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?
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