Chapter 4 - Sensation and Perception

SENSATION AND PERCEPTION

Objectives

  • Understand the definitions of sensation and perception.

  • Discuss concepts of threshold.

  • Explain signal detection theory and sensory adaptation.

  • Familiarize with the sensory system.

  • Explain movement perception.

  • Differentiate between perceptual illusion and sound perception.

  • Discuss the differences between olfactory and gustatory perception.

  • Understand special types of perception.

Definitions

Sensation

  • Definition: The process of experiencing perceiving through the senses.

  • Source: Information interacts with sensory receptors in eyes, ears, tongue, nostrils, and skin. (APA Dictionary)

Perception

  • Definition: The process or result of becoming aware of objects, relationships, and events via senses; involves recognizing, observing, and discriminating, which enables organisms to organize and interpret stimuli into meaningful knowledge. (APA Dictionary)

Thresholds

Definition

  • Level of sensitivity in each sensory system; divides detectable energy from non-detectable energy.

Types of Thresholds

  • Absolute Threshold: Minimal amount of energy required to produce a sensation.

  • Difference Threshold: Minimum difference in magnitude between two stimuli present.

Absolute Thresholds for Our Senses

Sense

Absolute Threshold

Vision

Candle thirty miles away on a clear, dark night

Hearing

Tick of a watch twenty feet away in a quiet room

Taste

Teaspoon of sugar dissolved in two gallons of water

Smell

One drop of perfume in a three-room apartment

Touch

A bee’s wing falling on the cheek from a height of 1 centimeter

Warmth/Cold

A 1 to 2 degrees Celsius change in skin

Thresholds for Touch

Body Part

Absolute Threshold Equivalent

Tip of Tongue

Sensitive to 2 grams of pressure

Fingers

Sensitive to 3 grams of pressure

Back of Hand

Sensitive to 12 grams of pressure

Back of Forearm

Sensitive to 33 grams of pressure

Sole of Foot

Sensitive to 250 grams of pressure

Thresholds for Pain

Body Part

Absolute Threshold Equivalent

Cornea

0.2 grams produces painful sensation

Forearm

20 grams produces painful sensation

Back of Hand

100 grams produces painful sensation

Sole of Foot

200 grams produces painful sensation

Fingertip

300 grams produces painful sensation

Signal-Detection Theory

  • Predicts how and when we detect faint and weak stimuli amid background noise.

  • Detection is influenced by experience, expectations, motivation, and fatigue levels.

  • Seeks to explain why responses to stimuli vary among individuals and circumstances.

Sensory Adaptation

  • Increased sensitivity to low magnitude stimuli (sensitization).

  • Reduced sensitivity due to constant stimulation (desensitization).

Sensory System Overview

Types of Sensation

  • Visual Sensation (Sight)

  • Auditory Sensation (Hearing)

  • Olfactory Sensation (Smell)

  • Gustatory Sensation (Taste)

  • Cutaneous or Skin Sensation (Touch)

Sensory System Detail

Sense

Organ

Receptor Cells

Eyes

Sight

Rods and Cones in Retina

Ears

Hearing

Hair Cells in Organ of Corti

Tongue

Taste

Taste Cells in Taste Buds

Nose

Olfactory

Olfactory Epithelium Cells

Skin

Touch

Pressure, Pain, Warmth, Cold receptors

Visual Sensation

Anatomy of the Eye

  • Key components for vision: Conjunctiva, Choroid, Retina, Sclera, Iris, Lens, etc.

  • Light rays through the cornea, pupil, and lens create an upside-down image on the retina, interpreted by rods and cones.

Auditory Sensation

Process

  1. Sound waves are collected by the outer ear (Pinna).

  2. Vibrations are amplified in the middle ear.

  3. Transduced into coded neural messages in the inner ear (Cochlea).

Gustatory Sensation

Taste Buds

  • No tongue "map" for taste; all areas can perceive the five basic tastes.

  • Taste buds have a short lifespan and are replaced every ten days.

Olfactory Sensation

Smell Process

  • Chemicals in air enter via nasal passage; olfactory receptors send neural impulses to the brain, closely linked to memory.

Cutaneous or Skin Sensation

Types of Touch Receptors

  • Various receptors for touch, pressure, temperature, and pain leading to tactile awareness.

Types of Perception

  1. Visual Perception

    Movement Perception

  2. Depth Perception

  3. Perceptual Illusion

  4. Sound Perception

  5. Olfactory Perception

  6. Gustatory Perception

  7. Tactual Perception

  8. Perception of Time

  9. Perception of Persons

  10. Extra-Sensory Perception (ESP)

Special Types of Perception

ESP Types

  • Precognition: Foretelling future events.

  • Clairvoyance: Perceiving objects/events without direct stimulation.

  • Telepathy: Sending messages through the mind.

  • Psychokinesis: Affecting the physical world with thoughts.