Sensation and Perception Chapter 5&6

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.

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 sensories 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.

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. Stimulus is Present Stimulus is Absent Response: “Present” HitFalse Alarm Response: “Absent” MissCorrect 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.

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

What We See Hue Visual experience specified by color names and related to the wavelength of light. Brightness Lightness and luminance; the visual experience related to the amount of light emitted from or reflected by an object. Saturation Vividness or purity of color; the visual experience related to the complexity of light waves.

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 in specific orientations (e.g. horizontal). Other cells in the cortex respond to other shapes (e.g., bulls-eyes, spirals, faces). Feature-detectors Cells in the visual cortex that are sensitive to specific features of the environment.

Hubel & Wiesel’s Experiment

How We See Colours Trichromatic theory Opponent process theory

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

Opponent-Process Theory A competing theory of colour vision, which assumes that the visual system treats pairs of colours as opposing or antagonistic. Opponent-Process cells are inhibited by a colour, and have a burst of activity when it is removed.

Afterimages

Test of Colour Deficiency

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

Top-Down Processing Information processing guided by higher- level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT

Example of Top-Down Processing Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Our perceptions are organized by meanings that our minds impose. We perceive the world not as it is, but as it is useful for us.

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. Convergence: Turning inward of the eyes, which occurs when they focus on a nearby object. Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

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 Colour 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 Loudness The dimension of auditory experience related to the intensity of a pressure wave. Pitch The dimension of auditory experience related to the frequency of a pressure wave. Timbre (pronounced “TAM-bur”) The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

An Ear on the World

Auditory Localization Sounds from different directions are not identical as they arrive at left and right ears Loudness Timing Phase The brain calculates a sound’s location by using these differences.

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

Taste: Savoury 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

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.

Neuromatrix Theory of Pain Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.

The Environment Within Kinesthesis The sense of body position and movement of body parts; also called kinesthesia. Equilibrium The sense of balance. Semicircular Canals Sense organs in the inner ear, which contribute to equilibrium by responding to rotation of the head.

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

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?

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?

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

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

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.