Chapter 7 - Visual Chapter 7 - Visual AttentionAttention

Cognitive overview of the Cognitive overview of the problem of attentionproblem of attention

What is Attention?What is Attention?““Everybody knows what attention is. It is Everybody knows what attention is. It is taking possession by the mind, in clear and taking possession by the mind, in clear and vivid form, of one out of what seem several vivid form, of one out of what seem several simultaneously possible objects or trains of simultaneously possible objects or trains of thought. Focalization, concentration of thought. Focalization, concentration of consciousness are of its essence. It implies consciousness are of its essence. It implies withdrawal from some things in order to deal withdrawal from some things in order to deal effectively with others , and is a condition effectively with others , and is a condition which has a real opposite in the confused, which has a real opposite in the confused, dazed scatterbrain state … “dazed scatterbrain state … “William James (1890)William James (1890)

What is Attention?What is Attention? ‘‘Taking possession of the mindTaking possession of the mind’’

– Controlling the focus of attention; intentionality; “Please Controlling the focus of attention; intentionality; “Please pay attention …”pay attention …”

‘‘one out of what seem several simultaneously one out of what seem several simultaneously possible objectspossible objects’’– Our apparent inability to attend to multiple things at onceOur apparent inability to attend to multiple things at once

‘‘It implies withdrawal from some things in order to It implies withdrawal from some things in order to deal effectively with othersdeal effectively with others’’– Attending has a costAttending has a cost– Attending is a limited capacity processAttending is a limited capacity process

‘‘has a real opposite in the confused, dazed has a real opposite in the confused, dazed scatterbrain statescatterbrain state’’– Attending is the glue that keeps perception togetherAttending is the glue that keeps perception together

AttentionAttention: S: Selecting some electing some stimuli over others for further stimuli over others for further

processingprocessing Why select? Why not process all visual Why select? Why not process all visual

input?input?– Limited processing capacityLimited processing capacity

Limited processing capacity of what?Limited processing capacity of what?– Response systems: Two hands, one mouth, Response systems: Two hands, one mouth,

etc.etc.– Input: One pair of foveasInput: One pair of foveas– Use of distributed representations: When more Use of distributed representations: When more

than one pattern is activated simultaneously, than one pattern is activated simultaneously, interference or cross-talk may occur.interference or cross-talk may occur.

Coping with the problem of Coping with the problem of interference and cross talk interference and cross talk

Reducing the degree of distributedness at Reducing the degree of distributedness at higher levels of visual representationhigher levels of visual representation

Evidence of sparse population codes (e.g., IT face Evidence of sparse population codes (e.g., IT face representations)representations)

Binding attributes via synchronized oscillationsBinding attributes via synchronized oscillations Selective Attention: Focusing processing Selective Attention: Focusing processing

on a selected portion of the sceneon a selected portion of the scene Reduces information overloadReduces information overload

Selective AttentionSelective Attention Selective attention: Limits the Selective attention: Limits the

processing to one portion of the processing to one portion of the scene at a time.scene at a time.

Stimulus selection could be based Stimulus selection could be based on:on:– location in a (retinotopic map)location in a (retinotopic map)– object representation object representation

Spatial-based SelectionSpatial-based Selection Posner’s Spatial Cuing Posner’s Spatial Cuing

Procedure.Procedure.- See fixation cross- See fixation cross- Brightness change- Brightness change- Respond to target - Respond to target onset onset

Fastest response to a Fastest response to a target that occurs on target that occurs on the cued side (valid) and the cued side (valid) and slowest when target slowest when target occurs on the non-cued occurs on the non-cued side (invalid).side (invalid).

Object-based SelectionObject-based Selection TaskTask

– Told what dimension(s) to reportTold what dimension(s) to report– Fixation pointFixation point– See target (~79 ms)See target (~79 ms)– Pattern mask Pattern mask – ReportReport

Target: Two overlapping objects, each with 2 Target: Two overlapping objects, each with 2 dimensions:dimensions:– Box: Height; GapBox: Height; Gap– Line: Texture; OrientationLine: Texture; Orientation

Equally accurate reporting one or two Equally accurate reporting one or two dimensions from the same objectdimensions from the same object

More accurate reporting two dimensions from More accurate reporting two dimensions from the same object than one dimension from each the same object than one dimension from each of two objects. (Vecera & Farah, 1994, E1: 86% of two objects. (Vecera & Farah, 1994, E1: 86% > 80%)> 80%)

After Duncan (1980)

Visual Attention: Visual Attention: The Glue that The Glue that BindsBinds

We normally experience our complex environments as a coherent We normally experience our complex environments as a coherent world of integrated objects.world of integrated objects.

Remember: Sensory information (i.e., shape, color, motion) Remember: Sensory information (i.e., shape, color, motion) arrives in parallel and is processed by different pathways in brain.arrives in parallel and is processed by different pathways in brain.

To create useful mental representations of objects, we collect To create useful mental representations of objects, we collect their features, bind them into the correct temporal and spatial their features, bind them into the correct temporal and spatial bundles, and interpret these bundles to specify their real world bundles, and interpret these bundles to specify their real world origins.origins.

This process depends upon focused attention.This process depends upon focused attention.

If focused attention fails, binding may fail and we perceive illusory If focused attention fails, binding may fail and we perceive illusory conjunctions (i.e., upon seeing two cars (red Focus and black conjunctions (i.e., upon seeing two cars (red Focus and black Echo, may falsely report a red Echo). Echo, may falsely report a red Echo).

Feature Integration Theory: Feature Integration Theory: Treisman (1998)Treisman (1998)

Limited Visual InputLimited Visual Input Although we seem to have a detailed, Although we seem to have a detailed,

highly veridical and continuous mental highly veridical and continuous mental representation of visual world about representation of visual world about us, visual input is limited.us, visual input is limited.– Visual acuity is good only for foveal focus.Visual acuity is good only for foveal focus.– Eyes movement from one fixation point to Eyes movement from one fixation point to

another while viewing a scene.another while viewing a scene. Saccades: 3-5 saccades/sec, 40 – 50 msec Saccades: 3-5 saccades/sec, 40 – 50 msec

each. each. Fixations: ~300 msec, during which we pick Fixations: ~300 msec, during which we pick

up visual information.up visual information.

Eye Movements: Eye Movements: Saccades and Saccades and FixationsFixations

Change BlindnessChange Blindness Failure to detect supraliminal changes in a Failure to detect supraliminal changes in a

visual scene. (i.e., editing discontinuities in visual scene. (i.e., editing discontinuities in movies).movies).

Flicker technique: In your demonstration, Flicker technique: In your demonstration, changes involved: color, size, location, changes involved: color, size, location, presence/absence of objects in scene.presence/absence of objects in scene.Winter 2006 data (Psych 3450)Winter 2006 data (Psych 3450)

AccuracyAccuracy Latency LatencyCentral InterestCentral Interest 96% 96% 5.5 sec 5.5 secMarginal Interest 84%Marginal Interest 84% 13.5 sec 13.5 sec

Two Empirical Issues to be Two Empirical Issues to be Addressed from the Neuroscience Addressed from the Neuroscience

PerspectivePerspective

1)1) How does attention affect visual How does attention affect visual information processing at different information processing at different stages?stages?

2)2) What neural systems control the What neural systems control the allocation of attention?allocation of attention?