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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 (H-H)

� High-Low (H-L)

� Low-High (L-H)

� Low-Low (L-L)

� Concrete words were

remembered better than

abstract words 0

2

4

6

8

10

12

14

H-H H-L L-H L-L

Mean

No

. R

ecalled

Imagery

� Dual Coding Theory (Pavio, 1971)

Sensory Systems

Logogens (lexical entries)

Images

Verbal Processes Non-Verbal Processes

representational connections

referentialconnections

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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 form mental image of object or not

Condition Example No Imagery 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 (1973)

� Mental 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)

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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?

� Propositional relationships – images can be represented by abstract symbols

Imagery Debate

Spatial (depictive) Representation

Propositional Representation

“Sarah Palinis on top ofthe dinosaur.”

Imagery Debate

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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)

PROPELLER HANDLE

MOTOR

REAR DECK CABIN

WINSHIELD PORTHOLE ANCHOR

FRONT DECK(behind) (behind)

(front of)(bottom of)

(rear of) (attached to)(side of)(top front of)

*each link-node is a propositional relationship

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?

Spatial Relations in Mental Images

� Kosslyn, Ball and Reiser (1978)

� Scanning time linearly related to the distance between points

� Evidence favors spatial relations

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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?

Spatial Relations in Mental Images

� Kosslyn (1975) Results

� RTs were influenced by size of objects in the mental visual field

� Features more distinct

Spatial Relations in Mental Images

� Finke and Pinker (1982)

� Participants judged whether arrow pointed to dots that were previously seen

� Not instructed to use visual imagery

� No time to memorize, no tacit knowledge

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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

Spatial Relations in Mental Images

� Galis et al. (2004)

� Spatial judgments about physical pictures or imagined pictures

� Measured BOLD signals in an fMRI

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?

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How Accurate are Mental Images?

� Tversky (1981)

� Subjects drew map of the

western hemisphere, with certain

cities

Santiago

Miami