Chapter 7: Sensation and Perception

Learning Objectives

• Explain the relationship of sensation and perception

• Discuss mechanism of sense organs and their functions in the body

• Explore different kinds of perception

• Understand the importance of maintaining a healthy sensory system

• Identify and explain different extrasensory perceptions

Introduction to Sensation and Perception

• Sensation: Process by which sensory receptors and nervous system receive stimulus energy from the environment.

• Perception: Process of organizing and interpreting sensory information to recognize meaningful objects and events.

• The brain interprets sensory input to give meaning to experiences.

Processing Sensory Information

• Bottom-up Processing: Assembling and integrating sensory information to perceive stimuli.

• Top-down Processing: Applying models, ideas, and expectations to interpret sensory information.

Mechanism of Sensation

Steps of Sensation

1. Reception: Stimulation of sensory receptor cells by energy (sound, light, heat, etc.)

2. Transduction: Conversion of cell stimulation into neural impulses.

3. Transmission: Delivery of neural information to the brain for processing.

Understanding Stimuli

• Stimulus: Any environmental factor that elicits a sensation.

• Classification of Stimuli:

  • Intensity:

    • Threshold

    • Subliminal

    • Terminal (pain-causing)

  • Nature: Describes physical characteristics of stimuli (light waves, sound waves, etc.)

Sensory Thresholds

• Absolute Threshold: Minimum stimulus intensity needed to detect a stimulus 50% of the time.

• Examples of Sensory Thresholds:

  • Vision: Candle flame at 30 miles on a dark night

  • Hearing: Tick of a watch at 20 ft in silence

  • Taste: One teaspoon of sugar in 2 gallons of water

  • Smell: One drop of perfume in a 3-room apartment

  • Touch: Wing of a bee falling on a cheek from 1 cm

Sensory Receptors

• Biological structures excitable to stimuli.

• Each sensation has specific receptor cells.

Vision

Mechanism of Vision

• Receptor: Eye

• Pathway of Light: Light through cornea → pupil → lens → retina

• Photoreceptors:

  • Rods: Function in dim light, peripheral vision, no color detection.

  • Cones: Responsible for color vision in bright light.

Color Vision Theories

Trichromatic Theory

• Proposes three types of color receptors (cones) sensitive to red, green, and blue.

• Colors created by combining light waves of these three colors.

Opponent-Process Theory

• Each of the three cone types corresponds to two opposing wavelengths (red-green, blue-yellow, black-white).

Common Vision Problems

• Cataracts: Clouding of lens affecting visual acuity and color.

• Retinopathy: Damage to blood vessels causing blurred vision and floaters.

• Glaucoma: Increased fluid pressure damaging optic nerve.

• Macular Degeneration: Distorted central vision.

• Myopia: Difficulty in seeing distant objects (nearsightedness).

• Hyperopia: Difficulty in seeing close objects (farsightedness).

Auditory Sense

Mechanism of Hearing

• Receptor: Ear

• Path of Sound: Sound waves → outer ear (pinna) → auditory canal → eardrum → ossicles → oval window → cochlea

• Hair Cells: Sensory receptors for hearing located in the cochlea.

Types of Hearing Loss

• Conduction Deafness: Issues with mechanical systems transmitting sound.

• Nerve Deafness: Damage to receptors in the inner ear or auditory nerve.

Olfactory Sense

• Receptor: Nose

• Mechanism: Inhaled gaseous substances stimulate olfactory cells generating neural impulses.

Gustatory Sense

• Receptor: Tongue

• Taste Buds: Approximately 9,000 taste receptors located on the tongue.

Cutaneous Sense

• Receptor Organ: Skin

• Sensation Types: Pressure, warmth, cold, pain.

Perception and Grouping

• Gestalt Principles: Refers to perceiving patterns or wholes that are more than just their parts.

• Primary laws of perceptual organization:

  • Law of Proximity

  • Law of Continuity

  • Law of Closure

  • Law of Similarity

• Figure-Ground: Distinction of an object (figure) from its background (ground).