First Exam. Sensation and Perception. Process of Forming Sensations. Sensation and Perception. The Eye. Our perceptual experience. Mean = 57.

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1 First Exam Sensation and Perception Mean = 57.5 SD = 11 Source of human knowledge Could we know anything without our senses? Empiricists - John Locke ( ), all knowledge comes from sensory experience Nativists - Immanuel Kant ( ), knowledge cannot come from sensory experience alone, the mind has preexisting categories which organizes sensory material. Sensation and Perception Sensation vs. perception Sensation: The basic processes by which sensory organs and the nervous system respond to stimuli in the environment and form elementary psychological experiences. This tastes bitter, That sound is loud, That object is very red, Perception: The way our nervous systems organizes and interprets sensory information (sensations) to give us a perceptual experiences. The brain organizes sensory input and translates it into something meaningful. Similar to the binding problem in the previous chapter. Strong coffee, Red Hot Chilli Peppers, Apple looks ripe. Process of Forming Sensations Physical stimulus Physiological response Sensory experience Physical stimulus is the matter or energy that produces a change in a sense receptor. Each sensory receptor sensitive to different form of energy e.g., light waves, sound waves, pressure, temperature. Each sense has special cells, sensory receptors, translate physical energy into neural responses e.g., retina of eye, cochlea of the ear, touch receptors in the skin The process of converting energy of stimuli into neural impulses, which are sent to the brain is called Transduction. Our perceptual experience If we went to some other planet would we see different colors? or Was there color before an animal evolved that saw color. Doctrine of Specific Nerve Energies Neural response (action potential) itself does not reflect the characteristics of the stimulus. Our perceptions are based on the part of the brain stimulated and not on the stimulus itself Johannes Mueller What would happen if the brain were miswired? Synesthesia people who when received stimulation from one sense receives additional stimulation in another. Sound producing visual effects. Stimulating neurons manually will create a perception even if no stimulus is present. The Eye Vision Between 25 and 40 percent of human brain devoted primarily to the analysis of visual input (Gross, 1998). Cornea Responsible for initial gross focusing. Iris Controls the size of the pupil that allows light into the eye. Negative feedback system. Why do my girlfriend s pupils get larger when she looks at me? Why do her father s? Pupil opening related to visual acuity-why do high intensity lamps improve acuity.

2 Lens Transparent part of the eye which focuses light on the retina. Changes in shape of the lens to focus light at various distances known as accommodation. Old age and Presbyopia. Retina Photosensitive surface on the back of the eye. Fovea - Place on the retina of greatest acuity. Figure 18.4 The retina s reaction to light Myers: Psychology, Ninth Edition in Modules Copyright 2010 by Worth Publishers Eye movements Myopia Hyperopia Convergence Eyes converge as objects approach. Saccadic The quick darting movement of the eyes when exploring the environment. Smooth Smooth movement of the eyes which is elicited by a moving target. Nystagmus Small tremors which probably maintain image on fresh receptors. Stabilized images. Miniature slide projector attached to a contact lens moves each time the eye moves. As a result, the projected image disappears in a few seconds because it does not move on the retina. Figure 17.4 Sensory adaptation: now you see it, now you don t! Myers: Psychology, Ninth Edition in Modules Copyright 2010 by Worth Publishers

3 Snellen Notation Eagles and Hawks have more acute Vision than humans, so why is his Head upside down? Visual Receptors Rods Receptor cells on periphery of retina, responsible for black and white vision. About 150 Million of them. Very sensitive to light. Cones Receptor cell on the central part of the retina(fovea), responsible for color vision. About 7 Million of them (5-10%). Problem: How come rods which are more sensitive to light are less acute then cones? Organization of Rods and Cones Dark and light Adaptation Photons of light break down Iodopsin (cones), Rhodopsin (rods) creating a neural pulse. Purkinje Effect Rods more sensitive to blue and green, cones to reds and yellows Plane and car instrument lighting

4 Details of the Retina Concept of a Visual Field Light Impulses produced by light Photoreceptors Receptive Fields Receptive field: The organization of bipolar cells that feed information about the light changes in the environment to the ganglion cell. Insert a microelectrode into a retinal ganglion cell: then record potentials as various stimuli are shown onto the cell Center-surround shape (a) baseline firing of cell (b) cell firing greater than baseline (c) cell firing less than baseline Mach Bands Fig. 4.10

5 Inhibition of center of visual field greatest Inhibition of center of visual field least Path of Visual Stimulation Light reaches visual receptors on the Retina Bipolar cells organize responses of receptors Ganglion cells, which form the optic nerve, organize responses of bipolar cells into receptive fields (center surround cells) Primary visual area, back of occipital lobe, receives signals from optic nerve and organize information into feature detectors. 4.2 Visual Pathway From Eye Through Brain 32 Feature Detectors Motion Detector Hubel and Wiesel Discovered cells in the visual cortex Feature Detectors that are organized so that they responded to specific features of the environment. Feature detectors can be explained by a collection of ganglion cells from the retina that are connected to one cell in the cortex so as to respond to specific stimulus features. This finding suggests we have feature detectors, specialized neurons that respond to the presence of certain simple features, such as angles and lines, which are then processed at higher levels to give us forms and objects.

6 Color Vision Our visual system sensitive to narrow band of electromagnetic radiation from 350 millimicrons (violet) to 750 millimicrons (Red) Why does your shirt look blue? Yellow? What if there is no blue or yellow wavelength shining on your shirt? What do you get when you mix blue and yellow paint? Trichromatic Theory of Color Vision Young-Helmholtz model Conjectured that color vision started at the retinal level. Retina has three types of cone receptors(red, Green, Blue) Additive versus subtractive color mixing. Additive-Each light adds its portion of the wavelength spectrum adding up to White Light Subtractive-Each pigment subtracts a portion of the wavelength that it absorbs leaving no light to reflect or black Young-Helmholtz model Problems with the Young-Helmholtz model People act as if there are four primaries, Red, Green, Blue AND YELLOW. Some color combinations make sense to us others don t. What do you get from combination of Red and Blue? Red and Yellow Green and Blue But Green and Red Yellow and Blue Color blindness tends to come in specific pairs. Red/Green and Blue/Yellow but not red/blue or yellow/green. Negative afterimages Color Blindness Test

7 He Lurks Among Us. Opponent Process Theory of Color Vision Because of these findings, Ewald Hering proposed that we perceive color in a system of paired colors. Red vs. green Yellow vs. blue White vs. black Opponent Process Cells Red /Green Stimulated experience, Red Inhibited experience, Green Blue/Yellow Stimulated experience, Blue Inhibited experience, Yellow Negative after image caused by fatigue one kind of receptor, so the opponent process cell rebounds with the other color experience.

8 Working against color constancy The ear is designed to detect and transmit sound waves to the brain. Sound waves are vibrations in the air or other medium. Sound waves vary according to frequency (pitch) and amplitude (loudness). Frequency is measured by the number of vibrations or cycles of the sound wave per second, referred to as hertz (Hz.). Human ear 15 20,000 Hz. Hearing Hearing The Ear Sound waves strike the tympanic membrane, or eardrum. The vibrations of the eardrum cause three very tiny bones, the malleus, the incus, and the stapes, (literally the hammer, anvil and stirrup) to work to make the sound waves become stronger signals. The stirrup causes the cochlea to vibrate. Sound waves create vibrations that displace hair cells along the basilar membrane within the cochlea. The Ear Hearing Hearing Loss There are two common forms of deafness. Conduction deafness results when the three special bones in the ear fail to transmit sound waves properly to the cochlea. Nerve deafness results from damage to the structures that receive and transmit the impulses - the cochlea, hair cells or auditory nerve. From ear drum to oval window, sound amplified 180 times through action of these small bones.

9 The Cochlea Hearing Pitch Perception Adult hearing range-- between 15 and 20,000 Hz. How we hear pitch depends in part on the frequency to which we are listening. Low frequencies (up to about 100 Hz), the frequency principle. Sound waves passing through the fluid in the cochlea cause all the hair cells to vibrate, producing action potentials that are synchronized with the sound waves. Mid frequencies ( Hz), volley principle. Fewer hair cells can fire at this pace, but those that do respond in groups, called volleys, and produce action potentials. High frequencies (beyond 4000 Hz), place principle. The place or location of the hair cells stimulated by the sound waves depends on their frequency and determines frequency perception. The highest frequency sounds vibrate hair cells near the stirrup. Thresholds Absolute Threshold-point at which you can detect any stimulation to that sense organ Difference Threshold-point at which you can detect an increase in stimulation Concept of a Threshold Thresholds Early psychological researchers thought it would be relatively simple to determine the weakest possible stimuli that humans could detect. They were wrong. Absolute Threshold the minimum amount of stimulus energy that allows us to perceive a sensation Thresholds are the result of a decision-making process. 50/50 point. Subliminal Perception? Difference Threshold

10 Perception vs. Sensation Weber s Law Difference Thresholds--The size of a Just Noticeable Difference(JND) is a constant. Sensitivity of senses based on difference thresholds. Weber's Fractions: Vision Kinesthesia(weight) Pain Audition Pressure Smell Taste Perceptions result from interpreting primitive sensations from sense receptors to produce more complex forms we see as objects and events in reality. Perception interprets, elaborates and organizes our sensations to provide us with a perceptual experience. 1/60 1/50 1/30 1/10 1/7 1/4 1/3 4.2 Pathways Damage in the What Pathway Visual streams Ventral (below) stream Visual Form Agnosia-can identify color and brightness of objects but not its shape. Visual Object Agnosia-can draw shapes but cannot identify objects across occipital lobe into lower levels of temporal lobes (shape and identity) Dorsal (above) stream travels up from occipital lobe to parietal lobes (location and motion) 76 Damage in the Where Pathway Gestalt Psychology Gestalt psychology focuses on the human ability to perceive overall patterns. According to Gestalt psychologists, visual perception is an active creation, not merely the adding up of lines and movement. Figure/ ground

11 Skull or Couple at a Party Gestalt Laws Perception of form and objects Good continuation

12 Figure 17.1 What s going on here? Myers: Psychology, Ninth Edition in Modules Copyright 2010 by Worth Publishers Perception Depends on Context Who are these Guys?

13 Object Recognition Image-based object recognition-top down processing Objects you recognize are stored in memory as a template which is then compared with objects you experience on your retina-based object recognition Parts-based object recognition-bottom up processing Objects represented in memory by structural description of how what parts I needed to create the object Bottom-up versus top-down processing. Bottom up Processing Bottom-up processing progresses from individual elements to whole elements Top-down processing progresses from the whole to the individual elements. Perception Top Down processing in audition Queen s Another one bites the dust Same song backwards Lewis Carrol s Jabberwocky backwards

14 Depth Perception Our retinas are two-dimensional surfaces, but they give us very good depth perception our ability to perceive distance. Binocular cues Convergence is the degree to which our eyes must turn in to allow us to focus on a very close object. Retinal disparity, which is the difference in apparent position of an object seen by each retina. Figure 4.53 Convergence of the eyes as a cue to distance. The more this viewer must converge her eyes toward each other in order to focus on an object, the closer the object must be. Depth Perception Monocular cues Object size Linear perspective is used when parallel lines are drawn so that they converge as they approach the horizon. Detail generally objects that are closer can be seen in greater detail than those that are farther away. Interposition nearby objects will obstruct objects that are farther away. Texture gradient refers to the fact that clusters of objects will seem more densely packed the farther away the clusters are. Shadows give clues to distance depending on size and position. Motion parallax is the principle that close objects will pass by faster than distant objects.

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16 Optical Illusions An optical illusion is a misinterpretation of a visual stimulus. It may be because of the way our brains process visual images in an attempt to make veridical judgments. Perceptual Constancies Color: Tendency to perceive object color as stable even under conditions of changing illumination Shape: We recognize an object as having the same shape although we may view it in a different angle, at a different distance... Size: Objects do not differ in size when viewed from different distances Our visual system is organized to give us true perceptions. Size Constancy Some illusions based on misinterpretation of depth

17 Table Top Illusion Wheel illusion

18 Does the sex of these people differ?