Chapter 3

Chapter 3: Sensation and Perception

Learning Objectives

• LO 3.1: How does sensation travel through the central nervous system, and why are some sensations ignored?

• LO 3.2: What is light, and how does it travel through the various parts of the eye?

• LO 3.3: How do the eyes see, and how do they perceive different colors?

• LO 3.4: What is sound, and how does it travel through the various parts of the ear?

• LO 3.5: Why are some people unable to hear, and how can their hearing be improved?

• LO 3.6: How do the senses of taste and smell work, and how are they alike?

• LO 3.7: What allows people to experience the sense of touch, pain, motion, and balance?

• LO 3.8: What are perception and perceptual constancies?

• LO 3.9: What are the Gestalt principles of perception?

• LO 3.10: What is depth perception and what cues are important for it to occur?

• LO 3.11: What are visual illusions and how can they influence perception?

Sensation

• Definition: Sensation refers to the activation of receptors in the various sense organs.

• Sensory Receptors: Specialized forms of neurons that respond to different types of energy instead of neurotransmitters.

Sense Organs

• Major Sense Organs: Includes eyes, ears, nose, skin, and taste buds.

• Transduction: The process of converting outside stimuli into neural activity, allowing the nervous system to process sensory information.

Sensory Thresholds

• Just Noticeable Difference (JND): The minimal difference in stimulation that can be detected 50% of the time.

• Absolute Threshold: The minimum amount of energy required for a person to consciously detect a stimulus 50% of the time.

Subliminal Sensation

• Subliminal Stimuli: Stimuli that are below conscious awareness, strong enough to activate sensory receptors but not enough for conscious detection.

• Subliminal Perception: The influence of subliminal stimuli on behavior, processing unconsciously.

Habituation and Sensory Adaptation

• Habituation: The brain's tendency to stop responding to constant, unchanging stimuli.

• Sensory Adaptation: The reduced responsiveness of sensory receptor cells over time when exposed to constant stimuli.

• Microsaccades: Small, involuntary movements of the eyes that help prevent sensory adaptation to visual stimuli.

Properties of Light

• Brightness: Determined by the amplitude of the light wave, with higher amplitudes resulting in brighter light.

• Color (Hue): Determined by the wavelength; longer wavelengths are red, while shorter ones are blue. Saturation refers to the purity of color.

Structure of the Eye

• Cornea: Clear membrane protecting and focusing light.

• Aqueous Humor: Watery fluid providing nourishment to the eye.

• Pupil: Opening that allows light to enter.

• Iris: Muscle controlling pupil size for focusing.

• Lens: Further focuses light onto the retina; involved in visual accommodation.

• Vitreous Humor: Jelly-like substance maintaining eye shape.

• Retina: Contains photoreceptors (rods and cones) for light detection; processes visual information before sending it to the brain.

Color Vision

• Trichromatic Theory: Suggests color vision is based on three types of cones (red, green, blue).

• Opponent-Process Theory: Proposes we have pairs of colors (red-green, blue-yellow) that work in opposition; explains afterimages.

• Color Blindness: Conditions where individuals may lack certain cones (e.g., monochrome or red-green color blindness).

Sound

• Wavelength: Related to sound frequency or pitch.

• Amplitude: Correlates to sound volume.

• Purity: Contributes to timbre; measured in Hertz (Hz).

Structure of the Ear

• Auditory Canal: Path from the outer ear to the eardrum.

• Eardrum: Vibrates in response to sound waves; causes tiny bones in the middle ear to move.

• Cochlea: Fluid-filled structure where sound waves are converted into neural signals via the Organ of Corti.

Types of Hearing Impairments

• Conduction Hearing Impairment: Results from damage to the eardrum or middle ear bones.

• Nerve Hearing Impairment: Results from damage in the inner ear or auditory pathways.

Taste and Smell

• Taste Buds: Receptor cells responsible for the sensation of taste (gustation).

• Basic Tastes: Include sweet, sour, salty, bitter, and umami.

• Olfaction: The sense of smell; olfactory receptors in the nasal cavity send signals to the brain.

Somesthetic Senses

• Definition: Body senses including touch, pain, temperature, and body position (kinesthetic sense).

• Gate-Control Theory: Explains how the brain can prioritize and block pain signals.

Gestalt Principles

• Figure-Ground: Objects are perceived as distinct from their backgrounds.

• Proximity: Closer objects are perceived as belonging together.

• Closure: The mind fills in gaps to create a complete image.

• Continuity: Perceiving patterns as continuous rather than fragmented.

Depth Perception

• Monocular Cues: Depth cues available to one eye (e.g., linear perspective, overlap, aerial perspective).

• Binocular Cues: Depth cues that involve both eyes (e.g., convergence, binocular disparity).

Visual Illusions

• Hermann Grid and Müller-Lyer Illusion: Examples of how context can alter perception.

• Motion Illusions: Illusions like the autokinetic effect demonstrate perceptual processing under certain conditions.