Cognitive ProcessesPSY 334

Chapter 3 – Attention

What is Attention?

Attention is the allocation of limited processing resources.Visual features such as shape, color, texture, motion are processed in parallel.Serial bottleneck – occurs when it is no longer possible to process in parallel.

When does it occur – early vs late selectionHow do we select what to attend to?

Visible Bottleneck Task

http://opl.apa.org/contributions/Pashler/prp.html

This task illustrates how difficult it is to pay attention to two things at the same time.

Both tasks require a choice of response and the same cognitive resource cannot be devoted to both tasks at the same time.The competition goes away when one task does not involve a choice (e.g., press any button when you hear a tone).

How we Experience Attention

Stream of consciousness -- we learn and remember what we attend to.Paying attention results in a feeling of mental effort.Can be directed internally but also pulled (attracted) by external events.Varies with arousal and fatigue.Studied by looking at response competition.

Auditory Attention

The response competition comes from having two ears.Dichotic listening task – uses “shadowing.”

Two different messages are presented, one to each ear. Subjects are asked to speak what they hear.People can attend to only one message at a time.

Auditory Shadowing

Broadbent’s Filter Theory

People do not remember the content of the unattended ear.

Voice or noise, sex, but little else.Broadbent’s filter theory proposed that filtering occurs early in processing based on physical characteristics (pitch, ear).

Neural evidence supports the ability to select one ear to listen to.

Cocktail party effect – attention switches based on content of unattended ear.

Broadbent’s Early Selection

Only the selected information gets through.

Gray & Weddeburn’s Study

Subjects can successfully shadow a message that jumps back and forth between ears.

This means that people can shadow based on meaning, not just physical characteristics.

Treisman’s Attenuation Theory

Treisman’s attenuation theory – subjects deemphasize but not filter out the unattended message.

Meaning switched from one ear to the other.Some subjects switch ears even when told not to, following the semantic content.

Semantic criteria apply to all messages, filtered or not.

Treisman’s Attentuation Theory

All information passes through but some is weaker (attenuated).

Late Selection Theory

Deutsch & Deutsch’s late selection theory – the limitation is in the response system, not the perception.

Both messages are perceived in terms of meaning, but only one can be shadowed at a time.The criterion for selecting what to say can change – based on ear or meaning.

Late Selection Theory

Shadow by ear

Shadow by meaning

Decide what to say

Testing the Theories

Dichotic listening task:Shadow one message but listen for a target word in both ears (tap when heard).

Late selection theory predicts no difficulty hearing the target in either ear.Attenuation theory predicts less detection in non-shadowed ear.

87% detection in shadowed ear8% detection in non-shadowed ear

Neural Evidence (Auditory)

An enhanced response occurs in the primary auditory cortex but not earlier in the auditory pathways.

Both EEG (using ERP) and PET show this.The enhancement occurs quickly, sooner than meaning can be interpreted.Effects are signal attenuation and enhancement, not complete filtering out.

Visual Attention

We can choose where to fixate our eyes for greatest visual acuity.

Other portions of the visual field are attenuated.

Visual attention need not be located where the eyes are fixed.Posner – subjects can attend to objects up to 24 degrees from the fovea.

Shift of attention precedes eye movement.

Spotlight Metaphor

Spotlight can be broad or narrow (degrees of visual angle).

Broad areas processed less well.A narrow focal point gives optimal processing but it takes time to move the focus to other areas of the visual field. We move our eyes around a complex visual stimulus.

Neisser & Becklen’s shadowing task.

Neural Evidence (Visual)

Attention consists of enhanced neural response in a particular spatial location in the visual cortex.

By increasing neural activity in a particular location, input to that location can be processed faster.

Specific details are “higher order” properties and take longer to recognize.Enhancement comes from V4 not V1.

Visual Search

Feature-based serial search – NeisserFind the letter K in a string of letters.

Pop-out – locate a distinctive feature in an array without searching each item.Treisman & Gelade – locating a conjunction of features takes longer than locating a single, distinctive feature.

T among I’s & Y’s 400 msT among I’s & Z’s 800 ms

Visual Pop-Out

Treisman & Gelade’s Data

The Binding Problem

If different neurons process different features of an object (color, motion, lines) how are such features combined?Feature integration theory (Treisman) –people must focus attention in order to synthesize features into a pattern.Illusory conjunctions – mistakes in binding when attention is disrupted.

See pink T, yellow S, blue N but report seeing a pink S that was never presented.

Attention Enhances Features

Attentional enhancement can be based on specific features not simply the contents of a visual field.

Blue and green bars (macaques) – cell firing is suppressed if green is attended.

Black and white teams and black gorilla:8% of those attending the white team saw the black gorilla67% of those attending the black team saw the black gorilla (both were black)http://viscog.beckman.illinois.edu/flashmovie/23.php

Selective Cell Firing

Blue is attended Green is attended

Cell fires despite presence of green Cell firing is greatly reduced despite presence of blue

Visual Neglect

Visual neglect may occur due to damage to:

posterior parietal lobepulvinar (thalamus)superior colliculus (eye-tracking)

People with injuries to the parietal lobe have difficulty shifting attention from one side of the visual field to the other.

The first neglect patient (a) has copied the right sides of both figures, ignoring the left.

The second patient (b, c) neglects the left sides when copying but draws a more complete figure from memory.

Halligan et al, 2003

Kinds of Deficits

Damage to the right parietal lobe produces deficits in cued attention tasks:

No problem with items on the right but inability to shift to items on the left.

Unilateral neglect – with severe damage people totally ignore the left visual field.Left parietal damage inhibits attention to details. Deficits occur across modalities

Object-Based Attention

Attention can be focused on particular objects, not just regions of space.

Sometimes it is easier to attend to an object (bumps on stimuli).

Inhibition of return – if we have already looked at a location it is harder to return to it.

Flickering squares take longer to identify because already viewed, even when rotated.

Two Theories

Spotlight theory – we move our attention to parts of the visual field.

Object-based theory – we move our attention to objects.

Object-Based Neglect

Just as objects can be attended to independent of their location, neglect can apply to objects, not locations.Some patients neglect one side of objects regardless of which visual field they occur in.

A Central Bottleneck

We can only process one thing at a time within a single modality (vision, hearing).Central cognition may be the most important bottleneck – the central bottleneck.Whether two tasks can be done at once depends on whether they compete for the same resources.

Schumacher dual-task experiment.

Dual Task Processing

Automaticity

Practice reduces the need for attention by reducing central cognition, making a task automatic.

Practice enables parallel processing.Spelke’s two tasks:

Read text for comprehensionWrite down words read by an experimenterAfter 6 weeks subjects could read at normal speed and answer questions.

Stroop Effect

Color words were presented printed in different ink colors.

Control stimuli were non-color words in different inks or color bars (not words)

Subjects were asked to name the ink color as quickly as possible.Demo

Stroop Demo

Why it Happens

Automatic processes are difficult to stop.It is nearly impossible to look at a word without reading it.Neutral words name non-colors so ink can be named without interference.Color words that conflict with ink color take longer because reading the word cannot be inhibited.

Practice With Stroop Tasks

What happens if you compare tasks that are not well-practiced?MacCleod & Dunbar asked subjects to associate color names with shapes.

MacCleod & Dunbar’s Conditions

Congruent – random shape was in the same ink color as its name.Control –

white shapes were presented and subjects said the name of the color for that shape colored shapes were presented and subjects named the ink color of the shape

Conflict – the random shape was in a different ink color than its name.

Results

At first, color naming was more automatic than shape naming and was unaffected by congruence with shape.After 20 days practice, shape naming was affected by congruence with ink colorPractice reversed the Stroop effect and made shape naming like color naming.

Executive Control

Control of attention occurs in the parietal lobes, but central cognition occurs in the prefrontal cortex.Damage to the prefrontal cortex impairs executive control.

Response is stimulus-driven not intentionalCannot do the Stroop task because automatic processing takes over

Arbitrates between competing processes