Sensation and Perception

Our Sensational Senses Defining sensation and perception The riddle of separate senses Measuring the senses Sensory adaptation Sensory overload

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. Perception The process by which the brain organizes and interprets sensory information.

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. Synesthesia A condition in which stimulation of one sense also evokes another.

Measuring Senses Absolute threshold Difference threshold Signal-detection theory

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.

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 Over-stimulation 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.

Vision What we see An eye on the world Why the visual system is not a camera How we see colors Constructing the visual world

What We See Hue Visual experience specified by color Brightness Lightness and luminance Saturation Vividness or purity of color

What We See Hue Brightness Saturation

An Eye on the World Cornea Protects eye and bends light toward lens. Lens Focuses on objects by changing shape. Iris Controls amount of light that gets into eye. Pupil Widens or dilates to let in more light.

An Eye on the World Retina Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision. Rods Visual receptors that respond to dim light. Cones Visual receptors involved in color vision Most humans have 3 types of cones.

The Structures of the Retina

Why the Visual System is not a Camera Much visual processing is done in the brain. Some cortical cells respond to lines Other cells in the cortex respond to shapes Feature-detectors Cells in the visual cortex that are sensitive to specific features of the environment.

Hubel & Wiesel’s Experiment

How We See Colors Trichromatic theory

Trichromatic Theory Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors: red, blue, & green All other colors can be derived by combining these three.

Test of Color Blindness

Afterimage An image that remains after stimulation of the retina has ended. Cones not used fire to bring the visual system back in balance

Constructing the Visual World Form perception Depth and distance perception Visual constancies: When seeing is believing Visual illusions: When seeing is misleading

Form Perception Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.

Figure and Ground Proximity Seeing 3 pair of lines in A. Similarity Seeing columns of orange and red dots in B. Continuity Seeing lines that connect 1 to 2 and 3 to 4 in C. Closure Seeing a horse in D.

Depth and Distance Perception Binocular Cues: Visual cues to depth or distance that require the use of both eyes.

Depth and Distance Perception Monocular Cues: Visual cues to depth or distance that can be used by one eye alone.

The Ames Room A specially-built room that makes people seem to change size as they move around in it The room is not a rectangle, as viewers assume it is A single peephole prevents using binocular depth cues

Visual Constancies The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce. Shape constancy Location constancy Size constancy Brightness constancy Color constancy

Shape Constancy Even though these images cast shadows of different shapes, we still see the quarter as round

Visual Illusions Illusions are valuable in understanding perception because they are systematic errors. Illusions provide hints about perceptual strategies. In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.

The Ponzo Illusion Linear perspective provides context Side lines seem to converge Top line seems farther away But the retinal images of the red lines are equal!

Fooling the Eye The cats in (a) are the same size The diagonal lines in (b) are parallel You can create a “floating fingertip frankfurter” by holding hands as shown, 5-10” in front of face.

Hearing What we hear An ear on the world Constructing the auditory world

What We Hear Intensity How loud something is - measured in decibels When a sound reaches 130 it can become painful. Pitch How high or low a sound is. Timbre (pronounced “TAM-bur”) Complexity of a tone The difference in the sounds made by a piano, a flute, and a guitar are caused by variations of timbre.

An Ear on the World

Structure of the Ear The outer ear catches waves and funnels the towards the Eardrum- waves hit drum and it vibrate Vibrations cause small bones to vibrate - third bone is attached to snail shaped unit Cochlea - filled with fluid and lined with cells

Hair Cells Key to hearing Cells have hair like extensions called Cilia - line the cochlea/tuned to receive different frequencies Respond to movement Movement causes flow of electrical impulses Impulses go through Auditory nerve- to the brain Where sound pattern is interpreted

Other Senses Taste: savory sensations Smell: The sense of scents Senses of the skin The mystery of pain The environment within

Taste: Savory Sensations Papillae Knoblike elevations on the tongue, containing the taste buds (Singular: papilla). Taste buds Nests of taste-receptor cells.

Taste Buds Photograph of tongue surface (top), magnified 75 times. 10,000 taste buds line the tongue and mouth. Taste receptors are down inside the “bud” Children have more taste buds than adults.

Four Tastes Four basic tastes Salty, sour, bitter and sweet. Different people have different tastes based on: Genetics Culture Learning Food attractiveness

Smell: The Sense of Scents Airborne chemical molecules enter the nose and circulate through the nasal cavity. Vapors can also enter through the mouth and pass into nasal cavity. Receptors on the roof of the nasal cavity detect these molecules.

Olfactory System

Cutaneous Sense (touch) 3 kinds of Cutaneous Receptors Send messages to the brain to be recorded Pressure Temperature Pain Remain active to record injury Can fire for hours

Sensitivity to Touch

Gate-Control Theory of Pain Experience of pain depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.

Perceptual Powers: Origins and Influences Inborn abilities Critical periods Psychological and cultural Influences on perception

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 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?

Puzzles of Perception Subliminal Perception Extrasensory Perception: Reality or Illusion?

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. 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.

Subliminal Perception Perceiving without awareness visual stimuli can affect your behavior even when you are unaware that you saw it Non-conscious processing also occurs in memory, thinking, and decision making

Subliminal Perception Perception versus Persuasion there is no empirical research to support popular notions that subliminal persuasion has any effect on a person’s behavior persuasion works best when messages, in the form of advertising or self-help tapes, are presented above-threshold, or at a supraliminal level