In this lesson, our instructor, Charles Schallhorn examines the absolute and difference thresholds and signal detection theory. He looks at Weber's Law and the concepts of top-down and bottom-up processing (feature analysis) . He looks at the concept of perpetual sets and shows some basic optical illusions which rely on one's error in top-down processing.
Psychophysics is the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them
Ernst Weber was a founder of early experimental psychology and studied absolute thresholds
Gustav Fechner founded psychophysics and showed the relationship between a psychological sensation and physical intensity of a stimulus
Sensory transduction is the conversion of one form of energy into another such as transforming wave energies of sight and sound into electrical signals the brain can interpret
Weber’s Law is the amount of change needed to produce a constant just-noticeable difference
Signal Detection theory predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness
Sensory adaptation is when neural or sensory receptors reduce their sensitivity to a continuous, unchanging stimuli
Top-down processing is information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations
Bottom-Up Processing is analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information
Hubel and Wiesel showed how there are neurons in the brain the deal with specific aspects of a stimulus and not the entire set of information entering the visual system
Perceptual set is a mental disposition to perceive one thing and not another
Subliminal perception is not what most people think of and is not a reliable way to change behavior
Thresholds & Signal Detection Theory
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
Everything That Organisms Know About the World is First Encountered When Stimuli in the Environment Activate Sensory Organs, Initiating Awareness of the External World.
Perception Involves the Interpretation of the Sensory Outputs as a Cognitive Process
Discuss Basic Principles of Sensory Transduction, Including Absolute Threshold, Difference Threshold, Signal Detection and Sensory Adaptation.
Discuss How Experience and Culture can Influence Perceptual Processes (e.g. Perceptual Set, Context Effects)
General Properties of Sensory Systems 1:16
Data Reduction System: Any System That Selects, Analyzes, and Condenses Information
Perceptual Features: Basic Stimulus Patterns
Sensory Coding: Converting Important Features of the World Into Neural Messages Understood by the Brain
Sensation and Perception 2:12
Sensation: Information Arriving From Sense Organs (Eye, Ear, Etc.)
Perception: Mental Process of Organizing Sensations Into Meaningful Patterns
The Study of the Relationships Between the Physical Characteristics of Stimuli, Such as Their Intensity, and Our Psychological Experience of Them
Ernst Weber 4:24
A Founder of Modern Experimental Psych
Studied Weight Perception and How There was a Proportional Relationship Between Increase of Magnitude of Weight and Ability to Make the Discrimination Between the Weights(Fechner Later Called it Weber's Law)
Weber-Fechner Law -- Ratio of Intensity to Have a Just Noticeable Difference (JND)
Studied Absolute Thresholds -- Our Awareness of Faint Stimuli
Gustav Fechner 6:29
Influenced Modern Experimental Psych
Founder of Psychophysics
Studied Absolute Thresholds -- Our Awareness of Faint Stimuli
Illustrated the Non-Linear Relationship Between Psychological Sensation and Physical Intensity of a Stimulus
Weber-Fechner Law -- Ratio of Intensity to Have a Just Noticeable Difference
Sensory Transduction 7:32
Conversion of One Form of Energy Into Another. In Sensation, The Transforming of Stimulus Energies, Such as Sights, Sounds, and Smells Into Neural Impulses Our Brains Can Interpret.
Absolute Threshold 8:22
The Minimum Stimulation Necessary to Detect a Particular Stimulus 50% of the Time
Exploited by Students Who May Use the Mosquito Ringtone to Evade Phone Use in Class
Vision -- Candle Flame Seen at 30 Miles on a Clear Dark Night
Hearing -- Tick of a Watch Under Quiet Conditions at 20 Feet (The Buzz of the Fluorescent Lights in a Quiet Room)
Taste -- One Teaspoon Sugar in 2 Gallons of Water
Smell -- One Drop Perfume Diffused Into a Three-Room Apartment
Touch -- A Bee's Wing Falling On Your Cheek from One Centimeter Above.
Difference Threshold 11:11
The Minimum Difference Between Two Stimuli Required for Detection. We Experience the Difference Threshold as a Just Noticeable Difference (JND).
The Detectable Difference Increases With the Magnitude -- is Done in a Constant Proportion
E.g. You Will Notice is One Ounce is Added to a 10 Ounce Weight, But Not if One Ounce is Added to a 100-Ounce Weight
Volume on the Television
Weber's Law 12:40
The Principle That, to be Perceived as Different, Stimuli Must Differ by a Constant Percentage (Rather Than a Constant Amount)
The Amount of Change Needed to Produce a Constant JND is a Constant Proportion of the Original Stimulus Intensity
Signal Detection 13:21
A Theory Predicting How and When We Detect the Presence of a Faint Stimulus (Signal) Amid Background Stimulation (Noise).
Assumes There is no Absolute Threshold and that Detection Depends Partly on a Person's Experience, Expectations, Motivation, and Alertness
Separating the Music From the Noise or the Signal From the Noise
Important Info Versus Background and Irrelevant
Sensory Adaptation 15:47
AKA Neural Adaptation
Neural or Sensory Receptors Change/Reduce Their Sensitivity to a Continuous, Unchanging Stimuli
This Occurs in the Brain at an Unconscious Level
E.g. The Smell of Your Own Car or Home
E.g. Adapting to Hot or Cold Water After a Brief Time in It.
E.g. The Eyes Adjusting to a Darker Room -- Rods and Cones Will Fire Differently to Adjust (Cones Take About 10 Minutes, the Rods 30 Minutes to Fully Adapt)
Why Certain Foods Do Not Taste the Same on the 20th Bite as They Did on the First
In Economics, This is Diminishing Marginal Utility
NOT The Same as Habituation (We Will Go Over That Later)
Top-Down Processing 19:42
Information Processing Guided by Higher-Level Mental Processes, as When We Construct Perceptions Drawing on Our Experience and Expectations
People Look at the Big Picture, the Whole, Try to Find Patterns to Make Meaning and Then Examine the Details (We Use Background Knowledge to Fill Gaps)
The Stroop Effect Was One Experiment That Dealt With This
Even Though the Second Letter in Each Word is Ambiguous, T-D Processing Allows for Context to Clarify For Us
Bottom-Up Processing (AKA Feature Analysis) 22:47
Analysis That Begins With the Sensory Receptors And Works Up to the Brain's Integration of Sensory Information
Works From the Details and Moves Out to the Whole Picture
Inductive Reasoning -- Going From the Examples First and Working One's Way Out to the General Propositions -- Uses Probabilities Based Upon Specific Observations
Based Upon Current Knowledge, So Potentially Biased (e.g. Confirmation Bias, Availability Heuristic, Illusory Correlation)
e.g. Since 100% of Bio Life Forms Depend on Liquid Water to Exist, if We Were to Discover a New Bio Form, It Will Probably Depend on Liquid Water to Exist
Man With Prosopagnosia
Sensation Chart Overview 27:06
Chart Looks at Sense, Stimulus, Sense Organ, Receptor, and Sensation
David Hubel and Torsten Wiesel 29:42
Nobel Prize with Wiesel and Sperry
Microelectrode in Cat Brain -- When Would Neurons Fire When Cat Presented With Simple Lines
Worked on Visual System Neurons and Processing Certain Neurons Responded Only to Certain Lines -- Simple Cells
Other Cells Detected Motion -- Complex Cells
Cats and Restricting Visual System
Showed How the Visual System Built an Image From Simple Stimuli by Combining Them Into More Complex Formats
Big Idea Here is Feature Detectors -- Certain Brain Cells Pick Up Certain Kinds of Visual Stimulation -- Vertical Lines, Curves. Motion, Etc.
Perceptual Set 31:51
A Mental Disposition to Perceive One Thing and Not Another
This Goes Back to the Simon and Garfunkel Song
We See What We Want to See
E.g. Friendliness Is Mistaken for Flirting if We Find The Other Person Attractive
Perceptual Set 34:29
Is This a Cloud or a Flying Saucer?
Perceptual Set -- Culture and Context Effects 35:34
Magic -- Creates Certain Expectations and Uses Movements to Distract the Eye
I am 6'3 -- When I'm Standing Next to 4th Graders, I Appear to be Huge. If at an NBA Game, I Look Pretty Small
Our Moods and Circumstances Can Create Some Top-Down Processing Errors -- Have You Ever Been in a Bad Mood and Thought Someone Slammed You But They Really Said Something Else?
Walter Cronkite Was Sailing Into a Port and Thought the Crowd was Saying Hello Walter Repeatedly. The Reality Was Low Water
Cultures -- Not All Cultures Perceive the Same Stimuli Equally -- Shaping Stereotypes, Directing Our Attention, and Telling Us What Is Important to Notice
Perceptual Set -- Culture and Context Effects 38:53
James Burke, an Historian, Had a Great Segment in The Day The Universe Changed -- We All See Our Own Witches -- We Change our Perceptions to Make it Fit the Reality of What We Think It Should Be
Rural Africans in One Study Live in an Environment Without Right Angles -- They Were Less Likely to Fall For the Muller-Lyer Illusion
Basic Illusions -- Muller-Lyer 41:12
Which of These Three Lines is Longer? (They are All The Same Length)
Basic Illusions -- Poggendorf 42:22
Is There One Straight Line or Two Line Segments on Each Side?
Basic Illusions -- Ponzo 43:19
Which Line Appears Longer? The one In Between Tracks or the One Lying Across It?
Basic Illusions -- Hermann Grid 44:06
The Appearance of White and Black Dots Moving Between Each Gray Line's Intersection
Selective Attention -- The Focusing of Conscious Awareness on a Particular Stimulus
Inattentional Blindness -- Failing to See Visible Objects When Our Attention is Directed Elsewhere
Change Blindness -- Failing to Notice Changes in the Environment
Perceptual Defense and Subliminal Perception 49:26
Subliminal Perception: Perception of a Stimulus Below the Threshold for Conscious Recognition
What's the Difference Between Sensation and Perception?
What Process Does the Brain Have of Converting Wave Signals into Electrical Signals?
Science of Physical Properties and Human Perceptions is Called…?
Describe Absolute Threshold, Difference Threshold, and Weber's Law
Describe the Impact of Hubel and Weisel
How Do Perceptual Sets Alter Our Views as Compared to Reality?
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