1. Sensation and Perception
(The process where by stimulation of receptor cells like eye, nose, ear …etc., send nerve impulses to the brain, where they register a touch, sound, color …etc.).
Perception:
- (process where the brain interprets sensation giving them order and meaning).

2. Sensation and Perception…cont.
- Without sensation: perception couldn’t occur, without perception sensations without meaning. - Impaired perception cause (illusion).

3. Stimulus
(Any form of energy (sound, light, heat, and pressure) to which an organism is capable of responding).
Stimuli and sensations have a cause and effect relationship.

4. Factors affects stimulus detection:
- (1) The intensity of stimulus.
- (2) Background noise interfere with stimulus detection.
- (3) Motivation (rewards or punishments ).
-(4) Prolonged constant stimulation: lead to sensory adaptation

5. How do perceptual processes develop?
1. Empiricist view of perceptual development:
- Babies enter the world with little or no ability to see depth, form, and perceptual constancy’s.
- Infants learn adult like perceptions on the basis of cues the environment provides.

6. 2. Nativist view of perceptual development:
Not all perceptual process are learned, some arise from the way our sensory system work, e.g. feeling of hunger or diaper wetting.

7. 3- Interactionism view of perceptual development:
- Through the interaction of both biological factors & experience perceptual process develop.
- what we see, hears, feel, and so forth, is partly the results of how our sensory systems are programmed and partly the result of what we are exposed to.

8. Expectations and perceptions
Psychologists have studied two ways in which learning and experience mold our expectations which in turn shape our perception

9. 1-Perceptual set:
- A frame of mind that “sets” a person to perceive things in a certain way.
We perceive what we think we should perceive.
- Perceptual sets establish expectations that guide our perception

10. * Example (illusion): person who was bitten by snake in the dark in specific area. The sight of snake become a perceptual set for this person. When he see a rope in the same area under similar conditions establish an expectation of snake this expectation guide his perception, so he perceive the rope as a snake.

11. 2- Perceptual schema:
Mental representation of objects and events against which incoming data are compared and interpreted. 
General knowledge of the world in the form of schemas also shape our expectations and hence our knowledge.
- Example: How quickly people process the information in photos with a real world scenes as a city street or a kitchen. When people view such scenes for only a second, they can remember almost half of the objects that scenes contain.