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Interim 2 Lectures Notes - From Perception to Consciousness - 7202BP02XY
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From Perception to ConsciousnessLecture Summary Interim 2
Table of Contents
Lecture 9-10 – Attention ......................................................................................................................... 2
Lecture 11 – States of Consciousness ................................................................................................... 31
Lecture 12 – Conscious Control ............................................................................................................ 48
Lecture 13 – Free Will ........................................................................................................................... 68
Lecture 14 – To See or Not To See ........................................................................................................ 89
Lecture 15 – Theories of Seeing .......................................................................................................... 114
Lecture 16 – What is it Like to be a Fly? ............................................................................................. 153
,Lecture 9-10 – Attention
A lot can happen without you noticing. “Change blindness”. Your processing ability is limited.
Somewhere some sort of selection needs to happen between two systems, so you don’t react to
everything you see.
You have reverse hierarchical coding in
You have (distributed) hierarchical coding in the
sensory cortex. motor cortex.
From abstract notions to specific
These features low & high levels
muscle movements
The PERCEPTION – ACTION CYCLE
Processing goes from low to high level sensory cortex (hierarchical
processing) to extract ever more meaningful features from the
environment. These are then translated to motor outputs in a
reverse hierarchy, going from abstract motor commands to the
activation of – eventually – muscles (that in turn will influence the
environment).
But which sensory inputs are selected for action?
Attention → Which particular precepts are selected to perform actions on
A simple Dichotic Listening experiment with shadowing shows the limits of the perception action
cycle. Subjects hear two different auditory streams in the two ears. They can only reproduce (and
remembers, etc.) one stream at a time: the stream they attend to. The is limited capacity in going
from perception to action (or memory etc.)
This is the core function of attention: SELECTION.
,In the visual domain, attending is either achieved via overt or covert attention.
Overt orienting and attending
Moving your eyes, body, ears, nose, etc. in the direction of a relevant stimulus (what the superior
colliculus does).
Covert attention
Shifting your attention towards something, without any external, overt signs, i.e., while maintaining
fixation. This mechanism has evolved particularly in social animals, in which direction of gaze often
has strong meaning (threat, aggression, sexual attraction).
So:
Overt → Looking at what you’re attending to
Covert → Attending to something in your periphery.
Covert attention is the main way of studying attention.
Covert attention also exists in the auditory domain: The cocktail party effect (Cherry, 1953).
One may pretend to listen to someone in front of you, while actually focusing on what is said in
another conversation.
Or, while listening to the person in front of you, your attention may be suddenly captured by
someone saying your name in another conversation: attentional capture.
Attention Overview
• Different types of attention
• What is the effect of attention of processing?
• What happens to unattended stimuli?
• Who ‘controls’ attention (→ what directs your attention?)
• Disorders of attention
Types of attention
• Top-down attention / voluntary attention
• Capture / bottom-up attention
• Object based attention.
• Feature based attention.
, Top-Down attention:
when subjects are
instructed to focus
their attention on
some location of the
visual field (such as in
the Posner cueing
task). The behavioural
effect typically is that
reaction times to
presented targets are
faster at the attended
location.
This is about covert attention. The results are about what you would expect. In valid trials,
reaction time is always shorter. There are always more valid trials to keep the effect. Otherwise,
people won’t listen to the cues anymore.
Bottom-Up attention: a suddenly appearing
stimulus will automatically ‘capture’ attention.
Shorter reaction time to primed location. This
happens even when subjects know the cue
(prime) is mostly invalid (which shows capture
is ‘automatic’ and not top down).
Here, reaction time will still be shorter for valid trials, even when these are rare. It’s impossible to
suppress the attention being drawn to a suddenly appearing stimulus.
Attentional capture transforms into ‘inhibition of return’ when the temporal interval between prime
and target >300 ms. Now, reaction time is longer for the cued location. The subject starts to actively
suppress attention to the location of the (mostly invalid) cue.
This is a form of top-down processing.
Object based attention.
(John Driver)
Instead of focusing on a particular location, attention can also
focus on a particular object.
How to show the difference: curing C leads to faster detection of S
than of D (even when there is an occlude overlying the bars).
Attention can be directed towards objects that overlap in space.
(Issue: are these really non-spatial forms of attention? Or is spatial
attention simply spreading faster along objects, and can spatial attention
also work in 3D?)
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