Visual AttentionVisual Attention

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

surrounding environment

• A reliable measure of attention is eye movement during

object (target) selection

• Early studies show that there are specific brain regions that

are involved in the process of target selection

Visual AttentionVisual Attention

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

surrounding environment

• A reliable measure of attention is eye movement during

object (target) selection

• Early studies show that there are specific brain regions that

are involved in the process of target selection

– Superior Colliculus

Visual AttentionVisual Attention

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

surrounding environment

• A reliable measure of attention is eye movement during

object (target) selection

• Early studies show that there are specific brain regions that

are involved in the process of target selection

– Superior Colliculus

– Frontal Eye Field

Visual AttentionVisual Attention

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

surrounding environment

• A reliable measure of attention is eye movement during

object (target) selection

• Early studies show that there are specific brain regions that

are involved in the process of target selection

– Superior Colliculus

– Frontal Eye Field

– Extrastriate Areas (V1, V4, IT)

Superior Colliculus & Target Superior Colliculus & Target Selection: Early StudiesSelection: Early Studies

• Cells in the superficial layers of the SC respond to light

falling on a specific area of the retina

• Visual response occurs 50ms after stimulus onset even

when the stimulus appears in the RF and the monkey

maintains fixation

Superior Colliculus & Target Superior Colliculus & Target Selection: Early StudiesSelection: Early Studies

• Enhanced visual response when the stimulus appears in the

cell’s receptive field AND the monkey selects it as a target

and saccades (overtly attends) to it. Latency of saccade is

about 200ms

• Activity is greater for target + saccade than for target

Superior Colliculus & Target Superior Colliculus & Target Selection: Early StudiesSelection: Early Studies

• No enhanced response when the monkey saccades to a

stimulus outside the receptive field (or in total darkness)

Superior Colliculus & Target Superior Colliculus & Target Selection: Early StudiesSelection: Early Studies

• No enhanced response when the monkey covertly attends

to the stimulus in the receptive field

• At least this is what they found back then

Conclusions from Early StudiesConclusions from Early Studies

• Early studies suggest that the superior colliculus is involved

in the selection of targets for eye movements

– Not just a visual response to stimulus

– Not just a motor response to saccade

• Greatest level of activity is found when both a target is

presented and a subsequent saccade is made to that target

Target Selection and UncertaintyTarget Selection and Uncertainty

• Behavioral Task – Uncertainty period: array of

possible targets presented

– Selection period: one of the

targets is dimmed

– Removal of fixation signaled

saccade initiation

• Manipulated uncertainty by

varying the # of possible

targets (distractors)

• Recorded activity in SC

intermediate layer neurons

Visual Response Modulated by Visual Response Modulated by Uncertainty / # of DistractorsUncertainty / # of Distractors

• Response during stimulus

onset in the uncertainty

period decreases as the #

of distractors (uncertainty

level) increases

• Response during selection

and saccade initiation were

not significantly different

regardless of uncertainty

The Frontal Eye Field & Target The Frontal Eye Field & Target SelectionSelection

• FEF cells respond to visual stimuli like the SC

– Greater activity for spots of light in the receptive field

– RF is larger: as big as a ¼ of an entire visual field

Decreased Activity with Increased Decreased Activity with Increased Uncertainty / # of DistractorsUncertainty / # of Distractors

Superficial LayersSuperficial Layers

Intermediate andIntermediate andDeep LayersDeep Layers

Extrastriate CortexExtrastriate Cortex(e.g. V4, MT)(e.g. V4, MT)

Parietal Cortex (LIP)Parietal Cortex (LIP)

Frontal Eye FieldFrontal Eye Field

Medio-Dorsal ThalamusMedio-Dorsal Thalamus

Striate Cortex (V1)Striate Cortex (V1)

RetinaRetina

Brainstem SaccadeBrainstem SaccadeGeneratorGenerator

SCSC

Major Connections of the Superior Major Connections of the Superior ColliculusColliculus

Superficial LayersSuperficial Layers

Intermediate andIntermediate andDeep LayersDeep Layers

Extrastriate CortexExtrastriate Cortex(e.g. V4, MT)(e.g. V4, MT)

Parietal Cortex (LIP)Parietal Cortex (LIP)

Frontal Eye FieldFrontal Eye Field

Medio-Dorsal ThalamusMedio-Dorsal Thalamus

Striate Cortex (V1)Striate Cortex (V1)

RetinaRetina

Brainstem SaccadeBrainstem SaccadeGeneratorGenerator

SCSC

Major Connections of the Superior Major Connections of the Superior ColliculusColliculus

Early Studies of Target Selection Early Studies of Target Selection Activity in FEFActivity in FEF

• Detection Task– Target presented alone– Goal: saccade to target

• Visual Search Task– Target with distractors– Goal: saccade to target

• Recorded neural activity in FEF at two time intervals:– 100ms after stimulus onset– 100ms before saccade

Selection-Dependent Visual ActivitySelection-Dependent Visual Activity

• Enhanced response when

the target is in the RF

• Greater response for target

alone (detection) than with

distractors (search)

• Suppressed activity when

the target is near the RF

only in search trials

Target Selection in FEF NeuronTarget Selection in FEF Neuron

• Detection Trials– Activity decreased as distance

from RF increased

• Search Trials– Initial activity is the same,

since a stimulus (distractor) is

always present

– Enhanced activity for target in

RF

– Suppressed activity for target

near RF

Go / No-go TaskGo / No-go Task

• Monkeys fixated on white spot

• Trigger signal: change of color

– Go trial (solid square): shift gaze to the target – saccade

– Nogo trial (asterisk): maintain fixation – no saccade

• Color change can occur before, during or after target onset

Neural Response for Go & No-go TrialsNeural Response for Go & No-go Trials

Evidence for Center-Surround ActivityEvidence for Center-Surround Activity

FEF Connects to Extrastriate CortexFEF Connects to Extrastriate Cortex

Target Selection in V4Target Selection in V4

Visual Properties of IT NeuronsVisual Properties of IT Neurons

• Neurons respond selectively to complex objects

– Input: V1 and V4 (feature detection)

– Output: entorhinal cortex hippocampus (memory)

• Large receptive fields that always include the fovea

• Retinotopic organization is absent

• Invariant Properties

– Scale invariance: insensitive to changes in stimulus size

– Translation invariance: insensitive to changes in position

• Columnar organization

• IT neurons are expected to be involved in more complex

aspects of target selection

Experimental DesignExperimental Design

• Good (square) and poor

(triangle) stimuli were

selected prior to task

• Sequence of Events

– cue delay target

– Saccade to target that

matches the cue

• Block trial: used one cue

for 20 – 30 trials

• Recorded activity in IT

IT Neurons Carry Target InformationIT Neurons Carry Target Information

Next Week’s ReadingsNext Week’s Readings

• McPeek & Keller: effects of superior colliculus inactivation

on target selection

• Bichot & Schall: responsiveness of FEF to target similarity

and history

• Sheinberg & Logothetis: inferotemporal cortex and natural

target selection of familiar objects