Transcript Lecture 20 Powerpoint File

Consequences of Attentional
Selection
Single unit recordings
Consequences of Attentional Selection
• Selection of one location or object or auditory
stream has consequences for sensory
responses evoked by that stimulus
– ERP responses in auditory and visual cortex
• Are there effects of attentional selection
observable at the cellular level?
– This is going to require intracranial recordings
– What animal would you choose?
Intracranial Recordings of Attentional
Selection
• Moran and Desimone (1985)
• Recall that:
– Cells in ventral stream pathway are selective for color,
orientation, complex shapes
– “classical” notion of RF is that a cell should fire actively
whenever its preferred stimulus is present in its RF
– V4 RFs are a few degrees of visual angle – much larger than the
resolution of attention
• What happens when attention selects an object in a cell’s
RF if that cell isn’t “tuned” to the features of the object?
Intracranial Recordings of Attentional
Selection
• Moran and Desimone (1985)
– Response properties of cells are identified a priori
– Each cell is characterized by what is an “effective” and
“ineffective” stimulus
– Monkeys were trained to attend to one of several
locations within a V4 RF
– Monkey is given a target in a delayed match-tosample task
– Respond when target stimulus occurs at cued location
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:
Target Response
Attend “effective” stimulus
Attend “ineffective” stimulus
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,
it’s responses are largely unmodulated
Intracranial Recordings of Attentional
Selection
• What about the time course of this attention
effect?
• Are cells modulated in advance by the cue?
• Or are they modulated by attention when it is shifted to
the target location?
• What is needed is a experiment design such
that the monkey orients attention after the
target appears
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
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
represents 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 distracter
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?
Orienting Spatial Attention
• Corbetta et al. (1993)
– Subjects oriented
attention according to a
light moving in the visual
field
Orienting Spatial Attention
• Results:
– Parietal and Pre-motor
areas were activated by
attention tracking task
– Hemisphere of activation
depended on which
visual field attention was
being shifted in
Orienting Spatial Attention
• Corbetta et al (1993)
confounded stimulus w/
orienting
• Hopfinger et al. (2000) used
event-related fMRI to
identify top-down orienting
processes (distinct from
stimulus-driven processes)
– Cue-target paradigm using
arrows
– What is the brain activity
caused by the cue?
Orienting Spatial Attention
• Result:
– Cue-related activations
indicate a distributed
network that mediates
voluntary orienting
– Network includes mainly
frontal and parietal
structures
Orienting to Left
Orienting to Right