Cognitive Processes PSY 334 Chapter 4 – Perception-Based Knowledge Representation April 21, 2003

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.