Covert AttentionMariel Velez4-28-2005

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

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

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

Direct gaze may be interpreted as hostile

Covert Attention

Frontal Eye

Fields

Posterier Parietal

Cortex (LIP)

SC

V4

1

2

3

4

FEF, SC

saccade-only enhancement

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

Effects of attention on PPC

Mountcastle VS Goldberg and Friends

Lynch, Mountcastle, Talbot and Yin-1977

MOTOR COMMAND HYPOTHESIS-presaccadic burst specific to saccade

Recording from Area 7 (Posterior Parietal Cortex

“Saccade Neurons”- presaccadic burst only when monkey makes a saccade—

NOT activated by visual stimulus

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

ATTENTION-Enhancements of presaccadic activity in the absence of saccades

Goldberg Task• What is the relationship between LIP activity and

enhanced behavioral performance during attention?

• Correlate firing of LIP with performance

Effects of attention on visual cortex

Moran and Desimone 1985Delayed Match to Sample Task

Attention filters out irrelevant stimuli

Attentional effects all over visual cortex-MT, MST

(Treue and Maunsell J Neurosci. 1999 )

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

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

Monkey attends to receptive field stimulus

Receptive Field (RF)of a V4 neuron

RF stimulus

Monkey attends elsewhere

Attention modulates V4 tuning

V4• But attentional signals can represent motor preparation

(intention ) AND visual selection (attention)

Information about visual targets guides the saccade

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)

Role of oculomotor mechanisms in spatial attention-

FEF, SC

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

Moore 2003How is FEF modulating individual V4 neurons?

Is the FEF an oculomotor salience map?

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?

Wurtz’ Change Blind Task

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

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

Change Blind Task

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

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?

Red-Bottom up Waldo-Top down

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

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