Sensation & Perception Chapter 5

Sensing & Perceiving Information Sensation: Receiving Perception: Organizing & Interpreting

Vision – The Eye Retina Light enters eye through the cornea Passes through the pupil and lens Focused into an image on the retina Retina Light sensitive inner surface of the eye Contains Rods & Cones Receptor cells convert light to neural impulses and send to brain Brain reassembles impulses into an image

Vision – The Eye

Vision – Retina Receptors Rods detect black, white, and gray necessary for peripheral and twilight vision Cones concentrated near the center of retina function in daylight or well-lit conditions detect fine detail color vision

Vision--Receptors Receptors in the Human Eye Cones Rods Number Location in retina Sensitivity in dim light Color sensitive? Yes Low Center 6 million No High Periphery 120 million

The Eye Optic Nerve: nerve that carries neural impulses from the eye to the brain Blind Spot: point at which the optic nerve leaves the eye No receptor cells creates a “blind spot”

Vision – Feature Detection Feature Detectors nerve cells that respond to specific features of a stimulus shape, angle, or movement fMRI can be used to determine what object a person is looking at

Visual Information Processing Parallel Processing processing many parts of a problem all at once the brain’s natural mode of information processing for many functions (including vision)

Visual Information Processing Scene Retinal processing: Receptor rods and conesbipolar cells  ganglion cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Abstraction: Brain’s higher-level cells respond to combined information from feature-detector cells Recognition: Brain matches the constructed image with stored images

Color-Deficient Vision People who suffer red-green blindness have trouble perceiving the number within the design

Color Vision Young-Helmholtz trichromatic (three-color) theory retina has 3 different color receptors (red, green, blue) different combinations allow for the perception of any color Opponent-process theory opposing processes of retina enable color vision e.g., some neurons are turned on by red and off by green

Audition Audition- the sense of hearing Frequency- the number of complete wavelengths that pass a point in a given time Pitch- a tone’s highness or lowness depends on frequency long sound waves = low frequency & low pitch short sound waves = high frequency & high pitch

Audition--The Ear Sound waves Middle Ear auditory canal eardrum (vibrates with the waves) middle ear cochlea (in inner ear)  triggers neural impulses (auditory nerve)  thalamus  auditory cortex (temporal lobe) Middle Ear chamber between the eardrum and cochlea contains 3 tiny bones (hammer, anvil, stirrup) that transmit vibrations to the cochlea

Audition--The Ear Inner Ear innermost part of ear Contains the Cochlea a fluid-filled tube through which sound waves trigger nerve impulses

Decibel Levels - Common Sounds

Locating Sounds sound reaches one ear more intensely and more quickly auditory system is able to detect tiny differences hearing loss in one ear = difficulty locating sounds

Touch Skin Sensations pressure warmth cold pain only skin sensation with identifiable receptors warmth cold pain Rubber hand illusion http://www.youtube.com/watch?v=TCQbygjG0RU

Pain Gate-Control Theory (1960s) No theory explains all available findings Gate-Control Theory (1960s) provides a useful model for understanding pain the spinal cord contains small fibers (conduct pain signals) and large fibers (conduct other sensory signals) “gate” opened by the activity of pain signals traveling up small nerve fibers “gate” closed by activity in larger fibers or by information coming from the brain

Pain Control Massaging area next to pain Distraction Diverting the brain’s attention may bring relief Pleasant imagery Count backward Virtual reality

Taste Taste Sensations sweet sour salty bitter savory (umami)

Taste Taste receptors Sensory Interaction reproduce themselves every 2 weeks taste sensitivity and # of taste buds decrease as we age Sensory Interaction one sense may influence another sense the smell of food influences its taste smell + texture = flavor rubber hand illusion (vision & touch interact)

Smell humans can detect 10,000 odors olfactory receptor cells respond to aromas messages sent through receptor axons to the olfactory bulb in the brain messages then travel from olfactory bulb to temporal lobe & limbic system odors can evoke memories

Smell

Body Position and Movement Sixth sense Kinesthesis the system for sensing the position and movement of individual body parts interacts with vision Vestibular sense monitors head and body position to maintain balance fluid in the inner ear moves when head moves messages are sent to the cerebellum

Perceptual Organization - organizing & interpreting info from senses Gestalt an organized whole tendency to integrate pieces of information into meaningful wholes Necker cube

Perceptual Organization First: Need to discriminate objects from backgrounds Figure and Ground perceiving an object (figure) as distinct from its surroundings (ground) In a busy restaurant: voice you attend to = figure all other voices = ground

Perceptual Organization- Gestalt Next step: Need to organize the figure into a meaningful form Grouping the tendency to organize stimuli into meaningful groups grouping rules identified by Gestalt psychologists the “whole” that we perceive differs from the sum of its parts

Perceptual Organization- Gestalt Grouping Rules proximity - we group nearby figures together similarity - we group similar figures together continuity – we perceive continuous patterns closure – we fill in gaps to create complete objects connectedness - spots, lines, and areas are seen as a unit when connected

Perceptual Organization- Gestalt Proximity Similarity Continuity Closure Connectedness We see not six separate lines, but three sets of two lines. We see the triangles and circles as vertical columns of similar shapes, not as horizontal rows of dissimilar shapes. Continuity – this pattern could be a series of alternating semicircles, but we perceive it as two continuous lines – one wavy, one straight. We can perceive a triangle even when it is not complete. Connectedness: We perceive the two dots and the line between them as a single unit.

Perceptual Organization-Depth Perception Visual Cliff

Perceptual Organization Depth Perception seeing objects in three dimensions allows us to estimate distance Visual Cliff laboratory technique used to test depth perception http://www.youtube.com/watch?v=eyxMq11xWzM

Perceptual Organization Depth Perception Binocular cues – depth cues depend on use of two eyes retinal disparity images from the two eyes differ brain compares the images to compute distance the larger the difference, the closer the object

Perceptual Organization Depth Perception Monocular Cues depth cues needed for objects at further distances available to each eye separately relative height higher objects seen as more distant relative size smaller image is more distant

Depth Perception Monocular Cues (continued) interposition if one object blocks our view of another, we perceive that object to be closer

Depth Perception Monocular Cues (continued) relative clarity hazy object seen as more distant relative motion as we move, stable objects appear to also move fix gaze on object: those beyond appear to move with you; those in front appear to move backward relative brightness dimmer objects seem farther away

Depth Perception Monocular Cues (continued) linear perspective parallel lines appear to converge with distance

Perceptual Constancy perceiving objects as unchanging despite changes in illumination and retinal image able to recognize objects despite changes in color, shape, & size

Shape Constancy Shape constancy – as a door opens the shape projected on retina looks more like a trapezoid…but we still perceive it as rectangular.

Perceptual Constancy Color depends on context Color Constancy we perceive familiar objects as having consistent color even if illumination changes and alters the wavelengths reflected by the object

Perceptual Organization Size-Distance Relationship Monsters are same size – but linear perspective tells brain that the monster in pursuit is farther away (and we therefore perceive it as larger). Ponzo illusion – same principle as monsters – two red bars are identical, but experience tells us that a more distant object can create the same-sized image as a nearer one only if it is actually larger. Therefore, we perceive the bar that seems farther away as larger.

Perceptual Organization- Size-Distance Relationship

Depth Perception

Perceptual Organization Müller-Lyer Illusion The two red arrows are of equal length. The arrow configuration “angles in” (near the ticket counter) is always the front side of an object, the “angles out” configuration occurs at the far end of a room, for instance (here next to the door). So, given no further information, the brain assumes the “angles in” configuration to be closer, computes size constancy on it, and - given identical retinal size of the two angle arrangements – concludes that the “angle in”-line is shorter.

Perceptual Organization Brightness Contrast Gray bars are the same color. The one on right appears brighter because of differences in the surrounding context.

Perceptual Interpretation Perceptual Adaptation (vision) ability to adjust to an artificially displaced visual field glasses that invert view of the world (looks upside down) humans can adapt relatively quickly and learn to coordinate movements accurately

Perceptual Interpretation Perceptual Set a mental predisposition to perceive one thing and not another our experiences and expectations influence what we perceive

Perceptual Set – context effect Pursuing monster may look more aggressive. Identical pursued monster may seem frightened.

Is There Extrasensory Perception? Parapsychology the study of paranormal phenomena Astrological predictions Psychic healing ESP Psychokinesis (“mind over matter”; levitating)

Is There ESP? Extrasensory Perception (ESP) controversial claim that perception can occur apart from sensory input types of ESP: Telepathy (mind-to-mind communication) Clairvoyance (sensing remote events) Precognition (perceiving future events)