Sensation and Perception Study Notes

Chapter 6: Sensation and Perception

Processing Sensations and Perceptions

  • Sensation

    • Definition: Process by which sensory receptors and the nervous system receive and represent stimulus energies from the environment.

    • Sensory receptors: Sensory nerve endings that respond to stimuli.

  • Perception

    • Definition: Process of organizing and interpreting sensory information, enabling recognition of meaningful objects and events.

Analysis of Sensations and Perceptions

  • Bottom-up processing

    • Definition: Information processing guided by the sensory receptors that begins with the sensory receptors and works up to the brain's integration of sensory information.

  • Top-down processing

    • Definition: Information processing guided by higher-level mental processes, such as when we construct perceptions drawing on our experience and expectations.

Steps Basic to All Sensory Systems

  • All senses share a similar process:

    1. Receive sensory stimulation, often using specialized receptor cells.

    2. Transform that stimulation into neural impulses.

    3. Deliver the neural information to our brain.

Thresholds

Absolute Thresholds

  • Absolute threshold

    • Definition: Minimum stimulus energy needed to detect a particular stimulus 50 percent of the time.

  • Subliminal

    • Definition: Input below the absolute threshold for conscious awareness.

Difference Threshold

  • Difference threshold (just noticeable difference)

    • Definition: Minimum difference a person can detect between any two stimuli half the time; this threshold increases with the size of the stimulus.

Subliminal Stimulation and Persuasion

  • Subliminal sensations

    • Description: Stimuli so weak that they are not consciously noticed.

  • Priming

    • Definition: The process used to activate unconscious associations.

  • Subliminal persuasion

    • Description: May produce a fleeting, subtle, but not powerful, enduring effect on behavior.

    • Observations: Experiments have largely discounted attempts at subliminal advertising and self-improvement.

Basic Concepts of Sensation and Perception

Perceptual Set

  • Perceptual set

    • Definition: Mental predisposition to perceive one thing and not another.

    • Shows how what one feels, sees, tastes, and hears can be influenced by stereotypes.

  • Schemas

    • Definition: Cognitive frameworks that help organize and interpret unfamiliar information through experience, influencing top-down processing.

Factors Determining Perceptual Set

  • Context

    • Explanation: Influences how we interpret stimuli, creating expectations that shape perception.

  • Motivation

    • Explanation: Provides energy for working towards goals and can bias interpretations of neutral stimuli.

  • Emotions

    • Explanation: Can shift our perceptions one way or another based on psychological state.

Vision: Sensory and Perceptual Processing

  • Wavelength

    • Definition: Distance from the peak of one light or sound wave to the peak of the next.

  • Hue

    • Definition: Dimension of color determined by wavelength of light, e.g., blue, green.

  • Intensity

    • Definition: Amount of energy in a light or sound wave, influencing perception of brightness or loudness.

    • Determined by wave’s amplitude (height).

Visible Wavelengths

  • Variance in wavelengths from 400 nm (violet) to 700 nm (red); includes the visible spectrum.

The Stimulus Input: Light Energy

  • Wave properties:

    • Frequency: Number of wavelengths that pass a point over time.

    • Amplitude: Height from peak to trough, influencing brightness and loudness.

The Eye

  • Pathway of light:

    1. Light enters the eye through the cornea.

    2. Passes through the pupil.

    3. Iris surrounds the pupil, controls its size, and reacts to cognitive and emotional states.

    4. Hits the lens, focusing rays on the retina.

  • Accommodation

    • Definition: Process in which the lens changes curvature and thickness to focus light.

Key Terms Related to the Eye

  • Rods

    • Definition: Retinal receptors detecting black, white, and gray; sensitive to movement, crucial for twilight vision.

  • Cones

    • Definition: Retinal receptors concentrated near the center of retina, active in daylight contributing to color perception and fine details.

  • Optic nerve

    • Definition: Transmits neural impulses from eye to brain.

  • Blind spot

    • Definition: Area where optic nerve leaves the eye, lacking receptor cells.

  • Fovea

    • Definition: Central focal point in retina where cones cluster.

Disappearing Dots

  • Visual phenomenon where typical vision detects the black dots in central focus but not in peripheral vision.

Color Processing

  • Two stages of color processing:

    1. Retina's cone responses to different colors (Young-Helmholtz trichromatic theory).

    2. Responses processed by opponent-process cells (Hering’s opponent-process theory).

Color-Deficient Vision

  • Approximately 1 in 12 males and 1 in 200 females experience color deficiency, often not entirely color-blind but lacking red or green-sensitive cones.

  • Types include monochromatic (one-color) or dichromatic (two-color).

Opponent-Process Theory

  • Definition: Opposing retinal processes (red-green, blue-yellow, white-black) enable color vision, with some cells stimulated by one color and inhibited by its opposite.

Sensory and Perceptual Processing: Gestalt Principles

  • Gestalt Principles: The concepts proposed by Gestalt psychologists to organize sensations into perceptions.

Form Perception

  • Figure-ground

    • Definition: The organization of visual fields into objects (figure) separate from their backgrounds (ground).

Depth Perception

  • Depth perception

    • Definition: Ability to perceive three-dimensional objects despite two-dimensional retinal images, allowing distance judgment.

    • Present from infancy in humans and other animals.

Visual Cliff Experiment

  • Findings: Most infants refuse to crawl across a visual cliff, suggesting an innate wariness of heights influenced by biology and amplified by experience.

Binocular Cues

  • Binocular cues

    • Definition: Depth cues dependent on the use of both eyes, such as retinal disparity.

  • Retinal disparity

    • Definition: The way the brain calculates distance by comparing images from each eye; closer objects present greater disparity.

Monocular Cues

  • Monocular cues

    • Definition: Depth cues available to one eye alone, including:

    • Light and shadow

    • Relative motion

    • Relative size

    • Linear perspective

    • Interposition

    • Relative height

Perceptual Constancy

  • Perceptual constancy: Perceiving objects as unchanging in terms of color, brightness, shape, and size despite changes in illumination and retinal images.

  • Types:

    • Color and brightness constancies

    • Shape and size constancies

Brightness Constancy

  • Brightness constancy (light constancy): Perception of an object as having a constant brightness despite varying illumination levels; dependent on relative luminance.

Shape and Size Constancy

  • Size constancy: Perception of an object as having constant size despite changes in distance.

  • Shape constancy: Perception of familiar objects as retaining constant form despite variations in retinal images.

  • Moon illusion: Example of size constancy where the moon looks larger on the horizon than when it's high in the sky.

Hearing, Skin, Chemical, and Body Senses

Hearing (Audition)

  • Definition: Aids in adaptation and survival by facilitating communication and relationships; also characterized as an invisible disability that can increase depression and anxiety risk.

The Stimulus Input: Sound Waves

  • Sound waves: Generated by compressing and expanding air molecules that the ears detect as pressure changes.

  • Pitch: Perceptual experience of highness or lowness determined by wave frequency.

Sound Intensity

  • Absolute threshold for sound: Zero decibels.

  • Decibel Scale: Every 10 decibels corresponds to a tenfold increase in sound intensity, e.g., 60 decibels (normal conversation) is 10,000 times more intense than a 20-decibel whisper.

  • Hearing loss risk: Prolonged exposure above 85 decibels can lead to hearing impairment.

The Physical Properties of Sound Waves

  • Basic relationships:

    • Short wavelength = high frequency (high-pitched sounds)

    • Long wavelength = low frequency (low-pitched sounds)

    • Greater amplitude = loud sounds

    • Smaller amplitude = soft sounds

The Ear: Anatomical Terms

  • Key components:

    • Eardrum

    • Middle ear

    • Cochlea

    • Inner ear

    • Oval window

    • Hair cells

    • Auditory nerve

Sound Waves to Neural Impulses

  • Sound pathways through the outer, middle, and inner ear, converting sound waves into nerve impulses interpreted by the brain.

Hearing Loss

  • Statistics: Approximately 1.57 billion people globally have hearing loss, with about half a billion experiencing disabling hearing loss.

  • Types of hearing loss:

    • Sensorineural hearing loss (nerve deafness): Damage to cochlea’s hair cells or auditory nerve.

    • Conduction hearing loss: Damage to the mechanical systems that conduct sound waves.

Cochlear Implant**:

  • Device that converts sounds into electrical signals and stimulates the auditory nerve through electrodes in the cochlea when nerve deafness occurs.

Perceiving Loudness

  • Loudness correlates with hair cell response intensity, where the brain interprets loudness based on the number of activated hair cells.

Skin, Chemical, and Body Senses

Touch

  • Sense of touch comprises four basic distinct skin sensations:

    1. Pressure

    2. Warmth

    3. Cold

    4. Pain

  • Variations in these sensations involve different somatosensory cortex responses influenced by cognition.

Gate-Control Theory of Pain

  • Gate-control theory

    • Definition: The spinal cord contains a neurological gate that controls the transmission of pain messages to the brain.

    • Endorphins: Natural painkillers that influence pain transmission, particularly during severe pain or exercise.

    • Includes phenomena such as phantom limb sensations and tinnitus.

The Survival Functions of Basic Tastes

  • Taste (gustation): Comprises several basic sensations:

    • Sweet: Energy source

    • Salty: Essential sodium for physiological processes

    • Sour: Potentially toxic acids

    • Bitter: Potential poisons

    • Umami: Proteins for growth and tissue repair

Chemical Senses: Taste

  • Taste receptors: Work in the brain’s temporal lobe and can be influenced by learning, expectations, and perceptual biases.

  • Reproduction of taste receptors: Occurs every week or two, maintaining sensitivity.

Chemical Senses: Smell (Olfaction)

  • Smell: A chemical sense involving multiple receptors activated by various odor molecules which trigger combinations that the brain interprets.

    • Strongly tied to memory and can be influenced by cultural experiences.

The Process of Smell

  • Sequential process includes binding of odorants to receptors, activation of olfactory cells, signal transmission to higher brain regions through axons.

Body Senses: Position and Movement

Kinesthesia

  • Definition: System for sensing the position and movement of individual body parts and interacting with vision.

Vestibular Sense

  • Definition: Sense of body movement and position concerning balance, necessary for overall body coordination.