Sensation & Perception

1. Sensation & Perception

2. Questions • How do we see right side up when the image is upside down? • What causes illusions?

3. How do we see right side up? • The images on our retinas are upside down and reversed left-to-right. • This is due to the focusing of light by the corneas and lenses in the eyes. • Somehow our brains figure out how to correctly perceive the environment.

4. Misconception Alert! • The eyes do not send beams into the environment! • Vision works because light enters the eyes.

5. How do we see right side up? • The brain does not have to flip the images. • The brain deals only with neural signals. • The sense organs convert energy from the environment into neural signals through the process called transduction.

6. What causes illusions? • The sensory information coming from the sense organs (bottom-up) is usually not sufficient for accurate perception. • The brain must use its knowledge (top-down) to strategically interpret the sensory information. • These top-down strategies cause both accurate perception and illusions.

7. What causes illusions? Example 1 • The Moon Illusion • Lack of depth information in the retinal images • Perceived size depends on both size of the image and perceived distance of the object.

8. What causes illusions? Example 2 • Müller-Lyer Illusion • Importance of context

9. What causes illusions? Example 2 • Why don’t we notice the blind spots in our eyes? • Axons of ganglion cells form the optic nerve. • Where the optic nerve exits from each retina, no photoreceptors exist; this is the blind spot. • Use of context

10. What causes illusions? Example 3 • How are colors perceived? • Trichromatic Theory • Opponent Process Theory

11. What causes illusions? Example 3 • Negative color afterimages • Sensory adaptation