Sensation and Perception - CH3 Notes

Sensation

• Definition of sensation: LO 1. Stimulation of sensory receptors located in the sense organs; transmission of sensory information to the central nervous system; activation of one’s sense organs.
• Definition of perception: LO 1. Active process by which sensations are organized and interpreted to form an inner representation of the world.

Perception

• Perception is an active process; involves knowledge, expectations, and motivations; sensation is the mechanical input.

Psychophysics

• LO 1. The study of the relationship between the physical aspects of stimuli and our psychological experience of them.
• Six Major Senses: Vision, Hearing, Balance, Taste, Olfaction (smell), Touch.
• Gustav Fechner (foundational figure).

Absolute Threshold (LO 1)

• The weakest level of a stimulus necessary to produce a sensation; detected 50% of the time.
• Individual differences: some people are more sensitive; within-person variability across time.
• Notation in practice: threshold concept used to describe detection probabilities, often at the 50% point.

Subliminal Stimulation (LO 1)

• Stimulus below a person’s absolute threshold for conscious perception.
• Subliminal perception refers to perception of such stimuli.
• Examples from the text:
  • Visual stimuli flashed too briefly can be processed without conscious awareness.
  • Auditory stimuli can be presented at a volume too low to consciously hear.
  • Backward masking as a subliminal presentation method.

Subliminal vs Absolute Threshold (LO 1)

• Subliminal threshold is below conscious perception; absolute threshold is the limit for conscious detection at 50%.

Difference Threshold (LO 1)

• Also called the just-noticeable difference (JND): the minimum difference in magnitude of two stimuli required to tell them apart.
• Detected 50% of the time.

Signal–Detection Theory (LO 1)

• A person’s ability to detect stimuli depends on multiple factors beyond raw intensity:
  • Training, motivation, psychological state (e.g., fatigue or alertness).
• Perception arises from the interaction of physical, biological, and psychological factors.
• The degree to which a signal can be distinguished from background noise.

Signal–Detection Theory (continued)

• Application: distinguishes sensory sensitivity from response bias; explains why identical stimuli may be reported differently by different observers.

Sensory Adaptation and Sensitization (LO 1)

• Sensitization (positive adaptation): becoming more sensitive to low-magnitude stimuli.
• Desensitization (negative adaptation): becoming less sensitive to stimuli of the same intensity.

Light and Vision Basics (LO 2)

• Light is a spectrum of electromagnetic energy; varies in wavelength.
• Examples of wavelength ranges: cosmic rays are extremely short; radio waves extend for miles.
• Within visible light, color is determined by wavelength; wavelength determines hue.

The Eye (LO 2)

• Retina: photoreceptors (rods and cones); bipolar cells; ganglion cells.
• Axons of ganglion cells converge to form the optic nerve, which transmits sensory input to the brain (occipital lobe).

Visual Acuity and Dark Adaptation (LO 2)

• Visual acuity relates to the shape of the eye.
• Refractive errors:
  • Myopia (nearsighted): need to be close to discriminate details.
  • Hyperopia (farsighted): difficulty focusing on near objects.
  • Presbyopia: difficulty perceiving nearby visual stimuli (age-related).
• Dark adaptation: adjusting to lower lighting.
  • Cones reach maximum adaptation in ~10 minutes.
  • Rods continue adapting up to ~45 minutes.

Perceptual Dimensions of Color (LO 2)

• Hue: color determined by wavelength.
• Value: brightness or darkness.
• Saturation: intensity of color perceived.
• Cultural associations of color.

Afterimages (LO 2)

• Afterimage: persistent sensations of color followed by perception of the complementary color when the first color is removed.
• Related figure: [Figure 3.6] Afterimages.

Theories of Color Vision (LO 2)

• Trichromatic theory: three types of cones selectively sensitive to red, green, and blue light.
• Opponent-process theory: color perception derived from opponent color channels (red-green, blue-yellow, and light-dark).

Color Blindness (LO 2)

• Categories:
  • Trichromats: normal color vision; sensitive to red–green, blue–yellow, and light–dark distinctions.
  • Dichromats: partial color blindness (two-color vision).
  • Monochromats: totally color-blind; only lightness/darkness discrimination.

Testing for Color Blindness (LO 2)

• Color vision tests often use Ishihara-style plates; examples show color-plate tasks (e.g., number differences like a 6 vs a 12 in different circles).

Visual Perception and Perceptual Organization (LO 3)

• Visual perception: process of organizing sensory impressions caused by light striking the eyes.
• Visual perception is active; knowledge, expectations, and motivations influence interpretation.
• Sensation is considered a more mechanical process.

The Principle of Closure (LO 3)

• Tendency to perceive a broken figure as complete or whole.
• Example figures illustrate the principle.

Perceptual Organization and Figure–Ground Perception (LO 3)

• Integration of sensory stimulation into meaningful wholes.
• Figure–ground perception: ambiguous relationships can lead to unstable perceptions.
• Rubin Vase example: figure-ground reversal.

Gestalt Rules of Perceptual Organization (LO 3)

• Proximity: group objects near one another.
• Similarity: group objects that are similar in appearance.
• Continuity: perceive a series of points/lines as having unity.
• Common Fate: elements moving together are perceived as belonging together.
• Closure: see complete figures even when parts are missing.

Top-Down vs Bottom-Up Processing (LO 3)

• Top-Down Processing: use of context, knowledge, expectations to organize patterns.
• Bottom-Up Processing: organization of parts of a pattern to recognize the pattern as a whole.

Perception of Motion and Constancies (LO 3)

• Motion perception: based on changes in position relative to other objects; motion perception can be studied via optical/temporal cues; stroboscopic motion as an example.
• Perceptual Constancies: stable perception of objects under varying conditions.
  • Size Constancy: object perceived as same size despite retinal image changes due to distance.
  • Brightness Constancy: perceived object brightness remains constant under different lighting.
  • Shape Constancy: perceived shape remains stable as retinal image changes during rotation.

The Rubin Vase (LO 3)

• Classic figure-ground illusion demonstrating how perception can switch between seeing a vase and two faces depending on figure-ground assignment.

The Ear and Hearing (LO 4)

• Sound requires a medium (air, water) to travel; vibrations are cycles of compression/expansion.
• Frequency range detectable by humans: $20 ext{ Hz} ext{ to } 20{,}000 ext{ Hz}$.
• Pitch is determined by frequency; higher frequency → higher pitch.
• Loudness is determined by amplitude; both frequency and amplitude influence perception independently.
• Decibels (dB) measure loudness.

Pitch and Loudness (LO 4)

• Pitch: determined by frequency, expressed in Hz (cycles per second): $f ext{ (Hz)}$.
• Loudness: determined by amplitude; quantified in decibels $ext{dB}$; frequency and amplitude are independent.

The Ear: Anatomy and Function (LO 4)

• Outer ear: funnels sound waves to the eardrum.
• Middle ear: eardrum, hammer (malleus), anvil (incus), stirrup (stapes); amplifies vibration.
• Inner ear: oval window transmits vibrations into the cochlea; basilar membrane inside the cochlea; organ of Corti with hair cells converts vibrations to neural signals; auditory nerve transmits to brain.

Deafness (LO 4)

• Conductive deafness: damage to the middle ear; hearing aids can help.
• Sensorineural deafness: damage to inner ear structures or auditory nerve; cochlear implants may help but do not restore the auditory nerve’s natural function.

Smell and Taste (LO 5)

• Smell (olfaction): contributes to flavor of foods; odors are molecules in the air; olfactory receptor neurons in the olfactory membrane detect them; olfactory nerve transmits to the brain.
• Taste: taste cells on taste buds; basic tastes are sweet, sour, salty, bitter, and umami (savory).
• Flavor perception arises from the combination of odor, texture, temperature, and taste.
• Individual differences: some people have superior taste sensitivity.

Touch, Temperature, and Pain (LO 5)

• Touch and pressure: skin receptors respond to surface contact; active touching involves continuous movement; provides data on pressure, texture, temperature, and kinesthetic feedback from muscles.
• Some body areas are more sensitive; receptor density varies; more sensory cortex devoted to those sensations.
• Temperature: warmth and cold receptors beneath the skin.
• Pain: nociceptors in the skin; some pain felt deep within the body; no nociceptors in brain tissue itself; pain originates at the point of contact.
• Prostaglandins: chemicals involved in pain signaling and inflammation; production inhibited by pain-relieving drugs; emotional response and stress influence pain perception.

Phantom Limb Pain and Gate Control (LO 5)

• Phantom limb pain occurs in amputated limbs; may involve nerve activity in the stump or cortical reorganization.
• Gate Theory of Pain: the nervous system can process only a limited amount of stimulation at a time; rubbing the painful area can compete for neural attention, alleviating pain by occupying neural pathways.

Kinesthesis and Vestibular Sense (LO 5)

• Kinesthesis: sense of body position and movement; information from joints, tendons, and muscles to the brain.
• Vestibular sense: tells the brain whether one is upright; detects motion and gravity via the semicircular canals and related structures in the ear.
• Classroom demonstration: Finger-to-nose task illustrating kinesthetic feedback.

Extrasensory Perception (ESP) (LO 6)

• Parapsychological or psi phenomena: perception through non-sensory means.
• Precognition: ability to perceive future events in advance.
• Psychokinesis: mental manipulation or movement of objects.
• Telepathy: direct transmission of thoughts or ideas between people.
• Clairvoyance: perception of objects not stimulated by sensory input.
• Psi communication: information transfer through unusual processes.
• Skepticism and scientific scrutiny about ESP claims.