1. Visual Imagery

2. Imagery  Forming a picture in the mind without sensory input  Mental imagery  Visual imagery  Paivio, Smyth and Yuille (1968)  Subject studied word-pairs with each member varying in imagery  High-High (H-H)  High-Low (H-L)  Low-High (L-H)  Low-Low (L-L)  Concrete words were remembered better than abstract words

3. Imagery  Dual Coding Theory (Pavio, 1971) Sensory Systems Logogens (lexical entries) Images Verbal ProcessesNon-Verbal Processes representational connections referential connections

4. Imagery  Are visual images different from verbal codes?  Kosslyn (1975)  Sentence verification task [A 1 has 2. ]  Semantic association between 1 and 2 varied  A mouse has a back.  A mouse has whisker.  Subject told to for mental image of object or not ConditionExampleNo ImageryImagery Low AssociationA mouse has a back.897 ms1480 ms Strong AssociationA mouse has whisker.825 ms1605 ms +72 ms-125 ms

5. Scanning Mental Images  Kosslyn (1973)  Mental scanning task  Focus on part of a mental image (or real picture)  Locate another part of the object

6. Scanning Mental Images  Shepard and Metzler (1971)

7. Imagery Debate  Do mental images exist?  Can we actually scan them, like a real picture?  Tacit knowledge explanation  Subjects may behave how they think that they should  Subjects unconsciously use knowledge of spatial relations  Zenon Pylyshyn  Are visual images supported by spatial relationships or propositional relationships?  Spatial, or depictive, relationships  Propositional relationships

8. Imagery Debate  Propositional theory (Pylyshyn, 1973)  Mental images are stored as propositions between parts  “All knowledge, including spatial knowledge and memory for images, can be expressed in semantically-based propositions.”  Explains mental scanning results of Kosslyn (1973) PROPELLERHANDLE MOTOR REAR DECKCABIN WINSHIELDPORTHOLEANCHOR FRONT DECK (behind) (front of)(bottom of) (rear of)(attached to)(side of)(top front of) *each link-node is a propositional relationship

9. Imagery Debate Spatial (depictive ) Representation Propositional Representation “Sarah Palin is on top of the dinosaur.”

10. Evidence for Spatial Relations in Mental Images  To show evidence for spatial relations  Performance (RTs) must vary as a function of distance  Distances cannot be confounded with propositional links  Kosslyn, Ball and Reiser (1978)  Subjects encode a map into memory  Scan between two points  Spatial relationships prediction?  Propositional theory prediction?

11. Evidence for Spatial Relations in Mental Images  Kosslyn, Ball and Reiser (1978)  Scanning time linearly related to the distance between points  Evidence favors spatial relations

12. Evidence for Spatial Relations in Mental Images  Kosslyn (1975)  Does size of mental image influence judgments of features?  Imagine animals side-by side and answer questions about one  Spatial relationships prediction?  Propositional theory prediction?

13. Evidence for Spatial Relations in Mental Images  Kosslyn (1975) Results  RTs were influenced by size of objects in the ‘mental visual field’  Features more distinct

14. Evidence for Spatial Relations in Mental Images  Neural Evidence?  LeBihan et al. (1993)  Perception and imagery activate visual cortex  Increased cerebral blood flow in visual cortex when mentally scanning

15. Evidence for Spatial Relations in Mental Images  Galis et al. (2004)  Spatial judgments about physical pictures or imagined pictures  Measured BOLD signals in an fMRI

16. How Accurate are Mental Images?  Relational information is distorted in mental maps  Stevens & Coupe (1978)  Asked subjects about where one geographical location was with respect to another  Example: Is San Diego east or west of Reno, Nevada?

17. How Accurate are Mental Images?  Tversky (1981)  Subjects drew map of the western hemisphere, with certain cities Santiago Miami