midterm 1 Flashcards
1
Q
Absolute threshold
A
smallest stimulus level that can just be detected E.g. smallest line width that can be detected in the grating experiment
- Fechner proposed that that the mind could be studied by measuring the relationship between changes in physical stimulation
- as physical stimulation is increased—for example, by increasing theintensityof a light—the person’s perception of thebrightnessof the light also increases
2
Q
Classical Psychophysical Methods
A
The choice among these methods is usually determined by the degree of accuracy needed and the amount of time available
- Method of limits
- Method of constant stimuli
- Method of Adjustment
3
Q
Method of limits
A
the experimenter presents stimuli in either ascending order (intensity is increased) or descending order (intensity is decreased), which indicates the results of an experiment that measures a person’s threshold for hearing a tone
4
Q
Method of Constant Stimuli
A
different stimulus intensities are presented one at a time at random, and the participant must respond whether they perceive it (“yes” or “no”) on each trial
- threshold is usually defined as the intensity that results in detection on 50 percent of trials.
- Most accurate method - It involves numerous observations, with stimuli presented in random order. This approach minimizes the influence of one trial’s presentation on the participant’s judgment of stimuli in subsequent trials.
- Disadvantage = time consuming
5
Q
Method of Adjustment
A
the participant—rather than the experimenter—adjusts the stimulus intensity continuously until he or she can just barely detect the stimulus
- Fasted method
6
Q
Difference Threshold
A
smallest differencebetween two stimuli that enables us to tell the difference between them
7
Q
Measuring Perception Above the Threshold
A
- Technique - Magnitude Estimation
- Technique - Recognition Testing
- Technique - Reaction Time
- Technique PhenomenologicalReport
- Technique Physical Tasks and Adjustment
8
Q
Magnitude estimation
A
- Experimenter presents a “standard” sound, rated 10.
- Participant hears sounds of different intensities.
- Participant assigns a number based on perceived loudness relative to the standard.
- Twice as loud = 20, half as loud = 5.
- The numerical ratings reflect the perceived magnitude of each sound.
9
Q
Recognition Testing
A
Naming objects is a form of categorization. This process, known as recognition, is evaluated through various perceptual experiments. One important application is assessing the cognitive abilities of individuals with brain damage.
E.g. as mentioned earlier in this chapter, Dr. P.’s brain injury resulted in difficulty recognizing everyday items, such as a glove. To measure the recognition capabilities of people with brain damage, researchers typically ask them to identify objects or images of objects.
Recognition is also used to assess the perceptual abilities of people without brain damage.
10
Q
Visual Agnosia
A
Inability to (step 6) recognize during perception
10
Q
Reaction Time
A
The time between presentation of a stimulus and theperson’s reaction to it.
11
Q
Phenomenological Report
A
Describing what an individual sees. They are important because they define the perceptual phenomena we want to explain, and once a phenomenon is identified, we can then study it using other methods.
12
Q
Neural Processing
A
Electrical signals are sent through interconnected neurons to primary receiving area - the cerebral cortex
- temporal, parietal, occipital lobe
- reduced with gaba
- amplified with glutamate
13
Q
Psychophysics
A
Studying behavioral response to stimuli
14
Q
JND
A
magnitude increases as difference threshold increases
if the original stimulus is larger, the JND difference must be larger for detection
Weber’s Law: Relationship between JND and original stimulus intensity is linear
15
Q
Signal Detection Theory
A
Either a low stimulus is presented or no stimulus presented
Hit = yes when presented
Miss = no when presented
False Alarm = yes when not presented
Correct Rejection = no when not presented
To manipulate participant to be more liberal, reward on hit
To manipulate participant to be more conservative, reward on correct rejection
16
Q
Propagate Response
A
Nerve impulse travels down nerve fiber without decreasing in amplitude
- enables neurons to transmit long distances
- action potential remains the same no matter how strong the stimulus is
- only frequency of firing is effected
- upper limit to nerve impulses per second due to refractory period
17
Q
Spontaneous Activity
A
Nerve firing occurs in absence of environmental stimuli
18
Q
Absolute Refractory
A
A period of 1-2ms after initiation of an action potential where it is impossible for another action potential to occur in the same neuron
19
Q
Relative Refractory
A
A period 2-4ms after an action potential where more stimulation is needed to trigger another action potential
20
Q
Rate Law
A
Strength of a stimulus is reflected in the rate f the neuron’s firing rather than the amplitude
20
Q
Excitatory Signal Response
A
- Occurs when the neuron becomes depolarized, and thus the inside of the neuron becomes more positive. Causes depolarization, an increased charge inside the neuron
- Increases the chances that a neuron will generate action potentials and is associated with increasing rates of nerve firing
- Glutamate
21
Q
Inhibitory Signal Response
A
- Occurs when the inside of the neuron becomes more negative, causing hyperpolarization
- Hyperpolarization is an inhibitory response because it makes the charge inside the axon more negative, moving it further from the threshold needed to trigger an action potential.
- Decreases the- chances that a neuron will generate action potentials and is associated with lowering rates of nerve firing.
- Gaba
22
Q
Neural Integration
A
Neurons in the brain and nervous system combine and process multiple signals from other neurons to produce a coordinated response. This process enables complex behaviors, thoughts, and responses to stimuli.
- Synaptic Input
- Threshold Level
- Summation (spatial/temporal)
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Spatial Summation
Inputs from multiple neurons are integrated across the neuron’s membrane. If multiple excitatory or inhibitory signals come in at the same time from different locations, their effects are combined.
24
Temporal Summation
Inputs from a single neuron arrive close together in time. The neuron sums these signals if they occur in quick succession.
25
Synaptic Input
Neurons receive signals through their dendrites from other neurons via synapses. These signals can be excitatory (EPSPs – excitatory postsynaptic potentials) or inhibitory (IPSPs – inhibitory postsynaptic potentials)
26
Threshold Potential
If the summation of these signals reaches a critical threshold at the **axon** **hillock** (the part of the neuron where the axon begins), the neuron will fire an action potential. This is the electrical signal that travels down the axon to communicate with other neurons or tissues.
27
Sensory Coding
1. Specificity coding
2. Sparse coding
3. Population coding
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Specificity coding
Specialized neuron that responds only to one concept or stimulus
- Grandmother Cell: A highly specific type of neuron that fires in response to a specific stimulus, such as a person’s grandmother. Not scientifically proven to exist.
- Neurons don’t respond only to visual cues of a stimulus, but rather the concept of the stimulus
29
Sparse coding
Occurs when a particular stimulus is represented by a pattern of firing of only a small group of neurons, with the majority of neurons remaining silent
The code for representing objects in the visual system, tones in the auditory system, and odors in the olfactory system may involve a pattern of activity across a relatively small number of neurons,
30
Population coding
- Our experiences are represented by the pattern of firing across a *large* number of neurons.
- Advantage = large number of stimuli - can be represented, because large groups of neurons can create a huge number of different patterns
31
Contralateral Organization
Crossing over of stimuli and brain hemisphere interpretation (does not occur for audition)
32
Fissures
Fissures = Deep sulci that reach ventricles
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Gyri
Gyri = Ridges
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Sulci
Sulci = Valleys/folds
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Hind brain
Regulates automatic processes that control live-support functions e.g. breathing, balance
36
Mid brain
Relay center (thalamus) for sensory info coming to the brain e.g. vision and audition
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Modularity
The idea that specific areas of the cortex are specialized to respond to specific types of stimuli.
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Forebrain
Cerebral cortex e.g. learning and memory
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Diencephalon
Contains thalamus and hypothalamus
Thalamus - contains many pairs of nuclei
- 2 halves and sits on top brain stem
- sensory relay center
- massa intermedia joins two thalami together
- not all info received is passed to be processed/perceived
40
Module
A structure that processes information about a specific behavior or perceptual quality. Often identified as a structure that contains a large proportion of neurons that respond selectively to a particular quality.
41
Brocas area
An area in the frontal lobe that is important for language perception and production. One effect of damage is difficulty in speaking.
42
Wernickes area
An area in the frontal lobe that is important for language perception and production. One effect of damage is difficulty in speaking.
43
Distributed Representation
Brain represents information in patterns distributed across the cortex, not in a single area
- Focuses on activity in multiple brain areas and connections between them
Ex.
1. Pain perception - Multiple components activated across the brain:
- Sensory component ("it feels burning hot")
- Emotional component ("it's unpleasant")
- Reflexive motor component (pulling hand away)
2. Object Recognition - Activity patterns for houses, faces, and chairs:
- Maximum activity occurs in separate cortical areas
- However, each stimulus also causes widespread activity across the cortex
3. Implications
- Single stimuli can cause widespread brain activity
- Challenges purely modular view of brain function
- Suggests complex interplay between specialized and distributed processing
44
Structural Connectivity
The structural “road map” of fibers connecting different areas of the brain.
45
Functional Connectivity
Neural connectivity between two areas of the brain that are activated when carrying out a specific function.
46
Neural Circuits
groups of interconnected neurons
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Convergence
Occurs when a number of neurons synapse onto a single neuron.
48
Light
1. Particles of energy (photons)
2. Waves of electromagnetic radiation
49
Visual Spectrum
380nm-760nm
50
Retinal Cells
rods and cones
51
Macular Degeneration
a condition where the cone-rich fovea and the area around it (macula) is destroyed.
- Creates blind region in central vision
- Common in elderly
- Functional receptors missing
52
Retintis Pigmentosa
- Degeneration of the retina that is passed from one generation to the next
1. This condition first attacks the peripheral rod receptors and results in poor vision in the peripheral visual field
2. Eventually, in severe cases, the 2. foveal cone receptors are also attacked, resulting in complete blindness.
53
Accomodation
Object close to the eye = focus point moves backwards past the retina
- This makes the image blurry because the light is hitting the back of the eye instead of the retina.
- Eye adjusts by thickening the lens to bring the light back onto the retina
- Ciliary muscles tighten and increase the curvature of the lens so that it gets thicker
Object far from the eye (>20ft) =
- Light more than 20ft away travels in parallel lines
- The eye focuses these lines onto a point on the retina, making a clear image.
54
Refractive error
when accommodation fails at focusing light
- Presbyopia
- Myopia
- Hypermyopia
55
Isomerization
Initiated when light hits the retina, causing the retinal within that molecule to change its shape, from being bent to straight
a) The molecules are in their resting state when in the dark
b) Light exposure triggers retinal absorbs photons of light and changes from the cis-retinal configuration to trans-retinal.
c) This activates the opsin protein and starts a signal cascade that eventually sends a visual signal to the brain.
- Causes a chemical chain reaction
- Activates thousands of charged molecules to create electrical signals in receptors
d) pigment bleaching
e) regeneration
56
Pigment bleaching
As the retinal changes shape and detaches from opsin, the visual pigment becomes **bleached**. It cannot respond to light again until it regenerates
57
Regeneration of isomerization
Retinal has to be converted back to its cis form and reattach to opsin.
In bright light, the pigments may bleach faster than they can regenerate, leading to temporary desensitization,
58
Presbyopia
Aging causing hardening of the lens and weakening of ciliary muscles
- can be fixed with glasses
59
Myopia
Occurs when optical system brings parallel rays of light into focus in front of the retina
a) refractive myopia - corenea/lens bends light too much
b) axial myopia - eyeball too lomg
60
Hyperopia
Difficulty seeing distant objects because of focus point of parallel rays of light hitting behind the retina
- usually because eyeball is too short
- young people can bring the image forward onto retina by accomodating
- elderly need glasses
61
Rod-cone break
The point in dark adaption when vision shifts from cone vision to rod vision
62
Visual pigment regeneration
Pigments returning to normal after bleaching
- more rapid in cones than rods
- in normal light levels, the eye always contains some bleached visual pigments
- **Sensitivity depends on concentration of visual pigment and speed of reaction**
63
Detached Retina
When visual pigments cannot regenerate due to injury of the eye
- Retina becomes detached from pigment **epithelium** that contains enzymes needed for pigment regeneration
= Blindness in areas of detachment
64
Purkinje Shift
Peak sensitivity of they eye shifting from the read end of the spectrum to blue
- Lighting conditions change from bright to dim
- In bright light, cone cells are more active and are most sensitive to yellow-green light
- In dim light, rod cells dominate, which are more sensitive to blue-green light
65
Dark Adaption
Visual adaptation that occurs in the dark. Sensitivity to light increases. This increase in sensitivity is associated with regeneration of the rod and cone visual pigments.
- Measured with method of adjustment
66
Dark Adaption Curve
The function relating sensitivity to light to time in the dark, beginning when the lights are extinguished.
shows that as adaptation proceeds, the participant becomes more sensitive to the light.
67
Measuring Dark Adaption
1. Participant looks at a small fixation point while paying attention to a flashing test light that is off to the side
The test light falls on the peripheral retina, which contains both rods and cones.
2. The participant turns a knob that adjusts the intensity of the flashing light until it can just barely be seen (method of adjustment)
3. threshold for seeing the light, the minimum amount of energy necessary to just barely see the light, is then converted to sensitivity.
Sensitivity = 1/threshold
This means that a *high threshold* corresponds to *low sensitivity*.
4. Sensitivity measured = light adapted sensitivity
5. Adapting light is turned off, leaving the participant in darkness.
The participant then continues adjusting the brightness of the flashing light to the point where it is just barely visible, allowing the tracking of the gradual increase in sensitivity that occurs as the eyes adapt to the dark.
6. As the participant's sensitivity to the light increases, they must reduce the light’s intensity to keep it barely visible.
68
Measuring Cone Adaption
- flashing test light fell on the peripheral retina, which contains both rods and cones.
- Cones stop adapting after 5-6min
- Cones are measured by making the participant look directly at the small enough test light so its image falls on the all-cone fovea,
- This curve matches the initial phase of our original dark adaptation curve but does not include the second phase
- Therefore, the second part of the lines is rods
69
Measuring Rod Adaption
- We need to measure dark adaptation in a person who has no cones to reveal the sensitivity of the initial changing rods.
- **Rod Monochromats** - A person with a retina only with rods
- Rods are much less sensitive than the cone light-adapted sensitivity
- Once dark adaptation begins, the rods increase their sensitivity and reach their final dark-adapted level in about 25 minutes
- The end of this rod adaptation measured in our monochromat matches the second part of the two-stage dark adaptation curve.
70
Spectral Sensitivity
= Sensitivity to light at each wavelength
- Measured by Spectral Sensitivity Cone (relationship of wavelength and sensitivity)
- Monochromatic light flashes (light of a single WL) is directed to our peripheral vision
- Variations of the WL is presented in a psychophysical experiment so individual thresholds can be graphed.
- High threshold = more light needed
- Low threshold = less light needed
- We are more sensitive to yellow, green, and red EM waves
- Threshold sensitivity uses the formula:
- sensitivity = 1/threshold
- Cones are more sensitive to longer WL (peak at 560)
- Rods are more sensitive to shorter WL (peak at 500)
- Night Vision - In the dark we rely more on rods for vision
- why we are sensitive more to blues and greens in dark
71
Absorption Spectra
Differences in spectral sensitivities between rods and cones is due to the absorption spectra of the visual light pigment molecules.
- Only 3 cones and only 1 for rods
Short WL - take up very little of the curve due to there being fewer of them, therefore, fewer short WL pigments
72
Neural circuits in retina
Long ganglion axons transmit signals out of the retina in the optic nerve
Bipolar cell = retinal neuron that receives inputs from the visual receptors and sends signals to the retinal ganglion cells.
Horizontal cell = neuron that transmits signals laterally across the retina. Horizontal cells synapse with receptors and bipolar cells.
Amacrine cell = neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.
73
Bipolar Cell
retinal neuron that receives inputs from the visual receptors and sends signals to the retinal ganglion cells.
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Horizontal Cell
neuron that transmits signals laterally across the retina. Horizontal cells synapse with receptors and bipolar cells.
Horizontal cells: integrate signals from photoreceptors, enhancing **contrast** and **spatial** **resolution**.
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Amacrine Cell
neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.
Amacrine cells: modulate signals between bipolar and ganglion cells, contributing to motion detection and temporal processing.
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Visual acuity
Visual acuity is highest in the fovea, objects that are imaged on the peripheral retina are not seen as clearly.
Foveal cones are tightly packed and peripheral cones are dispersed more widely
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(M)agnocellular ganglion cells/M-pathway
Input largely from rods
- fast pathway
- low acuity, high acuity, motion, fast conduction
78
(P)arvocellular ganglion cell/P-pathway
Input largely from cones
- high acuity, color sensitive, slower conduction
Both pathways remain separate until it reaches primary cortex
79
Receptive Fields
An area of the receptor that influences the firing rate of the neuron. Convergence networks in ganglion want specific photoreceptors
Center-surround receptive fields: “Center” of the receptive field responds differently to light than the area in the “surround”
80
Center surround receptive fields
“Center” of the receptive field responds differently to light than the area in the “surround”
81
Hermann Grid
Herman's Grid illusion (gray dots at intersections) occurs due to lateral inhibition in the retina.
Photoreceptors at intersections are more inhibited by surrounding white areas, creating the illusion of darker spots, while non-intersecting areas appear brighter.
This shows how lateral inhibition enhances contrast but can lead to perceptual distortions.
- At the intersections: The photoreceptors are inhibited by more white space (from all four directions), leading to a perception of a dimmer area (the gray dots).
- In the white lines (not at intersections): The photoreceptors are inhibited by fewer white areas (only from two directions), so the area looks brighter.
82
Geniculostriate pathway
1. info from retina is passed through optic chiasm = contralateral
2. 90% of info reaches LGN where it is filtered and sent to V1 in striate cortex (occipital lobes)
10% if sent to SC/superior colliculus
3.
83
LGN
- LGN neurons have the same receptive fields as the retinal ganglion cells
= center surround
- The LGN also receives input from the cortex, brainstem, thalamus, etc.
- feedback: LGN receives more info from cortex than retina
-
84
LGN organization
6 layers
Each layer receives info from only 1 eye
2,3,5 – ipsilateral eye
1,4,6 – contralateral eye
Information from the left and right eye is kept separate
LGN IS ORGANIZED BY EYE NOT VISUAL SYSTEM
85
Retinotopic maps
Each place on the retina corresponds to a place in the LGN and a place in the visual cortex
Damage to a piece of the map will result in blindness in the corresponding portion of the visual world
86
Cortical Magnification
Fovea accounts for ~ .01% of the area of the retina
However, 10% of visual cortex is devoted to the fovea
- results in more acuity
87
Simple cortical cells
have side-by-side opponent receptive fields = **Monocular** **receptive** **fields**
Neuron responds maximally when the stimulus is in the **preferred** **orientation**
Orientation selectivity
Different neurons respond to different orientations
V1 neurons as “**feature** **detectors**”
88
Complex cells
respond best to bars at a particular orientation that move in a specific direction
89
End-stop cells
fire when lines of a specific length move in a particular direction
Also respond to moving edges or angles
90
Striate cortex organization
6 layers- layer 4 receives sensory inputs
- Specifically, layer 4Cα (magnocellular), 4Cβ (parvocellular), 3 koniocelluar
91
Location Columns
Location columns- columns whose receptive fields are concentrated in the same part of the retina
Located perpendicular to the surface of the cortex
92
Orientation Columns
Orientation columns- columns whose receptive fields prefer a specific orientation (tied to location columns)
Adjacent columns have neurons with slightly different preferred orientations
e.g., neurons along electrode track A preferred horizontal lines
93
Ocular Dominance Columns
Ocular dominance columns- columns whose receptive fields are predominantly from one eye
Although about 80% of neurons respond to both eyes, they tend to prefer one eye over the other
94
Hypercolumns
Each region of visual space is represented by a V1 module
Blobs are sensitive to color, but not orientation or form
Color information sent to V4/V8
Neurons outside blobs respond to orientation and form but NOT color
95
Representation of objects
Objects activate numerous hypercolumns in V1 that correspond to stimulated portions of the retina
Features of the objects are coded by simple, complex, and end-stop cells in each of the hypercolumns
96
Dorsal Stream
Parietal lobe
Information flows up the streams, but also receives feedback from higher areas (bidirectional)
Fast response
M-channel
Absolute metrics
Moment-to-moment
Visually-guided action
‘Unconscious’
97
Ventral Stream
Temporal lobe
Information flows up the streams, but also receives feedback from higher areas (bidirectional)
Slow response
M + P channels
Scene based metrics
Long term memory
Object recognition
‘Conscious'
98
Object Discrimination
monkey has to remember under which object the food is placed
Inferior temporal ablation causes a deficit
“What” pathway
99
Landmark Discrimination
monkey has to remember that the food is in hidden under the object near the cylinder
Parietal ablation causes a deficit
“Where” pathway
100
Selective Adaption
Selectively exposed to one stimulus so firing causes neurons to eventually become fatigued, or adapt. This adaptation causes two physiological effects:
(1) the neuron’s firing rate decreases, and
(2) the neuron fires less when that stimulus is immediately presented again.
101
Selective Rearing
Definition: Feature detectors in the visual cortex can be shaped by perceptual experience (neural plasticity). Selective rearing exposes an animal to a limited set of stimuli, increasing the prevalence of neurons that respond to those stimuli.
Mechanism: Rearing animals in environments containing only certain orientations (e.g., vertical lines) leads to their visual cortex developing neurons that predominantly respond to those orientations.
102
Prosopagnosia
The inability to recognize faces despite normal perceptual abilities
Cannot even recognize their own family members!
Can recognize people using voices, hair, posture, etc.
Caused by lesions to the right fusiform gyrus (FFA)
