Introduction to Psychology I - Chapter 4: Sensation & Perception

PSY 102: Introduction to Psychology I

Chapter 4: Sensation & Perception

Sensation, Perception, and Illusion

  • Sensation: The detection of physical energy by the sense organs.

  • Perception: The brain’s interpretation of raw sensory data.

  • Illusion: Perception that does not match reality.

Measuring Thresholds

  • Thresholds:

    • Just Noticeable Difference (JND): Minimal change in a stimulus that can just barely be detected.

    • Weber’s Law: The JND of a stimulus is a constant proportion despite variations in intensity.

  • Absolute Thresholds for Different Senses:

    • Vision: A candle flame 30 miles away on a clear, dark night.

    • Hearing: A clock’s tick 20 feet away when all is quiet.

    • Touch: A fly’s wing falling on the cheek from 1 centimeter away.

    • Smell: A single drop of perfume diffused through an area equivalent to the volume of six rooms.

    • Taste: A teaspoon of sugar dissolved in two gallons of water.

Sensory Adaptation

  • Definition: The process whereby sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current (unchanging) conditions.

  • Sensitivity Changes: There is a stronger response to changes in stimulation than to constant stimulation.

Reading Challenge

  • A study from Cambridge University suggests that the order of letters in a word does not matter, as long as the first and last letters are in place. This phenomenon showcases how the human mind reads words as whole entities not letter by letter.

Sensation Principles

  • All senses rely on certain principles to function effectively.

  • Transduction: The external stimulus is converted by a sense receptor into neural activity.

  • Activation Patterns: Activation is highest when the stimulus is first detected, after which sensory adaptation occurs.

Cross-Talk Between Senses

  • Some phenomena illustrate how senses can influence each other:

    • McGurk Effect: A perception phenomenon where visual information can alter the perception of auditory information.

    • Rubber Hand Illusion: Demonstrates how visual and tactile sensations can combine in a way that alters the perception of one's own body.

  • Synesthesia: A condition where stimulation of one sensory modality leads to automatic experiences in a second modality (e.g., seeing sounds or tasting colors).

The Role of Attention

  • Selective Attention: The process of selecting one sensory channel and ignoring or minimizing others.

    • Even ignored channels are processed at some level; information from these can still reach awareness.

    • Cocktail Party Effect: The phenomenon of being able to focus on a single conversation in a noisy environment.

Inattentional Blindness

  • Definition: The phenomenon where individuals fail to perceive unexpected stimuli in plain sight when their attention is focused elsewhere.

    • Example: The famous monkey illusion; focusing on observing a bouncing ball may lead to missing a monkey that appears onscreen.

Change Blindness

  • Definition: The failure to detect changes in one’s environment; frequently studied in the context of traffic accidents.

The Binding Problem

  • Describes how the brain combines various stimuli into a coherent perception.

    • Different stimuli such as the look, feel, smell, and taste of an object (e.g., an apple) are processed by different areas of the brain but integrated into a singular experience.

    • Rapid, coordinated activity between brain areas may facilitate this binding process.

The Visual System

  • Brightness: Related to the amount of light reflected back to the eye.

  • Hue: Color of light, related to wavelength, with maximal sensitivity to blue, green, and red.

  • Light Mixing Principles:

    • Mixing lights produces white (additive color mixing).

    • Mixing pigments produces black (subtractive color mixing).

Structure of the Eye

  • Retina: Innermost layer of the eye, converts light into nerve impulses; contains photoreceptor cells.

  • Vitreous Humour: Jelly-like fluid that nourishes and shapes the eye.

  • Fovea: Central area of the retina with the highest density of cones, responsible for sharp vision.

  • Blind Spot (Optic Disc): Area where the optic nerve exits the eye; lacks photoreceptor cells.

  • Iris: Colored portion with muscles controlling pupil size.

  • Aqueous Humour: Liquid that nourishes the eye.

  • Pupil: Opening in the iris that adjusts size based on light levels.

  • Cornea: Curved, transparent surface that bends incoming light.

  • Lens: Transparent disc that changes shape for focusing objects at varying distances.

  • Blood Vessels: Provide nourishment to eye tissues.

  • Optic Nerve: Transmits visual information from the retina to the brain.

  • Eye Muscles: Six muscles surrounding the eye that facilitate movement in all directions.

Types of Photoreceptors

  • Rods: Responsible for low-light vision and dark adaptation; absent in the fovea.

  • Cones: Responsible for color vision and require bright light; located primarily in the fovea.

  • Statistics on Photoreceptor Numbers:

    • Rods: Approximately 120 million.

    • Cones: Approximately 6 million.

  • Sensitivity Overview:

    • Cones: High color and detail sensitivity in bright light.

    • Rods: High sensitivity in low light, low color sensitivity.

Visual Processing Pathway

  • The optic nerve consists of the axons of ganglion cells, causing a blind spot in the visual field.

  • Most axons project to the thalamus then to the visual cortex, with some directing to the midbrain for reflexive responses.

Visual Perception

  • Different cortical cells respond maximally to specific stimuli:

    • Feature Detector Cells: Allow the detection of lines and edges.

    • Simple Cells: Sensitive to orientation-specific slits of light in specific locations.

    • Complex Cells: Sensitive to orientation but less location-dependent.

Colour Perception Theories

  • Trichromatic Theory: Suggests color vision is based on sensitivity to three primary colors: blue, green, and red.

    • Explains color blindness linked to the types of cones present in the eyes.

  • Opponent Process Theory: Proposes color vision arises from complementary, opposing colors (e.g., red vs. green, blue vs. yellow).

    • Afterimages occur after viewing certain colors, demonstrating this concept.

Implications of Vision Loss

  • Blindness can lead to reorganized sensory cortices and enhanced perceptions in other senses, such as echolocation.

  • Visual Agnosia: A condition where individuals have deficits in object recognition due to damage in higher visual processing regions.

  • Blindsight: A condition in which individuals with damage to area V1 exhibit above-chance visual performance, indicating residue functional processing despite blindness.

Hearing (Audition)

  • The sense primarily relied upon after sight.

  • Sound Characteristics:

    • Pitch: Frequency of sound waves (measured in Hertz, Hz).

    • Loudness: Amplitude of sound waves (measured in decibels, dB).

    • Timbre: Complexity of sound that distinguishes different types of sound.

The Ear's Anatomy

  • The ear is divided into three main parts that contribute to sound processing:

    • Outer Ear: Includes the pinna and ear canal, which funnel sound waves to the eardrum.

    • Middle Ear: Contains ossicles (hammer, anvil, stirrup) which vibrate to transmit sound to the inner ear.

    • Inner Ear: Includes the cochlea, which converts vibrations into neural activity; contains the organ of Corti and the basilar membrane.

Pitch Perception Theories

  • Place Theory: Suggests specific locations on the basilar membrane correspond to specific tones and pitches; accounts for high-frequency sounds.

  • Frequency Theory: Proposes the rate of action potentials in the auditory nerve corresponds to the pitch of sound; effective for low-frequency sounds.

Smell and Taste

  • Olfaction (Smell) and Gustation (Taste) are referred to as the "chemical senses" as they rely on chemical stimuli.

  • These senses enhance the gustatory experience and shape preferences for foods.

Survival Functions of Basic Tastes

  • Taste Sensation:

    • Sweet: Indicates an energy source.

    • Salty: Important for sodium levels essential for physiological processes.

    • Sour: Indicates potentially toxic acids.

    • Bitter: Associated with potential poisons.

    • Umami: Signals presence of proteins necessary for growth and tissue repair.

Body Senses

  • Three body systems work together:

    • Somatosensory System: Deals with touch and pain.

    • Proprioception: The kinesthetic sense that tracks body position and movement.

    • Vestibular Sense: Pertains to equilibrium and balance.

Body Position and Balance

  • Proprioception: Maintains awareness of body position and aids in efficient movement; includes muscle stretch receptors and tendon force detectors.

  • Vestibular Sensation: Involves fluid-filled semicircular canals in the inner ear maintaining balance.

The Multitasking Brain

  • The brain engages in parallel processing, acknowledging multiple sensory inputs simultaneously.

  • Bottom-Up Processing: Starts from sensory stimuli and builds up to the final perception.

  • Top-Down Processing: Begins with existing knowledge or expectations that shape our perception.

Perceptual Hypotheses

  • Perceptual Sets: Expectations influence perception of stimuli.

  • Perceptual Constancy: The ability to perceive objects consistently despite changes in sensory input such as size, shape, or color, heavily reliant on context.

Gestalt Principles of Perception

  • Rules that govern perception in context:

    • Proximity: Objects that are close together are perceived as a group.

    • Similarity: Objects that share similar characteristics are perceived as belonging together.

    • Continuity: Lines are perceived to follow the smoothest path.

Visual Motion Perception

  • The brain computes motion by comparing frames of visual information over time, referred to as the Phi Phenomenon.

Depth Perception

  • Monocular Depth Cues: Can be gleaned from one eye, including relative size, texture gradient, interposition, linear perspective, height in plane, and light and shadow.

  • Binocular Depth Cues: Require both eyes, utilizing disparity and convergence for depth perception.

  • Visual Cliff Experiment: Demonstrates depth perception capabilities in infants as young as six months, suggesting it has innate components and is also shaped by experience.