1. Gregory’s Top-down Theory

2. Top-down Theories
Top-down theories suggest that we combine information from a variety of different sources in order to construct our perception of the visual world.

3. Top-down theories
Theorists such as Gregory suggest that there is insufficient information provided by the senses for us to make sense of what we are seeing.
Therefore we use our existing knowledge (schemas) to fill in the gaps.
Perception is an active and constructive process.

5. Hypothesis Testing
Gregory suggests perception is governed by hypothesis testing.
For example we might look at a scene and see something we cannot identify.
We will work out what it is by deciding what object would be most likely to be in that situation.

6. Hypothesis Testing
This means that it is possible to test and accept hypotheses that are wrong.
This is the reason, according to Gregory, we experience visual illusions.
Ponzo illusion

7. Factors Affecting Perception
Top-down theories have their origins in the work of Gestalt Psychologists.
One of their fundamental ideas is that we try to find order in the world around us.
They identified a number of different examples of this.

8. Gestalt Psychology

9. Gestalt Psychology
These ideas can be applied in other situations too for example biological motion.
Biomotion

10. Perceptual Set An example of top-down processing is perceptual set.
A person’s expectations about what they are seeing can affect what they perceive.

11. A 12 13 14 C

13. Conclusion Perception involves both top-down and bottom-up processing.
Gregory acknowledged that people use sensory cues especially those such as texture gradients or motion parallax to make sense of the world.
But he also believed that people use their knowledge to help construct their understanding of what they are seeing.