P&A Flashcards
Evolutionary needs of P&A
- Find food
- Avoid danger
- Reproduction
What is a modality?
A class of stimulus (energy transmitted) and the specialised receptors that ‘sense’ that energy, all perception occurs within certain modalities.
Why can the perceptual system be tricked?
Because the system often ‘estimates’, we have evolved to rapidly extract useful info from the environment.
What’s the more modern overall model corning the way we perceive and act?
Sample info - process info -interact with the world (in a loop)
What is the classic view of perception? Why is this no longer so relevant?
There is a distinction between perception and action in the classic model sensation leads to perception and separately cognition leads to action.
However the lines between perception and action are arbitrary - where does action begin and perception end.
Examples of a perceptual Energy?
Chemical energy i.e. taste, smell
Heat and tactile energy
Energy from waves of air pressure (audition)
What are the differences between light and sound energy that mean bats and dolphins are more adapted to using it?
Sound is present at all times (bats hunt in the dark)
Sound travels faster underwater (dolphins inhabit water)
What is filtering?
Active process of selectively keeping some information , and discarding others
Example of filtering in the eye?
The fact it uses only the visible light part of the spectrum.
What is sampling?
The active seeking of useful information
Are eye movements an example of filtering or sampling?
Sampling (looking for info)
Why is perception and action important to study?
Help humans with impairments in visuomotor activities i.e stroke survivors
What did Smith et al (2015) show (stroke patients)?
They developed novel computerised tools to assess whether stroke survival patients had adequately compensated for their impairments, this has implications on whether they could be allowed to drive in the future, driving offering a larger QoL.
What did Yarbus (1967) say about eye movements?
Human eyes fixate on those elements of a visual scene that carry essential and useful information.
Fixate for longer on more useful info, people who think differently see differently
- Related to the task
Model of P&A using eye-movements as an example?
Motor commands sent to eye to move - visual info sampled from new point of fixation - info informs future eye-movements - Loop back to start.
What are the different types of eye movements?
Conjugate movements (both eyes in same direction):
- Saccades
- Fixation
- Smooth pursuit
- Vestibulo-Ocular reflex
Disconjugate (different directions)
- Vergence
Most recent way to measure eye movements?
Electro-oculography
What are saccades?
Rapid ballistic eye-movements, very short duration (15-100ms)
The most frequent movement we make
What is saccadic suppression?
The mechanism by which we do not see motion blur during saccades - as we are effectively blind during saccades.
What is fixation?
Time where the eyes focus on one area in order to allow us to absorb the information from that area:
Not completely still as photoreceptors and neuronal connections would adapt/fatigue if completely still. (red dot test - Troxler effect)
Micro-saccades/ocular drifts and ocular tremors keep this from happening.
What is smooth pursuit movements? How are they accomplished?
Smoothly follow a moving target
Requires the system to make predictions about where the target will be moving
What is the vestibular ocular reflex?
The interaction of the vestibular system and eye movements when the head is moving - counter rotates the eye when the head moves, in order to maintain fixation when moving, does not need visual input.
What is Optokinetic (OKN) Nystagmus?
Optokinetic nystagmus - non-pathological behaviour, it is when making very large head turns or for example looking out a train, relies on both smooth pursuit movement and saccades. The smooth part is characterised by slow-phase velocity.
Findings of Costa (2011) on Down syndrome patients and OKN Nystagmus?
The DS patients had increased number and amplitude of intruding saccades during smooth pursuit movement.
May help understand why DS people struggle with everyday tasks - e.g. reading may affect intellectual capacity.
What interaction may eye-movements have on visual field loss i.e. after neurovascular incident. Study?
May help compensate.
What real-world functions do eye-movements have?
Locate objects
Direct actions towards those objects
Guide actions upon those objects
Check the status of actions
What type of scales does the human perceptual system use?
Lagarithmic scales
An example of the human perceptual system using logarithmic scales?
Small weight changes are easier to detect in lighter weights than heavier weights - Fechners law
6 extraoccular muscles?
Superior Rectus, Lateral Rectus, Inferior rectus, medial rectus
Superior oblique, inferior oblique
Nervous supply to the extraoccular muscles?
Lateral Rectus (VI), Superior Oblique (IV), Superior rectus (III) Inferior rectus (III) Medial rectus (III) Inferior oblique (III)
What movement does each muscle of the eye cause?
Superior rectus - Elevation and intorsion
Inferior rectus - depression and extorsion
Lateral rectus - abduction
Medial rectus - adduction
Inferior oblique - elevation extorsion
Superior oblique - depression intorsion
What are the two systems in the human perceptual system?
System I - Fast gut reactions (sensorimotor system - online cognition)
System II - Slow, rational (offline cognition)
What is the cognitive action interaction theory?
That ‘higher-order cognition’ should be considered as:
(i) a somewhat separate system that interacts with the ‘sensorimotor control system’;
(ii) a system that is underpinned by the sensorimotor control system.
What is the Weber-Fechner law?
The law that the perceived change in stimuli is proportional to the magnitude initial stimuli, Fechners law includes a measure of subjectivity (varies from person to person).
Information theory formula?
Who came up with it?
H = -ξ p(x) log2 p(x)
p(x) = probability of x
H = information entropy
log2 p(x) = information
Information = log2 1/p
p = number of possible events
Claude Shannon
Given that information is log2 1/p, how would you work out the amount of information given in a coin toss (expressed as ‘bits’)?
log2 1/0.5 = 1 bit
because the chance of heads/tails is 0.5 each
What has Friston suggested recently in terms of information theory?
That a unified brain theory could help us understand how the brain uses information to help minimise surprise.
What is DCD and what test is used in diagnosis?
Developmental discoordination disorder - CKAT
Deficits in the acquisition and automation of motor processes.
What is bayes rule?
A rule that can be used to determine the probability of something occurring.
The posterior probability that the child has DCD given a positive test is the likelihood probability of a positive test when the child has DCD times the prior probability of a child with DCD divided by the marginal probability that it’s a positive test
𝑝 𝐷𝐶𝐷 + 𝑡𝑒𝑠𝑡) =
𝑝 +𝑡𝑒𝑠𝑡 𝐷𝐶𝐷 𝑝(𝐷𝐶𝐷)
————————
𝑝(+𝑡𝑒𝑠𝑡)
Why is Bayes theory important?
Can allow us to determine probability of someone having a condition
The brain may use bayesian mechanics in functioning ‘bayesian brain hypothesis’ - why humans make decisions
An account of why humans learn to survive in uncertain environments
What is the classical theory about system I and II (old theory) ?
Embodied cognition (EC) thesis holds that the nature of the human mind is largely determined by the form of the human body. EC philosophers and psychologists argue that all aspects of cognition are shaped by aspects of the body
Evidence for The combined action interaction theory?
WM tasks are better when a preferred hand is used - system I and II are interacting
What is perception?
The decoding (and then encoding) about the world (which includes us) within any given modality.
What human perceptual system exploits chemical energy?
The olfactory system
The integumentary system - e.g. noxious substance on the skin
Taste receptors
What perceptual system exploits thermal energy?
Integumentary system - thermal receptors
What perceptual system exploits kinetic energy?
Touch receptors in the integumentary system
What is it about vision that allows us to be evolutionarily successful?
Lots of information - can hunt prey/avoid predators
What’s the Cambrian explosion?
A huge large number of different organisms, most plausible is that vision sparked it, as vision provided organisms with information about the environment
What is unique about colour information?
Can start to tell apart different organisms from each other - things to eat, predators e.t.c.
Why is the fact that physical laws of the universe were discovered by isaac newton important?
If everything obeys laws we can then make inferences about the external world leading to perception of the world using different modalities
What contributions did James Clark Maxwell make to scieince
Formulated the theory unifying electricity and magnetism - electromagnetism.
Who was Herman Helmoltz? His contribution to psychology.
He was a scientist that laid the fundaments of visual science. The light that reaches the retina is ambiguous - we use top down processing to produce an estimate of the information (top down information is information that has already been stored e.g. what a lion looks like.
What didi JJ Gibson contribute to psychology?
The ecological school of psychology. That visual perception interacts with the world. What is logically true is not necessarily ecologically true, the human perceptual system integrally relies on the environment.
- Turned out to be incomplete
What do modern accepted theories of visual perception suggest about top-down/bottom-up processing?
They are both important, we use both - Daniel Wolpert suggested that humans use bayesian principles to make predictions and guide our actions.
What has Karl Friston proposed?
The Free energy principle, may unify existing ‘brain theories’.
Two forms of visual information?
Vision for action, using visual information to interact with the world - this is cognitively impenetrable i.e. it is implicit.
Cognitive visual experience - this is partially conscious, it is things you can consciously recognise ie. object classification and recognition.
Process of neurological human visual perception processing anatomically? Two anatomical streams?
Retina to occipital cortex after this the information flows in two paths:
Ventral path: V4 to anterior inferotemporal cortex:
- Perception, stored for visual reference, allows us to think about the world.
Dorsal path: V3 to posterior parietal cortex
- Action. Guide our actions as we make them.
(Milner and Goodale hypothesis)
Evidence for the two pathways?
Milner and goodale: Patient DF, visual form agnosia.
Damage to lateral occipital cortex.
Relatively normal visuomotor coordination
But Impaired visual discrimination
(she can’t tell you what is front of her, but could pick it up.)
What are inferotemporal neurones?
Fire when certain objects are presented.
Not evidence for ‘granny cells’ (each individual cell leading to recognition of grandmothers expressions) - they do not work together to provide invariant interpretation of faces, but rather a subset of all faces
Damage to inferotemporal cortex can lead to prosopagnosia (face recognition problems)
What does cue refer to in psychology?
A particular source of information
What is the general structure for distance perception?
Monocular information vs Binocular information
Retinal vs Extra retinal information
All leading to fixation distance and 3D space.
Examples of monocular retinal cues?
Occlusion (What object is in front of which)
Perspective (point perspective - converging lines - using knowledge of the world (top-down processing).
Height in scene and relative size also use retinal monocular cues. (pictorial cues)
What are horizontal size ratio (disparity) (distance perception)
So if a flat image is close then the surface will appear different to each eye (horizontal disparity), if it is further it is more likely to appear the same - this is used to determine distance
What is vertical disparity? (distance perception)
A binocular distance perception technique. Needs a large field of view to work, uses the difference between the images from each eye.
What is accommodation?
Monocular extra-retinal distance cue, uses the scale of how convex/concave the eye is (so it can focus) to determine distance
What is vertical gaze angle?
Monocular extra retinal visual cue, the fact that we use simple subconscious trigonometry to work out how far we are from the floor. Used to determine distance, and to determine reach and grab movements.
What is vergence? In distance perception.
Binocular, extra retinal cue. It is the simultaneous movement of both eyes towards or away from one another when fixating on an object.
Used to think it was not a useful distance cue. However most of these studies used verbal reports, longer distances and contraction bias (regression towards the mean).
Mon-Williams, studied vergence through the use of a prism on one eye (distorting vergence and measuring using equipment how accurately they could point to an object)
Turned out people did use vergence but there was evidence of contraction bias (regression towards the mean in uncertainty)
What is modified weak fusion?
The human perceptual system has evolved to be ‘robust’ (not going to fail)
The noisier a cue, the less confidence is placed in it.
One cue can promote another to allow it to provide information to the system but no other interactions are allowed
Evidence for vergence being a useful distance cue in terms of modified weak fusion? (mark’s three hypotheses)
If Vergence is useful it should become more strong when other cues are removed.
The contribution should decrease when it becomes noisier.
With increasing target distance Vergence contribution should decrease (only used for short distances).
Brief summary of Mark Mon-wiiliams vergence research?
So they discovered through their first experiment and second experiment that:
- We DO use vergence as a distance cue (they point closer)
- We DO use nearness as a measure of distance
- Vergence is inversely proportional to discrepancy and fixation distance (accuracy). So the more information available, the less we listen to vergence.
- Discrepancy and fixation distance interact to determine weighting (how much you listen to it)
What is nearness as a distance measure?
The fact that the brain uses units based on angles.
The correct type of distance model for vergence?
Vergence is inversely proportional to discrepancy and fixation distance, and there is an interaction between discrepency and fixation distance.
What is prism bias ratio?
The amount you are using vergence - high value = high vergence.
Evidence for vergence with visual form agnosia?
DF uses vergence more than other forms - as she can’t access pictorial information - basically she can’t use monocular retinal cues.
What does Patient DF (visual agnosia) and her use of vergence tell us about the Milner and Goodale model for neurological visual perception?
DF has the orientation and the scale (ventral) but she can’t use the monocular pictorial cues (dorsal), so teh Milner and Goodale model works, however for healthy people they use both streams together to understand teh world around then
What is prehension? What are the phases of prehension?
Reaching and grasping movements: how you move through space and time to grasp an object.
Pre-contact phase
Grip and lift phase
Device to measure pre-contact phase of prehension? How is it used to measure pre-contact phase?
Optotrak - IR sensitive cameras, tracks the movement of objects through space and time (through IR emitting diodes).
Put diodes on soloed process and tip of forefinger.
Look at how the hand accelerates and decelerates, so as to quantify the different movements in prehension.
What are the three hypotheses surrounding prehensile movements?
Traditional: Transport wrist and control grasp (open and close the gap between thumb and fingers) procedure.
Digit hypothesis: No ‘transport’ and ‘grasp’ movements, simply two aiming movements. Two separate movements.
Vector matching hypothesis (best): Hybrid, the system controls a vector (with three components itself: Magnitude, direction and location).
What is the vector matching hypothesis?
Three functionally distinct components:
Transport: Placing hand in position, dependent on object size, distance and body-hand coupling.
Grasp: Formation of appropriate aperture size, intrinsic properties of the object (size, texture) and workspace layout
Rotation: Form appropriate orientation of the hand.
Evidence for the vector matching hypothesis?
We can do all the three components separately, seems conceivable that prehensile movements are putting all three together. Evidence shows that we learn behaviours through putting together of basic building blocks to make a higher order movement.
Looking at babies, it seems they develop prehensile movements separately, do all separately.
What seems to be the origin of the vector in prehensile movements?
The thumb - fixate on the thumb.
What are the components of the Pre-contact phase and the Grip and lift phase of prehension?
Pre-contact:
- Transport
- grasp
- rotation
Grip and lift:
- Loading phase
- movement phase
What does the fact that the hand moves in a straight line to reach and grasp an object (on constrained) tell us about how the brain controls prehension?
- The system is using bottom-up information (not just joint movements) but real-world environment.
- It is efficient: makes the most efficient movement.
When do we not use straight line paths to reach and grasp objects?
When hand starts on a flat surface: do not slide along surface due to friction. Hand lifts in proportion to object distance. Again tells us the system does not waste energy. (is parabolic - straight line)
What are the effects of depth, height, width and distance on the time it takes to grasp an object (MT)
MT increases with increased width and distance
MT decreased with increased depth and height
What is the formula for movement time in prehensile movements?
MT = a+b_log2(A)+c_log2(W)
A = Amplitude of movement W = Size of the target
a, b and c are constants
Similar to information theory
What was wrong with Fitts law?
Combines two parameters (A and W) that affect MT into one parameter
A = Amplitude of movement W = Size of the target
Two types of feed control?
Feed-forward control (positive):
- No loop: switch - boiler - radiators
Feed-back control (negative)
- Loop: switch - boiler - radiators - thermometer - radiators (loop)
Thermometer can stop the radiator when temp is at certain level.
Why does the larger the object width cause MT to increase?
Because the wider the object the more likely to knock it over, so you have to make error corrections - online feedback control.
What is the effect of width on maximum grip aperture? Why, what does this tell us?
Lawful positive proportional relationship
Open hand a little wider than the width of the object - system is planning and predicting movements in order to make movements as efficient as possible.
What is the effect of height and depth on maximum grip aperture? Why?
A lawful positive proportional relationship.
This is because when the height and depth are larger the movement time is reduced - less opportunity to make corrections and so it gives itself a safety margin.
What happens in the loading phase and the movement phase of the grip and lift component?
loading phase is the period where you start applying forces prior to movement.
Movement phase is when additional inertial forces are developed due to acceleration of the object. in healthy adults grip phase is precisely modulated in phase with movement induced forces.
How are the forces developed in loading component?
There is a appropriate grip force (normal) and also a load force (tangential)
Calculated before they are applied and adjusted in parallel to a target force (one finger applies force before the other)
The scaling of this target force is based on visual and tactile cues, together with memory - free energy principle - the brain is constantly making predictions and adjustments to minimise the chance of not knowing
During movement (in grip and lift) how are forces developed?
You are accelerating the object and so that changes the amount of forces you need to apply to the object (tangential) to keep gripping it
This is controlled through force control, there are two models for this:
- The forward model:
describes relationship between input and output of motor system, thus predicting future state of hand (feed forward)
The inverse model:
- Inverts the system and provides the command that causes a desired change in state - acts as a controller (feed-back loop/error correction?)
What functional psychology determines driving?
Visuomotor control of braking and steering - ensure speed and direction are appropriate. So speed and direction.
- also other tasks (gear changing, navigation and monitoring the scene for hazards).
What information do we use to determine the direction of motion in the world?
Surface cues from texture - distortion of texture can lead to observation of texture
This contributes to optic flow when they are moving.
What is optic flow?
Self-motion through a textured world causing relative movement of points making up a surface. This is used to determine the direction we are going.
Experimental evidence for optic flow?
Younger children fall when you move the walls of a room but not the room itself - suspended wall task
Gibson’s view of psychology?
Gibsonian view that it is impossible to explain behaviour by removing animal from environment - he put forward bottom down processing idea - behaviour unfolded from interaction with the environment.
Gibson’s view of optic flow?
The centre of the flow pattern during forward movement is the direction of movement essentially. Radical (optic ) flow.
The centre of flow is called the Focus of Expansion (FoE). You move the FoE to where you want to go and thus you steer.
This doesn’t require any stored information about roads, and so gibsonian view puts forward optic flow as THE source of steering
Problems with optic flow?
- When you start to include eye-moments and head movements optic flow is altered and the brain has to process retinal flow
- Other information than optic flow can also be used e.g. using reference points (visual direction) and steering towards or away from those points. Rushton et al (1998) - changed reference points with prisms and this affected direction (without affecting optic flow)
In conclusion, what main pieces of information do we use to control steering?
- Retinal Flow
- Visual direction
- Tangent point gaze strategy
Land & Lee (1994)? (Steering) Problems with the evidence
Observed tangent point gaze strategy when steering a bend - through eye tracking, proved that we don’t just use optic flow
80% of the time looked at the tangent 1-2s before entry to a bend.
Problems:
- N=3, v small group
- One unique road, which was one-way (no oncoming traffic) - the inside of the road edge is actually in some cases the furthest point ahead, and so would look at it.
What is the tangent point in steering? Why use it? (land and Lee., 1994)
The point at which gaze angle information will indicate the future curvature of the road. The angle of gaze tells the brain the angle of the road, does use some information about the world (top-down processing)
02 / 2d
The steering wheel held at an angle proportional to the gaze angle will steer you around the bend.
What did Wilkie and Wann (2003) find under controlled conditions?
80% of people did not look at the tangent point - people looked in the centre of the road.
What did Wilkie et al (2010) find?
When people were started at other points on the road, people again did not look at tangent point, but they looked where they wanted to go.
Why might tangent point fixation occur?
Wilkie et al., (2010) showed that when asked to cut corners people did look at the tangent point (take the racing line)
Conclusion on where people look when steering?
Where they want to go essentially, although evidence on both sides (i.e.. tangent point or direction). When you cannot rely on one point of information you may use others.
Things you could do to assess older adults on the road?
Controlled simulations.
What skills does catching rely on?
Interceptive timing, judging time to contact.
What is optic looming?
A technique that is used to determine when an object may reach you.
The fact the object increases in size (in relation to your retinal image) means it is getting closer to you, the faster it gets bigger the closer it is - if it increases a lot when close you know it is moving fast. Explosive magnification - getting close at the end indicates imminent collision.
Gibson propagated this idea.
What is Tau?
Lee (1976) showed that we sue an equation to judge how close an object is
We work out the velocity by doing the difference between the retinal size at time 1 and time 2 = Vr
Tau = Retinal size/Retinal velocity (= Time to contact)
In terms of the gibsonian view of the world how does Tau fit?
Very well - it requires no prior knowledge of the world:
- no object size
- no distance
- no speed
Three different theories of perception?
Top-down - e.g. Richard Gregory - Einstein face mask (you see the face as sticking out when it is not - must be using some store of processing)
Bottom up - e.g. David Marr: a CHANGE in pattern is all the visual system needs to extract form and shape.
Ecological optics: Somewhere in the middle of the two, we both use stimuli with top down interpretation and bottom up reconstruction which lead to perception (and also use tings such as optic flow and optic expansion directly)
Lee and Reddish (1981) (Evidence for Tau) Problems?
Lee and Reddish (1981): Diving Gannets, measured the time when they fold their leaves against duration of dive and time before water contact. Birds seemed to follow pattern predicted for Tau.
Only observational - no intervention
Lots of data points were from short distances (90% a meter) - some birds actually folded wings when below the water.
This evidence is inconclusive
Other evidence for Tau (lee et al) problems?
Lee et al., 1982: long jumpers regulate stride length
Punch away falling balls (1983)
All were consistent with Tau but did not test Tau directly.
Direct testing of Tau?
Rushton and Wann (1999) Used virtual reality - to control the effects of Tau and also stereo information.
Found that people would grasp based on the earliest signal, if tau was easy would grasp based on that and vice versa
People used both.
Two signals used to determine when object is going to hit you?
Binocular separation
Tau (looming)
Conclusions from direct testing of Tau (Rushton and Wann) on ecological psychology?
There is no single input variant that Gibson and Lee would have liked.
What did Land and McLeod (2000) show in terms of cricket batting and what info is used to determine ball impact?
The batsmen did not use Tau or binocular information were not used in the initial phase (too fast - not available) but may play a role after the ball hauled. At first they predicted where the ball would bounce and then when bounces track the ball (use tau and binocular info)
Problems with Tau?
Too fast
Not all objects travel at constant speed
Not all objects loon symmetrically
Prior knowledge of an object causes change in TTC predictions e.g. we know how big a tennis ball and basketball are (not gibsonian)
Two major limitations to human brain capacity?
The time needed to identify a stimulus
The Number of stimuli that can be processed at once
What is Rapid Serial Visual Presentation (RSVP)?
An experimental model often used to examinee temporal characteristics of attention. Ptps asked to identify letters/numbers that are rapidly presented after one another.
What is attentional blink?
When you try to identify two targets you will find it difficult to identify the second target when presented 500ms within the first one.
Attentional Blink reflects the limitation of the human attention system.
If they don’t have to report the first target then ptps can easily report the second target. This is because when we are asked to remember both targets we divert resources to remembering the first target and do not have enough resources to also monitor and identify the next.
Two attentional processes involved in the RSVP task?
Unlimited-capacity process that monitors and identifies all the stimuli
Limited capacity process that comes into play when we explicitly process one target
Why, in the RSVP task, can we identify two stimuli directly after each other - within 100ms?
Because the limited capacity process can capture both stimuli at once.
Shows we can process more than one stimuli at a time (if they are very close).
What is repetition blindness? Why dos it occur?
For example in the RSVP task if target 1 and 2 are similar it will be harder to identify the second.
If T2 is different from T1 then it will attract more attention - more resources will be diverted to it, if it is the same then it may be missed.
What is the psychological refectory period? (RSVP)
If ptps are able to detect T2, and asked to select a response to T1 and 2 then the response to T2 will be delayed.
Implication for driving - may not be able to respond as well to T2
Two different processes available when identifying the number of stimuli available?
For small numbers we undergo subitizing:
- Rapid confident and accurate recall of the numerosity of an array of elements presented for short periods
For larger numbers we have to ‘manually’ count, which requires serial shifts in spatial attention
Explanations for subitizing?
- It doesn’t require attention (pre attentional) allows us to automatically and immediately process a limited capacity of items - allows us to preserve attentional resources in order to direct them to something else Trick et al., (1993)
- It is pattern recognition, Mandler and Shebo (1982)
- It is a fast non-verbal form of counting (gallistel and Gelmen)
What is change blindness?
Failure to detect large changes in visual scenes. Shows the limitations in human attention.
Whats the capacity of visual short term memory (VSTM)?
3-4 objects, can eras low as 1-2, can be as high as 5-6.
What things influence the capacity of VSTM?
- Individual diff
- Visual integration - integrate features together so as to increase capacity
- Object complexity - simple objects are perhaps remembered better than complex objects.
- spatial distribution of objects in the visual field, based on the fact we process nasal and temporal visual fields in distinct hemispheres. Bilateral (involving both) is remembered better.
How many stimuli can you track simultaneously, what is the task called?
3-4 items, called Multiple Object Tracking (MOT)
What type of information does Vertical disparity (i), Horizontal disparity (ii) and Accommodation (iii) give you?
(I) Body-sclaed information - absolute information and whether it is near or far
(ii) - Relative information about the depth of objects in a visual scene
(iii) - Gives ordinal information (the order of distance)
What is strong and weak fusion?
Weak fusion - cues considered in isolation and cues are subsequently averaged
Strong fusion - the NS selects the statistically most probable interpretation
