Mental Imagery F What are mental images? F How are mental images used (or are they)?

Mental Imagery F What are mental images? – mental representations – can be related to any sense

Dual Coding Hypothesis (Paivio, 1965) F Two ways of representing information: – imagery – verbal F Easier to remember when you can use both codes: – higher recall for concrete words than for abstract words

Conceptual-Propositional Hypothesis (Anderson & Bower, 1973) F Information is represented by propositions. F Mental images are generated as byproducts (epiphenomena).

Functional Equivalency Hypothesis (Shepard, 1972) F Mental images are used like real images (they are “functionally equivalent”). F Mental images are not the same as real images: second-order isomorphic.

Size of Mental Images (Kosslyn, 1975) F Imagine a rabbit sitting next to an elephant. – Does the elephant have a tail? – Does the rabbit have a tail? F Imagine a huge rabbit next to a tiny elephant. – Does the elephant have a tail? – Does the rabbit have a tail?

Size of Mental Images: Results F Time to answer a question about a mental image depends on size of the image. F Result holds even when a normally large object is imagined to be small and vice- versa.

Indeterminacy Problem (Anderson, 1978) F Both hypotheses can explain the same results. F There is no way to determine which hypothesis is correct without biological evidence.

Biological Evidence On Imagery F Visual and memory areas of the brain are active during mental imagery tasks. –Primary visual cortex –Temporal lobe F The visual areas are MORE active during imagery than when actually seeing! (Kosslyn et al., 1993)

Biological Evidence On Imagery F Imagery neurons in medial temporal lobe – fire whether seeing or imagining a particular object (Kreiman et al., 2000) F Loss of perceptual ability and loss of imagery ability sometimes co-occur (Bisiach & Luzatti, 1978)

Double Dissociation Between Imagery and Perception F R.M. - Loss of imagery with intact perception (Farah et al., 1988) F C.K. – Loss of perceptual ability with intact imagery (Behrmann et al., 1994)

Is Imagery an Epiphenomenon? F Many similarities between imagery and perception F Double dissociation indicates they are not the same processes F Overlap in the processes involved, but not complete overlap

Evolutionary Psychology F How much overlap between imagery and perception is ideal?