mt 2 deck Flashcards
bottom up procesing
piece together info coming infrom the world to make sense of it
predictive coding mocels
stress the idea that we dont have direct access to the world. we only get signals that are interpreted by our sensory systems
bayesian statisticians priors:
hypothesis about how likely things are in general and how lilely they are tp be true in the current situation
feedforward based mocel
signal or info gets apssed forward from one node to the next.
bottom up processing
feed forward (mostly) processes as info gets passed from V1 forward. neurons respond to features of objects in an increasingly large scale and higher levels of abstraction
feedforward models illustrate info that is
coming in from the world and going from basic sensory areas to high level integration areas of the cortex
treatise on psychological optics
brain is a prediction machine, perception is just unconscious inference (we infer the cause of a sensation in the world via its effects)
von helmholtz view of perception
generation of a best guess (inference) about the state of the world, in view of the data.
how do predictive coding models view the role of visual cortex neurons
predictions based on the probability the stimulus will have particular features. error detection- they respond to a mismatch between predicted signal and actual signal
generative model
model of the world that our brain produces whose business is to use what we know about how the world works to generate predictions (hypothesis) about what the object or scene in question is
higher level hypothesis
ex “there are no bears in pacific spirit park” or “there are bears in the mountains”
lower level hypothesis
influenced by higher level hypothesis. ex “if there is a bear there should be movement and sound”
lowest level hypothesis
specific to each modality (taste, touch, smell, hearing, vision). hypothesis are compared with incoming info from the senses. happens in the primary visual cortex (V1) /IOC. prediction sent down to all the specialized detectors of features
what happens at each level according to predictive coding?
there are representational units that encode expectations, or the probability of a given stimulus under the circumstances
what do representational units do?
send down their predictions of what they expect to receive from the lower level
what do error units do?
encode or read suprise (mismatch between predictions and bottom up evidence from the senses)
what happens to error signals
sent forward up to the next higher level where the expectations are adjusted
what happens if a mismatch between prediction and reality?
prediction error is generated
what happens to the prediction error
sent up the heirarchy, causing the revision of the hypotheses at the level above. if the next level up cant minimize the prediction error, then the prediction error gets pushed farther up the system
what does a higher level in the hypothesis levels mean?
more substantail revision of the hypothesis
when does preception happen
when the prediction error is minimized with the winning hypothesis forming the contents of the preception
basics of the egner paper
used an encoding approach to fMRI to empirically test predictions stemming from predictive coding models against feature-based models of object perception in the ventral stream
egner paper big picture question
does the predicitive coding explain visual objects recognition better than classic heirarchal feature-based model?
how was the big picture question in the egner paper studied?
by taking advantage of what we know about category selective populations of neurons in the fusifor face area (FFA) and parahippocampal place area (PPA)
what are the 2 views of visual perception according to egner paper?
perdicitive coding:
perception is inference
2 units at every level of visual hierarchy (representation (expectation)) or error (surprise)
feature detection:
visual neurons just respond to features of an object
ex: FFA neurons respond to face features such as eyes, facial configuration, etc
what was the research question of the egner paper
does BOLD activity in the FFA refelect responses to expectation and surprise? Or just face features
what was the general hypothesis of the egner paper
FFA activity will be an additivie function of expectation and surprise
what was the alternative hypothesis of the egner paper
there will alays be more FFA activation to faces (expectation and surprise will not matter)
experimental design of egner paper
fMRI study
coloured fram was shown before a face or house stimulus appeared.
participant had to press a button whenever they saw an upside down face or house (target)
manipulated expectation by saying different coloured squares had different likelihood of face of house being shown
what was the point of the upside down target in the egner paper
keep attentional demands constant across condtions, so their results couldn’t just be explained by differences in attention
independent and dependent variables of egner paper
independent: stimulus probability (% of time it is a face vs a house), stimulus feature (house or face), target vs non target (upside down or not)
dependent: reaction time, BOLD in FFA and PPA
results of the fMRI in egner paper
predictive coding prediction: biggest difference btwn faces and houses with low face expectation
FFA activity looks most like the coding models predictions
conclusions of the egner paper
bottom up feature detection model: neurons respond to features that match preferred stimulus
predictive coding model: representation units code expected features. Error units code mismatched between expected signal and actual signal from the world
key points of feature detection model
feedforward volley of sensory information
heirarchal
feature focused
key points of feature detection model
feedforward volley of sensory information
heirarchal
feature focused
key points of predictive coding (PC) model
expectations/predictions: based on memory/experience
what is inattentional blindness
failure to see fairly major changes to a visual scene when you’re attending to something else
what is change blindness
failure to see gradual changes when they are not the center of focal attention
overt vs covert attention
whether you are attending something by using your eyes or just your mind
selective attention
select info that is relevant and filter out info that is irrelevant.
selective attention can be overt or covert
overt attention
the eye moves to focus on the objects of attention
covert attention
you attend to an area of spaces but the eye does not move
object of attention is in your peripheral vision
how does selective attention hapen
when you filter the world so that you attend to what is important and ignore what is not
top down attention system
deliberate, conscious, goal directed, attentional set
mental templates that allow us to selectively attend to a certain category of stimulus before it appears.
involve holding in mind features or location of the object you’re expecting
bottom up attention system
involuntary, captures attention, despite our goals, feature based
dorsal attentional networks
top down
frontal eye fields, intraparietal sulcus
ramps up brain regions for space or features that are relevant to what you are focused on
ventral attentional networks
bottom up
ventral frontal cortex, temporoparietal junction
both regions influence activity in the visual cortex
what is biased competition
even before you see something, holding an attentional set primes the neurons that respond to what you’re attending to and suppresses the ones to competing areas or features
what is feature based attention
bottom up
what is task based attention
top down
what mediates top down and bottom up
DAN and VAN respectively
how is sustained attention measured
by the sustained attention to response task (SART)
see a series of letters, usually have to press a button when you see all but one of the letters, but one letter signifies that you need NOT press the button
if you zone out and automatically press the button, it takes concentration to remember to not press the button
difficulties in sustained attention
easily distracted by non relevant stimuli
often forgetful in daily activities
difficulty sustaining attention during activities
difficulty following instructions/failing to complete tasks
missing details/making mistakes
avoidance of activities that require sustained mental effort
positive incentive/seeking system
motivational system linked to emotional feelings of hope, anticipation, and desire
DA is v important here
fear system
evoked by pain and threat of destruction
linked to emotions of anxiety, alarm, foreboding
high stimulation of the system is run, low stimulation is freeze, humans report intense anxiety when stimulated
rage system
when the body is restrained, irritated, or frustrated
associated with feelings of hate, anger, and indignation
panic system
triggered by social loss
feelings of separation distress, loneliness, grief
based on mammalian need for parental care/nursing when offspring are young and over the lifetime for warmth and affiliation
what is the amygdala the hub for
motivated attention
tags what is biologically important
what problem does the amygdala solve
limited capacity information processing system that receives a constant stream of diverse inputs selectively process those inputs that are the most relevant to the goals of the animal
how does the amygdala related to the visual cortex
it modulates it
emotionally salient
cature attention- something stands out from its surroundings because of its emotional relevance. grabs attention
how did we first learn about the role of the amygdala in emotionally biased attention
from the study of patient SP. SP had amygdala lesions on both sides from severe epilepsy (right was surgically removed and left was damaged by seizures).
how did they test SP’s emotions guided their attention?
attentional blink task
what is an attentional blink
when you fail to see a second target stimulus in a stream of stimuli when it comes too soon (within half a second) of a first target stimulus
what is emotional sparing
an emotional attention set for guiding attention to things that are emotionally relevant
what kind of attentional process does manipulating visual similarity get at?
bottom up - VAN
what was the conclusion of the study with SP
the amygdala influences selective attention for emotional relevance but not perceptual salience
emotional experience of SP and control people
they experience no difference in positive or negative emotions over a 30 day period
what happens in an attentional blink task with people who survived a near plane crash
they are more likely to see words related to a plane crash
what is the difference between fear and anxiety
fear is when there in an identifiable threat in the near future.
anxiety is about threatening things that could happen in the future, its the fear system kicking into over drive
how does anxiety affect our attentional bias for threat
amygdala is more sensitive to threat than reward
leads to elevated physiological response, sensory processing, memory, rumination
attention is captured by threatening stimuli
capture is followed by avoidance (you stop attending the thing you find threatening)
how have the grade A blue ribbon emotional systems been conserved
evolutionarily
what does the amygdala do
tags emotional salience and routes info to other brain regions to enhance attention (as well as learning and memory)
what can loss of amygdala result in
impaired attention to what is emotionally relevant
what is the amygdala key for
tuning attention to what is relevant in the world based on experience
what happens to amygdala and attentional bias in anxiety and PTSD
attentional bias to threat is extreme, and amygdala systems can go into overdrive and hurt more than they help
michael posner covert attention task
observers are instructed to look out for the appearance of a visual target in the periphery of their vision, but they are also told to keep their eyes fixed on a central dot
results of michael posner’s covert attention task
the targets on the attended side are detected more quickly than the targets on the unattended side.
if people are scanned during covert attending what is seen
an enhancement in activation in the intraparietal sulcus and in the frontal eye field
what makes up the dorsal attention system
frontal eye field and cortex in the intraparietal sulcus
what is an anatomical system
group of areas that are closely interconnected
what is resting state covariance
spontaneous activity in these areas varying in synchrony
in the dorsal attention system, how is the coretx in the intraparietal sulcus and the frontal eye field mapped
spatially
letter cancellation task
display of different letters is presented and the person is asked to cross out or cancel all the exemplars of a particular letter. usually used as a diagnostic test for the clinical syndrome of spatial neglect
how does spatial neglect tend to happen
strokes that involve the right parietal cortex, usually including the inferior parietal cortex
what forms the ventral attention system
inferior parietal cortex and TPJ (temoro-parietal junction)
TPJ implication
forms a critical node at which the temporal and parietal cortex can interact
shulman and corbetta task
had some features of the letter cancellation task.
had to detect a particular object amongst an array of objects presented on either side of the central point.
a cue specified which side there were to attend to and the target object always appeared amongst the objectives on the attended side.
attention was covert because the observers were required to keep their gaze on the central point
main findings of shulman and corbetta’s task?
when targets were detected there was activation on the right inferior parietal cortex and TPJ irrespective of whether the targets were on the left or right (activation on the left was only when targets were on the right)
dorsal and ventral attention systems activations were greater when attention was shifted to the other side rather than being directed to the same side as on previous trial. true for right TPJ irrespective of which side it switched, but in the left TPJ it was only greater for switches to the right
cortex in the intraparietal sulcus of each hemisphere is involved in
attending to the opposite side of space
what region is involved in recognizing targets
temporal lobe
Kaster’s experiment
photos shown of cluttered scenes, some had people, or cars, or trees.
critical displays had both people and cars
people were targets (positive), cars were distractors (negative), trees were not relevant (neutral)
results of Kaster’s experiment
MVPA identified patterns of activation to see what class of objects was being shown.
analysis was performed in the activations of temporal lobe involved in recognition of objects
it was easier to identify people than trees, but more difficult to identify cars than trees.
while representation of the targets was enhanced, the distractors was suppressed.
buchel task
scanned people while they had to remember a series of tine and at the same time they were presented with distracting pictures of objects.
distraction reduced the activation in the LO complex, especially when the auditory memory task was difficult
suggests that info in the irrelecant visual stream was inhibited
how does distraction affect pain
when someone is distracted while pain is applied, they report less pain
this originates from the prefrontal cortex. sends connections back to higher sensory areas (top down). these signals seem to evoke a release of opiates in the system and it is the release that moderates pain
what area is involved in setting up a task
prefrontal cortex
3 ways top down can signals can exert a selective effect
set up the task by enhancing processing in the relevant sensory stream
set up the targets by creating a template against which they can be matched
if the task is performed with distractions, the can inhibit the processing in the irrelevant stream
