Read this article for next week:

Read this article for next week:

A Neural Basis for Visual Search in Inferior Temporal CortexLeonardo Chelazzi et al. (1993) Nature

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By now you should have sorted out:The theory is that:The prediction is that:The best technique to test the prediction is:oThe experimental would work like this:

Attention Orienting System and Associated Disorders

Neglect, Extinction and Balint’s Syndrome

What system orients attention through space

• Attention is sometimes compared to a “mental spotlight”

• What system(s) control the spotlight?

What system orients attention through space

• 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 somewhat on which visual field attention was being shifted in

Orienting Attention

• Posner Cue - Target Paradigm:

Subject presses a button as soon as x appears

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

X

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

That was a validly cued trial because the x appeared in the box that flashed

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

X

Orienting Attention

• Posner Cue - Target Paradigm:

Orienting Attention

• Posner Cue - Target Paradigm:

That was an invalidly cued trial because the x appeared in the box that didn’t flash

Paradigms Used To Study Attention

• Posner Cue - Target Paradigm:

Attention Effect = Valid RT - Invalid RT

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, mainly on the left side (keep this in mind for discussing neglect)

Hemispatial Neglect

• Unilateral lesion to Parietal or Temporo-Parietal Junction

• Patients present with vision problems, but are not “blind”– Rather, they fail to

apprehend (and interact appropriately with) stimuli in the contralesional field

Hemispatial Neglect• E.g. line bisection

task

Hemispatial Neglect• E.g. reproducing visual forms

Investigation of Neglect with Cue-Target Paradigm

• Posner et al. (late 1970s) used a cue-target paradigm

• Parietal Lobe patients are profoundly impaired only when invalidly cued to attend to the ipsilesional (good) side

Attention as Information Selection

– Visual search

– 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)

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