Chapter Three

Module 3.1

Sensing Our World: Basic Concepts of Sensation

Sensation

• Sensation

– a process by which our sensory receptors and nervous system receive and represent stimulus energy

• Perception

– a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

Sensation

• Sensory receptors

– Eyes

– Ears

– Nose

– Mouth

– Joints, muscles

– Skin

Sensation

• Gustav Theodor Fechner: Elements of Psychophysics (1860)

Absolute and Difference Thresholds

• Absolute Threshold

– minimum stimulation needed to detect a particular stimulus

– usually defined as the stimulus needed for detection 50% of the time

• Difference Threshold

– minimum difference between two stimuli that a subject can detect 50% of the time

– just noticeable difference (JND)

– increases with magnitude

Psychophysical Theory

• Signal Detection Theory

– predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)

– assumes that there is no single absolute threshold

– detection depends partly on person’s

• experience

• expectations

• motivation

• level of fatigue

Absolute and Difference Thresholds

• Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion

– light intensity- 8%

– weight- 2%

– tone frequency- 0.3%

• Sensory adaptation- diminished sensitivity with constant stimulation

Module 3.2

Vision: Seeing the Light

Seeing the Light

• Vision

– Light energy converted to signals the brain interprets to produce experience of sight

• Light

– Physical energy, electromagnetic radiation

– Wavelength corresponds to color

Seeing the Light
The optics of vision

The Eye

• Parts of the eye

– Cornea

– Iris

– Pupil

– Lens: accommodation

– Retina: rods and cones

– Bipolar cells, ganglion cells

– Optic nerve (blind spot)

– Fovea

Parts of the Eye (Figure 3.3)

Visual pathways

Light to Neural Impulses
(Figure 3.5)

Feature Detectors

• Neurons that respond to specific features of the visual stimulus

– Within the visual cortex

– Discovered by Hubel and Wiesel

Color Vision

Negative Afterimages

Color-Deficient Vision

Module 3.3

Hearing: The Music of Sound

Sound Waves

• Based on vibrations

• Amplitude

– Height of wave

– Decibels

• Frequency

– Number of waves per second

– Pitch

Sound Waves (Figure 3.10)

The Ear

• Passage of sound waves

– Outer ear

– Eardrum

– Ossicles

– Oval window

– Cochlea: basilar membrane, hair cells

– Auditory nerve

Sound Waves to Neural Impulses
(Figure 3.11)

The cochlea

The Organ of Corti

Perception of Pitch

• Place theory

– Location on basilar membrane determines pitch

• Frequency theory

– Basilar membrane vibrates at same frequency as sound wave

• Volley principle

– Groups of neurons fire in rotation

Hearing Loss

• Conduction deafness

– Damage to middle ear

• Nerve deafness

– Damage to hair cells or auditory nerve

Sounds and Decibels (Figure 3.12)

Module 3.4

Our Other Senses: Chemical, Skin, and Body Senses

Olfaction

• Smell

• Chemical molecules

– Specific smells depend on shape

• Nose, olfactory nerve, olfactory bulb

• Important for food flavor

• Pheromones

Skin Senses

Pain

• Receptors in

– Skin, muscles, joints, ligaments, teeth

• Gate-control theory of pain

– Mechanism in spinal cord controls pain messages

– Bottleneck may block pain

– Role of endorphins

– Acupuncture

Kinesthesis

• Receptors in joints, ligaments, muscles

• Information about

– Movement of body parts

– Relative positive of body parts

• Allows for automatic movements

Vestibular Sense

Module 3.5

Perceiving Our World: Principles of Perception

Perception

Process by which the brain interprets sensations, turning them into meaningful representations of the world

Attention

• First step in perception

• Selective attention

• Influenced by

– Motivational states

– Repeated exposure

• Increased attention

• Habituation

Perceptual Set

Letter B or Number 13?
(Figure 3.18)

Visual Processing

• Bottom-up processing

– Focus on specific shapes, individual features

• Top-down processing

– Experience and knowledge shape perception

Gestalt Principles

• Gestalt: “unitary form,” “pattern,” “whole”

• Laws of perceptual organization

– Figure and ground

– Grouping

• Proximity

• Similarity

• Continuity

• Closure

• Connectedness

Gestalt Laws of Grouping
(Figure 3.24)

Perceptual Constancies

• Tendency to perceive an object as remaining the same even when retinal image changes

• Examples

– Shape constancy

– Size constancy

– Color constancy

– Brightness constancy

Shape Constancy (Figure 3.25)

Depth Perception

• Depth Perception

– ability to see objects in three dimensions

– allows us to judge distance

Depth Perception

• Binocular cues

– retinal disparity

• images from the two eyes differ

• closer the object, the larger the disparity

– convergence

• neuromuscular cue

• two eyes move inward for near objects

Depth Perception

• Monocular Cues

– relative size

• smaller image is more distant

– interposition

• closer object blocks distant object

– relative clarity

• hazy object seen as more distant

– texture coarse --> close fine --> distant

Illusions

Visual Illusions

• Examples

– Muller-Lyer illusion

• (Carpentered-world hypothesis)

– Ponzo illusion

– Impossible figures

– Moon illusion

– Apparent movement

• Stroboscopic movement

• Phi phenomenon

Visual Illusions (Figure 3.28)

Subliminal Perception

• Stimuli presented below level of conscious awareness

• Can it influence attitudes or behavior?

Extrasensory Perception

• Parapsychology: scientific study of psi and related phenomena

• Extrasensory perception (ESP) or psi

– Telepathy

– Clairvoyance

– Precognition

– Psychokinesis

Extrasensory Perception

Ganzfeld: Homogenous visual field.

Subjects in a ganzfeld experiment

sit in a comfortable chair, have their

eyes covered by ping-pong balls

and hear white noise (i.e., static).

The atmosphere is a relaxed one

and the subject reports any

impressions that he/she is aware

of.

Extrasensory Perception

Psi, as demonstrated under laboratory conditions, appears to be a very weak and unstable phenomenon. Parapsychologists have had a lot difficulty creating the exact experimental conditions under which acceptable and reliable psi effects can be demonstrated.

Module 3.6

Application: Psychology and Pain Management

Pain Management

• Distraction

• Bottleneck at the “gate”

– Such as rubbing, cold packs

• Changing thoughts and attitudes

– Negative pessimistic self-evaluations: more pain

– Rational alternatives: cope more effectively

• Accurate information

• Meditation

• Biofeedback: electromyographic, thermal