The Interpretation of Sensory Information

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”

Sensation x Perception

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.

The World and Our Perceptions of It

Perception of Minimal StimuliSensory 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

Perception of Minimal StimuliSensory 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)

Perception of Minimal StimuliSensory 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

Perception of Minimal StimuliSensory 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.

Perception of Minimal StimuliSensory 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.

Perception of Minimal StimuliSensory Thresholds and Signal Detection

Implication:

The people’s answers depend on the instructions and their strategies, not just their senses.

Perception of Minimal StimuliSensory 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)

Perception of Minimal StimuliSensory 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.

Perception of Minimal StimuliSensory 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

Perception of Minimal StimuliSubliminal 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

 

Perception of Minimal StimuliSubliminal 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

 

Perception of Minimal StimuliSubliminal 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.

Perception of Minimal StimuliSubliminal 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.

Perception of Minimal StimuliSubliminal 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)

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. 

Perception and the Recognition of Patterns

Face recognition

We recognize people by hair as well as facial features.

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