Sensation and Perception Defining Sensation and Perception n

Sensation and Perception

Defining Sensation and Perception n Sensation n The detection of physical energy emitted or reflected by physical objects. n It occurs when energy in the external environment or the body stimulates receptors in the sense organs. n The process by which we gain (sense) information from the outside world n Occurs through receptor cells- specialized cells, which carry energy message to neuron

n Perception n The process by which the brain organizes and interprets sensory information. n Occurs after sensation; the way our brain mentally assigns meaning to the raw material we sensed- influenced by individual expectation

Ambiguous Figure n Colored surface can be either the outside front surface or the inside back surface n n Cannot simultaneously be both Brain can interpret the ambiguous cues two different ways

The Riddle of Separate Sensations n Sense receptors n 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 n n Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain. Synthesia n A condition in which stimulation of one sense also evokes another.

n Our sense organs (ears, eyes, etc. ) are the vehicle which transports stimuli from the world to our BRAIN. n Our BRAIN does the sensing n. So, what we see, hear, etc… is our brains NEURAL REPRESENTATION of what actually exists

n n Bottom-up Processing and Topdown 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 n 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 Characteristics 1. 2. 3. Transduction- ability to convert physical energy (ex: sound waves) into a neural transmission n Once stimulated nerve impulses travel along sensory pathways to processing area of cortex Adaptation- responsiveness to sensations lessens over time (thalamus stops ranking it as important) Thresholds- study of is called psychophysics; determined by the least amount of energy you can detect at least ½ the time

The Questions 1. The detection question is concerned with the limits on our ability to detect very faint signals n How intense does a light have to be for us to see it? n How intense does a sound have to be for us to hear it?

The Detection Question n n 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 n Any effects of subliminal persuasion are shortlived with no long-term consequences on our behavior

Theoretical and Observed Absolute Thresholds

Four Possible Outcomes in a Signal Detection Study Observer’s Response Signal “Yes” “No” Present Absent Hit False Alarm Miss Correct Rejection

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 n What is the smallest difference in brightness between two lights that we can see? n What is the smallest difference in loudness between two sounds that we can hear?

The Difference Question n n 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 n 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 n 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 Questions 3. The scaling question is concerned with how we perceive the magnitudes (intensities) of clearly detectable stimuli n What is the relationship between the actual physical intensities of stimuli and our psychological perceptions of these intensities?

The Scaling Question n 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 n For instance, to perceive a light as twice as bright, its actual intensity has to be increased between and 8 and 9 times n Likewise, if an electric shock is doubled in intensity, we perceive it as being about 10 times more intense

Steven’s Law n Deals with real and perceived magnitude of stimulus n EX: Susie is listening to the radio, when she 1 st turns it on, she adjusts the volume a little and it makes a BIG difference. n. After listening for a while, she changes the volume by the same degree, but barely notices a difference.

The Scaling Question n Sensory adaptation is the disappearance to repetitive or unchanging stimuli n 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) n 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 n n Fight Club- our detection of “clips” the 1 st 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 n Perceiving without awareness n n n 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 n n Subliminal- below the threshold n 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 n Perception versus Persuasion n n 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 n The smallest quantity of physical energy that can be reliably detected by an observer.

Absolute Sensory Thresholds n Vision: n n Hearing: n n 1 drop of perfume in a 6 -room apartment Touch: n n The tick of a watch from 20 feet in total quiet Smell: n n A single candle flame from 30 miles on a dark, clear night The wing of a bee on your cheek, dropped from 1 cm Taste: n 1 tsp. Sugar in 2 gal. water

Difference Threshold n n 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 n A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process. Stimulus is Present Response: Hit “Present” Response: Miss “Absent” Stimulus is Absent False Alarm Correct Rejection

Sensory Adaptation and Deprivation n Adaptation n The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious. Prevents us from having to continuously respond to unimportant information. Deprivation n The absence of normal levels of sensory stimulation.

Sensory Overload n n Overstimulation of the senses. Can use selective attention to reduce sensory overload. n Selective attention n The focusing of attention on selected aspects of the environment and the blocking out of others.

n Glass surface, with checkerboard underneath at different heights n n 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

The Visual Cliff

Critical Periods n n n 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 n n 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. n Perceptual Set n n A habitual way of perceiving, based on expectations. All are influenced by our culture.

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

Context Effects n n n 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 n Extrasensory Perception (ESP): n n n The ability to perceive something without ordinary sensory information This has not been scientifically demonstrated Three types of ESP: n n n Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events

Parapsychology n n n 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 n n 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.