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Sensation and Perception - PS101 Lecture - October 14th, 2011.docx

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Iuliana Baciu

*All-or-None Law and Action Potential!!!* ON EXAM!!! th Sensation and Perception - PS101 Lecture – October 14 , 2011 Sensation and Perception: The Distinction:  Sensation: stimulation of sense organs (ex – absorbing E from light by eyes)  Perception: selection, organization, and interpretation of sensory input – translating sensory input into something meaningful (ex – looking at a photo of a rose – eyes sense light reflecting from the page; what you perceive is picture of the rose)  Sensation and perception are hard to separate, because people automatically start organizing incoming sensory stimulation the moment it arrives.  Psychophysics = the study of how physical stimuli are translated into psychological experience, therefore, psychologists in this area are interested mostly in sensation and perception. Psychophysics: Basic Concepts:  Sensation begins with a detectable stimulus…but what counts as detectable depends on whom or what is doing the detecting. Gustav Fechner (1860) questioned, for any given sense, what is the weakest detectable stimulus?  Fechner: the concept of the threshold  Threshold: a dividing point between E levels that do and don’t have detectable effect (ex – automatic lights turn on when a threshold is reached).  Absolute threshold: the minimal amount of stimulation than an organism can detect…depends on boundaries of an organism’s sensory capabilities…researchers discovered, however, that there is no single stimulus intensity that results in a jump from no detection to 100% detection every time…thus researchers use concept of the absolute threshold…the stimulus intensity can be detected 50% of the time.  Just noticeable difference (JND): the smallest difference in the amount of stimulation that a specific sense can detect (smallest difference detectable) – ex – musicians, pain, ect. - Weber’s law: size of JND proportional to size of initial stimulus…in general, as stimuli increase in magnitude, the JND becomes larger. o Ex – when music is louder, will hear a bigger difference than if music was quieter (will not perceive stimulus as quickly if quieter). Psychophysics: Concepts and Issues:  Psychophysical Scaling: Fechner’s Law  Being asked whether 1 light has 2x the E of another and is 2x as bright - ex. of scaling. Fechner’s Law asserts that larger and larger increases in stimulus intensity are required to produce JNDs in the magnitude of sensation.  Stated how we detect JNDs based on intensity of initial stimulus?  Signal-Detection Theory: Sensory processes + decision processes  Signal detection theory holds that the detection of sensory info is influenced 2 things: 1) noise in the system (irrelevant stimuli in the environment that elicit neural activity) and 2) decision making processes. Signal detection theory was important in that it emphasized factors other than stimulus intensity influencing detectability (in contrast to Fechner’s ideas).  Subliminal Perception: Existence vs. practical effects  Many researchers, using very diff. methods, have demonstrated that perception can occur without awareness. Many people believe that advertisers attempt to place subliminal messages in ads, while others say that people are just reading things into ads, like seeing familiar shapes in the clouds. Regardless, research shows that the effects of subliminal perception are relatively weak and of little practical impact.  Sensory Adaptation: Decline in sensitivity  Prolonged stimulation may lead to sensory adaptation, or a decline in sensitivity to the stimulus (ex - you don’t smell the skunk that sprayed you yesterday, but everybody else does…the pool is only cold at first, ect). Video 1:  Don’t think there’s any evidence that there’s 1 image for 2 diff. things  But there is evidence that they can be temporarily synchronized  Image of face and hearing a person’s voice – can be linked, but not 1 image  Everything we perceive is varying E’s (stimuli)  FMRI and PET scans – show networks that bind together to create perception  Brain is storing mechanisms that help create memory of a you (person)  Attempt of replicating patterns of producing perceptions that lead to the memory of you  Cannot store perception itself  Memory and perception will not be the exact same as real perception  Store images and memories assoc. with that person  Perceive world as a constant unified place – b/c brain is a filter  As baby, we create maps of senses with the brain  Everyone’s perception of the world is diff. b/c of our experiences  Perceptions of brain becomes reality  If brain reflects certain values, we can add to them or change them (changing map of interpreting)  Applies a lot in social perception - See people from same gender, race, culture group – you are more comfortable around them b/c they share the same perception and experiences as you Video 2:  Brain is able to experience world also through senses  Skin has 5 million senses, and it has nerves on the hair roots  Sense of hearing relies on special shapes of the cartilage – vibrations of sound  There are 9000 taste buds on the tongue – feel chemical differences with taste buds  Chemical diffs. dissolving in nostrils to detect sense of smell  Eyes – electromagnetic radiation  The nose and brain can distinguish up to 10 000 diff. smells  Top of nose is packed with nerve cells, where odour molecules dissolve in mucus around the nerve cells…they lock into specific receptors that transmit impulses – sent to memory and (smell?)  Ultimately, we smell with our brains  A wave of electromagnetic activity travels through the optic nerve to the brain  We process visual input more than anything else, therefore, we learn this way the most  Will expect to see JNDs creating impulses faster (smaller)  Hard for blind people to take in all info from surroundings as most info is processed at the visual level – even though their other senses are heightened  Brain is actually dispatching diff. parts of info (some colour, ect), then they come together and process the info as a whole *what type of info does each sense possess, how is perception formed for each of the senses, integration of info!* Vision: The Stimulus:  Light = electromagnetic radiation that travels as a wave (quickly – speed of light)  Light waves vary in height or amplitude and in wavelength or distance b/w peaks  Amplitude: perception of brightness  Wavelength: perception of colour  Purity: mix of wavelengths - Perception of saturation, or richness of colours The Eye: Converting Light into Neural Impulses:  The Eye: providing housing for neural tissue that receives light (retina) and channelling light toward retina  Components:  Cornea: where light enters the eye (transparent)  Lens: focuses the light rays on the retina (a crystalline structure that lies right behind the cornea)  Iris: coloured ring of muscle around pupil, constricts or dilates via amount of light – changes size of pupil  Pupil: regulates amount of light by constricting to let in less light and vice versa  Saccades The Retina: An Extension of the CNS:  Retina: absorbs light, processes images, and sends information to the brain (a piece of neural tissue that lines back of eye)  Optic disk: a hole in the retina where the optic nerve leaves the eye/ blind spot (where axons from the retina to brain converge at)  If an image falls on this hole, it can’t be seen (blind spot)  Receptor cells:  Rods: black and white/ low light vision  Cones: colour and daylight vision - Adaptation: becoming more or less sensitive to light as needed – occurs in part due to chemical changes in the rods and cones  Information processing:  Receptive fields – a collection of rod and cone receptors that funnel signals to a particular visual cell in the retina  Lateral antagonism (or lateral inhibition) – occurs when neural activity in a cell opposes activity in surrounding cells The Retina and the Brain: Visual Info Processing:  Light > rods and cones > neural signals > bipolar cells > ganglion cells > optic nerve > optic chiasm > opposite half brain >  Light striking the rods and cones trigger neural signals to move to bipolar cells then to ganglion cells, then along the optic nerve to the optic chiasm, where the optic nerves from the inside half of each eye cross over and project to the opposite half brain.  Crossing ensures that signals from both eyes go to both hemispheres of brain  After the crossing, 2 visual pathways exist  Main pathway: lateral geniculate nucleus (thalamus) > primary visual cortex (occipital lobe) – (goes through the lateral geniculate nucleus in the thalamus and on to the primary visual cortex in occipital lobe)  Main visual pathway subdivided into 2 subspecialty pathways:  These channels engage in parallel processing, which involves simultaneously extracting diff. kinds of info from the same input (ex – parvocellular channel handling perception of colour, and magnocellular channel handing brightness) - magnocellular: where (parietal lobe) - parvocellular: what (temporal lobe)  Second pathway: superior colliculus > thalamus > primary visual cortex  Goes through superior colliculus to the thalamus and on to the primary visual cortex Hubel and Wiesel: Feature Detectors and the Nobel Prize:  Early 1960’s: Hubel and Wiesel  Microelectrode recording of axons in primary visual cortex of animals - Initially, they had little success getting neurons to fire by having the cats look at flashing spots of light.  Accidentally, they introduced a straight line light…rapid firing occurred in the visual cortex.  Discovered feature detectors: neurons that respond selectively to very specific features of complex stimuli… lines, edges, etc. - Ground-breaking research: Nobel Prize in 1981  Later research: cells in temporal lobes of monkeys and humans (along the visual pathway) that specifically respond to pictures of faces…grandmother cells Basics of Colour Vision:  Wavelength determines colour  Longer = red / shorter = violet  Amplitude determines brightness
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