early 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

Early Selection

• Early Selection model failed to explain some findings

• Shadowing studies found that certain information could “intrude” into the attended stream– Subject’s name, loud

noises, etc.

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

• The theory is that attention acts as an early selection filter

• The prediction is that selective auditory attention modulates early responses in the auditory pathway

• Hernandez-Peon (1956)– Electrodes in cats– Attended tones elicited more rapid spike trains

What was the critical confound?


• Failed to rule out overt orienting– Cats can orient their ears without moving their heads– Not surprising that auditory responses went up when cat

swiveled its ears

• Solution was to careful monitor subject’s orienting with eye trackers and present stimuli through headphones

Modulation of Auditory Pathways• Hillyard et al. (1960s)

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


• 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


• 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 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



– 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!

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Tata et al. (2001)

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Tata, Prime, McDonald, & Ward (2001)

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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)

early selection

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