Mental Imagery

• When we form a mental image our experience seems much like seeing something in our mind. It seems a lot like vision.
• When we form a mental image we seem to be able to manipulate them and we seem to be solving problems some times by means of manipulating them.
• Mental images can be quite detailed but they tend to be less detailed than actual perception.
• Question: How accurate is our phenomenology at describing what is really going on in our heads?

How is imagery like vision?

• Subtle visual properties
• Properties that had not previously been labeled
• Properties which can't easily be deduced.
Can be used for pretend navigation

What do people use imagery for (Kosslyn, 1990)

• Memory retrieval
• Problem solving
• Producing descriptions
• Mental practice (this site describes using mental imagery in sports!)
• Motivational states
• Daydreaming and association

Theories of Mental Imagery

• Two types of representations
• Propositional Representations: Based on simple language like units called propositions that become tied together in what are called propositional networks.

--In a propositional representation there is an aribitrary relationship between the thing being represented and the representation.
--In a propositional representation relations are explicitly represented.  The concept of an apple being on the table is represented as (Apple, ON, Table)
• Analog Representations: Picture like representations (Kosslyn calls them quasi-pictorial or depictive representations).
--Rather than there being an arbitrary mapping between symbols and the thing being symbolized (as in language) there is a correspondence between the parts of the representation and the parts of the thing being represented.
--Relations are represented implicitly in an analog representation.
• According to this theory mental imagery is based on analog representations and these analog represntations are extremely useful things that are important in memory and thought.

• There's only one sort of representation.  Everything, including mental imagery is represented in terms of propositions connected together in propositional networks.
• The experience of mental imagery is epiphenomenonal.

Evidence for the analog account

• Object Scanning Experiments
• Scanning mental maps
• Mental Rotation (Shepard & Metzler, 1971)
• Image size and ease of inspection
• Neurological evidence

Arguments and Evidence Against the Analog Account

Demand Characteristics: In early scanning experiments it may have been obvious what the experimenter wanted.  Take longer for things that are further apart.  It was argued that participants may be relying on demand characteristics.

Parismony: The analog account posits two different types of representations.  The principle of parsimony says that scientists should always look for the simplest possible explanation that can account for all the data.  Because assuming one type of representation (propositions) is easier than assuming multiple types of representations (propositions and depictive) the propositional account is more parsimonious as long as it can account for all the data.