Chapter 3 Notes: Sensation and Perception (Rathus, 7th Edition)

Sensation and Perception — Chapter 3 (Notes from Rathus, 7th Edition)

Chapter Objectives

  • 03.01 Define and differentiate between sensation and perception.
  • 03.02 Identify the parts of the eye; explain the properties of light and the theories of color vision.
  • 03.03 Describe the organization of visual perceptions.
  • 03.04 Identify the parts of the ear; explain how the sense of hearing works.
  • 03.05 Describe the functioning of the chemical senses, the skin senses, kinesthesis, and the vestibular sense.
  • 03.06 Explain why psychologists are skeptical about extrasensory perception.

Sensation vs Perception

  • Sensation: stimulation of sensory receptors located in sense organs; transmission of sensory information to the central nervous system.
  • Perception: active process by which sensations are organized and interpreted into an inner representation of the world.
  • Example: A hammer hitting a foot may be just sensation if the message does not reach the brain; perception occurs once the brain interprets the signal.

Transduction

  • Sensation: activation of receptors in the various sense organs.
  • Sense organs include: eyes, ears, nose, skin, taste buds.
  • Transduction converts outside stimuli into neural activity that the brain can process.

How We Understand Stimuli

  • Transduction: turning outside stimuli into neural activity.
  • Sensory receptors: specialized neurons stimulated by energy (not neurotransmitters) to change neural activity.
  • Receptors respond to different kinds of energy (light, sound, chemical, touch).

Sensory Thresholds: What Gets Our Attention?

  • Absolute threshold: the minimum intensity of stimulation that must occur before you experience a sensation. Denoted as the minimum I such that sensation is detected.
  • Difference threshold: the minimum amount of change required for a person to detect a difference between two stimuli.
  • Just Noticeable Difference (JND): the smallest detectable difference between two stimuli.
  • Examples of absolute thresholds (from everyday senses):
    • Sight: a candle flame at 30 miles on a clear, dark night.
    • Hearing: the tick of a mechanical watch 20 feet away in a quiet room.
    • Smell: one drop of perfume diffused throughout a three-room apartment.
    • Taste: 1 teaspoon of sugar in 2 gallons of water.
    • Touch: a bee’s wing falling on the cheek from 1 centimeter above.

Signal-Detection Theory

  • Perception of sensory stimuli involves an interaction of physical, biological, and psychological factors.
  • Sensory adaptation:
    • Positive adaptation (sensitization): increased sensitivity to low-magnitude stimuli.
    • Negative adaptation (desensitization): decreased sensitivity to stimuli of the same intensity.
  • Note: Signal-detection theory emphasizes how thresholds can shift with expectancies, motivation, and fatigue.

Subliminal Stimulation and Perception

  • Subliminal stimuli: stimuli below the level of conscious awareness; just strong enough to activate receptors but not to create conscious experience.
  • Limin: “threshold”; sublimin: “below the threshold.”
  • Subliminal perception: the process by which subliminal stimuli influence the unconscious mind and potentially behavior, though effects are typically weak and context-dependent.

Light and Vision: Basic Concepts

  • Light is a spectrum of electromagnetic energy.
  • Humans see only a small portion of the spectrum.
  • Electromagnetic energy travels in wavelengths; within visible light, color is determined by wavelength.
  • Wavelength determines hue; intensity relates to brightness.

The Eye: Structure and Function

  • Light enters through a narrow opening.
  • Cornea: the transparent outer covering.
  • Iris: muscular, colored part of the eye.
  • Pupil: opening in the iris; size responds to light and emotional state.
  • Lens: changes thickness to adjust (accommodation) for focusing.
  • Retina: light is projected here for processing by photoreceptors.

Rods and Cones; Visual Processing

  • Cones:
    • Densely packed at the center of the retina (fovea).
    • Provide color vision.
  • Rods:
    • Provide vision in black and white; more sensitive to dim light.
  • Visual Acuity:
    • Linked to the shape of the eye.
    • Nearsighted (myopia): requires close objects; farsighted (hyperopia): difficulty focusing on nearby objects.
  • Presbyopia: aging-related lens change making near vision harder.
  • Blindspot: area where axons converge to form the optic nerve; no photoreceptors there.
  • Light adaptation vs. dark adaptation:
    • Light adaptation: improved clarity when moving from dark to light.
    • Dark adaptation: increased sensitivity over time in darkness; rods and cones adjust at different rates; brighter light is adjusted faster.

Color Vision

  • Hue: determined by wavelength; Value: brightness; Saturation: intensity of color perceived.
  • Cultural associations influence color perception.

Color Vision Deficiencies

  • Trichromat: normal color vision (sensitive to red/green, blue/yellow, and light/dark).
  • Monochromat: totally color-blind (only lightness/darkness discrimination).
  • Dichromat: partial color blindness (two colors discriminated; e.g., red/green or blue/yellow).
  • Prevalence varies; many people are not color-blind.

The Visual System (Transduction)

  • Transduction is the chemical message that gets back to the brain.
  • Pathway from retina to brain involves optic nerve and various brain regions that interpret the signal.

Hearing (Audition)

  • Audition: hearing; the sense of sound perception.
  • Sound wave: pattern of changes in air pressure over time; produces perception of sound.
  • Amplitude determines loudness; frequency determines pitch.
  • Sight and audition are different sensory modalities with distinct energy forms (light vs. sound).

The Ear: Outer, Middle, and Inner Structures

  • Outer ear: funnels sound waves to the eardrum (tympanic membrane).
  • Middle ear: contains tympanic membrane, hammer (malleus), anvil (incus), stirrup (stapes); acts as an amplifier.
  • Oval window and round window balance pressure for inner ear transduction.
  • Inner ear: cochlea; basilar membrane inside the cochlea; Organ of Corti attached to the basilar membrane.
  • Hair cells move in response to basilar membrane vibrations; neural impulses are triggered and transmitted via the auditory nerve.
  • Localization of sound: directional cues come from the timing and intensity differences as sounds reach each ear.

Pitch and Loudness in Hearing

  • Hertz (Hz): unit of frequency (pitch).
  • Decibels (dB): unit of loudness (amplitude of sound waves).
  • Frequency determines pitch; amplitude (and thus loudness) contributes to perceived intensity.

The Ear: Inner Details and Deafness

  • Inner ear processes vibrations into neural signals; the auditory nerve transmits to the brain.
  • Conductive deafness: due to damage to the middle ear; hearing aids can help.
  • Sensorineural deafness: due to damage to inner ear structures or auditory nerve; cochlear implants may help but cannot restore normal auditory nerve function if the nerve is damaged.

The Chemical Senses: Smell (Olfaction) and Taste (Gustation)

  • Smell: odors are molecules in the air that trigger receptor neurons in the olfactory membrane; information is sent to the brain via the olfactory nerve.
  • Taste: taste buds contain taste receptor cells; five basic tastes are Sweet, Sour, Salty, Bitter, and Umami (brothy taste).
  • Flavor is a combination of odor, texture, temperature, and taste.
  • Some people have superior taste sensitivity; taste sensitivity varies.
  • Taste pathways involve cranial nerves, the thalamus, and other brain areas.
  • Five basic tastes and possible sixth: oleogustus (fatty acids).

The Somatosensory Senses: Skin Senses

  • Touch and pressure: skin receptors fire when skin is touched; active touching involves moving the hand across a surface.
  • Temperature and pain: receptors for warmth and cold fire when appropriate; nociceptors detect pain.
  • Band of sensitivity varies by body region; more sensitive areas have more densely packed nerve endings; more brain area devoted to processing these sensations.

The Other Senses: Kinesthesis and Vestibular Sense

  • Kinesthesis: sense of body movement; information from joints, tendons, and muscles.
  • Proprioception: sense of position of body parts in relation to each other and to the ground.
  • Vestibular sense: sense of balance and head position relative to gravity; organs in semicircular canals monitor motion and orientation.
  • Sensory conflict theory explains motion sickness when visual and vestibular information conflict, causing dizziness and nausea.

The Sense of Smells: Olfaction

  • Olfactory bulbs: brain areas just above the sinus cavity and below the frontal lobes that receive information from olfactory receptor cells.
  • Information travels from olfactory bulbs to piriform cortex, orbitofrontal cortex, and amygdala.

Culture Influences Taste

  • Diets across cultures shape taste preferences.
  • Maternal diet can influence taste preferences in the womb and through breastfeeding.

Perception: The Nature of Organizing Sensations

  • Perception involves organizing and interpreting sensations to form meaningful experiences.
  • Perception can differ between individuals even when sensing the same stimulus (e.g., two people viewing the same cloud).
  • Perception processes can be influenced by expectations, prior knowledge, and context.

Perception vs. Sensation: Processing Levels

  • Perception arises from combining sensation (detection) with interpretation and organization.
  • Bottom-up processing: analysis of sensory input from the smallest features to a complete perception.
  • Top-down processing: use of preexisting knowledge to organize features into a unified whole.
  • Perceptual set: prior experiences or expectations influencing interpretation.

Visual Perception: Gestalt Principles

  • Closure: tendency to perceive incomplete figures as complete.
  • Perceptual organization: tendency to integrate elements into meaningful patterns.
  • Figure-ground perception: distinguishing a figure from its background; ambiguous relations can lead to unstable perceptions.

Gestalt Principles of Grouping

  • Proximity: nearby objects are grouped together.
  • Similarity: similar-looking objects are grouped together.
  • Continuity: perceive continuous patterns rather than disrupted ones.
  • Contiguity: events occurring close together in time are related.
  • Common fate: elements moving together are grouped together.
  • Proximity, Similarity, Closure, Continuity, Contiguity, Common Fate — these organize visual input into meaningful wholes.

Perceptual Illusions and Processing

  • Perceptual set: tendency to perceive things a certain way due to prior experiences.
  • Top-down processing: applying existing knowledge to understand features.
  • Bottom-up processing: building perception from smaller features.

Depth Perception

  • Binocular cues involve both eyes:
    • Retinal disparity: difference between the images on the two retinas as objects move closer or farther away.
    • Convergence: inward inward movement of the eyes as they focus on a near object.

Perceptual Constancies

  • Size constancy: objects are perceived as the same size despite distance changes.
  • Color constancy: perceived color remains constant under varying illumination.
  • Brightness constancy: perceived brightness stays constant under different lighting.
  • Shape constancy: shapes are perceived as constant even when retinal shape changes.

How We Organize Our Perceptions

  • Size constancy: objects appear the same size despite changes in distance.
  • Shape constancy: the perceived shape remains constant.
  • Brightness constancy: the perceived brightness remains constant under changing lighting.

Summary: Key Takeaways

  • Sensation vs perception: definitions and differences.
  • Eye anatomy, properties of light, and color vision theories.
  • Organization of visual perceptions and perceptual constancies.
  • Structure and function of the ear, hearing processes, and deafness types.
  • Chemical senses (smell and taste), skin senses, kinesthesis, and vestibular sense.
  • Skepticism about extrasensory perception.
  • Gestalt principles and perceptual organization.
  • Depth cues, perceptual constancies, perception processing.
  • Cultural influences on taste and practical implications for daily life and real-world applications.