Perception Flashcards
Bottom up concept of perception
Data driven
Receive sensory stimulus/take info from environment and react to it
Top down concept of perception
Our experiences/assumption/knowledge is applied to the info we receive from our environment
Previous knowledge affects what were seeing
Measuring perception
Psychophysics methods developed by Gustav Fechner
mind/brain + scientific study of matter/energy
“Precisely determined physical stimulus and precisley determined behavioural response”
Absolute Threshold
Method of Limits
Think staircase
In this task, stimuli are presented on a graduated scale and participants must judge whether they detect the stimuli or not. The values are presented in order, going from most intense to least intense vice versa, in an ascending and descending staircase
The experiment will be carried out going down the intensity and then again going up in intensity of stimuli. The threshold will be determined as
the average of these crossover points
Method of adjustment
Like participant is adjusting the brightness or volume
In this task, the subject is given control over the stimulus and allowed to adjust it until they can just detect it. The stimulus at this point is the threshold.
A new starting point for the stimuli is then chosen and the subject repeats the process.
The threshold is the mean of the threshold values on each trial.
The advantage of this technique is that it can quickly yield a threshold for a participant but a disadvantage is that it will yield great diffferneces from a participant to the next as well as between successive trials for each participant
Staircase method
Scientific
Method of constant stimuli
Scientific
No particular order just saying yes no i hear it or not
Threshold is determined by presenting the observer with a set of stimuli of which some are above the threshold, some below, and participants must judge whether they detected the stimulus or not
The threshold for stimulus detection is the smallest stimulus that is detected 50% of the time
Just Noticeable Difference
Difference threshold
Webers Law
Difference threshold
Magnitude Estimation
Brightness vs Loudness
Fundamental Criteria (Popper, 1960)
A good theory should be:
-Explanatory (not just describing data)
-Falsifiable (predictive)
-Parsimonious (explained in the simplest way possible)
Theoretical approach
Levels of explanation can be :
Anatomical and physiological
Behavioural and psychological
Theoretical and philosophical
Perceptual Theories:
Physiological approach
Ecological approach
Computational approach
Physiological approach (Horace Barlow (1921-2020))
What:
Look at the way neurons interact, what is going on inside bod, how is everything interacting is key to understanding perception
Techniques used:
originall electrophysiology with psychpysics
now Neuroimaging
Ecological approach (James Gibson (1904-1979))
What:
It is not enough to just look at what is inside of body, you need to look at perception in real world.
Techniques used:
Observation of behaviour in natural envornment
Analysis of how is optic array changing
VR for behavioural in simulated envormemt
Computational approach (David Marr (1945-1980))
What:
Perception is information processing. Brain is computer that transforms data from one form to another (take in sensory data and transform it into another interpretable form)
Techniques used:
Computer-based analysis of information content of stimuli (e.g. images) from which properties of perceptual systems can be inferred
Other theoretical approaches to perception:
Perception for Action (Milner/Goodale)
Bayesian Approaches (Mamassian/Ernst)
Active Vision (Findlay/Gilchrist)
Predictive Coding (Friston/Muckli)
Name 3 Gestalt rules and how these impact our perception
Rule of Proximity
Similarity
Good continuation
Cells in the visual system detect “features” of the world, other than objects. So to create percpetion on object, gestalt/grouping rules take elementary features and turn them into extended contours and shapes
Gestalt rule:Similarity
When you group objects with similiar features togethe eg size, color..
Rule of Proximity
Grouping things that are closer to each other together
Good continuation
expecting a line to continue so see lines as being attached rather than as separate lines
Simple cells - coarse and fine details
fatter recpetor cells will pick up on more coarse/general features (eg when you blur a picture ) while the thinner ones will pick up on fine lines (eg like when sketching)
Perceptual Segregation
Segregating figure from background
Eg knowing there is an apple behind banana in the fruit basket even though you can barely see it/its mostly hidden behind other fruit
but this isnt always easy to differnetiate what is figure and what is ground
Figure vs ground
Reversible figures that fools you —> eg the one that looks like vase but also can be two faces looking at eachother
Details can be more accurately discrminated if assigned which is foreground and background
Illusory Contours
Kanizca Triangle
Contours are inferred by visual system
Object categorization - what level of categorization comes first?
Superordinate - its an animal
Basic level - its a dog
Subordinate - its a pug
Which level will naturally come quickest? Probably depends on level of expertise
viewpoint invariance vs multiple views
Controversy:
Do we store a single, viewpoint invariant representation of a given object or do we have a number of “snapshots” of the object from different viewpoints which together make the object representation up?
What is meant by the “gist” of a scene ? And what determines the gist?
Its a general Description of a Scene
Available after only a fraction of a second
Get gist using “Global Image Features” such as degree of openness, expansion, color, naturalness..
Inferotemporal Cortex (IT)
End point of visual pathway
Face processing –> eg biggest response in monkey to other objects was to face of another monkey , monkey cortex that responds to faces
Gibsonian Theory - affordance vs objects
Thinking of an object tin terms of what u can do with it (chair u can sit on, pen u can write on) rather than thinking of it as visual properties
What are the two types of attention? Give examples of both
Divided attention - driving (youre talking, changing gears, looking out for pedestrians…)
Selective attention - Selective attention is the process of focusing on a particular object in the environment for a certain period of time. Attention is a limited resource, so selective attention allows us to tune out unimportant details and focus on what matters
Attention can be guided by the environment or by yourself - what is this referred to as?
Exogenous - guided by your eyes, and whats happening in the environment around you
Endogenous - Information that aligns with an observer’s behavioral goals are internally selected for further processing. It involves a more effortful process such as being instructed to orient attention to a particular location. You choose to listen to your lecturer instead of looking at laptop
What is inattentional blindness?
a perceptual phenomenon that occurs when you dont perceive something because youre attention was focused elsewhere eg experiment with counting number of passes and gorilla
What is change blindness
a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it.
Why does the spotlight analogy of attention not really hold up?
Because even if spotlight/focus is on one thing, we still do notice the things around it and dont just pay attention to objects but also locations
Expain attention as “glue” analogy
Theory that when we perceive things, we perceive their individual features such as color, motion, orientation/ edges, but attention is the glue that binds disconnected visual features into a coherent object.
Explain the Feature Integration Theory (Treisman, 1988)
When perceiving something, you go through two stages, the preattentive stage, then the focused attention stage. In the preattentive stage you can detect an object among distractors because the number/nature of the distractors isnt many. Called parallel searching/pop out as the object youre searching for will pop out wihtout your attention really having to be redirected to it
Then theres the focused attention stage, where there are more distractors and its harder to find what youre looking for. Here you will have ot focus your attention and look in greater detail and requires sustained effort. This is called conjuction searching
Conjunction search
In focused attention stage of Treismans Feature Integration Theory
Pop out/ Parallel search
In preattentive stage of Treismans Feature Integration Theory
What is binding through synchronization?
proposed mechanism by which the brain integrates and combines information from different sensory modalities or neural populations to create a unified perception of the world. In this process, neurons that represent different aspects of a sensory stimulus or object synchronize their activity patterns to encode and bind together the various features of the stimulus
What is the relevance of the fovia in perception
The image is focused here
there are the highest levels of cones so highest resolution image
What is the Stimulus Salience Theory?
that we will direct our attention to the most salient object in the scene - the thing that pops out the most
Trying to answer the question to do with how we direct our attention to different parts of a scene
What are some issues with Stimulus Salience theory?
More recent research suggests that simple salience model should be rejected
It works on a screen but less so in real life. In real life our eye gaze is allocated to the right place and at the right time to guide our actions, helps to plan ahead of our actions
Individual differences
People with autism may have their focus on different parts of a natural scene. While a non autistic person will look at a persons eyes, autistic people may center their eye pattern on the shoulder, hairline etc - just have a different pattern of eye movement
Explain attention as a perception enhancer
Attention helps us respond faster to attended objects/locations or in some cases a contrast is enhanced - eg its not a person walking theyre speeding towards us on a bike
Attent also enhances physiological responses - firing rates in the parietal cortex increases if the object is in the receptive field is attended to
What is Reichardts simple motion detector? What does it attempt to explain?
Motion sensitive neurons with motion sensitive receptive fields
Attempts to explain
What is the delay and compare mechanism?
Instead of seeing a blurry mess when things move fast, the object changes places on our retina. Delay and compare mechanism is when you know the distace travlled and time take, so you can know the velocity
What is apparent motion and what does it have to do with illusions?
Apparent motion refers to the perception of movement when there is no physical motion occurring. Instead, apparent motion occurs when the visual system processes a series of static images or stimuli presented in rapid succession, creating the illusion of continuous motion.
What is the motion correspondence problem?
Refers to the challenge faced by the visual system in :
Correctly matching local motion signals from different parts of the visual field to perceive coherent motion trajectories of objects
-The visual system receives motion information from numerous spatial locations and orientations simultaneously and must integrate these signals to accurately perceive the motion of objects.
What is nearest neighbor matching in the motion correspondence problem?
You use nearest neighbor matching when you see objects seeminlgy “move” from one position to the next. In our heads one spot has moved to the next because this new position is its nearest neighbor, giving shortest trajectory
What is the concept of common fate in the perception of motion?
Lots of individual objects that get grouped into a bigger moving mass because they are going in the same direction or same speed
What is the aperture problem? How does aperture influence perception of motion? Give an example and how it works
That apertrue influences the perceived direction of motion.
For example the barberpole illusion, which is essentially a massive correspondence problem, because you dont know which direciton a specific point is going.
So to figure it out our mind looks at the edges, which makes the motion look like its going upwards
Or straight vs crinkled aperture difference in motion
What is the optic flow and how can it be determined?
Optic flow is the visual motion patterns perceived by an observer as they move through their environment
To determine it we need to look at where the visual information is flowing from. Is it going away from you or towards you?
How do I know whether I am moving or if the world is moving?
- Is there retinal motion? Is the object moving on your retina?
- Are your eyes still or are you tracking the obejct
- Did you command your eyes to move?
What is corollary discharge?
What is the electromagnetic spectrum?
What is it caused by?
The electormagentic spectrum is energy that travels caused by the acceleration/decceleration of charged particles. We perceive variations in wavelength as color
What does Benhams disc do and what does it show?
That color is not in the light itself, but is rather produced by our visual system.
It is a black and white disc which, when rotated, looks to be colorful.
it shows that color cannot always be explained in terms of wavelength -> there is something internal happening that has to do with its temporal properties
What are spectral reflectence graphs?
On the x-axis is the wavelenght and on the y axis is the reflectance. So a spectral refelctance graph shows how much a certain wavelenght is being reflected aka what color it is (which wavelnghts are prominent causing a certain color sensation)
What is the diagnosticity of color?
That we attribute certain colors to go with certain shapes/objects, so that when the color is not one we associate with an object, we feel uncomfortable or confused if color doesnt correspond to particular class of object
Hansen et al (2006) looked at the link between color and our memory of objects, explain the findings
Our prior knowledge of an objects characteristic colors affects its appearance.
What is the Young-Helmholtz Theory? What does it have to do with trichromacy and cone cells?
That any colored light can be matched by adjusting the relative amounts of the three primary lights, this has to do with the physiology of vision, in that we have three types of cone cells with three different pigments with different spectral sensitivities
Because we have three types of cone cells, we are trichromatic, whereas dogs only have 2 and are dichromatic
What are metamers?
Different wavelenghts producing the same spectrum/perception of color because theyre stimulating the cones in the same relative amounts.
What is the Opponent Process theory?
its the idea that we have natural pairings of color
red-green
black-white
blue-yellow
This theory suggests that the mind can only register the presence of one color of a pair at a time because the two colors oppose one another
Which is why he questions whether aynone has seen a reddish green or blueish yellow –> though some authors argue this is possible
What is the physiological evidence for the opponent-process theory?
Discovery of opponent cells/neurons in the LGN and retina
The retinal ganglion cells which get excited by one color and surpressed by another
What are the three channels along on optic nerve?
Achromatic
(L+M)
Red-Green
(L vs M)
Blue-Yellow c
(L+M) vs S
what is the simultaneous color contrast theory?
That two surfaces with the same spectral composition will be perceived to have a different color when they are placed against different chromatic backgrounds
Colors of objects are dependent on which two things?
The color of an object is dependent on the objects and the source of light. To view a color it must be viewed with a certain illumination, but the type of illumination is going to affect the color
What is the concept of color constancy?
the idea that colors stay constant even when there are changes in luminosity/the illuminant
Through what mechanisms does color constancy occur?
Chromatic adaption - eg having sunglasses on, adding filters..
Contextual effects - is there a shadow on it, what time of day is it..
Memory - what do i remember this color being
What is the concept of lightness constancy?
That how intense we perceive a hue/color to be is dependent on the background. Eg the blackness of your TV screen cannot be blacker than when your TV is off/there is no image
What is proprioception vs Kinesthesis vs Somaesthesis?
Proprioception: sense of position of our limbs
Kinesthesis: sense of movement of the muscles
Somaesthesis: sense of object touching the skin
The somatosensory system consists of which two types of skin?
Hairy and glaborous
Name the 4 channels of the somatosensory system and what stimuli they respond to:
Merkel receptors - continuous pressure
Meissner corpuscles - onset/offset of stimuli
Pacinian corpuslces - responds to vibration
Ruffini endings - responds to stretching of the skin
What kind of stimuli do C-tactile mechanoreceptors respond to and where are they found? Where does it send signals
They are found in hairy skin (non-glaborous)
Responding to slow, gentle touches like a massage
Signals get sent to the insular cortex which has a part to play in emotion regulation
What is the sensory homunculus?
Is a sort of map that shows how much cortex is devoted to different parts of the body. Eg fingers and lips are small in size but have proportionatly large brain sensitivity
Describe the pathways in the somatosensory cortex
Area S1 –> Area S2 –> Hippocampus or Prefrontal Cortex
Area S1 –> posterior parietal cortex –> premotor cortex
What is active touch and why does is it more efficient than passive touch?
Active touch refers to when we acitvely use our hands to explore objects in the world. Its more efficient than passive touch, which is like moving smth passively in our hand
What are nociceptors?
Pain receptors - sensitive to stimuli that could be potentially damaging to the skin
What are A-delta fibre axons and C-fibre axons?
A-delta fibre axons are reponsible for the initial, sharp pain sensation. Neurons myelinated so signal travels fast
C-fibre axons are not myelinated and are responsible for the pain after the intial sharp pain. It arrives slower, and is more prolonged and less intense
Explain the gate theory of pain phenomena
L - normal touch receptors acitvate inhibitory interneuron and
So when pain comes through S fibres, and wants to go to Projection cells that will lead to the brain, activating L fibres will allow some inhibition of these signals, decreases the pain sensation
