Final Exam Review Notes Flashcards
What is Psychophysics?
Relates individual’s mental experience (Psyche) with stimulus
energy (Physics)
Experimental psychology applied to perception
– Present stimulus
– Query subject on their perception
What is the method of constant stimuli
- Randomly present many stimuli of varying intensities
* Find the least intense stimulus the participant can detect
What is the method of limits
- Stimuli aren’t presented randomly
* Constantly increasing then decreasing
What is the method of adjustment
• Participant adjusts stimulus level
What is the method of magnitude estimation
• Participant assigns intensity rating to stimuli
What is Weber’s Law
The Just Noticeable Difference (JND) between two stimuli is a
constant proportion of stimulus intensity
– e.g. when comparing weights that were 10g, participants
could detect a 1g change, but if the weights were 100g, then
a 10g difference was the smallest
• The JND was always one tenth, a constant proportion
What is Fechner’s Law?
• We are less sensitive to stimulus change as the stimuli
become more intense
– Our perception of stimulus difference grows slower than
stimulus intensity
• Just says Weber’s law in a different way
– As the overall intensity I gets bigger, the JND ΔI has to get
bigger too to keep the constant K the same.
Stevens’ Power Law
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• Fechner put this in a mathematical formula
Fechner’s Law
• We are less sensitive to stimulus change as the stimuli
become more intense
– Our perception of stimulus difference grows slower than
stimulus intensity
• Just says Weber’s law in a different way
– As the overall intensity I gets bigger, the JND ΔI has to get
bigger too to keep the constant K the same.
What is Steven’s Power Law
• Steven’s found some violations of Fechner’s law and revised
the log function to the more general exponential function
• Sensation is exponentially related to stimulus intensity
– Sign of exponent determines shape of curve
• Green: b > 1
• Blue: b = 1
* Red: b < 1
What is signal detection theory
• Perceptual Sensitivity – Our ability to distinguish signal from signal+noise is our perceptual sensitivity • Called d’ (“dee prime”) – The better we can distinguish signal, the higher our d’ • Response Criterion – We set some level of perceptual certainty as our response criterion • Above that level of perceptual certainty, we respond "target" • Below we don't • Four types of responses – Two correct • Hits – target present and response • Correct rejections – target not present, no response – Two incorrect • Missed targets – target present, no response • False alarms – target not present, response Receiver Operating Curve • Plots hits (correct responses to targets) vs. false alarms (responding ‘target’ when no target is there) for given 4 5 6 1 2 7 4/18/14 3 • Hits – target present and response • Correct rejections – target not present, no response – Two incorrect • Missed targets – target present, no response • False alarms – target not present, response
What is Receiver Operating Curve
• Plots hits (correct responses to targets) vs. false alarms
(responding ‘target’ when no target is there) for given
perceptual sensitivities
– Each curve has the same perceptual sensitivity
– Different places on a curve reflect different response biases
• Lower left is very careful to not make any false alarms, at
the cost of missing targets
• Upper right you don’t miss many targets but you get lots of
false alarms
• Upper left is a balance between the two
What are sensory transducers?
• Transforms environmental stimuli to electrochemical activity in the brain – Light • Photons – Sound • Waves of compressed and rarified air – Touch • Mechanical deformation of the skin – Taste & Smell • Chemicals (odorants & tastants)
What is the brain structure for the hind and midbrain? and what do they do?
• Hindbrain – Medulla • Respiration – Cerebellum • Motor – Pons • Arousal – Reticular activating system • Midbrain – Tectum • Superior colliculus – Optic tectum » Visual orienting 7 8 9 1 2 4/18/14 4 – Medulla • Respiration – Cerebellum • Motor – Pons • Arousal – Reticular activating system • Midbrain – Tectum • Superior colliculus – Optic tectum » Visual orienting • Inferior colliculus – Auditory tectum » Auditory orienting – Tegmentum • Pain regulation – Periaquiductal gray
What is in the forebrain? and what do they do?
• Thalamus – Sensory relay • Lateral Geniculate – Visual • Medial Geniculate – Auditory • Ventral Posterior – Somatosensation – Taste • Medial Dorsal – Smell • Basal Ganglia – Motor – Motivation • Limbic System – Emotion • Cortex – Primary & secondary sensory cortex • Perception – Motor cortex – Association cortex • Puts multiple modalities together Cortical Lobes • Occipital – Visual 2 10 1 2 11 1 4/18/14 5 • Limbic System – Emotion • Cortex – Primary & secondary sensory cortex • Perception – Motor cortex – Association cortex • Puts multiple modalities together
What is in the cortical lobe? and what do they do?
• Occipital – Visual • Parietal – Posterior • Visual “where” or “perception for action” • Association – Anterior • Somatosensation • Temporal – Inferior • Visual “what” or “perception for recognition: – Superior • Auditory • Language reception – Medial • Some smell (primitive) • Frontal – Motor – Language production – Smell
what are neurons? what is basic neuron structure? what do neurons do? What are the different types of neurons
• Basic neuron structure – Soma (cell body) • Metabolic center – Dendrites • Primary input to cell – Axon • Output pathway (nerves are bundles of axons) – Single output from soma – Multiple terminal branches (sometimes thousands) – Myelin sheath • Insulates axon – Terminal buttons • Output terminal • Types of neuron 11 1 2 12 1 2 4/18/14 6 • Metabolic center – Dendrites • Primary input to cell – Axon • Output pathway (nerves are bundles of axons) – Single output from soma – Multiple terminal branches (sometimes thousands) – Myelin sheath • Insulates axon – Terminal buttons • Output terminal • Types of neuron – Unipolar • One process from cell body • Sensory, primarily touch and pain – Bipolar • Two processes • Primarily sensory transduction – Multipolar • Multiple processes • Many different configurations • Ubiquitous in nervous system • Synapse – Small gap between neurons across which they communicate • Axo-dendritic • Axo-somatic • Axo-axonic • Dendro-dendritic
What are proteins in the neuron skin?
• Channel proteins
– Allow charged particles (ions) to flow in and out of neuron
• Chemically gated
– Ionotropic receptors
– Open in response to neurotransmitter binding
• Electrically gated
– Open in response to change in membrane potential
• Signal proteins
– Metabotropic receptors
• Initiates metabolic change inside neuron
– May produce second messenger
– May change the structure or function of the neuron or
synapse
Resting Potential
• The inside or a neuron is about -70 mV compared to outside
• Due to differential distribution of ions between the inside and
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– Open in response to neurotransmitter binding
• Electrically gated
– Open in response to change in membrane potential
• Signal proteins
– Metabotropic receptors
• Initiates metabolic change inside neuron
– May produce second messenger
– May change the structure or function of the neuron or
synapse
What is a neurons resting potential? What is resting potential?
• The inside or a neuron is about -70 mV compared to outside • Due to differential distribution of ions between the inside and outside – A- (large protein anions) • Negative charge • All inside cell • Primary source of resting potential – Na+ (sodium) ions • Positive charge • More outside cell • Does rising phase of action potential – K+ (potassium) ions • Positive charge • More inside cell • Does falling phase of action potential – Cl- (chloride) ions • Negative charge • More outside cell • Post-synaptic potentials
What is an action potential? how does one work?
• Depolarize the membrane from resting potential to threshhold – ~ -60mV • Voltage gated Na+ channels open – Na+ ions flow in – Membrane potential rises towards 40 mV • Na+ equilibrium potential • During rise, voltage gated K+ channels open – K+ flows out, slowing rise • At peak (40 mV) Na+ channels close – Na+ can’t flow in any more – K+ continues to flow out – Membrane potential falls towards -80 mV • K+ equilibrium potential • K+ channels close on the way down – Stops negative voltage fall • Excess negative charge dissipates 2 14 1 2 15 1 2 4/18/14 8 – Na+ ions flow in – Membrane potential rises towards 40 mV • Na+ equilibrium potential • During rise, voltage gated K+ channels open – K+ flows out, slowing rise • At peak (40 mV) Na+ channels close – Na+ can’t flow in any more – K+ continues to flow out – Membrane potential falls towards -80 mV • K+ equilibrium potential • K+ channels close on the way down – Stops negative voltage fall • Excess negative charge dissipates – Restores resting potential
What is synaptic transmission?
• Action potential travels down axon to terminal button
• Vesicles (little packages of chemicals) in button merge with
the cell membrane, dumping their contents (neurotransmitters)
into the synapse
• Transmitter molecules diffuse across the synaptic cleft
• Bind with receptor proteins in the postsynaptic membrane
– Ionotropic receptors
• Chemically gated ion channels
– Metabotropic receptors
• Second messenger systems
• Alter function and/or structure of receiving neuron
• Termination
– Deactivation
• Enzymes break transmitter down
– Reuptake
• Transmitter taken back up into sending neuron
Explain light in terms of perception
• Light as Particles
– Light behaves like discrete packets
• Photons
– Each photon is one quanta (piece) of light
• Light as Waves
– Light behaves like undulations in a medium
• Like waves in the ocean
• The visual system is sensitive to a small part of the
electromagnetic spectrum
– ~400 - 700 nm
– Different wavelengths of light correspond (under certain
conditions) to different perceived colors
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• Light as Particles
– Light behaves like discrete packets
• Photons
– Each photon is one quanta (piece) of light
• Light as Waves
– Light behaves like undulations in a medium
• Like waves in the ocean
• The visual system is sensitive to a small part of the
electromagnetic spectrum
– ~400 - 700 nm
– Different wavelengths of light correspond(under certain
conditions) to different perceived colors
What are our eyes? How do they work? What are the different parts of the eye and what do they do?
• A biological analog camera for focusing images (the proximal stimulus) of the distal stimulus (object) on the transducers (rods and cones in the retina) • Pupil – Controls amount of light allowed in • Lens – Focuses on close or distant objects • Accommodation – Change in shape of lens • Retina – Location of photosensitive receptors
What different kinds of cells are in the retina and what do they do?
• Rods & Cones – Phototransducers – At back of retina • Horizontal cells – Connect between transducers and bipolar cells – Provide convergence and lateral inhibition • Bipolar cells – Connect transducers to projection neurons • Retinal ganglion cells – Translate inhibition to excitation • Amacrine cells – Between bipolars & ganglion cells – Function unknown • Retinal ganglion cells – Carry signal to brain – Axons make up optic nerve Phototransduction • Rhodopsin – Rod photopigment – 2 submolecules 1 2 18 19 1 2 20 1 4/18/14 10 • Retinal ganglion cells – Translate inhibition to excitation • Amacrine cells – Between bipolars & ganglion cells – Function unknown • Retinal ganglion cells – Carry signal to brain – Axons make up optic nerve
What is phototransduction and how does it work?
• Rhodopsin – Rod photopigment – 2 submolecules • Opsin • Retinal (2 isomers) – 11-cis retinal – All-trans retinal • 1 photon of light converts one molecule of retinal from 11-cis to all trans isomer • Phototransduction is initially inhibitory – In the dark • Rhodopsin inactive • NA+ channels open • NA+ flows in, depolarizing membrane • Transmitter released – In the light • Rhodopsin active • NA+ channels close • NA+ flow blocked • Transmitter release stopped
What are lateral inhibition and mach bands? How do they work?
• Physical World
– Patches of uniform intensity adjacent to patches of different
intensity
• Psychological Response
– Perception of lighter and darker intensity bands at patch
boundaries
• Cognitive Model
– A computational network of convergent input with lateral
inhibition
• Biological Substrate
– The retinal mosaic has horizontal cells connected between
receptors and ganglion cells to provide convergence with
lateral inhibition
Retinal Ganglion and Lateral Geniculate Receptive Fields
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intensity
• Psychological Response
– Perception of lighter and darker intensity bands at patch
boundaries
• Cognitive Model
– A computational network of convergent input with lateral
inhibition
• Biological Substrate
– The retinal mosaic has horizontal cells connected between
receptors and ganglion cells to provide convergence with
lateral inhibition
What is the retinal ganglion and lateral geniculate receptive fields? How do they work?
• Retinal Ganglion Cells project to the Thalamus
– Lateral Geniculate Nucleus
• A Neuron’s Receptive Field
– That part of the visual field that can change the firing rate of
the cell (up or down) if the proper stimulus falls within it
• Retinal Ganglion and Lateral Geniculate cells respond best to
dots of light with a center/surround organization
– On-center/ Off-surround
– Off-center/ On-surround• Retinal Ganglion Cells project to the Thalamus
– Lateral Geniculate Nucleus
• A Neuron’s Receptive Field
– That part of the visual field that can change the firing rate of
the cell (up or down) if the proper stimulus falls within it
• Retinal Ganglion and Lateral Geniculate cells respond best to
dots of light with a center/surround organization
– On-center/ Off-surround
– Off-center/ On-surround`
What is the primary visual cortex of neurons? What different types of cells are in it and how do they work?
• Simple Cells – Oriented bars of light – Center surround • Complex Cells – Oriented bars of light – Moving in one, but not the other, direction – Not center surround • Hypercomplex Cells – Corner or end-stop cells – Oriented bars of light but only if end of bar is in receptive field • Hubel & Weisel’s model • A serial hierarchic model – Converge LGN input to make simple cell – Converge simple cell input to make complex cell – Converge complex cell input to make hypercomplex cell • Logically leads to ‘grandmother’ cell – Neuron that responds to one specific visual object • e.g. your grandmother Current Model • Parallel (rather than serial) – Multiple operations at once • Hierarchic 2 23 1 2 24 1 2 25 4/18/14 12 • Hubel & Weisel’s model • A serial hierarchic model – Converge LGN input to make simple cell – Converge simple cell input to make complex cell – Converge complex cell input to make hypercomplex cell • Logically leads to ‘grandmother’ cell – Neuron that responds to one specific visual object • e.g. your grandmother
What is the current model for how vision works?
• Parallel (rather than serial) – Multiple operations at once • Hierarchic – Build complex out of simple • Functionally segregated – Separate parts of the brain do different things
What is spatial frequency analysis in V1 and how does it work?
• V1 neurons respond best to different frequencies at different
orientations
• Thus V1 can break down a complex scene into its component
simple spatial frequencies
– The pattern of firing of V1 neurons can code the spatial
frequency content of a scene
– This is a Fourier analysis
• The deconstruction of a complex waveform into its
component simple sine waves
What is spatial frequency?
• Spatial frequency is stated in terms of cycles per degree of
visual angle
– If the visual angle below is one degree, then the spatial
frequency of the stimulus is one cycle per degree
What is the V1 Hypercolumns and how do they work?
• A computational unit in V1 is called a Hypercolumn – Gets input from one part of visual field – Optical dominance columns • Inputs from each eye – Contains complete map of feature • E.g. full orientation map – Orientation columns orthogonal to optical dominance columns – Input & output coded by layer • Functional columns are a fundamental organizing principle of sensory cortex – Similar features are represented next to each other in the brain V1 visual field mapping 2 25 26 27 28 29 4/18/14 13 – Optical dominance columns • Inputs from each eye – Contains complete map of feature • E.g. full orientation map – Orientation columns orthogonal to optical dominance columns – Input & output coded by layer • Functional columns are a fundamental organizing principle of sensory cortex – Similar features are represented next to each other in the brain
What is V1 visual field mapping and how does it work?
• A topographic map of visual space is maintained throughout
visual processing
– Things close to each other in visual space are represented
close to each other in the brain
• Although upside down and backwards
• This is called retinotopic mapping
• Topographic mapping is a fundamental organizing principle of
sensory systems
– Close in the world, close in the brain
What are the two visual pathways?
• Inferior temporal – Ventral “What” object feature stream – Perception for recognition • Posterior parietal – Dorsal “Where” spatial location stream – Perception for action
What is the gestalt perspective?
• Structuralism – Perception is just adding together the component pieces • Gestalt – “The whole is more (or different) than the sum of the parts” • Gestalt psychologists formulated a number of rules or ‘laws describing how the perceptual system groups things together that should belong together • Law of Simplicity (Pragnatz) – The simplest explanation is the best – Principle that the other laws are based on • Law of Proximity • Law of Similarity • Law of Good Continuation • Law of Common Fate Perception by Committee • A perceptual system metaphor 29 30 31 1 2 32 4/18/14 14 • Gestalt psychologists formulated a number of rules or ‘laws describing how the perceptual system groups things together that should belong together • Law of Simplicity (Pragnatz) – The simplest explanation is the best – Principle that the other laws are based on • Law of Proximity • Law of Similarity • Law of Good Continuation • Law of Common Fate
What is perception by committee
• A perceptual system metaphor
• The Pandemonium model
– Members (“demons”) at three levels
• Feature demons
– “shout” louder when they think their feature is present
• Cognitive demons
– “shout” louder when they think their object is present
• Decision demon
– Listens to the noise and determines who is shouting
loudest
• Committee rules
– Honor physics
• Don’t make interpretations that are physically impossible
– Avoid accidents
• Don’t make interpretation that relies on highly specific or
unusual perspective
what are non accidental features?
• When 3D objects overlap, they create some kinds of junctions that don’t vary by viewpoint – Y junctions • Corner • Not an occlusion – T junctions • Intersecting edges • When ‘T’s match up, we have occlusion and can tell what’s in front
what is color perception?
• Not a physical property of matter – Rather a psychophysical property of the perceptual system • Based on properties of matter – Most of the light we see is reflected • Typical light sources: Sun, light bulb; emit a br oad spectrum of wavelengths 400–700 nm • Different kind of materials absorb and reflect different wavelengths of light 2 32 33 34 1 4/18/14 15 – T junctions • Intersecting edges • When ‘T’s match up, we have occlusion and can tell what’s in front Color Perception • Not a physical property of matter – Rather a psychophysical property of the perceptual system • Based on properties of matter – Most of the light we see is reflected • Typical light sources: Sun, light bulb; emit a br oad spectrum of wavelengths 400–700 nm • Different kind of materials absorb and reflect different wavelengths of light • Perceived color is related to the wavelength of light – 400-450 nm ≈ violet – 450-500 mn ≈ blue – 5 00-570 mn ≈ green – 570-590 mn ≈ yellow – 590-620 nm ≈ orange – 620-700 nm ≈ red
what is the trichromatic theory?(young-helmholtz)
• We have three color receptors
– Short, middle, and long wavelength cones
• These receptors are sensitive to different parts of the visible
spectrum
• Differential relative activity in these receptors is the basis of
color vision
Opponent Process Theory
• Some color combinations are never described
– e.g. ‘reddish-green’ or ‘bluish-yellow”
• Stare at a color you get an afterimage
– Red gives green
– Yellow gives blue
• Color sensitive retinal ganglion and LGN cells have a color
opponent center/surround organization
– Yellow-blue
– Green-red
what is color constancy?
• Objects look the same color under very different lighting
conditions
– Incandescent and sunlight have very different spectral
content
– Thus the spectral content of light reflected from an object
will be very different depending on the illumination source
– Yet the perceptual system still extracts the same color for
the object
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• Color sensitive retinal ganglion and LGN cells have a color
opponent center/surround organization
– Yellow-blue
– Green-red
Color constancy
• Objects look the same color under very different lighting
conditions
– Incandescent and sunlight have very different spectral
content
– Thus the spectral content of light reflected from an object
will be very different depending on the illumination source
– Yet the perceptual system still extracts the same color for
the object
• It is able to “discount the illuminant”
• Retinex theory
– Extract reflectance (brightness) records across all the
surfaces in a scene for each of the three receptors
– Compare the proportions of each wavelength reflected by a
single surface
– Results in a color computation for that surface corrected for
the illuminant
What are types of depth cues?
• Monocular cues – Pictorial cues • Static cues in 2D representations – Movement cues • Dynamic cues in 2D representations • Binocular cues – Oculomotor cues • Physiological feedback from the eyes – Binocular disparity cues • Derived from the differences in images on the two retinas
what are monocular (pictorial) depth cues?
• Occlusion (things in front block things behind)
• Relative size (how big compared to scene)
• Texture gradient (equally spaced elements get packed in the
distance)
• Relative height (proximity to horizon)
• Familiar size (how big compared to knowledge)
• Atmospheric (aerial) perspective (haze)
• Linear perspective (convergence)
Movement cues
• Motion Parallax
– Near objects appear to move farther than far objects as we
go by them
– The retinal projection of a near object travels farther across
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• Relative size (how big compared to scene)
• Texture gradient (equally spaced elements get packed in the
distance)
• Relative height (proximity to horizon)
• Familiar size (how big compared to knowledge)
• Atmospheric (aerial) perspective (haze)
• Linear perspective (convergence)
What are movement cues?
• Motion Parallax
– Near objects appear to move farther than far objects as we
go by them
– The retinal projection of a near object travels farther across
the retina than a far object for the same movement
• Deletion and accretion
– Changes in occlusion due to movement
• Optic flow
– The distance on object is from us alters its apparent
direction and speed of movement
What are binocular cues?
• Oculomotor cues
– Physiological feedback from the eyes
• Convergence
– The movement of the eyes towards “crossed” to foveate
near objects
• Accommodation
– The change in lens thickness (fattening, mediated by
ciliary muscles) to focus on near objects
• Binocular disparity cues
– Derived from the differences in images on the two retinas
• The image on each retina is slightly different
What are binocular disparity terms?
• The Vieth-Müller circle
– An imaginary circle that runs through the eyes and the thing
we’re focusing on
• The Horopter
– Extend that circle so it’s a dome in front of the eyes
equidistant from fixation
• Corresponding retinal points
– Images on the retinas of items on that circle are the same
distance from the fovea on both eyes
– Items on the horopter will have corresponding retinal images
Binocular Disparity
• Objects on the horopter (including fixation) have zero
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• The Vieth-Müller circle
– An imaginary circle that runs through the eyes and the thing
we’re focusing on
• The Horopter
– Extend that circle so it’s a dome in front of the eyes
equidistant from fixation
• Corresponding retinal points
– Images on the retinas of items on that circle are the same
distance from the fovea on both eyes
– Items on the horopter will have corresponding retinal images
what is binocular disparity?
• Objects on the horopter (including fixation) have zero
binocular disparity
– Corresponding retinal points
• Objects off the horopter have binocular disparity
– Non-corresponding retinal points
– Unequal distances between the fovea and the object’s
projection on the retina
• The farther off the horopter the object is, the larger the
disparity
• This is a binocular depth cue
• Retinal image projections with the same disparity can have
either crossed or uncrossed disparity
– Crossed disparity
• Retinal projection is outside of fovea
• You’d have to ‘cross’ your eyes to focus on it
• Closer to you than fixation
– Uncrossed disparity
• Retinal projection is inside of fovea
• You’d have to ‘uncross’ your eyes to focus on it
• Farther from you than fixation
What is stereopsis?
• The perceptual phenomenon of depth
– Things appear to ‘pop-out’
• As opposed to flat appearing
– e.g. 3D movies or static images with stereoscopes/colored
glasses/polarizing glasses
• Binocular Disparity Produces Stereopsis
What is the bayesian theory?
• P = Probability
• Sx = Scene X
• I = Perceptual system input
• Our perception of a scene is influenced by ‘priors’
– Things we’ve seen before and how often we’ve seen them
– That’s the P(Sx) term
• If we’ve seen something before a bunch of times, then the
probability that the input we’re getting now is due to that
something is high
what is a motion detection circuit?
• Receptors connected either directly or via delay neurons to
multiplication neurons to motion detection neuron
– Sensitive to direction
• It’s one-way
– Can be velocity sensitive too
• By changing adaptation rates of D
What is apparent motion?
• Successions of still images can give rise to the perception of
motion
– Principle of animation and motion pictures
– Depends on
• Proximity
– Too far apart, no apparent motion
• Speed
– Too fast or too slow, no apparent motion
• Two types of apparent motion
– Phi motion
• Perception of motion without intermediate positions
• Happens at fast switch rates (ISIs)
– Beta motion
• Perception of motion with intermediate positions
• Happens at slower ISIs
The Correspondence & Aperture Problem
• The motion perception system has to figure out which element
at time T corresponds to which element at time T+1
• When viewed through a window or aperture you can’s see the
whole object and can’t always tell what part goes with what
– Which element at time T corresponds to which element at
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• Two types of apparent motion
– Phi motion
• Perception of motion without intermediate positions
• Happens at fast switch rates (ISIs)
– Beta motion
• Perception of motion with intermediate positions
• Happens at slower ISIs
what is correspondence and aperture problelm?
• The motion perception system has to figure out which element
at time T corresponds to which element at time T+1
• When viewed through a window or aperture you can’s see the
whole object and can’t always tell what part goes with what
– Which element at time T corresponds to which element at
time T+1
What is motion processing in the brain
• The motion sensitive area appears to be located in the medial
temporal lobe
– Area MT, AKA V5
• Humans with lesions near V5 have akinetopsia
– Inability to perceive motion
what are types of eye movements?
• Involuntary
– Small eye jerks to avoid retinal stabilization
• If your eyes don’t make those small jerks, the image of the
world would stabilize on your retina
• Receptors would adapt
• Within minutes the the world fades away
• Voluntary
– Vergence
• Convergent & divergent movements to focus
– Smooth eye pursuit
• Tracking a moving object
– Saccades
• Rapid eye movements to change location of fixation
eye movements and the comparator?
• Why doesn’t the world seem to move when we move our
eyes?
• A ‘copy’ of the eye movement motor program is sent to a
‘comparator’
– Compares visual scene changes with eye movement
changes and compensates perceptual system for retinal
image changes caused by eye movements
Uses for Motion Perception
• Object recognition
– Easier to see something if it’s moving
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• Rapid eye movements to change location of fixation
Eye Movements and the Comparator
• Why doesn’t the world seem to move when we move our
eyes?
• A ‘copy’ of the eye movement motor program is sent to a
‘comparator’
– Compares visual scene changes with eye movement
changes and compensates perceptual system for retinal
image changes caused by eye movements
what are uses for motion perception?
• Object recognition
– Easier to see something if it’s moving
• Guidance as we move through the environment
– The optic flow from the direction we are heading appears to
expand around us
– The source of the expansion is the point straight ahead
– This is the focus of expansion• Avoidance of moving objects
– The ratio of the retinal image size to the rate of its expansion
is Tao
• Provides good estimate of how fast something is
approaching based on fast calculation from retinal image
size alone
• Biological motion
– We seem particularly adept at recognizing people and
animals from very minimal motion cues
What is cued spatial orienting (posner) paradigm?
• One of the two boxes brightens just before the target appears – That’s the ‘cue’ • Most of the time (e.g. 80% of the trials), the target appears at the cued location – Valid cues – Cue is predictive • Some of the time (~20% of the time), the target appears on the opposite side from the cue – Invalid trials • Participants are – Fastest on valid trials • facilitation – Slowest on invalid trials • inhibition – In the middle on neutral trials Interpretation of the Results • You’re faster to respond to targets at cued locations because the cue drew your attention to that location before the target 51 52 1 2 53 1 2 54 4/18/14 22 • Some of the time (~20% of the time), the target appears on the opposite side from the cue – Invalid trials • Participants are – Fastest on valid trials • facilitation – Slowest on invalid trials • inhibition – In the middle on neutral trials
what are the spatial orienting paradigm results?
• You’re faster to respond to targets at cued locations because
the cue drew your attention to that location before the target
appeared
• You’re slower to respond to targets on invalid trials because
your attention has been drawn away to to the other location
and has to move back
• In all cases your eyes stayed at fixation
– Attention can be dissociated from eye movement and
fixation
what are models or metaphors of spatial attention?
• “Spotlight” model
– Attention can move smoothly from one point to the next
• “Zoom lens” model
– Attention expands from fixation – grows to fill whole region
– shrinks to include just cued location
what is the time course of spatial attention?
• How much time there is between the cue and the target
changes the reaction time effect
– Stimulus onset synchrony (SOA): the time between the
onset of one stimulus and the onset of another
• At very short SOAs there is no facilitation
– Not enough time for attention to ‘move’ to the cued location
• Facilitation peaks at about 150 ms SOA
– For this kind of design
• At long SOAs subjects are actually slower with a valid cue
– SOAs longer than about 300 ms
– Inhibition of return
what is visual search?
• Looking for a target in a display containing distracting elements • Target – What you’re looking for – the goal of visual search • Distractor – any stimulus other than the target • Set Size – the number of items in a visual display
What are the two types of search?
• Efficient Search
– When the target is defined by a single feature, the target
‘pops-out’
– Adding more distractors to the display doesn’t make the task
any harder
• As set size increases, reaction time stays the same
• The target ‘pops-out’ of the display
• Inefficient Search
– When the target is defined by feature conjunction, the target
no longer ‘pops-out’
• Each added element adds to the time it takes to locate the
target
– We have to scan every element until we find the target
– This is called a “serial self-terminating search”
What is treismans feature integration model of visual search?
• The visual system has primitive feature maps
– Maps of the locations of primitive features in space
• These are perceptual maps created and maintained in parallel
– i.e. you create a color map and a separate orientation map
at the same time and they are independent of each other
• Preattentive stage (efficient search)
– If target is based on a single feature, we can simply poll the
correct map and ask “is the feature present”
• e.g. is there anything in the ‘vertical’ orientation map or
the‘red’ color map
• Don’t need to know where it is
• Attentive stage (inefficient search)
– If the target is defined by a conjunction of features, the
attention ‘spotlight’ must scan the objects in the scene to
see if the target defining features exist in the same place on
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– i.e. you create a color map and a separate orientation map
at the same time and they are independent of each other
• Preattentive stage (efficient search)
– If target is based on a single feature, we can simply poll the
correct map and ask “is the feature present”
• e.g. is there anything in the ‘vertical’ orientation map or
the‘red’ color map
• Don’t need to know where it is
• Attentive stage (inefficient search)
– If the target is defined by a conjunction of features, the
attention ‘spotlight’ must scan the objects in the scene to
see if the target defining features exist in the same place on
the relevant feature maps
• e.g. are ‘red’ and ‘vertical’ in the same location
• If so, then the target is present
What is attentional blink?
• Rapid Serial Visual Presentation (RSVP)
– Present stream of items, one at a time, at fixation, very
quickly (e.g. one every 100 ms)
– Make items distinct from one another (e.g. letters and
numbers)
– Have participants respond to one category of the items (e.g.
the numbers) while ignoring the others
• If two targets occur between about 200 and 300 ms of each
other, the participant will miss the second target after getting
the first
– It’s as if their attention selection system ‘blinked’ for a
moment following correct identification of the first target
What is perception and meaning?
• Change Blindness
– The failure to notice differences between two images of a
scene
• Inattentional Blindness
– The failure to notice items in a scene that aren’t relevant to
the task
• To extract the scene quickly from perceptual elements, we
appear attend to the ‘gist’ of the scene and ignore detail
– A market is a market, independent of the color of some
guy’s pants
• Change perception depends on the meaning of the change
– If scene meaning stays the same, we don’t notice the
change
Scenes & Schemas
• Schema: A rough outline of a scene or situation with
placeholders for details
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the task
• To extract the scene quickly from perceptual elements, we
appear attend to the ‘gist’ of the scene and ignore detail
– A market is a market, independent of the color of some
guy’s pants
• Change perception depends on the meaning of the change
– If scene meaning stays the same, we don’t notice the
change
What are scenes and schemas?
• Schema: A rough outline of a scene or situation with
placeholders for details
– e.g. farm, classroom, mall
– Perhaps identified by rough spatial frequency analysis
• Specific objects in the schema filled in later
– e.g. chickens & cows, teachers & students, Cinnabon &
Abercrombe
What is an auditory stimulus?
• Waves of compressed and rarified air radiating away from a source of vibration – Vibration squashes together (compresses) and pulls apart (rarifies) air molecules – Creates pressure waves the air going in all directions from the sound source like ripples from a stone thrown into a pond • Except in 3D • Characteristics of sound – Amplitude • Decibels (Db) • Loudness – Frequency • Hertz (Hz) • Pitch – Complexity • Timbre
what is the ear structure?
• Outer ear – Pinna – Auditory canal – Tympanic membrane between outer and middle ears • Middle ear – Three bones • Malleus • Incus • Stapes – translate sound energy (vibrations) from air to liquid 2 62 63 1 2 64 1 4/18/14 26 – Complexity • Timbre Ear Structure • Outer ear – Pinna – Auditory canal – Tympanic membrane between outer and middle ears • Middle ear – Three bones • Malleus • Incus • Stapes – translate sound energy (vibrations) from air to liquid • Inner ear (Cochlea) – Rolled-up structure – Hollow with three channels inside – Channels filled with fluid • Vibrating in the presence of sound – Contains Organ of Corti • Auditory transduction structure • Hair cells on Basilar membrane – Inner hair cells do transduction • Hairs rest on Tectorial membrane above – Semicircular canals also in inner ear but due vestibular senses
What is auditory transduction? how does it work?
• Air pressure changes (vibrations) are translated via bone &
fluid into vibration in the basilar membrane
– Air vibrates eardrum
– Eardrum vibrates middle ear bones
– Middle ear bones create waves of vibration in inner ear fluid
– Inner ear fluid vibrates basilar membrane
• As the basilar membrane moves up and down it exerts a
shearing force on the cilia (hairs) resting against the tectorial
membrane
• As the hair cells shear, ion channels open and close in the
hair cells
• Ion flow changes in hair cells causes change in firing rate of
auditory nerve cells
what is frequency encoding in the basilar membrane?
• The basilar membrane is a tapered surface
– Wider and floppier at the apex (.5 mm)
• Vibrates more to lower frequencies
– Narrower and stiffer at the base (.08 mm)
• Vibrates more to higher frequencies
• This is location coding
– Different sounds deflect different locations on the membrane
• The pattern of peaks on the membrane represents the
component sine waves of the complex sound
– Basilar membrane performs a Fourier analysis of the sound
• Each membrane deflection represents a component sine
wave of the complex sound
What is the auditory pathway?
• Cochlear nucleus • Superior olives – Localization • Inferior colliculus – Orienting • Medial geniculate nucleus – Thalamic relay • Posterior superior temporal gyrus – Cortical area A1
What are the superior olives and what do they do?
• Localizing auditory sources by differences in timing or amplitude between the ears – ITD • Timing (phase or arrival time) • Medial superior olivary nucleus – ILD – Amplitude – Lateral superior olivary nucleus
