1. Psychology Ch. 3 Sensation and Perception
The Nature of Sensation
The Basic Process

2. In all sensory processes, some form of energy stimulates a receptor cell in one of the sense organs.
Def.- A specialized cell that responds to a particular type of energy.

3. The receptor cell connects that energy into a neural signal, which is further coded as it travels along sensory nerves.
Process:
Receptor cells- sensory discrimination
-specialized to respond to only one particular form of energy.
Example:
Vision- light waves
Hearing- sound waves

4. -specialized for one sense or another
Receptor cells- connected to neural pathways
-specialized for one sense or another
Sensory messages
-enter the brain on different channels:
sight, smell, hearing, taste or touch.

6. Signals
-produces an experience we call vision or hearing, etc. when they reach the proper areas of the brain.
If the experience in the optic nerves are by other than light, the result is still a visual experience.
Experiment:

7. Johannes Muller, a 19th century German physiologist discovered the
“Theory of the Doctrine of Specific Nerve Energies”:
-one to one relationship between stimulation of a specific nerve and the resulting type of sensory experience.

8. Sensory Thresholds (pg. 99)
The energy reaching a receptor must be sufficiently intense for it to have a noticeable effect. The minimum intensity of physical energy required to produce any sensation at all is called the Absolute Threshold.
Def.- the least amount of energy that can be detected as a stimulation 50% of the time.
*** Review chart on notes

9. Detection Absolute Threshold Intensity No No No Yes Yes Detected
Observer’s Response
Detected
Tell when you (the observer) detect the light.

10. How much sensory stimulation is needed to produce a sensation?
How loud does a sound have to be for a person to hear it?
Psychologists present stimulus at different intensities and ask people whether they sense anything. Problem?
Sensitivity to light, sound, pressure, or other stimuli varies from person to person- even moment to moment.

11. Standard: the Absolute threshold
Notice the charts on pgs Testing an Absolute Threshold
Adaptation:
Def.- an adjustment of the senses to the level of stimulation they are receiving.
-when confronted by a great deal of stimulation your senses become less sensitive.

12. Adaptation allows our senses to be keenly attuned to environmental conditions without becoming overloaded.
Examples:
Going from a quiet setting to loud
- the sound is not painful
Dark room to bright light
-you don’t damage your eyes

13. Difference threshold (just noticeable differences-jnd):
Def.- the smallest change in stimulation that can be detected 50% of the time.
-Varies from person to person and
from moment to moment
-Displays the flexibility of our sensory systems

14. Difference Threshold
Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND).
Difference
Threshold No No
Yes
Observer’s Response
Tell when you (observer) detect a difference in the light.

15. The difference threshold varies according to the strength or intensity of the original stimulus. In other words, the greater the existing stimulus, the greater the change necessary to produce a jnd.
Weber’s law: The principle that the jnd for any given sense is a constant fraction or proportion of the stimulation being judged.
-The values of these fractions vary significantly for the different senses.
Example: Hearing is very sensitive.

16. Weber’s Law
Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.
Stimulus
Constant (k)
Light 8%
Weight 2%
Tone 3%