Mental Imagery

Phenomenology of Mental Images

• 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?

Can be used to recognize properties of objects.
• 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
• Motivational states
• Daydreaming and association

Evidence for imagery based representations

Scanning visual images

Kosslyn, Ball & Reiser (1978): Scanning mental maps

Parallel vs. Sequential Processing(Nielsen & Smith,1970)

• Schematic faces developed which varied on 5 features: Eyebrows, Eyes, Nose, Mouth, Ears
• Subjects asked to memorize picture or memorize verbal description.
• All subjects shown a target picture and asked if it matched while response time was taken.
• Number of relevant features was varied (3,4,5)

Mental Rotation (Shepard & Metzler, 1971)

Neurological evidence (Bisiach & Luzzatti, 1978)

• Brain damaged patients with unilateral visual neglect
• Asked to image a scene that was familiar before their stroke
• Patients only report things on one side or the other

Image size and ease of inspection (Kosslyn, 1975)

• Ss asked to imagine two different sized animals side by side.
• A rabbit next to an elephant should be imagined smaller than a rabbit next to a fly.
• Ss asked about some detail of the animal (Does the rabbit have red eyes?)
• Ss respond faster when the imagined animal is large than when it is small

Limitations to mental imagery

Memory for a common object (Nickerson & Adams, 1979)

• Subjects asked to draw a penny or recognize a penny from an array.
• Most subjects did poorly at this
• Shows that images are often lacking in details.

Mental rotation by the congenitally blind

• Even congenitally blind show mental rotation effects
• Shows that mental imagery may be spatially not specifically perceptual