AP Psychology Chapter 4 Sensation and Perception

Chapter 4: Sensation and Perception ● Overview: o Transduction: sensory messages are transformed into neural impulses o The neural impulses are then sent to the thalamus, which sends them to other parts of the brain (other than smell) o Sensory Adaptation: decreasing responsiveness to stimuli due to constant stimulation (sensory receptors become less sensitive) o Sensory Habituation: our perception of sensations is partially due to how focused we are on them (brain ignores repetition) o Cocktail-Party Phenomenon: someone says your name, your attention involuntarily switches to them o Priming: exposure to a stimulus that influence a response to a subsequent stimulus o Change blindness: occurs when a change in a visual stimulus happens but isn’t noticed o Sensation and Perception ▪ Sensation: the activation of our senses ▪ Perception: the process of understanding/experiencing these sensations Vision ● Step one: gathering light (light is reflected off of objects and gathered by the eye) o the color we perceive depends on: ▪ intensity- how much energy the light contains. determines brightness ▪ wavelength- determines hue ▪ degree to which light waves producing a color are of the same wavelength-saturation ● Step two: within the eye o Cornea: light first enters the eye through it, helps to focus the light, it’s basically just a protective covering o Pupil: light goes through it after the cornea o Iris: determines how much light gets in the eye by controlling the size of the pupil o Lens: through accommodation, light that enters the pupil is focused by it, curved and flexible; as light passes through it, the image is flipped upside down and inverted o Retina: the focused inverted image projects on it ● Step three: transduction (occurs when light activates neurons in the retina) o Rods and cones: the first layer of cells in the retina, directly activated by light ▪ cones- activated by color, clustered around the fovea ▪ rods- peripheral vision, respond to black and white, outnumber cones o Bipolar cells and ganglion cells ▪ when enough cones and rods fire, they activate the next layer of bipolar cells ▪ if enough bipolar cells fire, the next layer of ganglion cells is activated ▪ the ganglion cells’ axons form the optic nerve o Optic nerve: where transduction takes place; sends impulses to the LGN ▪ impulses from the left side of each retina go to the left hemisphere of the brain, right right ▪ optic chiasm- spot where the nerves cross each other o Lateral Geniculate Nucleus (LGN): located in the thalamus, sends messages to the visual cortex o Blind Spot: where the optic nerve leaves the retina, has no cones or rods and thus, no vision ● Step four: in the brain o Feature detectors: visual perception of all features, recognizing visual input and categorizing it ▪ impulses travel from the retina to the visual cortex to them Theories of Color Vision ● Trichromatic theory: we have three types of cones for red, blue, and green and they are activated in combinations to produce other colors ● Opponent-process theory: the sensory receptors arranged in the retina come in pairs (red/green, blue/yellow, black/white) and when one sensor is stimulated, the other is inhibited from firing o Explains color blindness and after images Principles of Visual Perception ● Figure-Ground Relationship: o Figure: objects o Ground: surrounding background ● Gestalt Rules: we normally perceive objects as groups, not isolated elements o Proximity: objects close together → perceived as belonging to the same group o Similarity: objects are similar in appearance → perceived as part of the same group o Continuity: objects that make up a continuous form are grouped together o Closure: objects that make up a recognizable image are grouped, even if the mind needs to fill in gaps ▪ similar to top-down processing’ ● Constancy: our ability to maintain a constant perception of an object even as sensation from it changes o Size constancy: we keep a constant size in mind for an object if we are familiar with it, we know it doesn’t grow or shrink as distance changes o Shape constancy: we know the shape of an object remains constant, even as retinal images change o Brightness constancy: we perceive objects as being a constant color even as the light reflected from them changes ● Perceived Motion: our brains can perceive objects at rest to be moving o Stroboscopic effect: images in a series of still pictures presented at a certain speed seem to move (flip books) o Phi phenomenon: a series of light bulbs turned on and off at a particular rate appear to be one moving light o Autokinetic effect: spot of light is projected on a wall in a dark room and appears to move if you stare at it ● Depth Cues o Visual cliff experiment: by Eleanor Gibson, an infant that can crawl won’t cross the cliff, indicating that infants have depth perception o Monocular cues: depth cues that need only one eye ▪ Linear perspective: parallel lines converge with distance ▪ Relative size: larger objects appear closer ▪ Interposition: objects that block the view to other objects must be closer ▪ Texture gradient: we can see more details in the texture of objects that are closer ▪ Shadowing: implies where the light source is o Binocular cues: depth cues that need both eyes ▪ Binocular (retinal) disparity: the closer the object, the more disparity there will be between the images from each eye ▪ Convergence: the more the eyes converge, the closer the object must be ● The Effects of Culture on Perception o Some basic perceptual sets are learned from culture o Expectations and past experiences o Muller-Lyer Illusion: an optical illusion consisting of a stylized arrow. When viewers are asked to place a mark on the figure at the midpoint, they invariably place it more towards the "tail" end. o Ebbinghaus illusion: two same-size objects surrounded by different sizes can look like different sizes (circle surrounded by little circles vs same circle surrounded by big circles look different) Hearing ● Sound waves: created by vibrations which travel through the air that are collected by our ears o Amplitude: height of wave- determines loudness in decibels o Frequency/wavelength: length- determines pitch (megahertz) o Purity determines timber ● Outer ear: o Pinna- sound waves are collected in the outer ear o Auditory canal- waves travel down it o Eardrum/tympanic membrane- a thin membrane that vibrates as sound waves hit it ● Middle ear: o Ossicles- hammer, anvil, stirrup: transmit the vibrations to the oval window ● Inner ear: o Oval window-from ossicles to cochlea o Cochlea- shaped like a snail’s shell and filled with fluid (vibrates as the oval window moves) transmits vibrations into neural signals o Basilar membrane- (floor of cochlea) hairs move and the hair cells are connected to the organ of corti (neurons activated by movement of hair cells) o Transduction- Auditory nerve sends these impulses to the brain ● Pitch Theories o Place theory: hair cells in the cochlea respond to different frequencies of sound based on where they are located ▪ some bend to high pitches, others to low ▪ explains how we sense higher pitches o Frequency theory: the hair cells fire at different rates ▪ explains lower tones ● Deafness o Conduction deafness: problem with the system of conducting the sound to the cochlea; a problem in ear canal, eardrum, ossicles, or oval window o Sensorineural (nerve) deafness: hair cells in the cochlea are damaged and can’t regenerate, often results from loud noises Touch ● Pain, cold, warmth, pressure ● Some nerve endings respond to temperature, others to pressure ● Our brain interprets the amount of indentation (temperature change) as intensity of touch ● Nerve endings are very concentrated in the fingertips ● Pain o Pain receptors will fire when other receptors are stimulated sharply o Pain warns us of danger o Types of pain: ▪ Visceral pain: pain detected by receptors inside organs ▪ Somatic pain: pain from skin, muscles, tendons, and joints ● Gate-control theory: some pain messages have a higher priority that the gate is open to but shuts out lower priority messages o Endorphins (since they control pain) can shut the gate o Signals in small nerve fibers open and close Taste (Gustation) ● Chemicals from food are absorbed by taste buds ● Taste buds are located on papillae, some respond more intensely to different things o The more densely packed the taste buds, the more chemical absorbed → intense taste ● Tastes: sweet, salty, sour, bitter, and umami Smell (Olfaction) ● Process: molecules of substances rise into the air, drawn into the noise, and settle into a mucous membrane where they are absorbed by receptor cells ● Olfactory bulb: gathers messages from receptor cells are linked to it and sends the info to the brain o Connected to the brain by nerve fibers o Connected to the amygdala and hippocampus (one reason why smells trigger memories) Body Position Senses ● Vestibular Sense: tells us about how our body is oriented in space o Process: fluid in the 3 semicircular canals moves and sensor hairs pick up on the movement, then neurons are activated and impulses are sent to the brain ● Kinesthetic Sense: gives us feedback about the position and orientation of specific body parts Perception ● Psychophysics: the study of the interaction between the sensations we receive and our experience of them ● Thresholds o Absolute threshold: the minimum amount of stimulus we can detect 50% of the time (subliminal- below the absolute threshold) o Difference threshold (just noticeable difference): smallest amount of change needed in a stimulus before we detect a change ▪ computed by Weber’s Law, the change needed is proportional to the intensity of the original stimulus (ty Ernest Weber) ▪ hearing- 5% ▪ vision- 8% Perceptual Theories ● Signal Detection Theory: investigates the effects of the distractions and interference we experience while perceiving the world and tries to predict what we will perceive among competing stimuli o Takes into account response criteria: ▪ motivations and expectations ▪ also called receiver operating characteristics o False positive: we think we perceive a stimulus that isn’t there o False negative: not perceiving a stimulus that is present ● Top-Down Processing: we perceive by filling in gaps in what we sense with background knowledge (told what to see, then we see it) o Schemata: mental representation of how we expect the world to be created from experience, influences how we perceive it ▪ Perceptual set: a predisposition to perceive something in a certain way ● Bottom-Up Processing (Feature Analysis): perception starts at the bottom with the individual characteristics of the image (seeing something, then figuring out what it is) o Puts characteristics together into our final perception o More accurate than top-down processing since there are no biased perceptual sets