Attention as Information Selection. Early Selection Early Selection model postulated that attention...

Attention as Information Selection

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)

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

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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

• 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

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

– The ‘bottleneck’ in a sustained shadowing paradigm is at least as early as ~100 ms

– The ‘bottleneck’ in a visual search paradigm can be at least as early as ~200ms and appears at least as “low” in the visual system as V4 (but note that 200ms is long enough for substantial feedback connections to be active)