Cognitive Processes PSY 334

1. Cognitive ProcessesPSY 334 Chapter 4 – Perception-Based Knowledge Representation July 15, 2003

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.