Test Oct. 21
Review Session Oct 19 2pm in TH201
(that’s here)
Test Oct. 21
Test will cover everything including
vision (i.e. including the lecture on
Friday Oct. 9th)
Attention
Controlling how information flows
through the brain
The Theory Is…
• Be able to complete this sentence by Nov 20
– This means you’ve completed some background
reading including some primary literature
– You’ve put lots of thought into crafting a testable,
focused theory and predictions that follow from
that theory
Attention as Information Selection
– consider a simple visual scene:
Attention as Information Selection
– consider a simple visual scene:
Attention as Information Selection
– consider a simple visual scene:
– What happens in the brain when this scene appears?
Attention as Information Selection
– consider a slightly more complex scene
– What happens in the brain when this scene appears?
Attention as Information Selection
– consider a slightly more complex scene and a simple task:
“point to the vertical line”
– What has to happen in order for this task to be accomplished?
Attention as Information Selection
That might not seem complex
because the visual target and
the output “device” are
represented by the same
hemisphere
Attention as Information Selection
– What if the scene gets more complex?
– What has to happen in order for this task to be accomplished?
Attention as Information Selection
– What if the scene gets more complex?
– What has to happen in order for this task to be accomplished?
Attention as Information Selection
– What if the scene and task gets more complex: “Point to the red
vertical line”?
– What has to happen in order for this task to be accomplished?
Attention as Information Selection
• problem: When those stimuli appear, activity
begins simultaneously among many different
neurons in the cortex. How does the rest of
the brain (memory, motor planning,
consciousness) know which is the target?
Attention as Information Selection
• It get’s trickier:
– Recall that the visual system
has two pathways:
what(ventral) and where
(dorsal)
– the dorsal pathway doesn’t
“know” anything about
orientation (or color or
complex forms or identities)
– The ventral pathway doesn’t
“know” anything about
location
– What if the scene is really
complicated!?
Point to Waldo
Attention as Information Selection
• One conceptualization of attention is that it is
the process by which irrelevant neural
representations are disregarded
(deemphasized? suppressed?)
• Another subtly different conceptualization is
that attention is a process by which the neural
representations of relevant stimuli are
enhanced (emphasized? biased?)
Attention as Information Selection
• These ideas apply to other
modalities
– auditory “Cocktail Party”
problem
– somatosensory “I don’t feel
my socks” problem
Early Selection
• Early Selection model
postulated that
attention acted as a
strict gate at the lowest
levels of sensory
processing
• Based on concept of a
limited capacity
bottleneck
Late Selection
• Late Selection models
postulated that
attention acted on later
processing stages (not
sensory)
Early Selection
• Early Selection model was
intuitive and explained
most data but failed to
explain some findings
• Shadowing studies found
that certain information
could “intrude” into the
attended stream
– Subject’s name, loud
noises, etc.
Late vs. Early
• Various hybrid models have been proposed
– Early attenuation of non-attended input
– Late enhancement of attended input
Electrophysiological
Investigations of Attention
Modulation of Auditory Pathways
• Hillyard et al. (1960s)
showed attention effects in
human auditory pathway
using ERP
attending LEFT
Ignoring RIGHT
• Selective listening task using
headphones
– Every few minutes the
attended side was reversed
– Thus they could measure the
brain response to identical
stimuli when attended or
unattended
beep beep
beep beep
boop beep
beep beep
beep boop
beep beep
Modulation of Auditory Pathways
• Result: ERP elicited by attended and unattended
stimuli diverges by about 90ms post stimulus
– Long before response is made
– Probably in primary or nearby auditory cortex
Modulation of Auditory Pathways
• Other groups have found ERP modulation even earlier –
as early as Brainstem Auditory Response
• Probably no robust modulation as low as cochlea
• by ~40 ms, feed forward sweep is already well into
auditory and associated cortex
– Thus ERP effects may reflect recurrent rather than feed forward
processes
Modulation of Auditory Pathways
• Different ways to use attention in space
attending LEFT
Ignoring RIGHT
beep beep
beep beep
boop beep
beep beep
beep boop
beep beep
SUSTAINED
now left, now right,
now left, now right
beep beep
beep beep
boop beep
beep beep
beep boop
beep beep
TRANSIENT
Modulation of Auditory Pathways
• Response times are
faster for attended
relative to unattended
targets
• The theory is that
transient and sustained
attention act on
auditory pathways the
same way
now left, now right,
now left, now right
beep beep
beep beep
boop beep
beep beep
beep boop
beep beep
TRANSIENT
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
BEEP
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
BEEP
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
BEEP
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
BEEP
– Three speakers
– Steady stream of tones
– Respond to each tone
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– We can compare targets preceded by targets at
the same location with targets preceded by
targets on the other side
Modulation of Auditory Pathways
• Transient Attention: The Target-Target Paradigm
– Does transient attention modulate auditory system
like sustained attention?
Modulation of Auditory Pathways
• ERP is markedly different in the two
situations!
-
CZ
CZ
500
500
400
400
300
300
200
200
100
100
+
Tata et&al.
(2001)
Tata
Tata, Prime, McDonald,
Ward
(2001)
et al. (2001)
Modulation of Auditory Pathways
• ERP is markedly different in the two situations!
• One possibility:
– sustained attention allows for attentional
configuration of sensory cortex to modulate feedforward sweep but…
– Transient attention can only modulate recurrent
processes
Modulation of Auditory Pathways
• Earliest attention-related component (called the
Nd1) is over contralateral posterior scalp - not
primary cortex
Tata & Ward (2005)
Intracranial Recordings of Attentional Selection
• Moran and Desimone (1985)
• “Classical” RF prediction: there should be no
difference in responses in these two conditions
Intracranial Recordings of Attentional Selection
• Moran and Desimone (1985)
• Result:
Response to “Sample”
Response to “Sample”
Response to Target
Response to Target
“effective” stimulus at attended location –
attention spotlight has selected object with
features to which this neuron is tuned
“effective” stimulus at unattended location –
attention spotlight has selected object with
features to which this neuron is not tuned
Intracranial Recordings of Attentional Selection
• Moran and Desimone (1985)
• Result:
– Neuron responds vigorously only if its effective
stimulus is attended
– Interesting caveat: this only applies when there is
an ineffective stimulus (to which the monkey
attends) present in the V4 RF
• When the ineffective stimulus is outside of the cell’s RF,
its responses are largely unmodulated
Intracranial Recordings of Attentional Selection
• Chellazi et al ( 1993) Neural Correlates of Visual
Search
– Monkey is trained in a delayed match-to-sample task
• Cue appears 1.5 seconds before search array
• Monkey saccades to target
– “good” and “poor” stimuli are identified for each
recorded neuron
Intracranial Recordings of Attentional Selection
•
Note that monkey isn’t “pre-cued” to
attend to a location
– Only target features are known prior
to choice array onset
•
With this paradigm it is possible to
measure cell activity during delay,
during search, and after selection
•
Note that search array always
contains a “good” stimulus for the
recorded cell – but that might not be
the target
Intracranial Recordings of Attentional Selection
• Initial response of cells
is “classical”
Intracranial Recordings of Attentional Selection
• Initial response of cells
is “classical”
• Response during delay
maintains a
representation of the
target feature
Intracranial Recordings of Attentional Selection
• Initial response of cells is
“classical”
• Response during delay
represents the target
feature
• Initial response to search
array is “classical”
Intracranial Recordings of Attentional Selection
• About 200 ms after array
onset, response of cell begins
to depend on attention
– Response becomes more
vigorous if cell is tuned to
features of the target (i.e. the
selected stimulus)
– Response becomes suppressed
if cell is tuned to a non-target
distractor
Intracranial Recordings of Attentional Selection
• Conclusion:
– Attentional selection of locations and/or objects
has physiological correlates and consequences
• How does attention get to where it needs to
go?