Psych 216:Psych 216:MovementMovement

Attention

What is attention?What is attention?

Covert and overt selection appear to recruit the same areas of the brain.

Imaging studies of attentionImaging studies of attention

• Functional imaging studies have been conducted in which blood flow or oxygen consumption in the brain was measured while visual attention tasks were performed by to determine what parts of the brain control covert attentional selection.

• These studies show parietal lobe activation during visual search and cueing tasks. This activity is consistent with several existing hypotheses.– 1) That parietal cortex controls the voluntary orienting

of attention to a location of interest.– 2) That parietal cortex controls the reorienting of

attention to new locations once one object or location has been attended.

Corbetta et al. (2000)Corbetta et al. (2000)

Measured blood flow while subjects performed a cueing task.

Frontal-parietal networkFrontal-parietal network

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Is attention just movement-Is attention just movement-related activity?related activity?

• Because similar brain areas are active when people shift gave and shift attention, researchers have proposed that shifts of attention are simply due to subthreshold activity in the neurons that control gaze.

• This is known as the premotor theory of attention.– “There are no such things as selective attention

circuits defined as anatomical entities separted from the spatial maps [that perform goal-directed, spatially coded movements].” Rizzolati, Riggio, & Sheliga

Premotor EvidencePremotor Evidence

• Shifting attention to more eccentric locations takes more time and horizontal shifts are slower than vertical. This pattern is similar to what is found when people make eye movements.

Rizzolatti et al. 1987

• A shift of attention appears to precede a shift of gaze to a location.

Kowler et al. 1995

– Difficult to attend to one location and make a saccade to a different location

Stimulating a oculomotor Stimulating a oculomotor area and covertly attendingarea and covertly attending

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Visual-response discriminability of V4 neurons

Armstrong K M, Moore T PNAS 2007;104:9499-9504

©2007 by National Academy of Sciences

Subthreshold FEF microstimulation enhances V4 response discriminability

Armstrong K M, Moore T PNAS 2007;104:9499-9504

©2007 by National Academy of Sciences

However, …However, …

• The areas that are active during shifts of attention and control shifts of gaze have a diversity of cell types.

• Microstimulation in a brain area can effect all of they different cell types.

• Showing that attention and eye movements have similar spatial characteristics and may interact does not mean they are the same thing.– Remember the differences in timing we talked about

last class.

Let’s consider some evidence Let’s consider some evidence for which the premotor for which the premotor

theory has difficulty theory has difficulty accountingaccounting

• The oculomotor structures (like FEF, LIP, & SC) have a diversity of cell types within them.

Let’s consider some evidence Let’s consider some evidence for which the premotor for which the premotor

theory has difficulty theory has difficulty accountingaccounting

• Movement related cells in oculomotor structures (like FEF or SC) are not wired to visual cortex in the back of the brain (V4, etc.) where attention effects are observed.

Green = connected to visual cortexRed = connected to SC

Other attention effectsOther attention effects

• Object-based attention– These are attention effects in which attention is

deployed to one of two spatially overlapping objects which are both fixated.

• Negative priming– Attending to one of two spatially overlapping objects

causes long-lasting suppression of the distractor.

ConclusionsConclusions• The structural (connectivity of different types

of neurons), physiological (responses of different types of neurons within an area), and psychological (evidence for attention effects that are not spatial) evidence does not support the proposal that attention is just movement-related activity.

• So, what is it. Mechanisms of selection (I.e., attention) appear to exist throughout the brain to resolve competition.– To recognize objects one at a time, make

one response at a time, store some information in memory and not everything.