-level vision
inferring edges, texture grouping, figure vs. ground, occlusion, global vs. local
basic tools of Gestalt principles
similarity, good continuation, surroundedness, proximity, closure
ambiguous figures
doesn’t matter how they are perceived because they can be perceived so many different ways
top-down perception
-perception driven by experience, expectations, context, or learning
-the visual system is often making an educated guess about the actual state of the world
-problem? the visual system is susceptible to accidental viewpoints
3 basic challenges to imitate human object recognition
-multiple viewpoints
-multiple classes of the same object
-recognizing objects at different levels of specificity
template matching models
propose that the visual system recognizes objects by matching the neural representation of the image with a stored representation of the same “shape” in the brain
problem with template matching model?
how many templates would be needed to make this model actually function
structural description model
a description of an object in terms of its parts and the relationships between those parts
problem with structural description model?
some have argued this model does not do a good job of explaining a viewpoint specific effects
dorsal “where” pathway
-top back of brain
-processes information about the locations of objects and how to interact with them
-crucial for visual attention
-motor training and such
ventral “what” pathway
-bottom back to bottom middle of brain
-processes information about identity of objects
-crucial for object recognition
inferotemporal (IT) cortex
-this region of cortex seems to be particularly important for object recognition
-some neurons in IT visual cortex seemed tuned to very specific types of stimuli
-“grandmother cells”
-some neurons in IT visual cortex seemed tuned to very specific types of objects
-but there is probably not a special region (or neuron) for each type of object in the world
visual agnosia
-inability to recognize objects in spite of the ability of being able to see them
-low and mid-level vision are intact, but object recognition is impaired
-typically a result of brain damage to the IT cortex
visual form agnosia
-low-level vision intact, but cannot discriminate simple objects
-these patients have a hard time perceiving coherent objects
-cannot copy drawings of simple letters and shapes
associative agnosia
-can easily perceive objects as a whole but cannot verbally name the objects
-can perceive objects but not recognize them
-can copy the object but cannot name what they copied
prosopagnosia
can perceive and name objects normally, except for faces
Thatcher illusion
-“Face Inversion Effect”
-when you rearrange the parts of an upside down face, it’s hard to notice
why is face processing special?
global effects, expertise, and emotion
light is a…
waveform
light sources
objects that generate electromagnetic energy in the visible spectrum - sun, lamps, tvs
pigments
objects that reflect light from light sources - inks, clothes, leaves
subtractive color mixing
a mixture of pigments - the wavelengths of the two pigments act like filters when they combine
pigments absorb…
some light and reflect some light, we see the reflected light
additive color mixing
a mixture of lights - the wavelength of the two lights add together to form a new color
3 different types of cones
short (blue), medium (green), and long (red)
principle of univariance
a single photoreceptor cannot feasibly discriminate color
the trichromatic theory of color vision
three types of photoreceptors help us discriminate colors
the visible color spectrum
continuous, no discrete categorical borders, we create artificial borders when we talk about colors
basic color terms
single words that are used to describe a color - meaning is agree upon by speakers of a language
how many basic color terms are there in English?
11
mola
light-warm colors
mili
dark-cool colors
cultural relativism
the idea that basic perceptual experiences can be shaped by cultural history of the individual
negative afterimages
-we adapt to the colors that are viewed short periods of time
-when these colors are removed, we see the opponent colors
-this is because opponent color processes in the brain will habituate over short intervals
color constancy
-the tendency of a surface to appear the same color under a wide range of light sources
-result: viewing conditions can make the same physical colors look like a different color
human color vision is
trichromatic
color mixtures of light are
additive
color mixtures of pigments are
subtractive
color perception is greatly influenced by
context and recent experience (top-down processes)
