Sensation is the process by which our senses receive information from the environment. Perception is how the brain interprets these sensory inputs. Sensation occurs via our sense organs like the eyes, ears, and skin, while perception takes place in the brain. The brain processes information both bottom-up, from our senses, and top-down, using existing knowledge and expectations. Together, sensation and perception allow us to gather information about the world around us.

1. Sensation and Perception

2. Sensation
• Process by which body gathers information about
environment
• Connects us to the world
• Sensation generally occurs in the sense organs
– vision (detects light waves)
– olifaction (sense of smell)
– gustation (sense of taste)

3. Perception
• Process by which the brain organizes and interprets
sensory information (“sensation PLUS perception”)
• Perception occurs in the brain
• 3 basic principles
o adaptive
o active
o no one-on-one correspondence between physical and
psychological reality

8. Perception
• Top-down processing
o “Conceptually-driven processing”
o Take information already existing in the mind to
interpret environment
• Bottom-up processing
o “Data-driven processing”
o Take stimuli from the environment and make attempts
to determine its meaning

9. Sensation
• Sensory receptors – Eyes, ears, nose, etc. detect physical energy
(light/sound/smell)
• Transduction – Translates physical energy into neural signals
• Absolute threshold – Each system’s minimal amount of energy
required to activate it
• Difference threshold – Each system’s minimal amount of energy
required to detect change from one level
of stimulus to another
– Just-noticeable difference (Weber’s Law)

10. Stroop Effect
• In this experiment, say the color of the word (not what
the word says)
• Example: For the word RED you should say “Red”. For
the word RED you should say “Yellow“
• As soon as the words appear on your screen, read the list
as fast as you can

13. Stroop Effect
• In this experiment, look at a picture of an animal and
say the name of the animal. Do NOT read the word
placed on the picture.
• For example: You should say "Cow" because the
animal in the picture is a cow.
• You should sat “Cat” because the animal in the picture
is a cat.

16. Vision
• Allows for the detection of movement, light, depth
perception
• Transduction – impulses from optic nerve carry visual
information from retina to optic chiasm;
neural messages then travel to thalamus
and into the visual cortex

17. Vision
• Motion perception
o Rods in retina sensitive to motion activate neurons in
the visual cortex
o 2 systems for processing movement
- Eye stationary as object moves
- Eye moves to maintain object at same place on the
retina

20. Vision
• Photoreceptors
o Cones
- Highest concentration in the fovea
- Require light to be activated
- Color vision/trichromatic theory (“photopic vision”)
- High visual acuity
o Rods
- Highest concentration in the retina
- Night vision (“scoptic vision”)
- Low visual acuity
- High sensitivity (esp. motion detection)

24. Vision
• Color blindness
• Inability to distinguish colors
• “Disease” is linked to the X chromosome, thus
males more likely than females to be color blind
• Most common condition is red-green color
blindness (difficulty distinguishing red and green)

28. Hearing
• Transduction
o Outer ear collects physical stimuli (sound waves)
o Inner ear carries movements via waves of fluid (in
ear drum) that generate neural signals
o Signals sent to thalamus then to temporal lobe

30. Hearing
• Volume – “loudness” determined by the height of sound
wave (amplitude)
• Pitch – refers to the frequency of the sound wave
(low B flat/high C tone)

31. Touch
• Protects body from injury, helps identify objects,
maintain body temperature
• 4 basic skin sensors (heat, cold, pain, pressure)
• Touch sensations differ throughout the body
• Transduction
o Sensory neurons in skin send impulses to spinal cord or
communicate with interneurons (that in turn stimulate
motor neurons)

33. Taste
• Refers to four basic tastes (sweet, sour, salty, bitter)
and protects us from injecting toxic substances
• Transduction
o Occurs in the taste buds
o Physical stimulus (soluble chemicals) activate taste
receptor neurons which carry information to thalamus and
primary cortex to help identify taste

34. Smell
• Detect danger (e.g., smoke, spoiled food) and/or
recognize familiar odors
• Transduction
o Physical stimulus (air molecules) enter nasal cavity
through nose
o Receptors in olfactory epithelium pass information
through the olfactory bulb to the primary cortex