1. September 1998HKU Mental Images The visual system encodes patterns of light and their inter-relationships Images in the visual system are partly created by these patterns of light on the retina. However, the image on the retina, is two-dimensional, upside down, and mostly out of focus.

2. September 1998HKU Top-Down Processing in the Visual System The three-dimensional, right-side up, clear image that we see is created by our brain. Is it possible that cognitive processes such as problem-solving can use this access to the visual system even when there isn’t stimulation on the retina?

3. September 1998HKU Scanning Mental Images Kosslyn, Ball, and Reiser (1978) had subjects memorize picture of island. Asked them to focus on one location of their mental image, and then asked them to (mentally) go to another location on the image. The time to get to the new location was proportional to the distance on the actual picture.

4. September 1998HKU Mental Rotation The time required to mentally rotate objects in space (in order to recognize them) is linearly related to how much they need to be rotated to be in a familiar position Shepard, 1968 Cooper, 1975

5. September 1998HKU Concepts and Categories Is the world naturally divided into categories or are the categories we perceive a consequence of how our minds see the world? (Philosophy) Theories of concepts have changed significantly over the past 30 years.

6. September 1998HKU From Definitions to Theories For centuries, concepts were seen as sets of necessary and sufficient features that define categories. Rosch (1975) changed this view by presenting evidence that concepts are more probabilistic.

7. September 1998HKU Prototypes and Family Resemblance Concepts are collections of features that are neither necessary nor sufficient. When we learn category concepts, we compare sets of features: if most features are similar and few are dissimilar, then we group thing together --> family resemblance

8. September 1998HKU Concepts as collections of prototypical features From observing numerous examples of particular categories, we form prototypes --> non-existent category representatives that embody all of the most common features.

9. September 1998HKU The Basic Level Prototypes and family resemblance are strongest at what Rosch termed the basic level --> bird vegetable game car

10. September 1998HKU Empirical Evidence for the Basic Level Subjects are asked to rate properties of different instances of categories (e.g., how important is having two legs to being a bird?) These ratings are then used to compute family resemblance scores for different types of birds. Subjects typicality ratings are correlated with FR scores.

11. September 1998HKU Summary The basic-level cuts the world up into categories that have the most family resemblance. e.g., furnituremammal chairdog car seatpoodle

12. September 1998HKU Picking Out the Right Features Why don’t we compare objects in terms of volume, time in a specific location, distance from home, etc. --> infinite number of features How do we choose the right ones?

13. September 1998HKU Concepts as Theories Concepts are more than just collections of probabilistically inter- related features. They are held together by a theoretical /explanatory glue.