The Interpretation of Sensory Information (concise presentation)

1. The Interpretation of
Sensory Information

2. Psychophysics
Psychophysics - is the study of the
relationships between sensory experiences and
the physical stimuli that cause them.
Sensation – “window”
Perception – interpretation of what comes into
our “window”

3. Sensation x Perception

4. The World and Our Perceptions of It
“A picture is worth a thousand words.” – Napoleon
Bonaparte
"One look is worth a thousand words.“
A complex idea can be conveyed with just a single
still image.
One of the main goals of visualization is making it
possible to absorb large amounts of data quickly.

5. The World and Our Perceptions of It

6. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Some of the earliest psychological researchers tried to
determine the weakest sounds, lights, and touches that
people could detect.
Absolute Sensory Threshold – is intensity at which a
given individual detects a stimulus 50% of the time.
= lowest level at which a stimulus can be detected
Senses Minimum Stimuli
Vision A candle flame seen at 30 miles on a dark, clear night
Hearing The tick of a clock at 20 feet under quiet conditions
Taste One teaspoon of sugar in 2 gallons of water
Smell One drop of perfume diffused into six rooms
Touch The wing of a fly falling on your cheek from a distance of 1 cm

7. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Noise – is a background stimulation that interferes with the
perception of other stimuli, as defined by psychophysicists.
Terminal Threshold – is the maximum intensity of
stimulation that the individual perceives in a normal way.
Just Noticeable Difference or Difference Threshold – is
the smallest difference that people could detect between
one stimulus and another. (introduced by Ernst Weber)

8. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
When people try to detect weak stimuli, they can be correct
in two ways:
Stimulus actually
present
Stimulus actually
absent
Report stimulus
present
Hit False alarm
Report stimulus
absent
Miss Correct rejection

9. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Signal-Detection Theory – is the study of people’s
tendencies to make hits, correct rejection, misses, and
false alarms.
• The people’s responses depend on their willingness
to risk misses or false alarms.
Experiment 1 -- Instructions:
Suppose you are the participant and you are told that:
a.) you will receive a 10-cent reward for correctly
reporting that a light is present. You will be penalized 1
cent for reporting that a light is present when it is not.

10. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
b.) you will receive a 1-cent reward for correctly
reporting that a light is present. You will be
penalized 10 cents and subjected to an electric
shock for reporting that a light is present when it is
not.

11. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Implication:
The people’s answers depend on the instructions and their
strategies, not just their senses.

12. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Experiment 2:
Participants were asked to read words that flashed
briefly on a screen.
a.) Ordinary words (such as river or peach)
b.) Emotionally loaded words (profanity)

13. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
Results:
a.) The participants were able to perform well.
b.) The participants said that they were not sure with
what they saw.

14. Perception of Minimal Stimuli
Sensory Thresholds and Signal Detection
In other settings…
The legal system is also a signal-detection situation.
The jury can be right in two ways and wrong in two
ways:
Defendant is “guilty” Defendant is “innocent”
Jury votes “guilty” Hit False alarm
Jury votes “not guilty” Miss Correct rejection

15. Perception of Minimal Stimuli
Subliminal Perception
Subliminal Perception – is the idea that stimuli
sometimes influence our behavior even when they are
presented so faintly or briefly that we do not perceive them
consciously.
Choosing how to perceive them
has been an
interesting topic for
children of all ages and the
knowledge of their
existence keeps people up to all hours of the
Night

16. Perception of Minimal Stimuli
Subliminal Perception
Choosing how to perceive them
has been an
interesting topic for
children of all ages and the
knowledge of their
existence keeps people up to all hours of the
Night

17. Perception of Minimal Stimuli
Subliminal Perception
What Subliminal Perception Cannot Do
Claim: Subliminal messages could control people’s
buying habits.
“EAT POPCORN” – in the middle of a film
*Customers who were not aware of the message could
not resist so they would flock to the concession stand to
buy popcorn.
Claim: Certain rock-’n’-roll recordings contain satanic
messages that were recorded backward.
*Researchers found out that people listening to
backward message cannot determine what it would
sound like forward, and the messages do not influence
behavior.

18. Perception of Minimal Stimuli
Subliminal Perception
Claim: “Subliminal audiotapes” with faint, inaudible
messages can help you improve your memory, quit
smoking, lose weight, raise your self-esteem, and so
forth.
*The improvement depended on people’s expectations,
not the tapes.

19. Perception of Minimal Stimuli
Subliminal Perception
What Subliminal Perception Can Do
Claim: Subliminal messages do produce effects,
although most are brief and subtle.
*Happy --- Neutral --- Angry
*Fear x Scary movie --- Disgust x Strange food
*Handgrip response --> stronger handgrip (with reward)

20. Perception and the Recognition of Patterns
Brightness contrast – is the increase or decrease in an
object’s apparent brightness by comparison to objects around
it.

21. Perception and the Recognition of Patterns
Face recognition
We recognize people by hair as well as facial features.

22. Perception and the Recognition of Patterns
The Feature-Detector Approach
Feature Detectors – are specialized neurons in the visual
cortex which respond to the presence of simple features.
Do Feature Detectors Explain Perception?
Feature detectors cannot completely explain how we
perceive letters, much less faces. Perception of a
pattern requires more than just simple feature detectors