Sensation & Perception PDF

Sensation & Perception Chapter 4 1  Overview The interpretive nature of perception perceptions differs from reality Psychophysics: From stimulus energy to basic perceptions Attention: Selecting information The major senses: Including ones y...

Sensation & Perception Chapter 4 1  Overview The interpretive nature of perception perceptions differs from reality Psychophysics: From stimulus energy to basic perceptions Attention: Selecting information The major senses: Including ones you probably don't even know that you have 2  Sensation & Perception Sensation: The process of encoding stimulus energy registered in our sense organs into neural impulses. Perception: Organization, identification, and interpretation of sensory signals in order to form mental representations of events in the world The conscious experience of objects and scenes (relationships between objects) 3  Sensory Systems To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. Transduction is the transformation of physical stimuli (sights, sounds, smells) into neural impulses. Transducers are located in our sensory organs. Eyes, ears, skin... 4  Perception To construct a perception the brain uses both the sensory information (bottom-up processing) and information already stored in the brain (top-down processing). Loch Ness monster or a tree Flying saucers or clouds? branch? 5 What’s on the bottle? Not Exactly G Rated? Don't worry, children see dolphins. Why? Children have less knowledge and do not rely on top-down processing as much as adults. 6  Psychophysics Psychophysics investigates the relationship between physical events and conscious experience. For every physical energy we can detect there is a corresponding conscious experience. Physical World Psychological World Light Intensity Brightness Sound Intensity Loudness Sugar Concentration Sweetness 7  A simple Question: New scientific disciplines usually start by asking simple question. Psychophysics started with: What is the weakest stimuli (light, sound,etc.) that we can consciously detect? The quietest sound? The dimmest light? 8  Thresholds Absolute Threshold: Minimal intensity needed to just barely detect a stimulus. Conventionally set to equal to the stimulation needed to detect the stimulus 50% of the time. 9  Difference Threshold Difference threshold (or JND: just noticeable difference) refers to the minimum difference between stimuli (in colour, pitch, weight, etc.) that can just barely be detected. 10  Difference Threshold Weber's Law: two stimuli must differ by a minimum proportion (rather than a constant amount), to be perceived as different. Stimulus % difference Light 8% Weight 2% Tone 3% 11  Sensory Adaptation To detect novelty in our surroundings, our senses tune out a constant stimulus. Put a bandage on your arm and after awhile you don’t sense it. Sensory adaptation: Sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions 12  Selective Attention Our conscious awareness processes only a small part of all that we experience. Our sensory systems provide far more information than consciousness can handle. Selective attention filters information and only passes on a small subset of information to consciousness. 13 Video:Colour Changing Card Trick (2m:39s) 14  Inattentional Blindness When our attention is focused on an object or task we will often not notice even very salient events. Inattentional blindness: Failure to perceive objects that are not the focus of attention. More than half of observers fail to see a person in a gorilla suit when counting the number of times a ball was passed. 15  Change Blindness Even when our attention is focused on an object we often fail to notice many of it's characteristics. Change blindness: When people fail to detect changes to the visual details of a scene to which they are attending. Two-thirds of individuals giving directions failed to notice a change in the individual asking for directions. 16 Vision Visible light is a small segment of the electromagnetic spectrum. Our visual system encodes to basic physical characteristics of light: 1) Wavelength 2) Intensity 17  Intensity Intensity: Amount of energy in a wave determined by the amplitude. It is related to perceived brightness. 18  Wavelength Wavelength is the distance from the peak of one wave to the peak of the next. Hue (colour) is related to the wavelength of the light. 19  Wavelength Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Short wavelengths Long wavelengths Colours are related to different wavelengths of light. But the relationship isn't one-to-one. Colour vision is more complicated than that. 20  The Eye Cornea: Transparent tissue where light enters the eye. Acts as a lens to focus light into the eye. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses the light rays on the retina. Retina: Contains sensory receptors (transducers) that process visual information and sends it to the brain. 21 The Eye 22  The Lens Accommodation: The process by which the eye’s lens changes shape to focus near or far objects on the retina. If accommodation occurs improperly, myopia (nearsightedness) or hyperopia (farsightedness) may occur. 23  Retina Retina: The light- sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information. 24 Photoreceptors: Rods and Cones 25  Fovea Fovea: Central point in the retina around which the eye’s cones cluster. The fovea provides the highest visual acuity (ability to see fine details). 26  Bipolar & Ganglion Cells Bipolar cells receive messages from receptors and transmit them to ganglion cells, whose axons converge to form the optic nerve. 27  Optic Nerve and Blind Spot Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye there are no receptor cells located there. 28  Colour Vision Trichromatic theory: the eye contains three types of cone receptors that are sensitive to red, blue and green colours. The pattern of responding (number of action potentials) across the three types of cones provides unique codes for each colour. 29 RGB Colour Mixing 30  Two Visual Pathways What pathway: identification of objects perception and conscious awareness Where pathway (How): identifying an object’s location controlling & coordinating motor interactions with objects 31  What Pathway Damage Visual Form Agnosia: inability to recognize objects by sight Patient D.F. could not to orient her hand to match the angle of the slot in the testing apparatus. However, was able to insert a card into the slot at various angles. 32  Perceptual Constancy Perceptual Constancy: our ability to see objects as appearing the same even under different lighting conditions, at different distances 33  Lightness Constancy The squares A and B are exactly the same shade of grey but our perception is that A is a dark grey in a bright light and that B is a light grey in shadow. 34  Colour Constancy Colour constancy provides the ability to see a consistent colour in changing illumination. However, this system can be fooled: 35  Size Constancy Size constancy: we have an ability to use distance-related context cues to help us see objects as the same size even if the image on the retina becomes smaller. 36 Gestalt Rules of Perceptual Organization Gestalt Psychologist proposed that the perceptual system constructed perceptions by apply simple grouping rules. 37  Grouping & Reality Although grouping principles usually help us construct reality, they may occasionally lead us astray. 38  Depth Perception Depth perception is the ability to judge how far away an object is. Depth perceptions can be calculated by using two types of information: Binocular Cues and Monocular Cues. 39  Binocular Cues Binocular Disparity: our two eyes view the world from different angles. The difference in the retinal images of the two eyes provides information about depth. 40  Monocular Cues Interposition: When one object appears to block the view of another, we perceive the blocking object as being closer than the object being blocked. 41  Monocular Cues Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away. When we know the approximate size of an object we can compare the apparent size with the familiar size to judge distance. 42  Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance. 43  Monocular Cues Relative Height: We perceive objects that are closer to the horizon in our field of vision to be farther away than those that are lower. 44  Monocular Cues Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction. 45  Monocular Cues Light and Shadow and provide a great deal of evidence about the shape of objects; which parts are closer and which parts are farther away. 46 47 48  Hearing Sound Waves: Sound waves are changes in air pressure over time causing compressing and expanding of the air molecules 49  Sound Waves Intensity: Amount of energy in a wave, determines the amplitude, relates to the perceived loudness. 50  Sound Waves Pitch is related to the frequency of a sound. Frequency is the inverse of the wavelength of sound. Low frequency waves: low pitch High frequency waves: high pitch 51  Sound Waves Sounds are rarely composed of a single frequency (pure tone) of constant amplitude. Complexity refers to the mix of frequencies and changes in amplitude that make up a sound. This is related to the sound’s timbre. 52  The Ear Outer Ear: Collects and sends sounds to the eardrum. Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that amplify the vibrations of the eardrum on the cochlea’s oval window. Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs. 53 The Ear 54  Cochlea Cochlea: Coiled, bony, fluid-filled tube in the inner ear, it contains basilar membrane. The auditory receptors, know as hair cells, are attached to the basilar membrane. c e lls hair a hle Coc 55  Perceiving Loudness Large amplitude sound waves are perceived as louder than low amplitude waves. The greater the amplitude of the sound wave the larger the amplitude of the vibrations of the basilar membrane. This causes a greater number of hair cells to send signals to the brain. 56  Hearing Loss Exposure to loud sounds can cause damage to the inner ear, especially the hair cells (sensorineural hearing loss) Structures of the middle and inner ear can also be damaged by disease or physical trauma (conduction hearing loss) 57  Perceiving Pitch Place Code: Different frequencies stimulate hair cells in different places along the length of the basilar membrane. The brain determines pitch on the basis of which neurons are activated. Best at encoding high frequencies. Temporal Code: Sound frequencies stimulate hair cells to fire at a rate proportional to the sound frequency. Best at encoding low frequencies. 58  Perceiving Location Intensity differences: The head acts as a “shadow” or partial sound barrier. Time differences: Time differences as small as 1/100,000 of a second can cause us to localize sound. 59  Somatosenses The body senses are referred to as the somatosenses. Touch: pressure, texture, vibration Thermoreceptors: warmth, cold Nocioreceptors (pain) 60  Pain Circuit Nociceptors are sensory receptors whose signals are interpreted by the brain as pain. Nociceptors send signals along thin nerve fibres to interneurons in the spinal cord that may pass the signals to the brain. 61  Gate-Control Theory Gate-Control Theory: neurons in the spinal cord act as “gates” that can block or transmit pain signals to the brain. The “gate” is opened by the activity of pain signals travelling up the small nerve fibres and is closed by non-pain activity in larger fibres or by information coming from the brain. 62 Body Position, Movement and Balance The vestibular sense monitors the head (and body’s) position to maintain balance Relies on the semicircular canals and vestibular sacs of the inner ear Kinesthesis (“movement feeling”) refers to sensing the movement and position of individual body parts relative to each other. sensors in the joints and muscles send signals that coordinate with signals from the skin, eyes, and ears 63  Video: Losing proprioception (3m:56s) 64  Smell Humans have a poor sense of smell for an animal. Even so, humans have 350 different types olfactory receptor neurons (ORNs) allowing us to detect about 10,000 different odours. 65  Smells, Memories and Emotions Sensations of smell do not pass through the “sensory switchboard” (thalamus). The output of the ORNs is sent to the olfactory bulb. The olfactory bulb sends output to the temporal lobe and the limbic system, influencing memory and emotion. Smells are effective in triggering emotional responses and are powerful memory cues, especially for very old (childhood) and emotional memories. 66  Taste The tongue is covered with thousands of bumps (papillae) which contain taste buds (which house taste receptor cells). There are receptors for five different types of tastes, each of which may have had survival functions. Some aspects of taste perception are genetic, while others are learned. There are individual differences in taste perception and Sweet: tolerance of food textures and spicy foods. energy Umami: Bitter: source (savoriness) potential proteins to grow poisons and repair tissue Sour: potentially toxic acid Salty: sodium essential to physiological processes 67  Video: Supertasters (9m:3s) 68  Sensory Interaction Sensory interaction occurs when different senses influence each other. The flavour of a food is actually a sensory interaction between its taste, smell and, pain receptors (hot spice) and texture. Sensory interactions are a normal part of sensory function. 69