Jochen Triesch, UC San Diego, triesch 1 Attention Outline: Overview bottom-up attention top-down...

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Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 1

AttentionAttention

Outline:

• Overview

• bottom-up attention

• top-down attention

• physiology of attention and awareness

• inattention and change blindness

Credits: major sources of material, including figures and slides were:

• Itti and Koch. Computational Modeling of Visual Attention. Nature Reviews Neuroscience, 2001.

• Sprague, Ballard, and Robinson. Modeling Attention with Embodied Visual Behaviors, 2005.

• Fred Hamker. A dynamic model of how feature cues guide spatial attention. Vision Research, 2004.

• Frank Tong. Primary Visual Cortex and Visual Awareness. Nature Reviews Neuroscience, 2003.

• and various resources on the WWW

How to think about attention?

• William James: “Everyone knows what attention is”

• overt vs. covert attention

• attention as a filter

• attention as enhancing the signal produced by a stimulus

• tuning system to a specific stimulus attribute

• attention as a spotlight

• location-, feature-, object-, modality-, task- based

• attention as binding together features

• attention as something that speeds up processing

• attention as distributed competition

Important QuestionsImportant Questions

• what is affected by attention?

• where in the brain do we see differences between attended/unattended conditions?

• what controls attention?

• how many things can you attend to?

• is attention a useful notion at all? Or is it too blunt and unspecific?

Bottom-up AttentionBottom-up Attention

Points to note:

• saliency of location depends on its surround

• integration into single saliency map (where?)

• inhibition of return is important

• how are things updated across eye movements

• purely bottom-up models provide very poor fit to most experimental data

Looking to maximize visual Looking to maximize visual rewardreward

• infants may be primarily driven by visual saliency• at about a year of age they start with gaze-following:

• “looking where sombody else is looking”• foundational skill important for learning language, ...• does not emerge normally in certain developmental

disorders• theory: they learn to exploit the caregiver’s direction of gaze as

a cue to where interesting things are

G. Deák, R. Flom, and A. Pick(18 and 12 month-olds)

Infant:• can look at CG or any region of space• only sees what is in the region it looks at• decides when and where to shift gaze

discrete regionsof space (N=10)

interesting object/eventin one location, some-times moving randomlycaregiver (CG) looks at object

with probability pvalid

Carlson & Triesch (2003):

Overview of Infant ModelOverview of Infant Model

Infant model is simple two agent system (Findlay & Walker, 1999):• “when agent” decides when to shift gaze• “where agent” decides where to look

“when” agent:shift gaze?

“where” agent:where to?

yes/no

new location

fixation timeobject in view

inst. reward

CG in viewCG head pose

instantaneous reward(habituating)

Infant Model DetailsInfant Model DetailsHabituation: reward for looking at an object decreases over time:

),(),(

~ where,

exp),(

1 ttta

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asQasQ

asQasp

Softmax action selection balances exploration/exploitation (τ >0: temperature)

)exp()0(fixfix thRrt

β: habituation rate, hfix(0) habituation level at beginning of fixation,t: time since start of fixation

Q(st,at) = Q(st,at) + α[rt+1 + γQ(st+1,at+1) - Q(st,at)]

TDerror

Agents learn with tabular SARSA algorithm:Q: state action value, α: learning rate

Simulation ResultsSimulation Results

• basic set indeed sufficient for gaze following to emerge• model first learns to look at CG, then learns gaze following

Caregiver Index (CGI):ratio of gaze shifts to CG

Gaze Following Index (GFI):ratio of gaze shifts followingCG’s line of regard

learning time

(error bars are standarddeviations of 10 runs)

Variation of Reward Variation of Reward StructureStructure

no learning if things that CG looks atare not rewarding

learning poor if CGtoo rewarding

(Williams syndrome?)

no learning if CG aversive(Autism?)

time untilGFI>0.3

Scheduling Visual RoutinesScheduling Visual RoutinesSprague, Ballard, and Robinson (2005):• VR platform to study visual attention in complex behaviors

where several goals have to be negotiated (“Walter”)• rewards are coupled to successful completion of behaviors

Abstraction hierarchy:

Behaviors modeled as RL agents:

Maximum Q Values and best actions:

obstacle avoidance sidewalk following litter pickup

Growing uncertainty about state unless you look:

• control of eye gaze by behavior that experiences biggest loss due to uncertain state information

• switching contexts with a state machine:

• comparing Walter to Human subjects in same task: how often does a behavior control gaze in the “on sidewalk” context?

• comparing Walter to Human subjects in same task: which behavior controls the eye gaze across different contexts?

Modulation of V4 activityModulation of V4 activityMotter (1994)

ModelModelHamker (2004)

Feedback from higher level exerting input gain control:

a. switching from red to green.b. spatial effects due to feedback from premotor areas

Model vs. Experiment:

ExperimentModel

Detection of stimuli and V1 Detection of stimuli and V1 activityactivity

Super, Spekreijse, and Lamme (2001):• monkey’s task: detect texture defined region and saccade to it• record from orientation selective cell in V1• how is cell’s response correlated with monkey’s percept?

• enhancement of late (80-100ms) response only if target is actually detected by the monkey

“seen” “not seen”

Jochen Triesch, UC San Diego, triesch 1 Attention Outline: Overview bottom-up attention top-down...

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