1. CHAPTER 3
SENSATION

2. Sensation and Perception
Definitions
Sensation – stimulation of the senses
Perception – process of creating MEANING from sensations
The Nature of Sensory Processes
The general character of sensation
Some form of energy
Stimulates receptor cell
Sends out coded electrochemical signals
Signals go to the brain
Creation of sensory experiences
Every sensory experience is an illusion created by the brain

3. Sensory Thresholds ABSOLUTE THRESHOLD JUST NOTICEABLE DIFFERENCE (JND)
Minimum intensity of energy required for sensation
Detected 50% of the time
Differences between people
Differences day to day for same person
For each sense – low
JUST NOTICEABLE DIFFERENCE (JND)
Smallest change detectable (50% of the time)
Stronger the stimulation  larger JND
Some senses are more sensitive
Bright light more than skin pressure

4. Vision Most important sense for humans The visual system
Cellular path to the brain
Light through CORNEA
Through PUPIL – in center of IRIS
Muscles in iris open/close pupil
Through LENS – which focuses light
Onto RETINA
Inner lining back of eyeball
Contains FOVEA
Center of visual field
Sharpest focus of images
Receptor Cells
In retina
Sensitive to small part of spectrum of electromagnetic energy

5. THE HUMAN EYE

6. Receptor Cells (continued)
Rods
Light and dark only
Just outside of fovea
Chiefly responsible for night vision
Cones
Light, dark and COLORS
Operate chiefly in daylight
Mainly in center of fovea
Less sensitive to light
Need bright light
Bipolar Neurons
One axon – one dendrite
Cones: ONE cone connects to ONE bipolar neuron
Private line

7. THE VISUAL SYSTEM

8. AFTERIMAGES
Stare at the center of the upper square for about 20 seconds.
Shift your gaze to dot in the lower square
What happens?
Why?

9. Connections from eye to brain
Afterimage
Sense experience occurring after visual stimulus is removed
New image becomes gray – not white
Never adapt completely
All receptors would become insensitive
Would see nothing
Small eye movements move image on retina
Connections from eye to brain
Ganglion cells
Axon form OPTIC NERVE to the brain

10. AFTERIMAGE Look at GREEN bars, GREEN receptors become less sensitive;
Look away –
Only RED receptors able to respond, RED bars appear

11. Sensation and Perception
Hearing
Sound
Caused by physical stimuli of sound waves
Changes in pressure when molecules collide with one another then move apart
Pitch
High/low
Determined by frequency of wave
Measured by hertz – Hz

12. Hearing (continued) Loudness Timbre Intensity
Determined by amplitude of wave
Amplitude = height
Measured by decibels
Timbre
“Texture”
Pattern of overtones
Waves that are different multiples of basic frequency
(ex) Piano and violin playing same note sound different

13. SOUND MEASUREMENTS

14. THE HUMAN EAR

15. SMELL Very sensitive in humans 10,000 times as sensitive as taste
Pathway
Airborne molecules enter nose – activating odorant binding protein
2. Receptor Cells
Nerve cells die – replaced every few weeks
Only neurons to be replaced in the human body
1000 different receptors = 10,000 different odors
Requires little analysis by brain

16. SMELL (continued) Sensitivity Receptor cells carry messages
Messages received by Olfactory Bulbs
Information is recoded
Information is received in the olfactory projection area in cerebral cortex
Sensitivity
To odors even without being able to name them
Sex variable: females more sensitive
Age variable: older less sensitive

17. SMELL (continued) Sensitivity (continued)
4. Anosmia – loss of sense of smell
Lose interest in food
Reduce desire for sexual activity
Can be dangerous
Cultural variable
Korean-Americans more sensitive
Question as to influence of culture and learning

18. TASTE Flavor = taste + smell Pathway
Chemical substances in food dissolve in saliva
Substances go between Papillae (small bumps)
Small bumps contain Taste Buds – 10,000
Decrease with age
On tip, sides, back of tongue

19. Taste (continued) 4. Chemical interaction causes neurons to fire
5. Messages to brain’s parietal lobe and limbic system
Taste Qualities – Parts of Tongue
Sweet  tip
Salty  tip
Bitter  back
Sour  sides
No taste  middle of tongue

20. Taste (continued) Sensory Adaptation
Get “accustomed” to strong flavors
Cross-adaptation
Exposure to one
Modifies taste sensation of other
(ex) Brush teeth = sour orange juice