Test Oct. 21 Review Session Oct 19 2pm in TH201 (that’s here)

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:


– 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:

– What has to happen in order for this task to be accomplished?

“point to the vertical line”


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?


Attention as Information Selection– What if the scene gets more complex?


Attention as Information Selection– What if the scene and task gets more complex: “Point to the red vertical

line”?



• 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


• 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?)


• 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

• 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

attending LEFTIgnoring RIGHT

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


• Different ways to use attention in space



attending LEFTIgnoring RIGHT


now left, now right, now left, now right


SUSTAINED TRANSIENT


• 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


TRANSIENT


• Transient Attention: The Target-Target Paradigm

– Three speakers– Steady stream of tones– Respond to each tone




BEEP







BEEP







BEEP







BEEP



– We can compare targets preceded by targets at the same location with targets preceded by targets on the other side



– Does transient attention modulate auditory system like sustained attention?


• ERP is markedly different in the two situations!

100

200

300

400

500

Tata et al. (2001)

CZCZ

Tata, Prime, McDonald, & Ward (2001)

100

200

300

400

500

Tata et al. (2001)

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+


• ERP is markedly different in the two situations!

• One possibility:– sustained attention allows for attentional

configuration of sensory cortex to modulate feed-forward sweep but…

– Transient attention can only modulate recurrent processes


• Earliest attention-related component (called the Nd1) is over contralateral posterior scalp - not primary cortex

Tata & Ward (2005)

• 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:


“effective” stimulus at attended location – attention spotlight has selected object with features to which this neuron is tuned

Response to Target

“effective” stimulus at unattended location – attention spotlight has selected object with features to which this neuron is not tuned

Response to “Sample”

Response to Target

Response to “Sample”

• 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


• 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



• 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


• Initial response of cells is “classical”



• Response during delay maintains a representation of the target feature



• Response during delay represents the target feature

• Initial response to search array is “classical”


• 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


• Conclusion: – Attentional selection of locations and/or objects

has physiological correlates and consequences

• How does attention get to where it needs to go?

Documents

Test Oct. 21 Review Session Oct 19 2pm in TH201 (that’s here)