Visual Imagery Imagery Forming a picture in the

Visual Imagery

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 � Concrete words were remembered better than abstract words 12 Mean No. Recalled (H-H) � High-Low (H-L) � Low-High (L-H) � Low-Low (L-L) 14 10 8 6 4 2 0 H-H H-L L-H L-L

Imagery � Dual Coding Theory (Pavio, 1971) Sensory Systems representational connections Logogens (lexical entries) Images referential connections Verbal Processes Non-Verbal Processes

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 Condition Example No Imagery Low Association A mouse has a back. 897 ms 1480 ms Strong Association A mouse has whisker. 825 ms 1605 ms +72 ms -125 ms

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

Scanning Mental Images � Shepard and Metzler (1971)

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 � Are Pylyshyn visual images supported by spatial relationships or propositional relationships? � Spatial, or depictive, relationships � Propositional relationships

Imagery Debate � Propositional � Mental theory (Pylyshyn, 1973) 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) REAR DECK (rear of) (behind) CABIN (behind) FRONT DECK (top front of) (side of) (attached to) WINSHIELD PORTHOLE ANCHOR MOTOR (bottom of) PROPELLER (front of) HANDLE *each link-node is a propositional relationship

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

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?

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

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?

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

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

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

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?

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