Chapter 5: Sensation and Perception 

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• Sensation:  is the stimulus detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain
• Perception: making “sense” of what our senses tell us—is the active process of organizing this stimulus input and giving it meaning

Sensory Processes

• Transduction:  is the process whereby the characteristics of a stimulus are converted into nerve impulses
• Psychophysics: studies relations between the physical characteristics of stimuli and sensory capabilities
• Absolute Threshold: the lowest intensity at which a stimulus can be detected 50 percent of the time
• Decision Criterion: a standard of how certain they must be that a stimulus is present before they will say they detect it
• Signal-Detection Theory: is concerned with the factors that influence sensory judgments
• Difference Threshold (just noticeable difference(jnd)): is defined as the smallest difference between two stimuli that people can perceive 50 percent of the time
• Weber’s law: states that the difference threshold or jnd is directly proportional to the magnitude of the stimulus with which the comparison is being made
• Sensory adaptation: the diminishing sensitivity to an unchanging stimulus

Vision

• Lens: an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects
• Retina: a multi-layered light-sensitive tissue at the rear of the fluid-filled eyeball.
• Rods:  which function best in dim light, are primarily black-and-white brightness receptors
• Cones: are color receptors, function best in bright illumination
• Fovea: a small area in the center of the retina that contains no rods but many densely packed cones
• Visual Acuity: ability to see fine detail
• Photopigments: Rods and cones translate light waves into nerve impulses through the action of protein molecules
• Dark Adaption: the progressive improvement in brightness sensitivity that occurs over time under conditions of low illumination
• Young-Helmholtz trichromatic theory: there are three types of color receptors in the retina
• Hering’s opponent-process Theory: proposed that each of the three cone types responds to two different wavelengths
• Dual-Process Theory: combines the trichromatic and opponent-process theories to account for the color transduction process
• Feature Detectors: fire selectively in response to visual stimuli that have specific characteristics

Audition

• Frequency: the number of sound waves, or cycles, per second
• Hertz(Hz): the technical measure of cycles per second; 1 hertz equals 1 cycle per second
• Amplitude: refers to the vertical size of the sound waves—that is, the amount of compression and expansion of the molecules in the conducting medium
• Cochlea: a coiled, snail-shaped tube about 3.5 centimeters (1.4 inches) in length that is filled with fluid and contains the Basilar Membrane
• Basilar Membrane: a sheet of tissue that runs its length.
• Organ of Corti: contains about 16,000 tiny hair cells that are the actual sound receptors
• Frequency Theory of Pitch Perception: nerve impulses sent to the brain match the frequency of the sound wave
• Place Theory of Pitch Perception: suggesting that the specific point in the cochlea where the fluid wave peaks and most strongly bends the hair cells serves as a frequency coding cue
• Conduction Deafness:  involves problems with the mechanical system that transmits sound waves to the cochlea
• Nerve Deafness: caused by damaged receptors within the inner ear or damage to the auditory nerve itself

Taste and Smell: the Chemical Senses

• Gustation: the sense of taste
• Olfaction: the sense of smell
• Taste buds: chemical receptors concentrated along the tip, edges, and back surface of the tongue
• Olfactory Bulb: a forebrain structure immediately above the nasal cavity
• Pheromones: chemical signals found in natural body scents
  • Can affect human behavior in subtle ways

The Skin and Body Senses

• Gate Control Theory: proposes that the experience of pain results from the opening and closing of gating mechanisms in the nervous systems
• Kinesthesis: provides us with feedback about our muscles’ and joints’ positions and movements
• Vestibular sense: the sense of body orientation or equilibrium

Perception: The Creation of Experience

• Bottom-up Processing: the system takes in individual elements of the stimulus and then combines them into a unified perception
• Top-Down Processing:  sensory information is interpreted in light of existing knowledge, concepts, ideas, and expectations
• Inattentional Blindness: refers to the failure of unattended stimuli to register in consciousness
  • Backed up why you shouldn’t be on your phone while driving
• Gestalt Theories:
  • Figure-Ground relations: tendency to organize stimuli into a central or foreground figure and a background
  • Gestalt Theory of Perceptual Organization: similarity, proximity, closure, and continuity
  • Examples include the duck/rabbit image, is it a vase or two people kissing, etc
• Perceptual Schema: a mental representation or image containing the critical and distinctive features of a person, object, event, or other perceptual phenomena
• Perceptual set: a readiness to perceive stimuli in a particular way
• Perceptual Constancies: allow us to recognize familiar stimuli under varying conditions

Perception of Depth, Distance, and Movement

• Monocular Depth Cues: which require only one eye
  • Cues include patterns of light and shadow, linear perspective, interposition, height, relative size, motion parallax.
• Binocular Depth Cues: requires both eyes
  • Binocular Disparity: where each eye sees a slightly different image
  • Convergence: is produced by feedback from the muscles that turn your eyes inward to view a close object
• Stroboscopic movement: illusory movement produced when a light is briefly flashed in darkness, and then, a few milliseconds later, another light is flashed nearby
• Illusions: compelling but incorrect perceptions
• Critical Periods: during which certain kinds of experiences must occur if perceptual abilities and the brain mechanisms that underlie them are to develop normally

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