Sensation & Perception

Chapter 3

Sensation & Perception

Sensation

Stimulation of the senses

How input is registered by our senses

Perception

How we organize & interpret sensations

An active, not passive process

Enables us to understand & make sense of the sensations we continually experience

Perception & sensation are dual processes; you need both!

Sequence of events that produce a sensation:

1. Need a form of energy, either external or internal.

2. Stimulates a receptor cell in a sense organ (energy must be sufficient enough for receptor to respond).

3. Receptor sends out a coded electrochemical signal.

4. As a signal passes along sensory nerves to CNS, it is further coded.

5. Signal reaches the brain. 6. You respond!

Sensation

Sensory receptors:

Highly specialized cells

Located in eyes, ears, nose, tongue, skin, & elsewhere

Accomplishes coded task

The Brain “Creates” Sensory Experiences:

The brain is isolated within the skull, listening to the “clicking” of coded neural signals coming over millions of nerve fibers.

The “clicks” of an optical nerve are not any more visual than the “clicks” of an auditory nerve, but the brain interprets the “clicks” on an optic nerve as visual nerve energy & they give rise to visual experience instead of sounds, tastes, or smells.

Sensation: The Process

Transduction

Process by which physical properties of stimuli are converted into neural signals & then transmitted to brain

Sensory deprivation

When deprived of sensations, we create it by means of hallucinations

What is the least amount of sensation we can detect?

TASTE

SMELL

TOUCH

AUDITORY

VISUAL

What stimuli we can detect seems to be designed to maximize our survival.

Thresholds

Difference Threshold

`You have heard a sound. How much stronger does the sound have to be before you notice that it has become louder?`

Aka: “just noticeable difference”

Will vary from person to person

The stronger the stimulation, the bigger the difference must be in order for you to detect it

Some sense are more sensitive than others to change

Stimuli below threshold

Subliminal perception

Q: Can we sense or be affected by subthreshold stimuli that remain outside our conscious awareness?

Sensory Adaptation

Our sensitivity to an unchanging stimulus tends to decrease over time

Practical advantages

Disadvantages

Vision

The Eye:1. Light enters the eye

through the cornea

2. Light passes through the pupil

3. Light passes through the lens

4. Light leaving the lens is projected on the retina, in the back of the eyeball

2 Types of light-sensitive receptors:1. Cones (named for their shape)

Located in the center of the retinaResponds to light & dark & colorsOperates chiefly in daylightConnected to bipolar neurons

2. Rods (named for their shape)Responds to only varying degrees of light & dark, not colorsChiefly responsible for “night vision”Connected to bipolar neurons

Vision

Bipolar neuronsNeurons with only one axon & one dendriteCarry info to ganglion cells optic nerve brain

LightElectromagnetic spectrumWavelength determines what we experience as colorAs wavelength increases from small to large our sensations shift from violet-blue (short) to orange (med.) to red (long)

Brightness

Functions of the Visual System:Acuity

– 2 Types:– Static visual acuity– Dynamic visual acuity

Abnormalities– Nearsightedness– farsightedness

Vision

Dark adaptation– Rods & cones become more sensitive

to light in response to lowered levels of illumination

Light adaptation– Reverse process

Eye Movements– Version Movements

• Involuntary• Saccadic• pursuit

Eye Movements– Vergence Movements

Color Vision2 Theories:Trichromatic Theory

– Helmholtz suggested certain cones were sensitive to green, while others were sensitive to red, or blue & by mixing the three you could experience all hues

Opponent Processing Theory– Hering proposed the existence of 3

pairs of color recptors

Processing Visual Information

Research: feature detectors

3 Types:Simple cells

Complex cells

Hypercomplex Cells

Do we process visual information hierarchically?

Hearing

Q: If a tree falls in the woods and there is no one there to hear it, does it make a sound? (How would psychologists answer this question)A:

The EarPinna

Middle Ear– Malleus– Incus– stapes

Oval Window

Cochlea

Basilar Membrane

Receptor Cells– Thousands of tiny hair cells– Fibers are pushed & pulled by

vibrations of basilar membrane

Sound

Properties of Sound:Sound waves

1. Amplitude2. Frequency3. Timbre

Pitch Perception (2 Views)1. Place Theory2. -sound is detected by

different places that are vibrating on the basilar membrane

2. Frequency Theory• - sounds of different pitch cause

different rates of neural firing

Touch

Skin – largest sensory organ

Skin Senses– Different receptors for different sense?

Pain– Some have a high tolerance for

pain– Beliefs about pain can affect our

perception of it– Research has found that pain is

not related to level of tissue damage

2 Types of pain– Quick & sharp– Dull & throbbing

Pain Perception– Gate-Control Theory: a

“neurological gate” in the spinal cord controls transmission of pain impulses to the brain

– Current emotional state affects pain perception

Smell

Sense of smell is @ 10,000 x’s more sensitive than tasteAppears to decrease with age

How we smell:Substance enters nasal passageDissolves in moist nasal tissueReceptor cells in olfactory epithelium

Why can we smell alcohol in drinks and not sugar in drinks?

Odor Sensitivity:

Related to gender & age

Can people distinguish many different odors?

Taste

4 Basic Tastes:

SweetSaltySourBitter

Why do we perceive more flavors?

Kinesthesia & Vestibular Sense

Kinesthesia

Gives information about the location of our body partsAllows us to perform movementsWhere does information come from?

Vestibular Sense

Monitors equilibrium and gives information regarding body position, movement, and acceleration

2 Kinds of Vestibular Sensation:

Body Rotation – arises from 3 semicircular canals in inner ear.

Gravitation & Movement – forward, backward, up, and down.

– Sense arises from vestibular sacs

Perception

The “way” in which we select & organize sensory inputHow we experience meaningful patterns in the jumble of sensory information

Selective AttentionCan we attend to all stimuli?Advantages = we don’t get overwhelmedDisadvantages = we “miss” stimuli that may be meaningful

Laws of Perceptual Grouping:(108)

1. Laws of Similarity2. Law of Good Continuation3. Law of Proximity4. Law of Closure5. Laws of Common Region6. Laws of Simplicity

Perceptual Constancies

Tendency to perceive aspects of the world as unchanging despite varied sensory input

Size Constancy – tendency to perceive a physical object as having a constant size.

Shape Constancy – to perceive a physical object as having a constant shape.

Brightness Constancy – to perceive objects as having a constant brightness even when they are viewed under different illumination.

Figure & Ground Relationship:

Figure – has a definite shape & location in space.

Ground – has no shape, seems to continue behind the figure & has no definite location.