Sensation and Perception

Defining Sensation and Perception Sensation

The detection of physical energy emitted or reflected by physical objects.

It occurs when energy in the external environment or the body stimulates receptors in the sense organs.

The process by which we gain (sense) information from the outside world

Occurs through receptor cells- specialized cells, which carry energy message to neuron

Perception The process by which the brain

organizes and interprets sensory information.

Occurs after sensation; the way our brain mentally assigns meaning to the raw material we sensed- influenced by individual expectation

Ambiguous Figure

Colored surface can be either the outside front surface or the inside back surface Cannot

simultaneously be both

Brain can interpret the ambiguous cues two different ways

The Riddle of Separate Sensations Sense receptors

Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.

Sensation & Perception Processes

Doctrine of Specific Nerve Energies

Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.

Synthesia A condition in which stimulation of one sense

also evokes another.

Our sense organs (ears, eyes, etc.) are the vehicle which transports stimuli from the world to our BRAIN. Our BRAIN does the sensing

So, what we see, hear, etc… is our brains NEURAL REPRESENTATION of what actually exists

Bottom-up Processing and Top-down Processing

Bottom-up processing is the processing of sensory information as it enters the sensory structures and travels to the brain

Top-down processing is the brain’s use of existing knowledge, beliefs, and expectations to interpret the sensory stimulation Perception is subjective because of top-down processing Perceptual set occurs when we interpret an ambiguous

stimulus in accordance with our past experiences A contextual effect occurs when we use the present context

of sensory input to determine its meaning

All Senses share these 3 Characteristics1. Transduction- ability to convert physical

energy (ex: sound waves) into a neural transmission

Once stimulated nerve impulses travel along sensory pathways to processing area of cortex

2. Adaptation- responsiveness to sensations lessens over time (thalamus stops ranking it as important)

3. Thresholds- study of is called psychophysics; determined by the least amount of energy you can detect at least ½ the time

The Questions1. The detection question is concerned

with the limits on our ability to detect very faint signals How intense does a light have to be for

us to see it?

How intense does a sound have to be for us to hear it?

The Detection Question Absolute threshold is the minimum amount

of energy in a sensory stimulus that is detected 50% of the time

Subliminal stimulus is one that is detected only up to 49% of the time Any effects of subliminal persuasion are short-

lived with no long-term consequences on our behavior

Theoretical and Observed Absolute Thresholds

Four Possible Outcomes in a Signal Detection Study

Present Absent

“Yes” HitFalse Alarm

“No” MissCorrect

RejectionOb

serv

er’

s

Resp

on

se

Signal

The Questions

2. The difference question is concerned with limits on our detection abilities, but in this case with our ability to detect very small differences between stimuli What is the smallest difference in brightness

between two lights that we can see?

What is the smallest difference in loudness between two sounds that we can hear?

The Difference Question

A difference threshold (also called a just noticeable difference, or jnd) is the minimum difference between two stimuli that is detected 50% of the time

Weber’s Law says that for each type of sensory judgment, the difference threshold is a constant fraction of the standard stimulus value used to measure it

Weber’s Law

Applied: Bob lifts 10 lb weights and his JND is 2 additional lbs. If Bob lifts 100 lbs, his JND is going to be 20 lbs

This means the JND is large (takes more difference) when the stimulus intensity is high and small (takes little difference) when intensity is low

The Questions3. The scaling question is concerned with how we

perceive the magnitudes (intensities) of clearly detectable stimuli What is the relationship between the actual physical

intensities of stimuli and our psychological perceptions of these intensities?

The Scaling Question Steven’s Power Law states that the perceived

magnitude of a stimulus is equal to its actual physical intensity raised to a constant power for each type of judgment For instance, to perceive a light as twice as bright,

its actual intensity has to be increased between and 8 and 9 times

Likewise, if an electric shock is doubled in intensity, we perceive it as being about 10 times more intense

Steven’s Law

Deals with real and perceived magnitude of stimulus EX: Susie is listening to the radio, when

she 1st turns it on, she adjusts the volume a little and it makes a BIG difference.After listening for a while, she changes the volume by the same degree, but barely notices a difference.

The Scaling Question

Sensory adaptation is the disappearance to repetitive or unchanging stimuli This sensory adaptation has survival value, as

it is more important to detect new stimuli (which may signal danger) than constant stimuli

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a

faint stimulus (signal) amid background noise (other stimulation). SDT assumes that there is no single absolute threshold and detection depends on: person’s experience, expectations, motivation, & level of fatigue

Fight Club- our detection of “clips” the 1st time we see it is far LESS then subsequent viewings

Implication: we can “turn up or down” our ability to detect the presence of stimuli

Subliminal Perception Perceiving without awareness

visual stimuli can affect your behaviour even when you are unaware that you saw it

nonconscious processing also occurs in memory, thinking, and decision making

these effects are often small, however, and difficult to demonstrate and work best with simple stimuli

Subliminal Messages Subliminal- below the threshold

Subliminal Priming- suggestions No proof that this can influence a mass

audience or that tapes played while asleep can make you quit smoking; however, evidence indicates a positive correlation between exposure to SM and achieving a desired outcome

Subliminal Perception Perception versus Persuasion

there is no empirical research to support popular notions that subliminal persuasion has any effect on a person’s behaviour

persuasion works best when messages, in the form of advertising or self-help tapes, are presented above-threshold, or at a supraliminal level

Absolute Threshold The smallest quantity of physical energy that can

be reliably detected by an observer.

Absolute Sensory Thresholds Vision:

A single candle flame from 30 miles on a dark, clear night Hearing:

The tick of a watch from 20 feet in total quiet Smell:

1 drop of perfume in a 6-room apartment Touch:

The wing of a bee on your cheek, dropped from 1 cm Taste:

1 tsp. Sugar in 2 gal. water

Difference Threshold The smallest difference in stimulation that

can be reliably detected by an observer when two stimuli are compared;

Also called Just Noticeable Difference (JND).

Signal-Detection Theory A psychophysical theory that divides the detection of

a sensory signal into a sensory process and a decision process.

Stimulus is

Present

Stimulus is

Absent

Response: “Present”

Hit False Alarm

Response: “Absent”

Miss Correct Rejection

Sensory Adaptation and Deprivation Adaptation

The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious.

Prevents us from having to continuously respond to unimportant information.

Deprivation The absence of normal levels of sensory

stimulation.

Sensory Overload Overstimulation of the senses. Can use selective attention to reduce

sensory overload. Selective attention

The focusing of attention on selected aspects of the environment and the blocking out of others.

The Visual Cliff

Glass surface, with checkerboard underneath at different heights Visual illusion of a cliff Baby can’t fall

Mom stands across the gap Babies show increased

attention over deep side at age 2 months, but aren’t afraid until about the age they can crawl (Gibson & Walk, 1960)

The Visual Cliff

Critical Periods If infants miss out on

experiences during a crucial period of time, perception will be impaired.

When adults who have been blind since birth have vision restored, they may not see well

Other senses such has hearing may be influenced similarly.

Psychological and Cultural Influences on Perception

We are more likely to perceive something when we need it.

What we believe can affect what we perceive. Emotions, such as fear, can influence perceptions

of sensory information. Expectations based on our previous experiences

influence how we perceive the world. Perceptual Set

A habitual way of perceiving, based on expectations.

All are influenced by our culture.

Perceptual Set

What you see in the centre figures depends on the order in which you look at the figures: If you scan from the left, see an old woman If you scan from the right, see a woman’s figure

Context Effects The same physical

stimulus can be interpreted differently

We use other cues in the situation to resolve ambiguities

Is this the letter B or the number 13?

Extrasensory Perception Extrasensory Perception (ESP):

The ability to perceive something without ordinary sensory information

This has not been scientifically demonstrated Three types of ESP:

Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events

Parapsychology The study of purported psychic phenomena

such as ESP and mental telepathy. Persinger suggests that psychic phenomena

are related to signs of temporal lobe epilepsy in otherwise neurologically normal individuals.

Most ESP studies produce negative findings and are not easily replicated.

Parapsychology

J. B. Rhine conducted many experiments on ESP using stimuli such as these.

Rhine believed that his evidence supported the existence of ESP, but his findings were flawed.