PSYCH50 Chapters 3-4
PSYCH50 Chapters 3-4 PSYCH 50
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This 9 page Class Notes was uploaded by Emily Wu on Thursday January 28, 2016. The Class Notes belongs to PSYCH 50 at Stanford University taught by Justin Gardner in Winter 2016. Since its upload, it has received 56 views. For similar materials see Intro to Cognitive Neuroscience in Psychlogy at Stanford University.
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Date Created: 01/28/16
Emily Wu email@example.com Chapter 3: Sensory Systems and Perceptions: Vision The Initiation of Vision ● begins in nonneural elements: cornea, lens, ocular media → focus and filter light ● next step: sensory processing, transform light energy to neural signals via rods/cones of retina ○ rods: perceive low levels of light ○ cones: perceive higher levels of light, detail and color ● sensory adaptation resetting of sensitivity according to surrounding conditions ○ ensures max efficiency of sensory processing over range of environmental conditions ● acuity degree of precision ○ depends on distribution of receptor cells across retina ○ lessened acuity outside of central retina ○ fovea has highest acuity ● fovea: central region of retina, most density of cones here ○ rods absent in fovea ● saccades: movement of eyes to focus on different positions ○ is a result of having lessened acuity outside of fovea Subcortical Visual Processing ● primary visual pathwaprocessing of stimuli in retina → info converges into retinal ganglion cells → leaves retina via optic nerateral geniculate nuclein the thalamus → primary visual cortex of occipital lobe Cortical Visual Processing ● primary visual cor: also known as V1 or striate cortex; projeextrastriate visual cortical are, which are a part of cortical association areas ● cortical association arecortical regions not sensory or motor, deal with higherorder processing ● V4 areaimportant in processing color vision ● MT and MST: middle temporal and middle superior temporal lobes; important for perception of motion ● pathways of the extrastriate cortical area: ○ ventral stream (“what” pathwayisual cortex → inferior temporal lobe ■ analysis of form and color ○ dorsal stream (“where” pathwaystriate cortex → parietal lobe ■ analysis of motion and spatial relations Other Characteristics of the Visual Cortex 1. Topography ○ organization of retinal receptors is reflected in corresponding regions of thalamus and visual cortex ○ ex: stimulate area of retina → area of visual cortex activated; stimulate area adjacent to first area → area adjacent to first area of visual cortex activated 2. Cortical magnification ○ size of a unit area in fovea is disproportionately represented by a lot more area in visual cortex than area of peripheral retinal ○ perceiving visual detail from fovea requires more neural activity than peripheral areas 3. Cortical modularity ○ neurons of similar functions are arranged in iterated groups ortical columns 4. Visual receptive fields ○ receptive fiel region of retina that, when stimulated, elicits a response in neuron being examined ○ data obtained by singleunit recordings Visual Perception 1. Lightness/brightness ○ lightness appearance of a surface ○ brightness: appearance of a light source (e.g., sun, lightbulb) ○ luminance: measure of light by photometer (units=candelas) ○ luminance and perception of lightness/brightness are not directly proportional ○ simultaneous lightness/brightness contrapatch on low luminance background appears lighter than same patch on high luminance background (picture above) ○ retinal luminance determined by three aspectlluminatioof objectsreflectance of object surfacetransmittance of space between objects and observer ○ same value of luminance can be produced by different values of the three aspects 2. Color ○ created by distribution of light across the visible spectrumwavelengths ○ hue: relative red, blue, green, or yellowness ○ saturationhow close color is to neutral gray ○ color brightnesbrightness but applied to a hue ○ all three contributecolor space ○ humans are trichromat color vision based on three cone types, each sensitive to specific wavelengths ○ color perception is not needed as much for survival (like brightness/lightness perception is), but helps us discern things more easily ○ color perception is influenced by surrounding scene: i. color contras same light energy perceived as different colors ii. color constancy different light energy perceived as same colors ○ cerebral achromatopsia loss of ability to see color; V4 area seems important to color perception 3. Form ○ the geometrical characteristics of objects ○ perception of form also influenced by surroundings 4. Depth ○ the perception of 3D world from 2D images ○ monocular cues:only need one eye to perceive 3D i. occlusion if object A covers object B, we know object B is farther from us ii. relating size and distance: smaller objects perceived as farther away iii. motion paralla when observer moves, background position in reference to a nearby object changes more than that of farther objects ○ binocular cues needs two eyes to perceive 3D i. retinal dispar each eye perceives slightly different image of same object ii. cyclopean fusionperceived image of both eyes is unified; possibly explained by fact that inputs of both eyes converge onto same neurons in primary visual cortex 5. Motion ○ perception of speed and direction (associated with MT and MST) ○ apparent motion:static images presented quickly in sequence appear to be in motion (basis of movies and videos) ○ motion aftereffec staring at motion going in one direction then perceiving motion in opposite direction when looking away → “waterfall effect” i. possible explanation: neurons adapt to motion of one direction, so other neurons detecting other motion directions become more active and cause one to perceive the other direction of motion after looking away ○ Newsome experiment with rhesus monkeys: found neurons in MT with selective activity for a specific direction of motion Object recognition ○ depends on associating the previous fundamental qualities of vision to identify the stimulus ○ some neurons in temporal lobe specifically responsive to faces (fusiform face area) ○ some neurons respond to face and voice of face; suggests they are part of network that integrate multiple modalities ○ humans are better at recognizing faces with extreme features; suggests that faces are identified in comparison to a norm/standard ○ prosopagnosia: inability to recognize faces (related to damage in fusiform gyrus) Remembering images ● many of the same neurons in visual cortex used for visual perception activate when remembering visual scenes Emily Wu firstname.lastname@example.org Chapter 4: Sensory Systems and Perception: Auditory, Mechanical, and Chemical Senses The Auditory System Sound stimuli ● form from changes in local air pressures due to displacement in air molecules ● pressure changes that fall within range of perception trigger receptor cells of inner ear ● auditory stimuli (pressure changes) → mechanical changes in ear → neural signals in brain ● resonance:tendency of object to vibrate in ongoing manner ○ producestoneif vibrations are periodic ○ producesnoiseif aperiodic ● resulting compression of air molecules proound wave ● most natural stimuli don’t generate tones, most are just noise ● harmonic serie characterizes stimuli that systematically resonate ○ ex: when plucking a guitar string, standing waves will be produced ○ fundamental frequenc greatest updown movement is across entire length of string ○ next mode is at half length, ⅓ length, ¼ length, etc. (picture below) Peripheral auditory system ● preneural effects: local pressure change → mechanical changes in ear ● begins witexternal eaand middle ear ○ collect sound energy and amplify local pressure ○ external ear: concha and pinna focus sound energy ○ 3 bones of middle ear: link deflections of souympanic membrane (eardrum) to inner ear ○ enhanced sound energy sent tval window ● oval window enters inochlea ○ neural effects here: mechanical changes in ear → neural signals ○ houses basilar membran and its receptor ceair cells ○ movement from oval window moves fluid → moves tips of hair cells (stereocilia) ○ movement of stereocilia depolarizes hair cells → releases transmitter molecules → elicits action potentials → travels to auditory nerve ○ tonotopic organization: ■ basilar part near oval window: detects higher frequencies ■ near cochlear apex: detects lower frequencies ■ rest of auditory system also shows tonotopic organization ● primary auditory pathway of the brain: ○ auditory nerve → cochlear nucleus in rostral medulla→ diverge to several places: ■ inferior colliculus in midbrain (integrates auditory info with motor system) ■ superior olivary complex (integrates info from both ears) ■ nucleus of the lateral lemniscus in midbrain (localization of sound source) ○ all this info goemedial geniculate nuclin thalamus → relayed rimary auditory cortex (A1) TO RECAP: sound stimulus → external ear → middle ear → oval window → cochlea of the inner ear → basilar membrane cells stimulated → auditory nerve → cochlear nucleus → medial geniculate nucleus of thalamus → primary auditory cortex The auditory cortices ● located in superior temporal lobe + adjacent areas in parietal lobe ● includes primary (main recipient of auditory info) and secondary auditory cortices (also called A2, does higherorder processing like speech comprehension) The perception of sound 1. Loudness ○ perception of sound intensity ○ measured as sound pressure level (P=F/A) ○ units in decibels 2. Pitch ○ perception of tones related to frequencies of periodic wave stimuli ○ hearing the missing fundamental: perception of hearing a fundamental frequency even when the stimulus isn’t actually producing energy at the fundamental frequency 3. Timbre ○ perception of differences between sound stimuli when loudness and pitch are the same ○ ex: telling the difference between a flute and clarinet 4. Auditory scenes ○ group of stimuli usually naturally present in the environment, like background noise ○ we can focus on one auditory stimuli and tune out the background noise (ex: focusing on the person you’re talking to in a busy crowd) Perceiving the location of sound sources ● humans can locate the source of a sound in horizontal/lefttoright direction, but less sensitive in vertical (updown) and frontback directions ● to locate sound, we use interaural time differenc (for frequencies <3 kHz) and interaural intensity differen (freq >3 kHz) ● interaural time differenc: arise because of distance between ears; auditory input arrives at same spot in brain at the same time, but take different distances to get there, so analysis of the difference in distances helps us locate where the sound came from (if the left ear input took a shorter distance to reach the spot, source is most likely coming from left) ● interaural intensity differencuses the fact that sound intensities at the two ears depends on location of the sound source The Mechanosensory Systems 1. The cutaneous/subcutaneous system ○ deals with perception of touch, pressure, vibration, and cutaneous tension ○ some areas have more touch receptors than others (ex: more dense in fingers than forearm) ○ somatosensory system: receptors receive info → dorsal root ganglia → spinal cord → ventral posterior nuclear complex of thalamus → primary somatosensory cortex (S1) in parietal lobe ○ secondary somatosensory cortex (S2): “higherorder” processing, receives info from S1 and sends it to limbic structures (which have emotional properties) 2. The pain system ○ perceives sensations harmful or potentially harmful to the body ○ perception begins by free nerve endings in skin calleociceptors ○ pain information from nociceptors → dorsal root ganglia → spinal cord → thalamus → primary somatosensory cortex ○ pain pathway is similar to the cutaneous pathway i. somatosensory percepts are mental constructs → we don’t simply translate physical stimuli into our brain, we construct our perception of it ○ placebo effect physiological response after receiving inert medical treatment The Chemosensory Modalities 1. The olfactory system ○ olfactory epitheliumsheet of receptor cells that lines nasal cavity ○ cilia extend from receptor cells and detect odors ○ receptor neurons only express one receptor protein on its surface ○ neurons with same receptor neurons arranged together; their axons converge together int lomerulclusters in thlfactory bulb ○ pathway: odor → receptor cells in olfactory epithelium → glomeruli in olfactory bulb → olfactory tract → pyriform cortex in temporal lobe → thalamus, hippocampus, amygdala, orbitofrontal cortex i. info about odors influence aspects of emotion, memory, homeostasis, etc. ○ small changes in odor molecular structure can lead to big changes in perceived odor ○ most natural smells are made up of a combo of odorant molecules even though they’re experienced as a single smell ○ pheromones: biochemical signals as a means of social communication 2. The taste system ○ pathway: taste buds → cranial nerve ganglia → nucleus of the solitary tract in the brainstem → ventral posterior complex of thalamus → anterior insula in temporal and frontal lobes ○ interneurons link gustatory and visceral regions i. eating something gross makes you gag/spit it out ○ secondary taste area for higherorder processing; tells when certain food is consumed to satiety, orbitofrontal cortex involved with motivation to eat certain foods 3. Trigeminal chemosensation ○ system that detects irritants, which alert us to potentially harmful stimuli (like air pollutants) ○ neurons in mouth, nasal cavity, and lips Final Points about Sensory Systems Coding and labeled lines ● unlikely that systems follow a labeled line theory, which says that specific receptors receive specific stimuli information for specific pathways through central nervous system Plasticity ● greater use of certain body parts results in enlarged corresponding brain area ● if an area loses function, another area can take over its function to some degree ● plasticity happens more in early life but lessens as one grows older Awareness of sensory stimuli ● we don’t perceive many stimuli consciously Representation of sensory percepts ● what are sensory percepts? (represented in a neurobiological perspective) ● percept arises from activity in neurons of relevant regions of primary sensory cortices ● individual neurons respond to many different stimuli; can’t say that one neuron is responds to one specific stimulus ● perception of stimulus qualities is nonlinear to the stimulus’s actual properties; perception is not simply a translation of the physical world Note: I don’t think it’s that important to remember the specific details of the sensory pathways and memorize all the names. The big takeaway is that the pathways begin with receptors that receive sensory information, which gets processed in subthalamic nuclei, gets sent to the thalamus, and relayed to the primary somatosensory cortex.
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