Introduction to Sensation and Perception

1. Introduction to Sensation and Perception They are apart of one continuous process….but we will break them apart!

2. Sensation v. Perception • Process by which our sensory systems receive stimuli from the environment and bring it to the nervous system • Systems have developed through natural selection • Differences do occur from person to person, but are relatively subtle • Process of interpreting sensory information • Organizing, recognizing, and using our sensory information • Individual differences are much more evident Example: Presidential Debate

3. Bottom-Up v. Top Down Processing • Analysis that begins with the raw materials that enters through our sense organs • Used by sensation • No prior knowledge, start from the bottom up • Analysis that uses the knowledge gained from prior experience with stimuli to perceive them • If the brain expects something • Without this, we would have to interpret the world like it was always new

4. Selective Attention • Our senses take in 11,000,000 bits of information per second • You only consciously process about 40 • We cannot process all of the information converging simultaneously on our sensory systems • We use selective attention to prioritize input • Cocktail Party Effect • Ability to attend to only one voice among many • Ability to hear your name being called • People with ADHD appear to lack the ability to be selectively attentive; Instead of filtering out unimportant information, they focus on everything!

5. How is your selective attention? • Test Your Awareness

6. Sensory Adaptation • The reduced response to an unchanging stimulus • After constant exposure to a stimulus, our nerve cells fire less frequently • Why do things we stare at not disappear then? Our eyes are actually always moving! • Bright lights, loud noises, etc. draw our attention • Why? • Allows us to focus on informative changes in our environment without being constantly distracted! • Example: clothing, smells • Advertisements: use novelty, change, and intensity to get our attention!

7. Zimbardo Time

8. Psychophysics • Studying of relationship between stimuli (the physics part) and perception of those stimuli (the psyche or mind part) • Developed by Gustav Fechner

9. Thresholds • Psychophysics has allowed us to establish the limits of awareness, or thresholds • Absolute Threshold: the smallest possible stimulus that can be detected 50% of the time; Can vary with age • Wing of a fly/bee from 1 cm • Drop of perfume in a 6 room apartment • Teaspoon of sugar in two gallons of water • Tick of a watch at 20 ft • Candle flame on a clear night 30 miles away • Differences Threshold (just noticeable difference – jnd): smallest difference between two stimuli that can be detected 50% of the time • The larger the stimuli, the larger the difference that is needed • Easier to detect 5lb from 10lb than 400 from 405lb

10. Your turn • Mosquito Ringtones • FrequencyAge Range • 8khz Everyone • 10khz 60 & Younger • 12khz 50 & Younger • 14khz 49 & Younger • 15kh 39 & Younger • 16khz 30 & Younger • 17khz 24 & Younger • 17.4khz 24 & Younger • 18khz 24 & Younger •  19khz 24 & Younger •  20khz 18 & Younger •  21khz 18 & Younger • 22khz 18 & Younger

11. Weber’s law • Ernst Weber • For their difference to be perceptible, two stimuli must differ by a constant proportion, not a constant amount • Found that we can detect • 10% change in loudness • 20% change in taste • 2% change in weight

12. Signal Detection Theory • Perception involves uncertainty • How do expectations affect your decisions? Personal feelings? • Is that a cop car behind you? • Signal Detection: Analysis of sensory and decision making processes in the detection of faint, uncertain stimuli; Predicts when we will detect weak signals • Adds cognitive process of decision-making to sensation • Want to understand why people respond differently to the same stimuli and why the same person’s reactions vary as circumstances change

13. Signal Detection continued • In experiments… • A faint stimulus is presented at times, other times no stimulus is detected • See number 4 • Who cares? • Radiologists • Jury’s decision • Seismologist • Air traffic controller • Airport security • Soldiers

14. How does Sensory information get to the brain? • Through the process of transduction • Receptor cells are present in all sensory systems • Take one form of energy (pressure, light waves, vibrations, heat, etc.) and turn it into a neural impulse • The ONLY thing you brain can understand • Entire process is called transduction • Doctrine of specific nerve energies: even if the impulse on your optic nerve isn’t light, you will “see”