Chapter 4: Sensation and Perception

4.1 Understanding Sensation and Perception

• Main Idea:  Sensation is the process by which our five senses gather information and send it to the brain. Perception is the way in which we interpret this information.

• Reading Focus Questions:  What processes and concepts affect the stimulation of the senses? How does the process of sensory adaptation work? What is signal-detection theory?

Stimulation of the Senses

• Sensation: The stimulation of sensory receptors and the transmission of sensory information to the central nervous system (The spinal cord and brain).
• Perception: The psychological process through which we interpret sensory stimulation.
  • Perception reflects learning, expectations, and attitudes.
• Our senses are constantly absorbing information from our environment.

Absolute Threshold

• Absolute threshold: The weakest amount of stimulus that can be sensed.

Difference Threshold

• Difference threshold: The minimum amount of difference that can be detected between two stimuli.

Sensory Adaptation

• Sensory adaptation: The process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli.

Signal-Detection Theory

• Signal-detection theory: A method of distinguishing sensory stimuli that takes into account not only the stimuli’s strengths but also such variable elements as the setting, your physical state, your mood, and your attitudes.
  • Also considers psychological factors such as motivations, expectations, and learning.
• Under certain psychological factors, we make active decisions about what we perceive.

4.5 Perception

• Main Idea: Perception is the way in which we organize our sensory impressions. Movement, depth, and constancy are some of the ways in which we make sense of these impressions.
• Reading Focus Questions: What are the main rules of perceptual organization? How is movement perceived? What cues do we use for depth perception? What are perceptual constancies? Why do we see visual illusions?

Rules of Perceptual Organization

• Perception is the way we organize and make sense of all our sensory impressions

Closure

• Closure: The tendency to perceive a complete or whole figure even when there are gaps in what your senses tell you.

Figure-Ground Perception

• Figure-ground perception is the perception of figures against a background.
• What we perceive as the figure and what we perceive as the background influence our perception.

Other Rules of Organization

• Proximity: Two objects near each other belong together.
• Similarity: Similar objects belong together.
• Continuity: Continuing objects are organized rather than disrupted objects.
• Common fate: Things moving together belong together.

Movement

• We need to organized our perceptions of movements that only seem to occur but are actually illusions.

Perception of Movement

• To sense movement, humans need to see an object change its position relative to other objects.

Stroboscopic Motion

• Stroboscopic Motion: The illusion of movement is produced by showing the rapid progression of images or objects that are not moving at all.
  • Because of the law of continuity, humans prefer to see things as one continuous image,

Depth Perception

• The depth of objects is perceived through monocular and binocular cues.

Monocular Cues for Depth

• Monocular cues: Need only one eye to be perceived
  • Cause certain objects in a piece of artwork to appear more distant from viewer than others.
• Perspective is the tendency to see parallel lines as coming closer together, or converging, as they move away from us.
• Overlap is the perception of one object as being in front of another.
  • A monocular cue that tells us which objects are far away and which ones are near.
• Shadows and highlights also give us information about object’s three-dimensional shapes and where they are placed in relation to the source of light.
• Texture gradient is the surface quality and appearance of an object.
  • A monocular cue that is a progressive change (Denser when it is farther, less dense when it is closer).
• Motion parallax is the tendency of objects to seem to move forward or backward depending on how far away they are from the viewer.

Binocular Cues for Depth

• Binocular cues: need both eyes to be perceived
• Retinal disparity: Gives us a cue about the depth of an object.
  • For closer objects.
• Convergence is how close we feel out eyes moving toward each other when the object we look at becomes nearer.

Perceptual Constancies

Size Constancy

• Size constancy is the tendency to perceive an object as being of one size no matter how far away the object is.
  • Through experience, people acquire a sense of size constancy.

Color Constancy

• Color constancy is the tendency to perceive objects as keeping their color even though different light might change the appearance of their color.

Shape Constancy

• Shape constancy is the knowledge that an item has only one shape no matter what angle you view it from.

Brightness Constancy

• Brightness constancy is the tendency to perceive objects as being equally bright even when the intensity of the light around it changes.
  • We judge the brightness of an object by the brightness of other objects around it.

Visual Illusions

• Your brain can trick your eye because of its use of perceptual constancies.