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Perception Final Exam Flashcards
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- 1What is light?Electromagnetic radiation
Periodic changes in electric and magnetic field (wave) over time/space - 2What is wavelength, and what wavelengths constitute visible light?How many metres in a wave.
?? - 3How do we measure light intensity? How does the brightness of a light source affect this?Luminence.
It doesn't really - relatively constant as objects reflect a different % of the incident light - 4What is contrast and how does it affect how we see?The difference in luminence between an object and its background.
The ability to see is basically the ability to detect the difference between these two components. The point of no difference is where the object would become invisible. - 5What are the roles of the cornea and the lens in focussing?Cornea: does most of the work, but cannot change shape, therefore always does the same amount
Lens: uses accommodation to adjust the amount of light it refracts, refining the focus (stretching allows focus on far objects and vice versa) - 6Describe the different focussing errors.Emmetropia: normal
Myopia: short-sighted --> focal length too short --> needs concave lenses
Hyperopia: long-sighted --> opposite
Presbyopia: old age --> inability to accommodate due to stiffening of ciliary muscles
Astigmatism: different focal lengths for different orientations - 7Explain the transduction process for vision.Retina contains rods and cones, which pass electrical impulses to ganglion cells (long axon exiting via the optic nerve).
From here, it reaches the LGN (section of the thalamus), which projects to the primary visual cortex (V1) in the occipital lobe via radiations. - 8Explain the relationship between receptive fields and acuity.Receptive fields for foveal vision = smaller and more densely packed.
Therefore, cortical magnification for foveal vision = greater acuity/precision - 9Which visual field projects to the right side of the thalamus?Left visual field, and true for vice versa.
This crossover occurs in the optic chiasm.
Visual fields are defined as to the left or right of an object, regardless of which eye is used. - 10What does retinotopic mean?Cells next to each other on the retina project to receptive fields next to each other in the cortex
- 11What is an optimal stimulus for an ON centre cell?A central spot of light which will increase firing above the spontaneous/baseline rate.
- 12How do OFF and ON centre cells differ in purpose?ON: Tells where changes are in the image by exaggerating edges
Allows us to compensate for intensity of light source by being sensitive to contrast, rather than overall changes in brightness
OFF: help us detect luminence decrements to compliment ON centre cells - 13What are the properties of the lateral geniculate nucleus (LGN)?- Use centre surround antagonism
Retinotopically organised
All cells monocular (both eyes have inputs but each eye goes to separate layers)
Only one visual hemifield (contra)
Magnocellular and parvocellular cells (and maybe koniocellular) - 14Compare and contrast magno- and parvocellular layers.Magno: large RFs, low resolution, fast response, high sensitivity, process motion
Parvo: smaller RFs, high resolution, slow response, low sensitivity, R-G colour - 15What is the primary visual cortex mainly selective for?V1 selective for orientation
- 16What is orientation tuning?Cells respond to an edge with its preferred orientation --> activity reduces as orientation departs from the preferred
Bandwidth: range of orientations for which a cell fires (small = sharp i.e. not many orientations) - 17What is a filter? What types of visual filters exist?Only allows neural signals to pass for stimuli to which they are tuned - filter out all the others
Orientation, size (spatial frequency), colour (wavelength), etc. - 18How is the V1 organised?Orientation columns: cells with the same preferred orientation
Columns of ocular dominance: inputs from the same eye
Together, these make a hypercolumn - 19Explain the different types of V1 cells.Simple: respond to an oriented stimulus in a particular location in their RF (detect straight bars of light)
Complex: will fire for stimuli anywhere within their RF
Hypercomplex: prefer stimuli with an end within the RF ("end-stopped") - 20How do you 'build' cells?Complex: combination of simple cells with same orientation preference --> now have different edge locations
Hypercomplex: combine complex cells - 21What is population coding?Ability to define the orientation of a stimulus via the firing of surrounding cells (i.e. distribution of activity), even if there's not a specific neuron for it
Creates size and orientation channels - 22What is the effect of prolonged stimulation?Decreased sensitivity --> decreased firing rate = adaptation
- 23What is spatial frequency?How many stripes can you fit per degree of visual angle (i.e. set space on the retina)?
Thin stripes = high SF, and vice versa - 24How does spatial frequency relate to the type of information processed?Low SF = coarse scale info. --> low pass filter
High SF = fine scale info. --> high pass filter - 25What are the advantages of having two eyes?Laterally placed gives a larger field of vision
Binocular summation - lower thresholds for detection/discrimination
Depth perception - 26Do we judge motion directly?To judge motion directly, we would have to identify the position of the moving stimulus and know the duration of interval between displacement.
Our ability to do this is not sufficient for precision in speed discrimination, which suggests motion is sensed by specialised mechanisms. - 27What is a Reichardt Detector?Type of correlational model
- Units sensitive for a particular part of the brain
- Connected to a neuron that fires when it has simultaneous inputs from both cells
- Delay in one connection
- Must be rightward movement; if left, the delay is too late and signals don't arrive simultaneously (null direction = opposite direction) - 28How did Reichardt refine his model?Would need many units with many delays and separations to represent all speeds.
Motion detectors for opposite directions could be combined so that we don't need separate receptors on the retina. - 29What is the Wa270gon Wheel Effect?Tend to perceive the motion corresponding to the shorter displacement e.g. will view a 270 clockwise displacement as a 45 anticlockwise displacement
- 30How do we test face perception and memory?Recognition/recall tasks:
- Learning phase (exposure to set of faces)
- Retention interval
- Test phase: view again but with new faces
Matching tasks - must always use different faces as in real life we never see the same image twice (Lighting, viewpoint, etc.) - 31From what age do infants begin to process faces?Viewing preferences for normal vs. 'scrambled' faces from < 1 hour
2 day olds track picture of their own mother vs. other plausible mothers (recognition/discrimination of identity) - 32What does the composite face effect tell us about face perception?Composite face effect: when faces are combined, a new perceptual whole is created, hindering us from being able to identify the individual components.
Shows we process faces holistically - 33What other evidence/effects support holistic processing?Part/Whole Effect: Easier to detect the correct feature when shown as part of a whole face, than as an individual nose
- 34What disables holistic processing?Inversion (i.e. turning upside down)
Affects faces more than normal objects
Thatcher Illusion: difficult to detect expressions when inverted - 35What parts of the brain process faces?Fusiform Face Area (FFA) found in the inferotemporal cortex --> contains cells that are face selective
Single-cell recordings in monkeys showed diff. cell activities for diff. monkey expressions as well as specific monkeys
fMRI: Greater blood flow to the FFA when shown a face than an object - 36What does the neuropsychological disorder prosopagnosia demonstrates about face perception?Prosopagnosia: face blindness - visual perception otherwise intact
Suggests separateness of processing for faces - 37What is the argument against the specialness of faces?Prosopagnosics often show impairments for recognition of non-face objects within a category and, after training, can shift their brain activity to the FFA for these (increased performance)
Better performance for familiar faces irrespective of viewpoint, lighting, expression - 38What are the different features utilised in face recognition?External: constantly changing, can be intentional/unintentional e.g. beard, clothing, weight
Internal: relatively stable over time, thus more reliable at signalling identity - 39Do we get aftereffects for faces?Yes, adaptation similar to that of other areas of perception e.g. look at a face looking right, following face will appear to be looking left
Categorical perception: classification of facial expressions --> aftereffect strongest for neutral stimuli - 40What is delusional misidentification?Recognition of face but no familiarity (emotional valence)
- 41What are the different properties of depth cues?Monocular vs. Binocular (one/two eyes)
Pictorial vs. Non-Pictorial
Visual (retina image) vs. Oculomotor (eye muscle signals)
Ordinal (which is closer) vs. metric (by how much) - 42What is stereopsis?A.k.a. retinal disparity
Objects closer = negative retinal disparity or crossed disparity (think cross-eyed)
Objects further away = positive disparity or uncrossed
Fixated objects fall on our fovea i.e. the same point in each eye, therefore no retinal disparity - 43What is vergence? Why is it weak for detecting depth?The use of the angular position of each eye to calculate the depth of a fixated object (each eye needs to be pointed in the correct direction for fusion of inputs on the fovea).
Small vergence = long distance and vice versa
Can only do this accurately for <100m
B, NP, O, M - 44Explain how non-corresponding points demonstrate binocular disparity.Fixated images fall on corresponding points on the retina
Non-corresponding points fall on different positions on the retina for each eye, demonstrating BD - 45What is the significance of the horopter?The horopter dictates all possible locations where an object's half-images fall on corresponding points i.e. locations with zero disparity
Closer than the horopter = crossed disparity; further = uncrossed - 46What is the area surrounding the horopter and what does it dictate?Panum's fusional area: where single vision occurs i.e. where we are able to fuse two retinal images into one
Outside of this area, diplopia occurs i.e. double vision - 47What are the components necessary when seeking to stimulate stereoscopic vision?Two images: one for left eye, one for right
e.g. photos taken approx. 6.5cm apart
Reversal of these images - 48Describe anaglyphs.Image for the right eye coloured green, red for the left eye
Viewers wear filtered glasses (G, R respectively) which allow them to only see one image --> natural vergence - 49What were some early methods of viewing images in 3D?Wheatstone (1838): Mirror Stereoscopes - reversed images using 45 degree mirrors
Brewster (1856): Prism/Lens Stereoscope - Diverted the direction of light whilst eyes converge on a central point - 50What is polarisation and what is it used in?Different polarisation orientations for two projectors and glasses e.g. Imax
- 51What type of stereoscopic simulation is used in modern 3D TVs?Shutter glasses help give the left/right eye images one at a time (really quickly at the same speed as the TV is shuttering)
Won't work if it's too slow - 52How do vertically interlaced displays differ to temporal ones?Divide stereo half-images into odd/even vertical columns, with the right/left eye image in either one
Microscopic barriers
Limited viewing positions - 53How does familiarity affect depth perception?Objects of a stereotypical size can appear further away when their retinal image is smaller because retinal image size for objects of constant size varies with distance
- M, P, V, M - 54What are the different types of perspective?Linear (convergence): assume lines are parallel
Detail (texture gradient): assume texture elements are of similar size
M, P, V, M - 55What is motion parallax?As the observer moves, objects at different depths appear to move at different velocities (things closer move quicker + vice versa)
M, V, M, not strictly P - 56How do we view height in the visual field?We assume things rest flat on the floor, therefore things high up in the visual field are further away
M, P, V, M - 57How does aerial (atmospheric) perspective differ from linear/detail perspective?Depends on surround rather than object
More distant objects tend to be lower contrast, lighter and more blue --> faded by particles in the air scattering light
Depends on local atmosphere e.g. pollution
M, V, M, P - 58What is occlusion?a.k.a. interposition
Opaque foreground objects block more distant objects for areas lying along the same line
M, V, P, O - 59What is the assumption necessary for using cast shadows for depth perception? What is specific about the shading on a circular object?Assumes light source is constant and from above
Separation between object and shadow represents height of object in image
M, P, V, M
Known as attached shadow - circular objects appear convex/concave depending on pattern of shading - 60How can blurred boundaries tell us which object is closer?Boundary between clear and blurred object is blurred = blurred object in front (occlusion)
If Boundary edge is sharp, focussed object in front.
M, P, V, M - 61How do we accommodate to maintain a sharply focussed image?Distant object: relaxed ciliary muscles with a thin lens
Nearer object: tensed ciliary muscles to allow for a thicker lens - 62What is Emmert's Law?For a given retinal image size, perceived size is proportional to perceived distance.
- 63What is the difference between two plaid gratings due to?Plaid: two gratings at different orientations placed over one another
When in motion, plaids with the same spatial frequency and contrast should appear to move left and up when moved vertically - 64What did Newton's Prism Experiments demonstrate?White light passed through a prism, which splits it into a spectrum of different lights which appear coloured (refraction).
Demonstrated the diff. wavelengths - 65Which wavelengths appear as which colours?Short = Blue
Medium = Green
Long = Red - 66What is important to remember about wavelength as colour?Wavelength is an objective property of the stimulus; colour is a subjective property of the percept i.e. it's in your head!
- 67How does reflection allow us to see colour?Objects either reflect (white) or absorb (black) light.
They then appear to be the colour they reflect (i.e. the colour they don't absorb) - 68Which type of cells responds at low luminence? How does this affect our ability to see colour?Rods
Essentially colour blind - cones are better for determining wavelengths that constitute colour - 69What is acuity?The degree to which fine detail can be resolved
- 70How do we infer that most people have three cone types?Colour matching experiments:
To create a metamer i.e. match any single pure wavelength of light, humans need three primaries of adjustable intensity. - 71What are the different types of colour deficiency?Anomalous Trichromats: three cone types but deficient in one (protanomaly - red; deutranomaly - green; tritanomaly - blue)
Dichromats: lack one cone type entirely (Protanopia - red; deuteranopia - green; fritanopia - blue)
Monochromats: only one type of cone and lack colour vision day and night (rod monochromats = no cones at all - highly sensitive)
Cerebral Achromotopsia: damage to V4 - 72What is preferential looking?Where a baby is looking implies its attention, which implies it can see something
- 73What are ototype cards and what are they used for?Black and white areas on a card cancel to reflect the same amount of light as the grey background/
Used to assess acuity, as without it they would not be able to discriminate between picture and background - 74What is the contrast sensitivity function?Ability to discriminate between dark and light
Babies are poor for medium and low spatial frequencies
Adult CSF reached by approx. 8 years old - 75What can babies detect changes in?Show a change in firing rate for phase but not orientation
Restricted to dynamic stimuli i.e. needs to be movement - 76Explain what deprivation studies have shown.Deliberately deprive an animal of visual experience to observe results
Kittens reared monocularly don't have many cells for the eye that was covered (unable to process binocular stimuli)
Demonstrate the existence of a critical period - in order for normal sensory development, need to be exposed to a wide variety of stimuli for this period. - 77What are some problems with visual development and how can they be corrected?Strabismus: abnormal development of binocular cells resulting in the failure of the two eyes to align (lazy eye) --> eyepatch
- 78Describe active vs. passive vision.Need to actively explore our environments for proper development (esp. depth perception)
- 79What happens when we adapt to a distorted envrionment?Use of prisms to displace our view of the world --> initially difficult to operate but eventually adapted.
Not compensation, recalibration, as returning to the 'right side up' world felt strange - 80What is the Three Stage Model of object perception?Local features extraction e.g. edges, colour, motion --> Shape Representation --> object representation
Reflects the hierarchical nature of visual processing
Ventral (what) and dorsal (where) pathways in the brain - 81Explain each of the Gestalt Laws.1. Proximity: enables us to group what we see according to closeness e.g. pairs
2. Similarity: if distances between elements are the same, grouping is based on physical similarity e.g. colour
3. Good Continuation: elements grouped in same direction e.g. dotted lines
4. Common Fate: elements moving in the same direction at the same speed tend to be grouped together - 82What is image-based segmentation?Groups parts of the image together in segments based on:
Texture: (proximity and similarity)
Motion and depth - 83What components make up image-based contour integration?Collector units: local edge responses fed forward to neurons that collate them
Cooperative interactions: propagated laterally to produce mutual facilitation when nearby neurons are simultaneously active
Feedback from extrastriate cortex - 84What affects object representation/Intrinsic factors: features of individual objects
Extrinsic factors: viewpoint, lighting, occlduingo bjects etc - 85What characterises view-independent theories?Generalised cones
3D structural description
Hierarchical i.e. split into subparts
Axis is crucial as it determines the cone
Relies heavily on symbolic/abstract ideas about the object - 86What is view dependent theory?Multiple-view recognition: we store how an objects looks from different views in our memory
Then interpolate immediate views between stored views to determine the alignment between them
Recognition based on prototypical items closest to it in its feature space - 87How does experience impact object perception?Experts utilise the FFA for objects they are experienced with (like how we process faces)
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