Sensation and Perception

Ciccarelli and WhiteChapter 3

Introductory Psychology Spring 2014

Sensation and Perception

• Sense- a system that translates outside information into activity in the nervous system

• Sensation- the stimulus message coming from the senses

• Transduction- process of converting stimuli• Perception- the process of giving meaning to

that message

Figure: What Do You See?

ABC’s of Sensation

• Sensation is the activation of receptors in the various sense organs• Sensory Receptors

– Specialized forms of neurons– Not stimulated by other neurons– Stimulated directly by different kinds of energy (light waves,

sound waves, etc)

Sensory Energy

• Wavelength- the distance between peaks in a wave of light and sound

• Frequency- number of complete waves, or cycles, that pass a given point per unit of time

• Amplitude- the distance between the peak and the baseline of a wave

Figure: The Dimensions of a Wave

Sensory Systems- How Information gets from Sensation to Perception• Your senses gather information through

various forms of energy• This energy is encoded into neuronal activity • Neuronal activity relays signals to the brain

Modification of Energy into Neuronal Activity

• In some sensory systems the first step in sensation involves modifying the incoming stimulus– Accessory structures complete this modification

• The second step in modification is transduction– Transduction is the process of converting incoming energy

into neuronal activity– Transduction takes place at structures called receptors

Transfer of Information through CNS

• Coding translates the physical properties of a stimulus into neural activity

• Sensory nerves transfer coded activity to the brain (Thalamus)

• Coded information for all senses except smell goes to the Thalamus

• Thalamus does some initial processing and sends information to the Cerebral Cortex

• Cortex receives input and produces sensation and perception

Review of Structures of Forebrain

Review: Elements of a Sensory System

Sensory Threshold

– Sensory Thresholds• Weber’s Law of just noticeable differences

– Ex: Sugar in Coffee (20%) » Already have 5 teaspoons, must add 1 teaspoon» Already have 10 teaspoons, must add 2 teaspoons» Coffee regular

• Absolute Threshold• Subliminal Perception• Movie

• Habituation and Sensory Adaptation

The Science of Seeing

• The Science of Seeing– Psychological Properties of Light• Three psychological aspects to light

– Brightness– Color– Saturation

Figure: The Spectrum of Electromagnetic Energy

Structures of the Eye– The structure of the eye

• Cornea• Aqueous humor• Iris• Pupil• Lens• Vitreous humor• Retina

– Cones– Rods

• Fovea• Optic Nerve• Blind Spot/ Optic Disc

Figure: Major Structures of the Eye

Figure: The Lens and the Retinal Image

How the Eye Works

• Left and Right Visual Fields• Areas of the Retinas• Where the information goes• Optic chiasm• Photoreceptors– Rods– Dark adaptation– Light adaptation– Cones

Color vision

– Color Vision• Trichromatic Theory• The Afterimage• Opponent-process theory

– Lateral geniculate nucleus

• Color Blindness

Perception of Sound

• What is sound• Properties of sound waves• Auditory Spectrum

The Structure of the Ear

The structure of the ear• The outer ear• The Middle ear• The inner ear

– Cochlea– Basilar Membrane-resting place of the organ of Corti– Organ of Corti- contains receptor cells for the sense of hearing– Auditory Nerve- bundle of axons from the hair cells in the

inner ear that run to the brain

Figure: Structures of the Ear

Figure: The Cochlea

Perceiving Pitch

– Theories of Pitch• Pitch- psychological experience of sound that

corresponds to the frequency of the sound waves; higher frequencies are perceived as higher pitches• Place Theory• Frequency Theory• Volley Principle

Types of Hearing Impairments

– Types of Hearing Impairments• Conduction Hearing Impairment

– Hearing aids

• Nerve hearing impairment– Tinnitus– Cochlear implants

Figure: Sound Waves and Waveforms

Table: Intensity of Sound Sources

Auditory Pathways to the Brain

• Auditory nerve conveys information to the thalamus which then relays it.– Thalamus relays the information to the primary

auditory cortex

• Cells in the auditory cortex have preferred frequencies.

• Auditory cortex also receives information from other senses.

Chemical Senses

• Chemical Senses– Gustation• Taste buds• Five basic tastes• Supertasters

– Olfaction• Definitions• Olfactory receptor cells• Olfactory bulbs

Smell, Taste, and Flavor

• Smell and taste act as two components of a single system, known as flavor.– Scent and taste pathways converge in the cerebral

cortex.• Both tastes and odors prompt strong

emotional responses.• Variations in nutritional state affects:– One’s experience of taste and flavor.– One’s motivation to eat particular foods.

Figure: The Olfactory System

Olfactory System

• Unique relationship between smell and memory.

• Species variability in sensitivity to odor and dependency on smell for survival.– E.g., humans have about 9 million olfactory

neurons while dogs have 225 million.– Many species have an accessory olfactory system

that detects pheromones.

Somesthetic Senses

– Touch, Pressure, Temperature• Types of sensory receptors• Visceral pain, somatic pain• Congenital analgesia• Congenital insensitivity to pain with anhidrosis• Phantom limb• Pain Gate Control Theory

Kinesthetic Sense/ Vestibular Sense

– Kinesthetic Sense– Vestibular Sense• Otolith organs• Semicircular canals• Motion sickness

ABC’s of perception

• The ABC’s of Perception– Size, Shape, and Brightness– Gestalt Principles• Figure-ground• Proximity• Similarity• Closure• Continuity• contiguity

Figure 3.20: Gestalt Principles of Perceptual Grouping

Depth Perceptions

Monocular Cues– Linear perspective– Relative size– Overlap– Aerial perspective– Texture gradient– Motion parallax– accommodation

Linear perspective

Relative Size

Overlap

Aerial Perspective

Texture gradient

Depth Perception

• Binocular Cues– Convergence– Binocular Disparity

Perceptual Illusions

• Hermann Grid• Muller-Lyer Illusion• The Moon Illusion• Illusions of motion

Hermann Grid

Muller- Lyer

Other factors that Influence perception

• Perceptual sets• Top down processing• Bottom up processing

Figure 3.18: Misperceiving Reality

From Gardner "Optical Illusions from Figures that are Undecidable to Hot Dogs That Float, Scientific American, 222, 124, 127 Reprinted with permission

Which Line Is Longer?

Figure: Reversible Images

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Synesthsia

• Disorder in which the signals from the various sensory organs are processed in the wrong cortical areas resulting in the sense information being interpreted as more than one sensation.