Cognitive Processes PSY 334 Chapter 4 – Perception-Based Knowledge Representation July 15, 2003

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.

Dual-Code Theory  The mind operates upon internal representations of knowledge.  How is visual information (imagery) represented in memory?  Paivio’s Dual-Code Theory – memory is better if we encode information visually and verbally. Separate representations are maintained for verbal and visual information.

Evidence for Dual Codes  Santa compared linear and spatial arrays of: Three geometric objects Three names of geometric objects  Subjects were asked whether the arrays contained the same objects or names.  Subjects were faster when shapes were in the same spatial arrangement but faster when words were linear.

Evidence From Brain Imaging  Subjects were asked to mentally rehearse: A word jingle Navigating their neighborhood  Increased blood flow occurred in different areas of the brain, depending upon the task.  The same brain areas were active as when actually speaking or seeing.

No Homunculus  Homunculus -- the idea that there are “pictures in the head” implies someone to look at those pictures. Both images and percepts are represented topographically in the brain, but there is no homunculus to view them.  Kosslyn -- the same processes are used to view mental images and external percepts.

Mental Rotation  Shepard – two-dimensional and three- dimensional mental images are rotated in the same way as actual objects. The more an object is rotated, the longer it takes to respond in a same/different task.  Georgopoulos et al. – measured neurons firing in monkey brains when moving a handle. Intermediate cells fire showing rotation.

Image Scanning  Brooks – subjects scanned imagined diagrams (like letter F) and noted outside corners, or sentences noting nouns. Respond by saying “yes” or “no” Tap left hand for “yes,” right hand for “no” Point to Y or N on a sheet  Scanning a sheet for Y’s & N’s conflicted with scanning the mental image. Conflict is spatial not visual.

Comparing Visual Quantities  Time to make a judgment decreases as the difference in size between objects increases. The smaller the difference the longer it takes to make a judgment.  Which is larger: moose or roach, wolf or lion?  The same pattern emerges when asked to judge actual differences, line lengths.

Two Types of Imagery  Images involving visual properties.  Images involving spatial properties.  Bilateral temporal lobe damage: Difficulty judging color, size, shape. No deficit in mental rotation, image or letter scanning, judgment of relative positions.

Are Images Like Perception?  A series of experiments to compare perception and imagery: Imagining transformations of mental images vs perceived stimuli. Ponzo illusions occurs with imagery. Difficulty with reversible figures – depends on instructions, harder.  MRI plots show same brain activity.