Sensation and Perception

Sensation

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Sensation Stimulus- any aspect of or change in the environment to which an organism responds Sensation- what occurs when a stimulus activates a receptor Perception- the organization of sensory information into meaningful experiences

Processing Bottom-Up Processing- analysis that begins with the sense receptors and works up to the brain’s integration of sensory information Top-Down Processing- information processing guided by higher-level mental processes as when we construct perceptions drawing on our experience and expectations

Threshold Laws of sensation are found by figuring out how much of a stimulus is necessary for a person to sense it Absolute threshold- the weakest amount of a stimulus that a person can detect half the time Our senses: vision (candle flame= 30 miles); hearing (watch ticking 20 feet); taste (1 tsp of sugar in 2 gallons of water); smell (1 drop of perfume in 3 room house); touch (bee’s wing falling a distance of 1 cm onto your cheek) Humans are limited

Thresholds 25 50 75 100 Low Absolute threshold Medium 25 50 75 100 Low Absolute threshold Medium Intensity of stimulus Percentage of correct detections Subliminal stimuli Thresholds

Sensory Differences and Ratios Difference threshold- the smallest change in a physical stimulus that can be detected half the time Depends more on change than the absolute size Weber’s law- the larger or stronger a stimulus, the larger the change required for a person to notice that anything has happened to it Some people are more sensitive to these changes

Sensory Adaptation Senses are most responsive to change, instead of constants Our senses “get used” to stimuli

Signal- Detection Theory = the study of people’s tendencies to make correct judgments in detecting the presence of stimuli No single absolute threshold for a stimulus Depending on ability to block other stimuli, affects ability to sense stimulus

The Senses

Senses Five main senses: vision, hearing, taste, smell, and touch Also skin senses Two internal senses Vestibular- regulates sense of balance Kinesthetic- sense of movement and body position

Vision Light enters the pupil (opening in the iris that regulates the amount of light entering the eye) Reaches the lens (flexible structure that changes its shape to focus light on the retina (innermost coating of the back of the eye, containing the light-sensitive receptor cells- rods and cones) Rods and cones change light into neuronal impulses to send along the optic nerve (nerve that carries impulses from the retina to the brain’s occipital lobe

Vision continued

Vision continued Blind spot= point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there Psychological factors for pupil size Disgusted= smaller Like something= larger Afraid= open wide

Vision continued Light- form of electromagnetic radiation Objects absorb and reflect light Color Deficiency- hereditary When a person’s cones do not function properly Most see some colors

Vision continued Binocular fusion- the process of combining the images received from the two eyes into a single, fused image Retinal disparity- the differences between the images stimulating each eye Nearsightedness (eyeball is too long) vs. farsightedness (eyeball is too short)

Hearing Vibrations of the air (sound waves) pass through bones to reach inner ear with hairlike cells Hair cells change vibrations into neuronal signals that travel through auditory nerve to the brain

Hearing continued Loudness is from heigh of sound waves measured in decibels (0-140) 80-110 damages hearing Pitch depends on frequency of waves Deafness- conduction (hearing aids) vs. sensorineural (cochlear implant)

Smell and Taste (chemical senses) Gaseous molecules enter your nose in vapors to reach membrane in nasal passages with receptors that send messages through olfactory nerve Taste Liquid chemicals stimulate receptors on taste buds Four experiences- sour, salty, bitter, sweet Most of taste is produced by sense of smell Also by warmth, cold, and pressure

Skin Senses (touch) Receptors tell: pressure, warmth, cold, and pain Sensitivity varies based on amount of receptors Some are sensitive to hot or cold stimuli

Skin Senses (touch): Pain Functions as emergency system Relies on many stimuli Gate control theory- we can lesson some pains by shifting our attention away from the pain impulses or by sending other signals to compete with the pain signals

Perception

Components Translating a physical stimulus into the language of the nervous system (neural impulses) Comprehending the basic components of the stimulus, such as shape, size and color Organizing the components into an understandable explanation

Gestalt =the experience that comes from organizing bits and piece of information into meaningful wholes Principles- proximity, continuity, similarity, simplicity, closure

Gestalt continued Figure-ground perception- perceptual organization that is the ability to discriminate between a figure and its background Perceptual inference- filling in the gaps if what our senses tell us Example- seat is solid

Learning to Perceive We learn to perceive Size of a human face...actual face Active involvement in environment is important for accuracy Influenced by our needs, beliefs, and expectations Subliminal messages- brief auditory or visual messages that are presented below the aboslute threshold Concerns about subliminal advertising

Depth Perception =ability to recognize distances and three-dimensionality, develops in infancy Monocular depth cues- cues that can be used with a single-eye Relative height, interposition, light and shadows, texture-density gradient, linear perspective, relative motion Motion parallax- the apparent movement of stationary objects relative to one another that occurs when the observer changes position Binocular depth cues-depends on both eyes Convergence, retinal disparity

Constancy and Illusions Constancy- the tendency to perceive certain objects in the same way regardless of changing angle, distance, or lighting Illusions- perceptions that misrepresent physical stimuli Cues are distorted so that our brains cannot correctly interpret space ,size, and depth cues

ESP =Extrasensory Perception, an ability to gain information by some means other than the ordinary senses Clairvoyance, telepathy, psychokinesis, precognition

EXTRA TOPICS The survival of many animals is dependent upon their senses. For example, deer have a heightened sense of smell that allows them to detect predators. Research the sensory skills of one of the following and write a one-page summary on how the animal uses the sense as a primary means of survival. Hearing in dogs, dolphins, or bats Smell in lobsters, honeybees, or ants Vision in predatory birds like hawks or owls

EXTRA TOPICS Psychologists usually apply Weber’s law and sensory adaptation to one of the five senses, such as taste. Do you think the same concept can be applied to the effects of the media upon behavior? For example, does the prevalence of violence on television make people less shocked by violence in general? Or does the use of disrespectful language make people less courteous in their day-to-day lives/ find at least two magazine or newspaper articles on the subject and write summaries of the points made by the articles.

EXTRA TOPICS Stroop Effect

EXTRA TOPICS Our perception of ourselves is based, in large parge, on our mirror image, since this is the image we see most frequently. Lewis Carroll, the author of Alice in Wonderland, was fascinated by words that appeared the same when viewed in a mirror. Print the following words in block, capital letters: BEECH, COOKBOOK, BOX. hold the paper in the mirror. Now turn the paper upside down. Think of other words that would look the same when turned upside down and viewed in a mirror

EXTRA TOPICS Research ESP and prepare a chart showing the different types of ESP experiences that you have uncovered. Present this chart and an overview of opinions on ESP. Do you think parapsychology is a legitimate offshoot of psychology?

EXTRA TOPICS Search the internet for information and examples of optical illusions. Present examples to the class and explain how the illusions were created.