Chapter 4 Sensation & Perception

Chapter 4: Sensation & Perception

Overview

  • Sensation: The process of receiving information from the environment through the five senses: touch, taste, sight, sound, and smell.

  • Perception: The interpretation of these signals or sensations to make sense of surroundings.

  • Recommended resource: Crash Course’s Sensation & Perception video.

Sensation

  • Senses: Receptors in our eyes, skin, tongue, nose, and ears collect stimuli from the environment.

  • Stimulus: Energy transmitted from the environment, such as light, chemicals, pressure, and heat.

  • Transduction: The transformation of environmental stimuli into neural impulses that the brain can process.

Sensation: General Terms

  • Sensory Adaptation: Decreased responsiveness to constant stimulation. Example: A frog in gradually heated water.

  • Sensory Habituation: Perception of sensations depends on focus and attention.

  • Cocktail Party Effect: Ability to focus on a specific conversation while ignoring background noise.

  • Selective Attention: Concentrating on one thing while ignoring others.

Understanding Light

  • Visible Light: A portion of the electromagnetic spectrum that includes various wavelengths of light.

    • Types of electromagnetic waves: radio, microwave, infrared, visible light, ultraviolet, X-ray, gamma.

Understanding Light: Properties

  • Wavelength: Determines hue; visible spectrum includes red (longest wavelength) to violet (shortest).

  • Amplitude: Determines brightness; can be muted or bright.

Sensation: Vision

  • Objects reflect specific wavelengths of light determining their color.

    • Example: A red shirt reflects red light and absorbs others; black absorbs all, white reflects all.

  • The Eye Structure:

    • Cornea: Focuses incoming light.

    • Pupil: Opening that allows light to reach the retina.

    • Iris: Controls the size of the pupil.

    • Lens: Adjusts shape for focusing (accommodation).

Sensation: Vision Continued

  • Retina: Processes light using photoreceptors (rods and cones).

    • Rods: Detect light intensity (dark/light).

    • Cones: Detect color.

  • Fovea Centralis: Area of the retina with highest visual acuity.

Sensation: Transmission to the Brain

  • Light enters through the cornea -> passes through pupil -> focused by the lens -> transduced in the retina to neural signals.

  • Signals transmitted via the optic nerve to the Lateral Geniculate Nucleus (LGN) in the thalamus, then to the visual cortex (occipital lobe).

Theories of Color Vision

  • Trichromatic Theory: Three types of cones sensitive to blue, green, red; combined activations yield all perceived colors.

  • Opponent Process Theory: Color perception based on opposing pairs: red/green, yellow/blue, black/white.

    • Fatigue in one sensor (e.g., red) reveals its counterpart’s activity (green).

Understanding Sound

  • Auditory Input: Uses sound waves created by vibrations.

  • Wave characteristics:

    • Wavelength: Determines pitch.

    • Amplitude: Determines loudness.

Sensation: The Ear Structure

  • Parts of the ear: pinna, ear canal, eardrum, ossicles (tiny bones), cochlea.

  • Hearing Process:

    • Sound waves -> Vibrations of eardrum -> Amplified by ossicles -> Trigger hair cells in cochlea -> Neural signals sent via auditory nerve to the brain.

Theories of Hearing

  • Place Theory: Hair cells in cochlea respond to different frequencies, producing pitch perception based on hair cell location.

  • Frequency Theory: Lower frequencies signaled by the rate of hair cell firing.

Sensation: Skin

  • Skin detects temperature and pressure via specialized nerve endings, differing in sensitivity across body areas.

Sensation: Taste

  • Taste buds located on tongue papillae detect chemical stimuli.

  • Basic tastes include sweet, salty, sour, bitter, umami (savory).

Sensation: Olfaction (Smell)

  • Reliant on chemical receptors and processed in the olfactory bulb, connected to regions responsible for emotion and memory (amygdala, hippocampus).

Sensation: Pain

  • Gate Control Theory: Pain perception can be modified by other stimuli; e.g., stimulating other areas can reduce pain.

Sensation: Orientation

  • Vestibular Sense: Balances body orientation, managed by fluid in semicircular canals of the inner ear.

  • Kinesthetic Sense: Monitors specific body part positions via receptors in muscles and joints.

Perception

  • Transitioning from sensation to interpreting stimuli and making sense of the environment.

Perception: Threshold

  • Absolute Threshold: Minimum stimulus intensity able to be detected; below it is subliminal.

  • Just-Noticeable Difference (JND): Smallest change in stimulus detectable; defined by Weber’s Law (change proportional to original stimulus).

Perception: Theories

  • Signal Detection Theory: Examines how distractions and interferences alter perception.

    • Response Criteria: Factors affecting detection decisions.

    • False Positive: Incorrectly perceived presence of stimulus.

    • False Negative: Failing to notice actual stimuli.

Perception: Processing

  • Top Down Processing: Uses prior knowledge to interpret stimuli (e.g., filling in gaps).

  • Bottom Up Processing: Starts with sensory information and builds to complex perceptions (e.g., recognizing new concepts).

Gestalt Principles

  • Humans organize perceptions into patterns and objects.

    • Principles: Proximity, Similarity, Enclosure, Symmetry, Figure & Ground, Closure, Continuity, Connectedness.

Perception: Constancies

  • Size Constancy: Awareness that object size remains constant despite distance-related image changes.

  • Shape Constancy: Recognition that shape remains unchanged even under different viewing angles.

  • Brightness Constancy: Consistent color perception despite changes in lighting conditions.

Perception: Motion

  • Stroboscopic Effect: Illusion of motion from rapidly presented still images.

  • Phi Phenomenon: Lights blinking in sequence appear to move.

  • Autokinetic Effect: Stationary light seems to move in the absence of reference points.

Perception: Cues for Depth

  • Monocular Cues: Linear perspective, relative size, interposition, texture gradient, shadowing.

  • Binocular Cues: Binocular disparity, convergence informs depth perception.

Perception: Cultural Influences

  • Perceptions shaped by cultural learning, impacting use of depth cues in visual interpretation.