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Covert Attention Mariel Velez 4-28-2005. What is attention? . Attention is the ability to select objects of interest from the surrounding environment Involuntary vs Voluntary Spatial vs Object Overt vs. Covert. Attending to a stimulus enhances neural response to that stimulus.

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Covert Attention Mariel Velez 4-28-2005

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Covert attention mariel velez 4 28 2005 l.jpg

Covert AttentionMariel Velez4-28-2005


What is attention l.jpg

What is attention?

  • Attention is the ability to select objects of interest from the surrounding environment

  • Involuntary vs Voluntary

  • Spatial vs Object

  • Overt vs. Covert

Attending to a stimulus enhances neural response to that stimulus

Salience: Represents how important a visual signal is: adds weights to incoming signals according to some feature


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Covert Attention

Ability to attend to a stimulus without shifting one’s gaze towards it

Direct gaze may be interpreted as hostile


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3

1

Frontal Eye Fields

Posterier Parietal Cortex (LIP)

2

V4

4

SC

FEF, SC

saccade-only enhancement


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LIP, FEF, SC

  • Bisley JW and Goldberg ME. Neuronal activity in the lateral intraparietal area and spatial attention. Science 299:81-86, 2003

  • Moore T, Armstrong KM. Selective gating of visual signals by microstimulation of frontal cortex. Nature 421:370-3, 2003  

  • Cavanaugh, J and Wurtz, R.H. Subcortical Modulation of Attention Counters Change Blindness. JofNeuroscience 24(50): 11236-11243, 2004


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Effects of attention on PPC

Mountcastle VS Goldberg and Friends


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Recording from Area 7 (Posterior Parietal Cortex

Lynch, Mountcastle, Talbot and Yin-1977

“Saccade Neurons”- presaccadic burst only when monkey makes a saccade—NOT activated by visual stimulus

MOTOR COMMAND HYPOTHESIS-presaccadic burst specific to saccade


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ATTENTION-Enhancements of presaccadic activity in the absence of saccades

Bushnell, Goldberg, Robinson 1981

  • “Impossible to determine whether the relationship of neuronal response to eye movements was specific to that movement or more related to the attentional mechanisms that are associated with eye movement”

  • Need to dissociate the oculomotor process with the attention of the stimulus----COVERT ATTENTION


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Goldberg Task

  • What is the relationship between LIP activity and enhanced behavioral performance during attention?

  • Correlate firing of LIP with performance


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Effects of attention on visual cortex


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Moran and Desimone 1985

Delayed Match to Sample Task

Attention filters out irrelevant stimuli


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Attentional effects all over visual cortex-MT, MST

When one of the receptive field stimuli was the attended dot, the response of the neuron was strong whenever that dot moved in the preferred direction

(Treue and Maunsell J Neurosci. 1999 )


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McAdams and Maunsell (1999) J Neurosci. 19:431-441.

Attention modulates V4 tuning

Monkey attends to

receptive field stimulus

Receptive Field (RF)

of a V4 neuron

RF stimulus

Monkey attendselsewhere


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V4

  • But attentional signals can represent motor preparation (intention ) AND visual selection (attention)

Fovea’s landing point along the bar could be predicted by the degree to which V4 cells coded that bar prior to the saccade (Moore 1999)

Information about visual targets guides the saccade


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Role of oculomotor mechanisms in spatial attention-FEF, SC


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FEF

  • Stimulation evokes saccades-Amplitude and direction of saccades are organized retinotopically

  • Goldberg-no covert attn effects. Related to saccades specifically

  • Reciprocally connected to lots of posterior visual areas including V4

  • Should be able to drive spatial attn by perturbing oculomotor signals


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Moore 2003

How is FEF modulating individual V4 neurons?

Is the FEF an oculomotor salience map?


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SC: target selection vs attention

  • SC presaccadic activity—gateway to the Brainstem Saccade Generator

  • McPeek and Keller (2004) SC inactivation causes defects in target selection by reducing behavioral salience.

  • SC is providing some info to visual cortical areas:

  • Can SC microstimulation affect attention?


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Wurtz’ Change Blind Task

Change blindness-”failure to see large changes in a visual scene that occur simultaneously with a global transient (ie blanks between visual scenes)”

Cue to the area of visual change counters change blindness

Replace visual cue with SC microstimulation to see if this counters change blindness


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Change Blind Task

ftp://lsr-ftp.nei.nih.gov/web/jc/cb_demo.htm


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Salience map

  • Represents how important a visual signal is: adds weights to incoming signals according to some feature

  • “ Activation of a particular subset of the map would strengthen the representation of whatever stimulus is positioned at the corresponding point in space, while failing to alter its identity”

  • Where is (are) the salience map (s)?

  • What other features are in a salience map?

  • Is there a corresponding “not salient map” ?

  • Are there multiple salience maps? How would these multiple maps interact?

  • Top down vs bottom up?


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Red-Bottom up Waldo-Top down


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LIP, FEF, SC

  • Bisley JW and Goldberg ME. Neuronal activity in the lateral intraparietal area and spatial attention. Science 299:81-86, 2003

  • Moore T, Armstrong KM. Selective gating of visual signals by microstimulation of frontal cortex. Nature 421:370-3, 2003  

  • Cavanaugh, J and Wurtz, R.H. Subcortical Modulation of Attention Counters Change Blindness. JofNeuroscience 24(50): 11236-11243, 2004


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Covert Attention-Early Psychophysical Studies

Premotor Theory—(Rizzolatti et al. 1983, 1987)

Subjects instructed to hit button as soon as the stimulus appeared

RT increased when stimulus is presented in a location different than the attended one. An even larger increase in RT occurs when stimulus appears in non-attended location in the opposite hemifield

Premotor Theory-Motor Program controls covert orienting: distance and direction changes modify the program which increases the RT


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