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Sensation and perception
Terms in this set (185)
Definition of sensation
sensation is the ability to detect a stimulus and perhap's to turn that detection into a private experience
sensation reflects the transformation of stimulus enegry into nerve signals in our sense organs ( sensory transduction)
Definition of perception
The act of giving meaning to a detected sensation
Perception is the interpertation and processing of sensations ( nerve signals)
Both process are acting in concert and are influencing each other
if there is no change in stimulation our senses adapt and we no longer notice the stimulation
adaptation is the reduction is response caused by prior or continuing stimulation
is the minimum amount of stimulation necessary for a person to detect a stimulus
it is basic detection the minimum amount of energy needed to become aware of a stimulus
Method of constant stimuli
is one known way to measure absolute threshold
the method requires creating many stimuli with different intensities in order to find the tiniest intensity that can be detected.
5-9 stimuli of different intensities are presented in random order
multiple trials are presented
Threshold is the intensity that results in detection in 50 percent of trials
It is simple to use but can be somewhat inefficient in an experiment because much of the subjects time can be spend with stimuli that are clearly above or below the threshold
The method of limits
A more efficient approach rather then the method of constant stimuli. -The experimenter begins with the same set of stimuli
- stimuli of different intensities are presented in ascending and descending order
-the observer responds to whether he percieved the stimulus
-the cross over point is the threshold
It is a method in which the particular dimension of a stimulus or the difference between two stimuli is varied incrementally until the participant responds differently
Method of adjustment
similar to the method of limits but the participant controls the stimuli directly
The subject increases or decreases the intensity of the stimulus
It is a method of limits inwhich the subject controls the change in the stimulus
not usually used to measure thresholds
The participant assigns values according to perceived magnitudes of the stimuli
ex- tasting solutions of sugar and rating the sweetness
What is the minimum difference needed to detect a change in the stimulus. like the frequency of two sounds or the brightness of two objects
The is called the differential threshold (DL) or the just noticeable difference (JND)
The task is to judge two events as same or different
describes the relationship between stimulus and resulting sensation that says the just noticeable difference is a constant fraction of the comparison stimulus
as magnitude of a stimulus increase so does JND, webers law explains this relationship
the experience of a stimulus increases less quickly than the actual stimulus strengths increases
A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithim of the stimulus
Signal detection theory(SDT)
It is a method that quantifies the response of an observer to the presentation of a signal in the presence of noise and personal bias to report the signal
it examines two components of detection judgments
-sensitivity- how much sensory evidence is there that a signal is present, bottom up effect
-Bias- how much evidence does the perceiver require before saying yes in an ambigous situation, top down effect
Stimulus detection depends not only on how strong the signal is but also on perceiver bias
an observers sensitivity ( d" ) is how well the observer can differentiate items coming from the signal absent and present distributions
represents the minimum level of internal certinty needed for the observer to decide that a signal was present
represent the relationship between hits and false alarms, and can be used to describe performance in therms of d.
specialized neurons that respond to specific kinds of enegry
carry information to the CNS brain
connect sensory and motor neurons or communicate with other interneurons
What is the difference between sensation and perception?
Sensation is the ability to detect a stimulus and perhaps to turn that detection into a private experience. Perception is the act of giving meaning to a detected sensation.
information integreation decision making live support
How do the movement of ions create electrical potentials in neurons?
diffusion- movement of ions from an area of high concentration to low concentration
concentration gradient- differences in concentration of a substance from an area of higher concerntration to an area of lower concentration
Electric potential- differences in electrial charge between two regions, opposite charges attract, similar charges repel
there is a high concentration if Na + ions outside the cell and K+ inside. -70 mV membrane potential
occur when permeability of the membrane changes depolarization of the membrane by a receptor neuron
Na + flows into the cell making it more positive, then K+ flows out making the neuron more negative
action potentials remain the same size
increase in stimulus intensity can increase the firing rate of neurons
refraction period is 1 ms largest of 500-800 imulses per second
How does the action potential encode information of intensity of a stimulus?
all or none law- the strength of an action potential is independent of the intensity of the stimulus that elicits it
intensity is by the firing rate of a neuron and by the number of neurons firing
released by the presynaptic neuron from vesicles, received by the postsynaptic neuron on receptor sites, used as triggers for voltage change in the postsynaptic neuron
at the synaptic cleft
1- arrival of action potential at presynaptic terminal
2- entry of ca2+ into presynaptic terminal and release of neurotransmitter molecules into synaptic cleft
3-binding of neurotransmitters to receptors and depolarization of postsynaptic membrane
there are excitatory or inhibitory effects on the postsynaptic membrane
ESPS- causes depolarization neuon becomes more negative increases likelihood of action potential
IPSP- hyperpoletization neuron becomes more negative
decreases action potential
temporal- at the same time
spatial at the same location
Light is in the form of
electromagnatic radiation, energy produced by vibrations of electrical charged material
Light is the stimulus for vision
the human visual range for humans is from 400 nm to 700 nm
most percieved light is reflected light
Light can be reflected absorbed scattered transmitted or refracted
enegry that is redirected when it strikes a surface, most percieved light is reflected light
absorbed energy that is taken up and is not transmitted at all
scattered-energy that is dispersed in an irregular fashion, when light enters the atmosphere much of it is absorbed or scattered
transmitted- energy that is passed on through a surface window lens
refracted- energy that is altered as it passes into another medium, light entering water from air
it is the first tissue that light will enter is the cornea. The cornea provides a window to the world because it is transparent- most light photons are transmitted through it rather then being reflected or absorbed. The cornea has a rich supply of sensory endings.
The lens inside the eye which allows changing focus, it is controlled by the ciliary muscle
The dark circular opening at the center of the iris in the eye where light enters the eye. which is a hole in a muscular structure called the iris
a light sensitive membrane in the back of the eye that contains rods and cones which receive an image from the lens and send it to the brain through the optic nerve
contains 5 major classes or neurons photoreceptors
horizontal cells, bipolar cells, amacrine cells and glanglion cells
Refraction is necessary to focus light rays and this is accomplished by
the cornea and the lens
the process in which the lens changes its shape altering its refractive power, allowing for the focus
This is resulted when ciliary muscles are tightened which causes the lens to become more spherical
-ciliary muscles relaxed lens flattened for distance vision
-ciliary muscles contracted lens rounded for close vision
This increases the refractive power of the lens, light rays are bent more sharply and focus near objects on retina
the light is focused in front of the retina and distant objects cannot be seen sharply nearsightedness
eye bulb to long
when light entering the eye is focused behind the retina, farsightness
eye bulb to short
a light sensitive receptor in the retina. When photoreceptors sense light they can stimulate neurons in the intermediate layers, and these neurons then connect with the frontmost layer of the retina.
photoreceptor specilized for daylight vision fine visual acuity and color
used for day vision
not as sensitive as rods
concentrated in the fovea
three types of photosensitive pigment in humans
color vision, more emphasis on detecting the fine details
a photoreceptor specialized for night vision
used for dim light vision
highly sensitive to light
22 times as numerous as cones in the retina
not present in the fovea
one type of photosensitive pigment
achromatic vision emphasis on detecting motion
the visual pigment found in rods
a photopigment that is sensitive to ambient light
When light hits the eye the process of photoactivation begins
Both types of photoreceptors consist of an outer segment , inner segment, and synaptic terminal. Visual pigments are made in the inner segment and is stored in the outer segment, where they are incorporated into the membrane.
Receptors have outer segments
they contain visual pigment molecules which have two components
retinal- a light sensitive molecule
visual transduction occurs when the retinal absorbs one photon. Retinal changes its shape called isomerization
interconnect several photoreceptors and bipolar cells.
horizontal integration lateral inhibition
They run perp. to the photoreceptors making contacts between nearby photoreceptors. These lateral connections play an important functional role in the form of lateral inhibition.
which enables the signals that reach retinal ganglion cells to be based on differences in activation between nearby photoreceptors.
Antagonistic neural interaction between adjacent regions of the retina
interconnect several bipolar and ganglion cells
interneurons that collect signals from signal or numerous photoreceptors
output cells that encode information into action potentials, small type receives input from cones
large type receives input from many cones and rods implicated in lightness contrast movement
Higher convergence of rods than cones
average of 120 rods to one ganglion cell , average 6 cones to one ganglion cells
convergence and sensitivity of rods
rods are more sensitive to light than cones,
rods take less light to respond, they have greater convergence which results in summation of the input of many rods into ganglion cells increasing the likelihood of response
tradeoff rods cannot distinguish detail
All cone foveal vision results in high visual acuity
one to one wiring leads to ability to discriminate details, trade off is that cones need more light to respond than rods
The mach band effect
receptors on the border receive differential inhibition, the resulting perception gives a boost for detecting contours of objects
Receptive field on center and off center
What is the function of receptive fields?
Receptive fields emphasize differences in light rather than absolute light intensity
contrast engancement- detection of edges and contours. reduces the amount of information that has to be transmitted and processed by the CNS
Perceptual constancy under a wide range of light conditions- allows reading indoor or outdoor
The range of pupil sizes changes in light conditons
bring light small pupil 2 mm
dark large pupil 8 mm
Lateral geniculate nucleus
a structure in the thalamus that receives input from the retinal ganglion cells and has input and output connections to the visual cortex
there is one in each hemisphere of the brain
primary visual cortex area 17 striate cortex
The area of the cerebral cortex of the brain that receives direct input from the LGN as well as feedback from other brain areas and is responsible for processing visual infromation
Topographical mapping: Close
by areas in the visual field are
'mapped' onto close by areas
in the cortex
amount of cortex devoted to
processing the fovea is
proportionally much more than
the amount of cortex devoted to
processing the periphery
the tendency of neurons in striate cortex to respond optimally to certian orientations and less to others
respond to distinct orientations, a cortical neuron with clearly defined excitatory and inhibitory regions
respond also to a certian widths of a light bar, spatial frequecny, and sometimes also to movement in a specific direction
Neurons with similar orientation preferences are arranged in
columns that extend vertically through the cortex.
Within each column, all neurons have the same orientation tuning
• Hubel and Wiesel: Found systematic, progressive change in
preferred orientation; all orientations were encountered in a distance
of about 0.5 mm
Neurons in a given column respond preferentially to the left or right eye
The columns alternate in a left-right pattern every .25 to .50 mm across
A 1 millimeter block of striate cortex containing two sets of columns each covering every possible orientation with one set preferring left eye input and one preferring right
Neurons within columns fire maximally to the same orientation of stimuli
Adjacent columns change orientation preference in an
Ocular dominance columns
Neurons in a given column respond preferentially to the
left or right eye
The columns alternate in a left-right pattern every .25 to .
50 mm across the cortex
a reduction in response caused by prior or continuing stimulation
the diminishing response of a sense organ to a sustained stimulus
The psychologists electrode diagram shows
how selective adaptation may alter the distribution of neural responses and therefore perception
Neurons tuned to specific stimuli fatigue when exposure is long. fatigue causes adaptation to stimulus, neurons firing rate decreases, neurons will fire less when stimulus presented again
means that only those neurons that respond to the specific stimulus adapt, resulting in a loss of sensitivity for spatial frequencies close to the adapting frequency, but not for spatial frequencies that are much higher or lower than the adapting frequency.
carry information from CNS to muscles to control their functioning
What is dualism?
The idea that the mind has an existence separate from the material world of the body.
What is visual acuity and how can it be measured?
Visual acuity is the smallest spatial detail that can be seen accurately. It can be measured by doing a visual acuity test, which requires looking at figures from a distance and identifying them
Explain the meaning of being able to see 20/20.
Being able to see 20/20 means that the person being tested can identify an object at 20 feet as well as somebody with normal vision would be able to identify it at 20 feet. If the observer's vision is 20/40, that means that the observer can see at 20 feet what somebody with normal vision can see at 40 feet (meaning the observer needs glasses!)
What can we infer from the contrast sensitivity function?
The contrast sensitivity function describes our window of visibility. Any object whose spatial frequencies and contrast fall within the region specified by the contrast sensitivity function will be visible. Those objects outside the region are outside our window of visibility. We can infer from this function that sensitivity to contrast depends on the spatial frequency of the stimulus.
Explain how retinal ganglion cells respond to stripes.
Each ganglion cell responds to certain types of stripes or gratings. For instance, an ON ganglion cell responds to gratings with spatial frequencies and phases that make the lightest part of the grating fall on the center of the cell and the darkest part of the grating fall on the surround. When the spatial frequency of the grating is too low, the ganglion cell responds weakly because part of the bar of the grating lands in the inhibitory surround, dampening the cell's response. Similarly, when the grating's spatial frequency is too high, the ganglion cell responds weakly because both dark and light stripes fall within the receptive field's center and surround, washing out the response. When the frequency is just right, the cell responds vigorously.
What is the role of the lateral geniculate nucleus (LGN)?
The lateral geniculate nucleus is a structure in the thalamus (part of the midbrain) that shares connections with both the retina and visual cortex.
What are the two types of layers in the LGN and how are they different from each other?
The two types of layers in the LGN are the magnocellular layers and the parvocellular layers. The magnocellular layers are the two bottom layers of the LGN, and contain neurons that are physically larger than those in the parvocellular layers. Neurons in these layers respond to large, fast-moving objects and do not represent color information. The parvocellular layers are the top four layers of the LGN. They contain neurons that respond to the fine spatial details and color of stationary objects.
Explain the notion of topographical mapping.
opographical mapping is the orderly mapping of the world in the lateral geniculate nucleus and the visual cortex. Points of light that are near each other in the world fall on parts of the retina that are near each other and will be processed by neurons that are near each other in the brain. This orderly representation provides us with a neural basis of knowing where things are in space.
What are two important features of the visual cortex? Explain.
One important feature of the visual cortex is topographical mapping, which is the orderly mapping of the world in the brain. The second feature is magnification, or the dramatic scaling of information from different parts of the visual field. Objects on or near the fovea are processed by neurons in a large part of the striate cortex, while objects imaged in the periphery are allocated a much smaller portion of the striate cortex.
In what way do striate cortex neurons function as filters?
Each striate cortex neuron responds to a particular location and is tuned to a particular spatial frequency, orientation, and phase. These narrow tuning functions mean that each striate cortex neuron functions as a filter for the portion of the image that excites the cell.
What is the difference between simple and complex cells?
Simple cells are cortical neurons with clearly defined excitatory and inhibitory regions, while complex cells are neurons whose receptive field responds to any properly oriented bar of light, regardless of whether it is light or dark.
What is a column in primary visual cortex?
A column is a vertical arrangement of neurons in striate cortex that tend to have similar receptive fields and similar orientation preferences.
What does a hypercolumn contain?
A hypercolumn is a 1-mm block of striate cortex contains two sets of columns, each covering every possible orientation (0-180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye.
How can adaptation provide insights into the properties of cortical neurons?
Adaptation is the diminishing response of a sense organ to a sustained stimulus. It is helpful in learning about the properties of cortical neurons because, by exposing an observer to a particular stimulus for an extended period of time, the experimenter can make inferences about the visual system due to the observer's changing responses. If two stimuli are processed by unrelated sets of neurons, then selectively adapting one set of neurons should have no effect on the other set
Spatial-frequency theory proposes any visual scene can
be broken into areas of lightness and darkness
(represented by a sine-wave grating
Why would the visual system use spatial-frequency to
Different spatial frequencies emphasize
different types of information
A contour that is perceived even though nothing changes from one side of it to the other in an image.
Illusory contours are a phenomenon that the structural approach could not
explain since the observer sees things that have no structural elements
Gestalt psychologists suggested that understanding perception could not be
done by breaking it down into parts, but by considering the whole experience
Gestalt psychologists attempt to define principles or laws that allow us to
Gestalt grouping rules: A set of 'rules' that describe when elements in an
image will appear to group together
Ambiguous figure: A visual stimulus that gives rise
to two or more interpretations of its identity or
Surroundedness: The surrounding region is likely to be ground
Elements located in the lower part of displays tend to be seen
Symmetry: A symmetrical region tends to be seen as figure
The smaller region is likely to be figure
determining what part of environment
is the figure so that it "stands out" from the background
• Properties of figure and ground
§ The figure is more "thinglike" and more memorable than
§ The figure is seen in front of the ground
§ The ground is more uniform and extends behind figure
§ The contour separating figure from ground belongs to the
Summarizing middle vision
• Goals of middle vision:
1. Bring together that which should be brought
2. Split apart that which should be split apart
3. Use what you know
4. Seek consensus and avoid ambiguity
Structural description model
Structural models propose that objects are recognized by the
relationship of parts.
• Objects are recognized by matching them to a 'library' of
memorized components (object structures)
• 3-D objects are based on a set of volumetric features that are
combined for a given shape
• In their pure form, such models are viewpoint-independent
complex objects are made up of arrangements of basic, component parts ('geons').
Image description naive template
Ability to identify 3-D objects comes from stored 2-D
viewpoints from different perspectives
• For a familiar object, view invariance occurs
• For a novel object, view invariance does not occur
• Prediction: The farther an novel object is rotated
away from a learned view, the longer it takes to
Viewpoint invariance likely involves both:
• Matching views of objects to memorized views
Template representations are easy to generate but hard
to match (because there are so many).
• Matching a novel object to memorized elementary
Structural description representations are hard to generate
but easy to match (because they describe the object
abstractly and so are immune to variations in viewpoint,
Extrastriate cortex: The region of cortex bordering the primary
visual cortex and containing multiple areas involved in visual
After extrastriate cortex, processing of object information is split
into a "what" pathway and a "where" pathway
"Where" pathway is concerned with the locations and
shapes of objects but not their names or functions
"What" pathway is concerned with the names and
functions of objects regardless of where they are
Module - a brain structure that processes information
about a particular type of stimuli
• Inferotemporal (IT) cortex in monkeys
§ One part responds best to faces while another
responds best to heads
§ Results have led to proposal that IT cortex is a
form perception module
Evidence for modules in human brain
Temporal lobe damage in humans results in agnosia,
i.e., a failure to recognize objects in spite of the ability to
Specific case: prosopagnosia, i.e., the inability to
Retina ganglion cells:
Striate cortex (V1) Bars
Retina ganglion cells: Center/surround spots (contrast)
nucleus (LGN) Center/surround spots (contrast)
Striate cortex (V1) Bars (orientation/movement)
(what and where pathways) Objects, faces
What cortical brain structures does visual information pass through as it is processed?
Answer: Information first reaches the cortex in a region called striate cortex, so-called because it has a distinctive striped pattern under the microscope. Early vision processes are carried out here. Then information is passed to extrastriate cortex, where the tasks of middle vision are carried out (for example, this is where illusory contours are processed). From there, information travels via two separate pathways, one that ends in the parietal lobe, and one that terminates in inferotemporal (IT; lower temporal lobe) cortex. It is in IT cortex that the end-stage processing of face and object recognition is carried out.
What are the receptive field characteristics of cells in inferotemporal (IT) cortex?
Answer: Many neurons in IT have been shown to respond most actively to particular objects or faces. The term "grandmother cell" was coined to describe these neurons, the implication being that a single cell might be ultimately responsible for deciding whether an image was of one's grandmother's face. In support of the grandmother cell hypothesis, recordings of single cells in the IT of humans have identified cells that only respond to the actress Jennifer Aniston.
What is the guiding philosophy behind Gestalt psychology? How does it contrast with the earlier approach known as structuralism?
Answer: The structuralists believed that perception of a complex scene was simply the sum of the basic "atoms" of perception (color, orientation, etc.) in the scene. Gestalt psychologists reacted to this position, arguing that a perceptual whole was much more than the sum of its elemental parts.
What do the Gestalt grouping rules seek to describe?
Answer: The grouping rules describe which elements in an image will appear to group together.
What evidence is there that the visual system starts with large objects and then divides them into smaller parts, rather than processing scenes the other way around?
Answer: Evidence for this proposition comes from the global superiority effect. In displays like those at the left, it was found that identifying the small (local) letters took longer than identifying the larger (global) letter, indicating that the global information is more readily available than the local information. That is, in the figure at left, you tend to see the E before the Gs.
What is the fundamental goal of object recognition?
Answer: To match a perceived stimulus to a representation of a previously encountered object encoded in memory.
What is a naive template theory, and why can such theories be rejected as a complete theory of object recognition?
Answer: The formal definition of a template is complicated, but template theories essentially follow a "lock and key" principle. The perceived image is the key, and the template is the lock. The naive template approach says that we store templates for all the images of all the objects we have ever seen. When we perceive an object that we want to recognize, we try to match this perception to all the templates stored in memory until we find a lock in which the key fits exactly. This doesn't strike most people as being a very efficient process. One of the most important problems is that it seems unlikely that we have enough brain capacity to store templates to match every single object in every single viewpoint that we are likely to encounter in our lives.
What is the basic idea behind a structural description, and how do structural description theories improve on template theories?
Answer: A structural description describes the structure of an object in terms of its constituent parts and the relationships between those parts. The advantage over templates is that a single structural description can potentially match a large number of slightly different shapes. For example, if an X is described as two oblique lines that cross near their centers, this description will match all the figures at left. However, each figure would require a different template in a naive template theory.
What is a geon?
Answer: Geons are "geometric ions" and are the three-dimensional building blocks of structural descriptions in Biederman's recognition-by-components theory of object recognition. The defining quality of geons is that they are discriminable from each other based on non-accidental features, so they should be easily recognizable from any viewpoint.
Describe the essence of the viewpoint invariance versus viewpoint dependence debate in the object recognition literature
Answer: Many structural description theories, such as recognition-by-components, predict that in most circumstances, object recognition should be equally efficient (i.e., equally fast) regardless of whatever viewpoint you see the object from. Such a pattern of performance, in which recognition time does not vary across changes in viewpoints, is known as viewpoint invariance. However, many empirical studies have revealed that object recognition times are in fact dependent on viewpoint. If subjects study a novel object from a single viewpoint, they are usually slower at recognizing the object later when shown from a new viewpoint than when shown from the trained viewpoint.
Why is face recognition thought to be accomplished via different mechanisms than object recognition?
Answer: Most objects require considerably more time to recognize at the subordinate than at the basic level. However, recognition of individual faces, which is a subordinate-level task, is a very fast process—so fast that many researchers believe the visual system must use "special" mechanisms to recognize faces. Also, face recognition and object recognition can be doubly dissociated—people with object agnosia can recognize faces but not objects whereas people with prosopagnosia can recognize objects but not faces.
What is the face inversion effect, and how does it relate to the special mechanisms thought to be operating when we recognize faces?
Answer: Faces are more difficult than other objects to recognize when inverted. Researchers have proposed that when faces are inverted, the special processes that are usually brought to bear in recognizing faces cannot operate, so we are forced to rely on our "normal" object recognition processes, which are not as efficient for subordinate-level objects, like faces.
What is materialsim?
The idea that the only thing that exists is matter, and that all things including the mind and consciousness are the results of interaction between bits if matter.
What is prosopagnosia, and what does it say about special face recognition processes?
Answer: Prosopagnosia is a neuropsychological disorder in which people cannot recognize faces, although they can recognize other objects normally. It is due to damage in fusiform face area (FFA) of the brain where special face recognition processes are carried out.
What is the difference between dualism and materialism?
Dualism is the idea that the mind and body are separate, that the mind has a non-material existence independent of the material world of the body. Materialism is the idea that the only thing that exists in the universe is matter, and that both the mind and body are made of matter- the mind is what the brain does.
The idea that the mind exists as a property of all matter that is that all matter has consciousness
What is the difference between myopia and hyperopia?
Myopia (i.e., "nearsightedness") is a condition in which light entering the eye is focused in front of the retina, whereas hyperopia (i.e., "farsightedness") is a condition in which light entering the eye is focused behind the retina. In both cases the retinal image is blurry without some sort of correction.
the science of defining quantitative relationships
What is the just noticeable difference?
The JND is the smallest detectable difference between two stimuli or the minimum change in a stimulus that can be correctly judged as difference from a referece stimulus. It is also known as the difference threshold. it is a key tool for investigating psychophysiological phenomena.
What is psychophysics?
psychophysics is the science of defining quantitative relationship between physical and psychological events.
Explain weber's law
Webers law is the principle describing the relationship between stimulus and resulating sensation that says the JND is a constant fraction of the comparison stimulus. The JND is proportional to the stimulus magnitude.
Why can't rods signal differences in color?
Rods cannot signal differences in color because they only have one type of photopigment. Cones, on the other hand, have three types of photopigments, which help them differentiate between colors.
Explain Fechner's law
it is a principle describing the relationship between stimulus magnitude and resulting sensation magnitude such that the magnitude of subjective sensations increases proportionally to the logarithm of the stimulus intensity. As the stimulus grows larger, larger changes are required for the changes to be detected by the perceiver
Describe the method of constant stimuli
The method of constant stimuli involves the presentation of many stimuli ranging from rarely to almost perceivable. They are present one at a time and participants responds to each presentation yes/no same/ different
What is the difference between an "ON" bipolar cell and an "OFF" bipolar cell?
An "ON" bipolar cell is a cone bipolar cell that depolarizes in response to an increase in light intensity. An "OFF" bipolar cell is a cone bipolar cell that depolarizes in response to a decrease in light intensity. These two cells have opposite reactions to light.
What is the methods of limits?
The method of limits involves presenting stimuli that vary incrementally in one dimension until the participant responds differently.
Why is the center-surround organization of retinal ganglion cells so important?
The center-surround organization of retinal ganglion cells is important because it allows for sensitivity to contrast rather than absolute illumination levels. Ganglion cells are most sensitive to differences in the intensity of light in the center and in the surround, and they are relatively unaffected by the average intensity of light. This is useful because the average intensity of light falling on the retina will be quite variable, depending on whether the observer is indoors, outdoors, etc., but contrasts of light are relatively constant.
What is a filter and how is it important in vision?
A filter is an acoustic, electrical, electronic, biological, or optical device, instrument, or computer program that allows the passage of some frequencies or digital elements and blocks others. Filters are important in vision because they allow the transformation of raw images into representations in the brain. Filters highlight certain important visual information while eliminating other unimportant information. The center-surround receptive fields of retinal ganglion cells are filters.
What is the method of adjustment?
The method of adjustment is a psychophysical method which uses the method of limits idea but in which the participant controlsthe change in stimulus
What is magnitude estimation?
Magnitude estimation is a psychophysical method in which the participant assigns values according to perceived magnitudes of stimuli.
What is stevens power law?
It is a principle of describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sesation is proportional to the stimulus magnitude raised to an exponent.
less then one the curve flattens as the stimulus increases
more then one the curve continuously increases
of one a stright line
How does cross modality matching work?
In cross modality matching the observer adjusts the intensity of one kind of stimulus until it matches the percieved intensity of another kind of stimulus.
example adjusting the brightness of a light to match the spiciness of some food
What are the signal and noise in signal detection theory?
Signal detection theory is psychophysical theory that quantifies the response of an observer to the persentation of a signal in the presence of noise. The signal is the target stimulus and the noise is the intereference that occurs and is sometimes confused with signal.
What is the difference between sensitivity and criterion in signal detection theory?
Sensitivity is the ease with which an observer can distinguish a signal from noise regardles of any bias they may have in responding. The criterion represents your willingness to say yes or no to whether you perceived a potential signal and thus is a measure of your bias in responding
What can be inferred by doing a fourier analysis?
A Fourier analysis is a mathematical theorem by which any signal can be divided into a set of sine waves. Combining these sine waves will reproduce the original signal. Fourier analysis can be performed on sound waves and images
What is the purpose of the cornea?
The cornea is a transparent surface on the exterior of the eye. t protects the eye from the outside world. Being transparent, it allows light to be transmitted through it and into the eye.
What is the purpose of the retina?
The retina is a light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve.
How does the process of accommodation take place in the eye?
Accommodation takes place in the lens of the eye. The lens changes its refractive power by changing its shape. This causes the eye to be able to focus on a given object, whether it is near or far.
define spatial frequency
spatial frequency is the number of repetitions of a sine wave per unit area. in audition it is the number of cycles per second. In vision it is the number of cycles per degree
What is astigmatism and how can it be fixed?
Astigmatism is a visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea. It can be fixed by wearing lenses that have two focal points (that provide different amounts of focusing power in the horizontal and vertical planes).
Why are photoreceptors important in the process of seeing?
Photoreceptors are the cells that make up the backmost layer of the retina. They are sensitive to light, and as soon as they sense it, they can cause neurons in the intermediate layers to fire action potentials. Photoreceptors are important in the process of seeing because they transduce the physical energy of light into neural energy that our brains can analyze.
What are rods and cones?
Rods and cones are photoreceptors present in the retina. Rods are specialized for night vision; cones are specialized for daylight vision, fine visual acuity, and color.
What is the role of horizontal cells?
Horizontal cells are specialized retinal cells that contact both photoreceptors and bipolar cells. They produce lateral inhibition, which allows the signals that reach retinal ganglion cells to be based on differences in activations between nearby photoreceptors rather than absolute levels of activation.
What is visual acuity?
Visual acuity is a measure of the finest detail that one can resolve.
What is a receptive field?
A receptive field is the region on the retina in which stimuli will activate a neuron. Receptive fields vary in size, shape, and complexity.
What are some consequences of the differing sizes of M ganglion cell and P ganglion cell receptive fields?
P ganglion cells have smaller receptive fields than M ganglion cells at all eccentricities. This allows the M ganglion cells to respond to a larger portion of the visual field. In addition, they are much more sensitive to visual stimuli under low lighting conditions than P ganglion cells. P ganglion cells, on the other hand, provide finer resolution (greater acuity) than M ganglion cells, as long as there is enough light for them to operate.
Explain how the pupil adapts to dark and light conditions.
The pupil has the ability to dilate and constrict, depending on amount of light. For example, under well-lit conditions, the pupil tends to constrict to let less light into the eye. Under dark conditions, the pupil dilates to allow more light into the eye.
Explain why it is that we are generally not bothered by variations in overall light levels
We are generally not bothered by variations in overall light levels because we have several mechanisms for regulating how much light enters the eye. One mechanism is pupil size. Another is the regeneration rates of pigments in our photoreceptors. Yet another is the rod/cone dichotomy—cones operate at moderate and high light levels while rods take over for low light levels. Finally, the neural circuitry of the retina itself helps stabilize external light variations by emphasizing contrasts in luminance rather than absolute light levels.
What is the difference between age-related macular degeneration (AMD) and retinitis pigmentosa (RP)?
AMD is a disease associated with aging that affects the macula, or central visual field. RP is a progressive degenerative disease of the retina that affects peripheral vision.
What is the central idea of mullers doctrine of specific nerve energies?
The central idea of Mullers doctrine of specific nerve energies is that we are aware only of the activity in our nerves and we cannot be aware of the world itself
What are cranial nerves?
Cranial nerves are twelve pairs of nerves that originate in the brain stem and reach the periphery through opening in the skull. They are dedicated mainly to sensory and motor systems
Explain how neurons communicate with each other?
Neurons have axon terminals as well as dendrites. The axon terminal of the persynaptic neuron releases neurotransmitters that bind to receptors on the dendrite of the postsynaptic neuron thus communicating from the axon of the first neuron to the dendrite of the second neuron.
What are neurotransimitters?
Neurotransmitters are chemical substances used in neuronal communication at synapses
When is an action potential created?
An a ction potential or firing of a neuron is created when the membrane of the neuron permits sodium ions to rush into the cell increasing voltage. Very quickly afterward potassium flows out of the cell bringing the voltage back to resting voltage
Which forms of non invasive brain imaging have the highest temporal resolution?
EEG and MEG both have very high temporal resolution but low spatial resolution. They are the best techniques for making fine observations of an observers neural responses to as stimulus over time.
Which forms of non invasive brain imaging have the highest spatial resolution?
Computerized tomography and MRI both have extremely high spatial resolution. They are the best options for creating non invasive structural images of the brain
Which forms of non invasive brain imaging are good for investigating how the brain functions?
FMRI and PET are both capable of visualizing the brains metabolic activity over time FMRI tracks the flow of oxygenated blood in the brain while PET tracks the metabolism of safe radioactive isotopes
Sensation and perception are two interdependent processes in the brain.
The perceptual starts with stimuli from the environment
Describe the two ways used to conceptualize light?
one way to think of it as a wave that travels through a medium. Another is to think of it as a stream of photons each consisting of one quantum of enegry
Describe the difference between light that is reflected and light that is transmitted?
Reflected light occurs when a ray of light strikes a surface and then bounces back towards its point of origin. Transmitted light occurs when light is neither reflected nor absorbed. a window light passes through the surface and transmitted to the other side.
Weber proposed that the smallest change in a stimulus that can be detected is a(n) _______ proportion of the stimulus level.
The chemical substance used in neuronal communication at synapses is known as
A synapse is the junction between _______ that permits information transfer.
The method of _______ requires the experimenter to vary a perceptible stimulus until it is no longer perceived or an imperceptible stimulus until it is finally perceived.
If a stimulus is present and the observer reports it as present, this is called a
JND is the
smallest detectable difference between two stimuli
Sensory transducers are
receptors that convert physical energy into neural activity.
Spatial frequency refers to the
number of cycles of a grating per unit of visual angle.
End stopping is the process by which cells in the cortex first _______ their firing rate as the bar length _______ to fill up its receptive field, and then _______ their firing rate as the bar is lengthened further.
increase increae decrease
Scientists study contrast sensitivity for sine wave gratings across many different spatial frequencies because
patterns of stripes with fuzzy boundaries are common in the real world.
he right visual field projects to the _______ half of each eye and then is analyzed by the LGN in the ______ hemisphere.
Visual angle is a measure of the
size an object takes up on the retina.
The smallest spatial detail that can be resolved is known as
Which of the following is a viewing position that produces some regularity in the visual image that is not present in the world?
Tarr and his colleagues have found that the amount of time needed to recognize novel objects is at least partially determined by
the amount the object is rotated from its studied view.
Which of the following is a loosely defined stage of visual processing that comes after basic features have been extracted from the image, and before object recognition and scene understanding?
The term "grandmother cell" refers to a neuron that
responds best to one specific object.
Which of the following is not a cortical area that has been identified as processing very specific forms of visual stimuli?
Extrastriate motion pericomplex (EMP)
A major problem with template theories of object recognition is that
we cannot possibly store enough templates in memory to match every object we might encounter.
Prosopagnosia is a neuropsychological disorder in which the patient
cannot identify faces, but can recognize other types of objects
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