Gen Psych - Sensation & Perception pt 1

Sensation & Perception

Part 1

Lesson Coverage

• Sensation and perception overview

• Moving from sensation to perception / psychophysics

• Thresholds, attention, and adaptation

• Vision

  • Biology of the eye

  • Visual perception

​Let's kick today off with an overview video

Perception

• Process of receiving stimulus energies from external environment and transmitting to brain
  - Top-down processing

Sensation

Sensation & Perception

• Process of processing, organizing, and interpreting sensory information
  - Bottom-up processing

Top-down vs. Bottom-up Processing

• With sensation, we are primarily concerned with what is known as “bottom-up processing”. Bottom-up processing is analysis that begins with the sense receptors and works up to the brain’s integration of sensory information.

• With perception, we are typically concerned with “top-down processing”. This is information processing that is guided by higher-level mental processes – as when we construct perceptions drawing on our own experience and expectations.

Moving from Sensation to Perception

Physics 101 - Transduction

• conversion of one form of energy to another

• in sensation, transforming of stimulus energies into neural impulses

For vision, this energy is electromagnetic – a spectrum ranging from imperceptible gamma rays to visible light to radio waves.

Our eyes are sensitive to one part of this spectrum, whereas other organisms are sensitive to other parts.

Transduction

Moving from Sensation to Perception

Moving from Sensation to Perception

Physics 101 - Physical Properties of Waves

• Wavelength / Frequency

  • distance from peak of one wave to peak of next

    • Hue (color)

    • pitch

• Intensity / Amplitude

  • amount of energy in a wave determined by amplitude

    • brightness

    • loudness

Physical Properties of Waves

Psychophysics

Study of the relationship between physical characteristics of stimuli and our psychological experience of them

• Light -  brightness

• Sound -  volume

• Pressure -  weight

• Taste -  sweetness

Sensation: Thresholds

• Absolute Threshold 

  • minimum stimulation needed to detect a particular stimulus 50% of the time

• Subliminal Perceptions

  • When stimuli are below one’s absolute threshold for conscious awareness

Sensation: Thresholds

• Signal Detection Theory

  • predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)

  • detection depends partly on person’s experience, expectations, motivation, and level of fatigue - e.g., more "hits" when motivated, more "misses" when tired...

Sensation: Thresholds

• Difference Threshold (just noticeable difference)

  • minimum difference between two stimuli required for detection 50% of the time

• Weber’s Law

  • to perceive as different, two stimuli must differ by a constant minimum percentage

    l light intensity - 8%

    l weight - 2%

    l tone frequency - 0.3%

Attention

• Attention

  • Selective

    • Cocktail party effect

  • Shiftable

    • Novelty, size, color movement

    • Inattentional blindness

Sensory Adaptation

• Diminished sensitivity as a consequence of constant stimulation

• AKA: "getting used to it" (video on next slide explains this nicely)

Sensory Adaptation

• Diminished sensitivity as a consequence of constant stimulation

• AKA: "getting used to it"

Not with vision - thank goodness!

The Senses

Yes, Virginia, there are more than 5 senses.

But we're going to cover the traditional five.
- Vision (seeing)
- Audition (hearing)
- Gustation (touching)
- Olfaction (smelling)
- Somatosensation (touching/feeling)

The Senses

Yes, Virginia, there are more than 5 senses.

But we're going to cover the traditional five.
- Vision (seeing)
- Audition (hearing)
- Gustation (touching)
- Olfaction (smelling)
- Somatosensation (touching/feeling)

​This lesson



Next lesson

Vision

Biology 101: The Eye

Vision: The Parts of the Eye

• Sclera

  • White, outer part of the eye; helps maintain shape of eye and protect eye from injury

• Pupil

  • Hole in the center of the eye
    that allows light to enter

• Iris

  • ring of colored muscle
    surrounding the pupil; controls size of pupil opening

Vision: The Parts of the Eye

• Cornea

  • transparent, dome-shaped window covering the front of the eye

​Fun fact: The cornea is extremely sensitive - there are more nerve endings in the cornea than anywhere else in the body.

Vision: The Parts of the Eye

• Lens

  • flexible piece of tissue that helps focus light toward the back of the eye

    • Focuses images on the retina…

Vision: The Parts of the Eye

• Retina - thin layer of tissue that covers the back of the eye and contains the light-sensitive receptor cells for vision

• Optic nerve - nerve that carries neural impulses from the eye to the brain

• Blind Spot - point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

• Fovea – “central pit” area in the retina where the cone receptors are located

Visual Receptor Cells

• Rods

  • Periphery of retina

  • detect black, white and gray

  • twilight or low light

  • ~ 120 million

• Cones

  • near center of retina, clustered at fovea

  • fine detail and color vision

  • daylight or well-lit conditions

  • ~ 6 million

"Hi. We are all named Rod."

Visual Processing

Optic Nerve à Optic Chiasm à Visual Cortex

Optic nerve fibers divide at optic chiasm:

• Left Visual Field  à   Right Hemisphere

• Right Visual Field  à   Left Hemisphere

Color Vision

Trichromatic (three color) theory

• Three types of cones, sensitive to different (but overlapping) ranges of wavelength

  • red

  • green

  • blue

​(This is what the previous video just covered...)

Color Vision

Color Blindness as support for Trichromatic Theory

• Color-deficient vision

  • People who suffer red-green blindness have trouble perceiving the number within the design

Color Vision

Opponent Processing theory

• Opposing retinal processes enable color vision 

​

​ “ON”  “OFF”

  red   green

  green   red

  blue   yellow

  yellow   blue

  black     white

  white      black

Perceiving Shape

• Gestalt Psychology

  • School of thought interested in how people naturally organize perception according to certain patterns

  • ‘Whole is different from sum of its parts.’

• Figure-Ground Relationship

  • Principle by which perceptual field is organized into stimuli that stand out (figure) and those left over (ground)

Perceiving Shape

• Figure-Ground Relationship

  • Principle by which perceptual field is organized into stimuli that stand out (figure) and those left over (ground)

Perceiving Shape

• What determines the figure vs. the ground?

  • Objective elements (e.g., shading)

  • Subjective elements (e.g., experiences & expectations)

Perceiving Shape

• Grouping

  • AKA Gestalt Laws

Perceiving Depth

• Ability to perceive objects three-dimensionally

• Learned:

  • Visual cliff experiment

Perceiving Depth

Binocular Cues à combined images from two eyes

• Disparity

• Convergence

​Disparity

Convergence

Perceiving Depth

Monocular Cues à available from image in one eye

• Occlusion

• Height in field

• Relative size

• Familiar size

• Linear perspective

• Texture gradiant

Perceiving Motion

• Motion aftereffects may occur when you gaze at a moving image for a long time and then look at a stationary scene.

• The waterfall effect is a momentary impression that the new scene is moving in the opposite direction from the moving image.

  • If you stare at a waterfall and then turn away, the new scenery may seem to move upward for a moment.

  • Motion aftereffects are strong evidence that motion-sensitive neurons exist in the brain.

Perceiving Motion

• Stroboscopic motion

  • Movies are made up of still images, each of which is slightly different from the one before it. When the series is presented fast enough, we perceive the illusion of motion pictures.

Perceiving Constancy

• Recognition that objects are constant even though sensory input is changing

  • Size

  • Shape

  • Color

  • Brightness

Attention / Comprehension Check Questions

6 questions @1 point each
5 points possible (so you can miss 1 and still get full points)

Multiple Choice

Which of the following is an example of sensory adaptation?

• Finding the cold water of a swimming pool warmer after you've been in it a while.

• Developing an increased sensitivity to salt the more you use it in foods.

• Becoming very irritated at the continuing sound of a dripping faucet.

• Zoning out on a long drive and not remembering seeing a house you passed.

Multiple Choice

When you can tell the difference between "OSU orange", "Oregon green", and "University of Portland purple", it is partly because the light stimuli differ in their _______. Said differently, this is the aspect of light waves that determines the color that we experience.

• amplitude

• rod density

• wavelength

• retinal intensity

Multiple Choice

In shopping for a new stereo, you discover that you cannot differentiate between the sounds of models X and Y. The difference between X and Y is below your:

• absolute threshold

• signal threshold

• difference threshold

• receptor threshold

Multiple Choice

After watching a scary movie at home one evening, Mariah became acutely aware of every small sound inside and outside of the house. She now heard noises that she may not have noticed before, like the hum of the refrigerator and the buzz of the lamp. The reason for her enhanced ability to notice these faint sounds can best be explained by which theory?

• dual processing theory

• opponent processing theory

• sensory inhibition theory

• signal detection theory

Multiple Choice

The quote, "Don't shoot until you can see the whites of their eyes" - usually attributed to William Prescott - refers to which structure of the eye?

• iris

• cornea

• retina

• sclera

Multiple Choice

When I look at an object, my left eye perceives the object slightly differently than my right eye perceives it. This provides me with which depth perception cue?

• disparity

• convergence

• relative size

• occlusion

Coming up...

We will finish our coverage of sensation and perception during our next class. You should begin studying (if you haven't already) for our first exam, which will be next Thursday. You can get ahead by doing the Chapter 5 InQuizitive quiz...

See you Tuesday!