Sensation & Perception

06-A: Sensation vs. Perception

  • What is the difference between sensing and perceiving?

  • What is a stimulus?

First, it is important to distinguish between the two terms we are using.

Sensation occurs when a stimulus (e.g., a sound, light, smell, touch or taste) is detected by receptors in your body. So, for example, your skin might sense a change in temperature, your eyes might sense an increase in orange light, your nose might sense the odor of smoke. Sensory organs like your eyes, ears, nose and tongue are designed to receive stimuli.

Perception occurs when the brain receives the sensory input coming in from the body, organizes it, and interprets it. In our example, your eye senses green and brown light, long and round shapes, and you perceive a tree.

06-B: The Eye

  • What is the location and function of each of the following parts in your eye?

    • Aqueous humor (E)

    • Ciliary muscle (F)

    • Cones

    • Cornea (A)

    • Fovea (I)

    • Iris (B)

    • Lens (C)

    • Optic nerve (K)

    • Optic disk (also called optic nerve head) (J)

    • Pupil (D)

    • Retina (H)

    • Rods

    • Vitreous body (G)

  • How does your eye allow you to focus on objects at different distances?

  • What do rods and cones do on the retina?

READ: Use The Human Eye to help label the parts listed above and learn why there is a blind spot, how and why the lens changes shape, and the general difference between rods and cones. The page goes into more details than you will need.

READ: Human Eye Anatomy: Parts of the Eye - Note that you should scroll over the different parts of the eye on the diagram to learn more about what each does

READ: The Retina for more on the fovea

WATCH: How the Body Works: The Focusing Mechanism

06-C: Perceiving Depth

  • How do each of the monocular cues help us perceive our three-dimensional world with the sensory input of only one eye?

    • Accommodation

    • Familiar size

    • Interposition

    • Linear perspective

    • Motion parallax

    • Relative height

    • Shadow

    • Texture gradient

  • How does your brain use sensory input from two eyes (binocular cues) to perceive depth in even greater detail using binocular disparity?

  • How do 3D glasses trick your eyes into perceiving depth from a flat screen?

  • What are the advantages and disadvantages of having two forward-facing eyes vs. two side-facing eyes?


VISIT: Depth Cues

06-D: The Ear

  • What is the location and function of each of the following parts of your ear?

    • Outer ear

      • Pinna

      • Auditory canal

      • Tympanic membrane

    • Middle ear

      • Malleus

      • Incus

      • Stapes

    • Inner Ear

      • Cochlea

      • Semicircular canals

  • How does the ear sense sound waves? Be sure that your explanation describes how waves enter the ear and the role of the tympanic membrane, bones, and cochlea. Also clarify at what point vibrations are converted to electrical impulses that your brain can receive.


VISIT: The Ear

06-E: Localizing Sounds

  • Why is it important that organisms are able to determine where a sound is coming from?

  • How does the brain use sensory input from the ears to localize sound?

    • Arrival time

    • Intensity

    • Visual Capture

  • How do bats and dolphins use a similar process echolocation to localize prey?


READ: Localization (Sensory)

VISIT: Echolocation

06-F: Smell

  • How does the nose detect smell?

  • How does what we smell influence what we taste?


WATCH: How do we smell?

WATCH: Smelling and Tasting

06-G: Bottom-up vs. Top-down Processing

  • What happens when we process stimuli in a bottom-up fashion?

  • What does it mean to say we are processing a stimulus in a top-down fashion? Be sure that you can provide several examples, including

    • Pattern recognition

    • Phonemic restoration

    • Visual capture

    • Reading comprehension

    • Perceptual contrast

  • Why would we say that perception is subjective?


VISIT: Bottom-up vs Top-down Processing

06-H: Gestalt Psychology

  • What does "gestalt" mean?

  • What are some of the key ways in which our personal experience is influenced by our expectations?

    • Proximity

    • Similarity

    • Good continuation

    • Closure

  • What are some of the ways we tend to detect the figure as separate from the ground?

    • Area

    • Symmetry

The word Gestalt is German for “whole” or “form” and, in psychology, refers to the idea that what we perceive from top-down processing has more meaning than what would be perceived from simply bottom-up processing. Psychologists that study perception have identified a number of principles that influence our perception. Think of these specific principles as further examples of top-down processing, but know and be able to draw diagrams for the principles listed above:

READ: Gestalt Theory of Visual Perception

You can also see the following for more examples:

http://courses.csail.mit.edu/6.831/archive/2008/lectures/L15-graphic-design/image024.png

06-I: Proprioception

  • What is proprioception? How is it distinct from your other senses (especially touch)?


VISIT: What Is Proprioception?

Interested in learning more?

Ever wonder why dogs have such an amazing sense of smell? Did you know there is a great reason why their noses evolved to have an opening slit on the sides? For this and a lot of other fascinating facts about your puppy's nose, read:

Dogs' Dazzling Sense of Smell (PBS)