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Thresholds & Signal Detection Theory

  • 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.

  1. Intro
    • Sensation and Perception (6-8%)
    • General Properties of Sensory Systems
    • Sensation and Perception
    • Terms
    • Psychophysics
    • Ernst Weber
    • Gustav Fechner
    • Sensory Transduction
    • Absolute Threshold
    • Difference Threshold
    • Weber's Law
    • Signal Detection
    • Sensory Adaptation
    • Top-Down Processing
    • Bottom-Up Processing (AKA Feature Analysis)
    • Sensation Chart Overview
    • David Hubel and Torsten Wiesel
    • Perceptual Set
    • Perceptual Set
    • Perceptual Set -- Culture and Context Effects
    • Perceptual Set -- Culture and Context Effects
    • Basic Illusions -- Muller-Lyer
    • Basic Illusions -- Poggendorf
    • Basic Illusions -- Ponzo
    • Basic Illusions -- Hermann Grid
    • Attention
    • Perceptual Defense and Subliminal Perception
    • Review
    • Intro 0:00
    • Sensation and Perception (6-8%) 0:09
      • 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
    • Terms 2:58
      • Psychophysics
      • Sensory Transduction
      • Absolute Threshold
      • Difference Threshold
      • Signal Detection
      • Sensory Adaptation
      • Bottom-Up Processing
      • Top-Down Processing
      • Weber's Law
    • Psychophysics 3:22
      • 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
      • Influenced Psychophysics
      • 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
      • Deductive Reasoning
      • 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
    • Attention 45:04
      • 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
    • Review 51:26
      • 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?
      • Do We Really Share the Same Reality? Explain.