Sensation and perception
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Sensation and Perception. Unit 4. The Basics of Sensation. Sensation Behavior often begins with sensory input Process by which we receive, transform, and process stimuli presented to sensory organs Sensory receptors – in sensory organs Detect stimuli from the outside world

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Sensation and Perception

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Sensation and perception

Sensation and Perception

Unit 4

The basics of sensation

The Basics of Sensation

  • Sensation

    • Behavior often begins with sensory input

    • Process by which we receive, transform, and process stimuli presented to sensory organs

    • Sensory receptors – in sensory organs

      • Detect stimuli from the outside world

      • Very sensitive to certain types of stimuli

      • Form of light, sound , odors

      • Psychophysics – how we experience such stimuli

The basics of sensation1

The Basics of Sensation

  • Absolute and Difference Thresholds

    • Absolute threshold

      • Smallest amount of stimulus reliably detected

      • Variation in sensitivity among individuals

  • Difference threshold: amount to determine difference of level of same stimulus

    • Just-noticeable difference (JND)

    • Weber’s law

    • Must change stimulus by a constant proportion for change to be detected

What do you see

What do You See?

The eye

The Eye

The Image

The Parts

The Eye: The Visionary Sensory Organ

Contains the sensory receptors to detect light

Cornea – transparent covering on the surface of the eye

Iris – Muscle surrounding pupil; adjust to permit entry of light – adjustment is a reflex

Pupil – size of opening is controlled by iris

The eye1

The Eye

The Image

The Parts

The Eye: The Visionary Sensory Organ

Lens – changes shape to adjust to distance of object (accommodation)

Retina – receives the image created by light striking it; contains photoreceptors – rods and cones

The eye2

The Eye

The Image

The Parts

Bipolar cells – interconnection cells

Ganglion cells – each projection axon is one nerve fiber

Optic nerve

Large bundle of ganglion nerve fibers

Transmits visual information to the brain

Creates blind spot


Contains only cones

Site for sharpest vision

Vision options

Vision Options

  • Color Vision: Sensing Color

    • Color Receptors (cones) transmit different messages to the brain

    • Hermann von Helmholtz – trichromatic theory

      • Three types of color receptors – red, green, and blue-violet

      • Dichromatic: only see two of the three color receptors

Vision options1

Vision Options

  • Color Vision: Sensing Color

    • Monochromatic: only see in shades of grey

The ear

The Ear

The ear1

The Ear

  • Sound: Sensing Waves of Vibrations

    • Energy that travels in waves (vibrations)

    • Must have a medium in order to exist

    • Characteristics

      • Amplitude (loudness) – the height of the wave

      • Frequency – number of complete waves, or cycles per second

      • Travels much more slowly than light

      • Measured in decibels (dB), and indication of perceived loudness

The ear2

The Ear

  • The Ear: A Sound machine

    • Sound waves are captured and converted to neural form

    • Ear components

      • Eardrum – membrane that vibrates in response to sound waves

      • Ossicles – three tiny bones in middle ear

        • Hammer (malleus)

        • Anvil (incus)

        • Stirrup (stapes)

      • Perception of pitch is related to wave frequency

The ear3

The Ear

  • Cochlea – fluid filled snail-shaped bony tube

  • Basilar membrane – vibrates within the cochlea

  • Organ of Corti – gelatinous structure lined with hairs cells

  • Hair cells – auditory receptors

  • Auditory nerve – transmits auditory messages to brain

  • Perception of pitch is related to wave frequency

Sensation and perception

Theories & Principles

  • Frequency theory

    • Perceived frequency depends on how often the auditory nerve fires

  • Volley principle

  • - If neurons work together and alternate their firing, they can exceed the limitations of 1,000 firing per second

  • Place Theory

    • Idea the each frequency vibrates at a particular spot on the basilar membrane

Sensation and perception

  • Olfaction: What Your Nose Knows

    • Chemicals in the air that the nose can respond to

    • Lock-and-key fitting of molecules into odor receptors

    • Olfactory nerve – transmits odor information to brain

    • Olfactory bulb – brain destination; odor information does not travel through thalamus

    • Pheromones – chemical substances that play a role in behavior

  • Taste: The Flavorful Sense

    • Four basic tastes: sweet, sour, salty and bitter

    • Flavors are a result of combinations of tastes

    • Taste cell – taste receptors

    • Taste buds – pores or opening on tongue

    • Taste sensitivity partly genetic

The sense of touch

The Sense of Touch

  • Sensed by the nerves just below the skin

    • Pressure

    • Pain

    • Temperature

The sense of touch1

The Sense of Touch

Sensation and perception

  • The Kinesthetic and Vestibular Senses: Of Grace and Balance

    • Kinesthetic sense tells us bout body position and body movement

    • Vestibular sense monitors body position in space

      • Aids in keeping one’s balance

      • Informs whether we are moving quickly or slowly

      • In ear’s semicircular canals – movement of fluid relates body position

      • Dizziness: semicircular canal fluid still moving though we have stopped

Sensation and perception

  • Perception: The Brain organizes and interprets sensations

  • Attention: did you Notice that?

    • Attention: the first step in perception

    • Selective attention: limit attention to certain stimuli

    • Habituation: results from exposure to a constant stimulus


Sensation and perception

  • Perceptual Constancies

    • Shape constancy – shape seen as the same across various perspectives

    • Size constancy – size perceived as same regardless of distance from perceiver

    • Color constancy – color perceived the same despite changes in lighting

    • Brightness constancy – brightness seen as the same though illumination may change

  • Cues to Depth Perception

    • Binocular cues – need both eyes

    • Retinal disparity – slightly differing image, what each eyes

What do you see1

What do You See?

  • Continuity

    • We tend to perceive figures or objects as belonging together if they appear to form a continuous pattern

  • Closure (Connectedness)

    • We perceive figures with gaps in them to be complete

  • Similarity

    • We perceive figures which look alike as being grouped together

  • Proximity

    • We perceive things close together as being in sets

What do you see2

What do You See?

Top down vs bottom up

Top-Down Vs. Bottom-UP

Top-Down processing looks first at the whole picture and then breaks it apart into pieces (deductive reasoning)

Top down vs bottom up1

Top-Down Vs. Bottom-UP

Bottom-Up looks first at the pieces and then creates the big picture (inductive reasoning)




Mashed Potatoes


Green Beans


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