Cognitive ProcessesPSY 334

Chapter 3 – Attention

July 10, 2003

Feature-Integration Theory

Treisman – people must focus attention on a stimulus in order to synthesize its features into a pattern. Feature integration takes much longer than

simply recognizing a feature, especially with larger display sizes.

Single features can be identified without fixating upon them.

Illusory conjunctions occur when attention is not possible.

Visual Selection in Art

American Gothic – Grant Wood Gestalt reversible figures:

Vase & faces Jack & Jacques (Canadian flag) Gossip & Satan Old & young woman

Escher drawings Hidden images

Visual Search

Treisman argued that search occurs based on a single feature. When that feature is located, then the

second feature is analyzed in that location. Wolfe argued that two features can be

searched for in conjunction (together). Conjunction searches are noisier and less

accurate than single searches. Wolfe’s model requires direct attention too.

Visual Neglect

Visual neglect may occur due to damage to the posterior parietal lobe of brain. People with such injuries have difficulty

shifting attention from one side of visual field in order to look at the other side.

Cued attention tasks show one-sided deficit. Visual extinction – when a competing

object is present, the other disappears. Unilateral neglect – one side ignored.

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.

Object-Based Neglect

Just as objects can be attended to independent of their location, neglect can apply to objects, not just 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).

What happens when we combine modalities? Dual-task studies How does stimulus onset asynchrony

(SOA) affect performance of the second task?

If the two tasks can be done in parallel there should be no effect of SOA.

Dual-Task Performance

The first task must be completed before the second task can be done.

There is some time gained by overlapping the tasks. The stimulus is encoded while doing the

other task – two modalities can be processed at once.

The bottleneck occurs at the thinking – the subject cannot think about both tasks at once.

Automaticity

Practice reduces the demand on cognition by making a task automatic.

Spelke’s two tasks: Read text for comprehension Write down words read by an experimenter After 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

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 color

Practice reversed the Stroop effect and made shape naming like color naming.

Current Views of Attention

Theorists no longer associate attention with consciousness. Many attentional phenomena (such as

moving one’s eyes) are unconscious. Each modality has its own attentive

processes and a bottleneck when it must process a single thing.

Interference occurs with competing demands on a single system.