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Lecture 7

PSYB51H3 Lecture Notes - Lecture 7: Change Blindness, Extrastriate Cortex, Search Theory


Department
Psychology
Course Code
PSYB51H3
Professor
Niemier
Lecture
7

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PSYB51-lecture 7
What is the univariance problem in colour perception? How does our colour solve the
problem?What is the horopter?
Univariance problem is where you might have a photoreceptor that might itself contribute
to colour perception but alone is not colour sensitive because signal is ambiguous. SO
whatever light enters and stimulates photoreceptor, we dont know what wavelength it is
because any combination of wavelength and light energy can produce any kind of output of
this. The solution is that you have more than one colour sensitive photoreceptor (ie
red,green and blue cones in retina, the combination of the output of these 3 cones tells us
what colour we are looking at)
What is the heropter?
We get visions from 2 sources (eyes) so we have two versions (we have double vision)
But you can avoid it when you fixate your eyes on some object where the eyes
converge/diverge on that object; that means the fovea of the two eyes there is no double
image (there is one point of heropter, but there are many other points where its like this,
there are many other points in space where you dont have double vision, creating a circle)
Horopter-area where we dont have double vision
Selective attention is a cognitive brain mechanism that enables one to process(facilitating
mechanism) relevant inputs, thoughts, or actions while ignoring(suppressing) others that
are less important, irrelevant or distracting
-Arousal: several processes in brain are inhibited during sleep to ignore it,
it has to do with arousal
-Arousal and attention can interact, when you have very little arousal your
attention is low, as arousal increases attention increases as well, however
if arousal increases to a very high point, attention might be comprised
-Too much arousal can be detrimental to attention because you can have
motor deficiencies, problems concentrating, arousal activates all sorts of
sensitive input and too many to suppress
Why we need attention?
-Bottlenecks: it is impossible to process everything at once. Lace of brain,
lack of arms(just way too many information to process at the same time,
cant process all the details, too much going on); will need a big brain
which is a disadvantage, it will take up way too much energy
- Bottleneck exists at sensory, cognitive(thoughts etc)
- motor bottleneck involving muscle activity-we only have two arms etc.
-when something is relevant to us, we can focus on one thing and ignore
other things; ultimately we need to survive(so maybe we might miss
important details)
-in order to solve this problem we have various heuristics which dont work
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- attention helps us focus on things which have certain probability of being
more important than others
Where does attention play a role?
Attention to vision, audition/touch/smell, across modalities, thoughts (ie. Memory), motor
tasks
How can we study attention? We usually study it by looking at its effects
How can we measure attention?
-Look at how quickly the person is at responding(are the responding
appropriately or delaying, if delayed then chances are they are not paying
attention or looking at wrong thing); reaction times: a measure of the time
from onset of a stimulus to a response
-Perceptual thresholds: changes with attention
-Motor accuracy- athletes are very good at intentional tasks, they ahve to
look at motor tasks on regular basis
-Brain activity changes as a function of attention
-Behavioural change in attention (eye movements): indicates what we are
paying attention to, not a one on one connection (not completely
connected), can reflect overt shifts of attention. But careful; attention can
shift without eye movements: covert attention (you can shift attention
from where eyes are looking at but you can have trouble shifting eyes
without shifting attention- indicator of existence of eye motor programs
which cause shifting of attention
Cueing as a tool for examining attention
-Dont manipulate attention; first you see a stimulus on screen that you
asked to fixate on; later a stimulus comes up and press a button
depending on which side it comes from; or as soon as you see the object
(try to respond asap)
-Another stimulus(cue) is different from the stimulus you need to respond
to because it does not require a behaviour(ignore them, meaningless, dont
need to press button, these cues can appear anywhere)
-2 conditions: cue appears on same side or opposite side
-If cue is on the valid side(same side as stimulus you need to respond to)
reaction times are faster compared to the first condition where you have
cues which give neutral information(dont indicate which direction); more
prepared to responding to the red circle
-If cues appear on invalid side reaction time is slower
-This was taken as evidence for the fact that attention shifts between valid
and invalid side, and this shift seems to be involuntary( you were told to
ignore the circle, since here it was only accurate 50% of the time there is
no reason to expect it, but you cant help but shift attention) aka
Stimulus-driven shifts of attention
-3rd picture: arrow predicts which side the target appears, can be
incorrect, the arrow will point in the valid way 80% of that time maybe,
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then people learn/know that they can use the arrow to shift attention; it
make senses to process the arrow and then shift attention according to
arrow because most of the time its right; you find that people are more
faster valid condition than invalid or neutral conditions; this case there is
voluntary shifts of attention(some kind of cognitive process which is
intentionally used to shift attention; recent research seems to suggest
that arrow is actually involuntary, there are several symbols and cues
which seem to shift attn even if you dont want to)
What is the difference between stimulus-driven/peripheral and voluntary/symbolic?
-These two parts are made of two independent structures
-SOA: the time when arrow appears and the target stimulus for ie; it order
to figure out that arrow is a symbol it needs time because some require
longer time to process and thus SOA can have different effects, the point
at which you see there is a benefit in the paradigm will measured through
difference between invalid and valid reaction time and this will eventually
make you faster
-Benefit kicks in with some delay because it takes time to process, blue
curve(rises later on) versus red curve which is stimulus onset is automatic
where you have short delay, short delay and SOA plays a role more
quickly(attention shifts more quick)
-If you wait longer by making SOA really long, the voluntary cue you keep
attention there but at some point the benefit will decline at some
point(you see the benefit for a very long time)
-However for stimulus driven cue the benefit declines and the benefit is
gone at some point and then there is negative benefit(the place where you
had square appearing you respond slower than on the other side-called
inhibition of return(IOR) invented by Posner
-Indicates the difference between the two
When the smiley face gazes at certain side, your attention is diverted to that direction as
well
-Gaze is a social cue, you pay attention to what others pay attention
Covert attention is when you look at something, posner paradigm you are told to fixate eyes
on star
We are human beings who are asymmetrical leading to biases
-When it comes to gender, age perception etc we pay attention to left visual
field(the right part of the face) illustrates asymmetry...for motor control
the lips on the right side starts moving faster than left side, the side we
pay attention matters since language is primarily in left hemisphere
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