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Chapter 5

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Psychology 1000

Chapter 5: Sensation and Perception Synesthesia: experience sounds as colours and taste as touch sensation. We’re born this way and it’s a mixing of senses and undifferentiated neural pathways - Your brain is specialized for specific recognition and activity - With cross wiring, activity in one brain evokes responses in another brain dedicated to another sensation. Thus you can “see” taste - Theories of how it happens o The mixing of connections from infancy stay with patients that have synaesthesia o Theres a deficit in neural inhibitory processes which doesn’t stop one sensory inputs from “overflowing” into other brain areas which then evoke many responses  Both of these result into the Binding Problem: How do we bind our perceptions into a whole while keeping its sensors separate  Ex. That dish smells so good and looks nice. Its making me hungry Stimuli activate sensory receptors Transduction: Sensory receptors translate certain stimulates into nerve impulses. These nerve impulses help us understand what the stimuli is Feature Detectors: specialized neurons break down and analyze the specific features of the stimulus - These features are made into a neural representation - Its matched against our records, if something like that has been perceived before, we recognize the stimulus, otherwise it’s new - This is called perception Sensation: stimulus detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses and send them to the brain Perception: making “sense” of what our senses tell us. Giving meaning to the stimulus Thus, sensation comes first and then perception. You touch, feel and taste the snow and your brain then says yea its snow Some sensations can be perceived in many different ways, since perception is an active process The way you perceive things depends on the context they are in - E.g: A, 13, C or 12, 13, 14 - They both send identical input but their context changes their perception Sensory Processes Sensationstimulus received by sensory receptorsreceptors translate the stimulus into nerve impulses (transduction)feature detectors analyze stimulus features features reconstructed into neural representationmatched against internal recordsthey are recognized - Sensory equipments for species are an adaptation to their environment - The energy from stimulation must be converted into nerve impulses - There are more than 5 forms of senses and even in those 5 each sense is divided into many senses Psychophysics: - Studies relations between the physical characteristics of stimuli and sensory capabilities o Its concerned with first the limits of sensitivity (whats the softest sound that we can hear) o Second is the differences between stimuli. Can we observe a difference between the two lights. Stimulus Detection: The absolute Threshold - Whats the minimum intensity f a stimulus before we can detect it - Absolute Threshold: the minimum intensity needed so a stimulus can be detected correctl 50% of the time - Therefore, the low your absolute threshold for a specific stimulus is, the greater its sensitivity because you can perceive it all the time Signal Detection Theory: - The concept of an absolute threshold is false as individuals differ in their requirement for minimum intensity - There is instead a range of uncertainty - Decision Criterion: how certain an individual is before they can say that they detected a stimulus o this can change for each individual depending on their fatigue, mood or environment and importance of the stimulus - Signal detection theory is concerned with the factors that influence sensory judgements - At low stimulus intensities, the participant and the situation play a factor in detecting a stimulus - Putting prizes on detection makes a lower detection thres hold o Example during the wartime the navy is always on full lookout and responding to every little thing vs peace time voyage - Perception at the end is part of a decision (because it depends on the person and their environment/conditions) - Hit, miss, false alarm, correct rejection The Difference Threshold - Defined as the smallest difference between two stimuli that people can perceive half the time (50%) - Sometimes called the just noticeable difference - Weber’s Law: the difference threshold is proportional to the magnitude of the stimulus with which the comparison is being made (first stimuli) o ex: if the weber fraction for weights is 1/50. If your first weight is 50 grams, your second must atleast be 51grams for you to notice a difference o this law usually doesn’t work for really extreme or low intensities of stimulation o the smaller the fraction, the greater the sensitivity to differences o Our visual systems have the greatest sensitivity o We’re also really sensitive to pitch, but not that much to loudness - Fechner’s Law: the perceived sensation is proportional to the logarithm of physical stimulus activity Sensory Adaptation - Our sensory systems are attuned to changes in stimulation due to the environment - Sensory Adaptation: diminishing sensitivity to an unchanging stimulus - So say you hear a stimulus, at first you sense it and eorcive it and its loud, but say that continues for a while, you start to perceive it less because your sensitivity to it is decreasing - This is really important for is as its adapted to pick up informative changes in our environment - Pritchard had a study where a projector was mounted to a lens, the participant was shown an object through the projector and after a while it disappeared. The Neuroscience of subliminal Perception and Prosopagnosia - Subliminal Stimulus: a stimulus so weak that it is received by the senses but we cannot perceive it consciously. - These stimuli register in the nervous system - To a limited extent, these can affect our behaviour - James Vicary sent subliminal messages during a movie on the screen, said he raised popcorn sales by 50% o After a while he said his research was a hoax o In consumer behaviour, messages above the threshold are better for us as we “get the message” - But Krosnick showed that subliminal messages can change our attitude o he showed some people slides of a person and subliminally a negative image and then some he subliminally showed a positive image o the one showed the negative image didn’t like the person as much and the one who were shown the positive image liked the person a bit o this is called subconscious attitude conditioning - Individuals with Prosopagnosia can’t recognize familiar faces - Steeves performed a study on a patient who lost her senses for everything except colour o She can remember things by colour o Person was called D.F o The LOA was damaged In both areas and it dealt with object perception o The higher order facial recognition involves many parts of the brain  D.F could recognize it’s a face, but not whose it is  D.F probably uses some internal memory to recognize shapes as face, ovals with skin tones etc o Marikle argues that subliminal cues can bias what we perceive at a conscious level and may alter our conscience experience of those stimuli o D.F was not consciously aware that they were faces, but subliminal senses told her it was a face. - Thus at the end, subliminal messages aren’t as strong to control our behaviour, but can affect our memory and attitude The Sensory Systems Vision - Stimulus for vision is electromagnetic radiation or light waves - We can only see vis light (400-700 nm) The Human Eye - Light waves enter the eye through the cornea (transparent protective layer on the front of the eye) - Behind it is the pupil (a small narrow opening) that can dilate or constrict the amount of light that goes in o The pupils size is controlled by the iris (coloured part around the pupil) o The iris is a muscle o When amounts of light are low, pupils dilate (make the pupil bigger and iris smaller) vs constriction - Behind the pupil is the lens an elastic part that becomes thin to see distant object and thick to see close up objects - The lens focuses the image on the light sensitive retina (multilayers tissue at the end of the fluid eyeball) - The lens switches the image onto the retina (left to right and top to bottom). But then the brain recognizes this and reswitches it to perceive what we see - The ability to see clearly depends on the focusing of the lens and how it depicts the image to the retina - Myopia- good at seeing nearby objects but hard to see further objects (nearsightedness) o the lens focuses the visual image in front of the retina (to close to the lens) making further objects blurry. Usually happens because the eyeball is longer (front to back) - Hyperopia- opposite of myopia so people are far sightedness o the lens does not thicken enough resulting in the image being focused on a point behind the retina (too far from the lens) o aging results in this as the eye ball becomes shorter o this aging improves the vision for myopic people as the eyeball starts to shorten from a longer one Photoreceptors: The Rods and Cones - the retina contains layers of cells - it contains two types of light-sensitive receptor cells: rods and cones - 120 million rods and 6 million cones in the eye - Rods: o Function best in dim lights o They are black and white brightness receptors o They are 500x more sensitive than cones but don’t sense colours - Cones: o Function best in bright situations o Colour receptors - Humans have both o Rods are found everywhere except the fovea  Fovea contains only cones and is located in the centre of the retina at the back o Cones are concentrated in the centre of the retina but they decrease as you move away o Therefore rods are mostly found on the sides (peripheral) - Rods and cones both send their signals to two more layers of cells - They first synapse with bipolar layer cells (horizontal cells and bipolar cells) which in turn synapse with ganglion layer cells (ganglion cells and amacrine cells) ganglion cells axons are bunched together and are called the optic nerve which take info to the brain - Theres around 1 million ganglion cells so 126 million info  100 million cells - Rods and cones are actually at the back of the eye rear side of the retina and their light sensitive ends point towards the back which means that they recieve only fraction of the light energy that enters in after going through the pupil - Typically, many rods connect to A bipolar cell so they funnel in all their information o This makes the addition of messages strong enough to fire an action potential o We can detect a faint stimulus if we see it from the side of our eyes where the rods are packed in more densely - Many cones also share bipolar cells except for the cones in the fovea o In the fovea each cone has its own bipolar cell o Thus this is called visual acuity, we can see sharp details and small things best when they’re infront of us o This results in a lot of cones firing action potentials and with greater intensity cuz its right infront of the fovea o The optic nerve is a bunch of ganglion axons connected near the fovea and is at the front of the retina but rear side of the eye and over there we have a blindspot  There are no photoreceptors there  That dot and x thing was cool  Your perceptual system fills in the blank from your blindspot Visual Transduction: From Light to Nerve Impulses - Rods and cones translate light waves into nerve impulses using photopigments - Photopigments absorb the light and then chemical reactions change the amount of neurotransmitters they release from the cone/rod cells to the bipolar cells (synapse) - The greater the change in transmitter release, the stronger the signal sent to the brain - If the nerve response goes through all three layers, it eventually reaches the visual cortex Brightness Vision and Dark Adaptation - Brightness sensitivity of both rods and cones depend on the wavelength of the light - Rods are more sensitive than cones everywhere in the vis range except for red - Cones are most sensitive to low illumination in the greenish-yellow range - Even though rods are more sensitive to low light, they’re not always ready to do that - Dark Adaptation: progress of improving vision in low illumination after coming in from the bright o after absorbing light, cones and rods are depleted of photopigments for a small period of time o in the bright, photopigments are depleted a lot therefore cones get theirs depleted a ton o once you go into the dark, the pigment molecules are slowly being regenerated and the receptors sensitivity increase - for cones one you are put into the dark after bright o the cone gradually becomes sensitive to the dark but after 10 minutes their sensitivity has reached a maximum - for the rods o their photpigments generate relatively slower and thus they reach a better max after 30 mins. They are able to detect light intensity at 1/10000 great in the dark as they did in the bright - they tell pilots to wear red glasses in the dark because rods are good at seeing things in the dark and are insensitive to red light Colour Vision The Trichromatic Theory - blue, green, red can produce any colour in the vis spectrum - Young-Helmholtz Trichromatic Theory: o There are three types of colour receptors in the retina o Cones can be stimulated by any wavelength but are mostly stimulated to red, blue and green o Depending on the intensity of each colour, the impulses then add up and a colour is perceived. If all cones are equally activated its white. If its none, its black o In additive mixture: the colours are red, blue and green o In subtractive Mixture: its red, blue, yellow - Although this theory was good, it wasn’t the best as red + green produces yellow but red and green blind people can still see yellow - Another problem was that you see an image for a while, then look at a white space and you see the image there with its opponent colours Opponent Process Theory - Theory by Hering - He also said that there are three types of cones but each cone responds to two wavelengths - 1. Yellow OR blue 2. Red OR Green 3. Black OR White - So say you look at an object that’s black and green. The pigments in the cones which take those in were fatigued so then when you look onto a white paper you see red and white because white transmits all light and the pigments responded with its opponent colours Dual Processes in Colour Transduction - Uses both the theories above - Young and helm were right about certain cones responding to certain wavelengths. The addition of all those wavelengths produces a colour - Opponent process does not occur at the cone level, it occurs at the ganglion cell level o Ganglion cells respond in an opponent-process fashion by altering their rate of firing o If a red light is shown on the retina, the ganglion cells may fire at a high rate (green frequency) but if a green is shown it might fire at red (low) o It does this for blue and yellow too. The red and green are activated by the light that is seen but the blue and yellow work differently o The activity due to blue light in the ganglion cells is due to blue receptor cones o But the activity due to yellow light in the ganglion cells is due to the red and green receptor cones Colour Deficient Vision - Normal colour vision is called trichromats - Some people have a deficiency in the red-green system or the yellow-blue system - Caused by the absence of some photopigments in cones - Dichromat is a person who is colour blind to one, so has 2 in total - Monochromat is totally colour blind - Most are dichromats losing green-red pigments Analysis and Reconstruction of Visual Scenes - Light energy to nerve impulses has occurred Feature Detectors - The optic nerve sends nerve impulses to a visual relay station in the thalamus which then sends it to the primary visual cortex - Specific regions in the retina are connected to specific regions in the visual cortex o Ensures safety of image if one area gets damaged in the brain - Cells known as feature detectors are in the cortex receiving nerve impulses o These cells fire selectively in response to stimuli with specific cahracteristics o Certain neurons fire most frequently when lines of certain orientations were presented  Some fire largely due to horizontal lines and some due to vertical o The letter A can be constructed using /,\,- o Found many cells firing to many different characteristics and tgen these are analyzed by complex systems o Feature detectors subdivide visual scenes into their individual components  This is called parallel processing  A red, white, green beach ball is analyzed interms of colour, shape, size all at the same time - The information from the detectors in the visual cortex is sent to the visual association cortex o More complex features of the visual scene is analyzed and compared to our memory and knowledge o We starts from the rods and cones and end in here o We give meaning to visual scenes - Recently we have found that cells don’t only respond to basic shapes and colours but also to complex ones that have acquired meaning through experience. Audition - Stimuli for hearing is sound waves - Sound is actually pressure is air, water and other mediums - Frequency is the number of waves cycles per second (Hz): one Hertz = one cycle per second - Frequency is proportional to pitch - Amplitude- vertical size of the waves o Related to amount of compression and expandion of pressure waves o Differences in amplitude is measured in db o Absolute threshold is at 0db and then it increases by 10 Auditory Transduction: From Pressure Waves to Nerve Impulses - Translate pressure waves into nerve impulses - Sound waves travel to the auditory canal leading to the eardrum ( a membrane that vibrates in response to the waves) - From here it goes to the middle ear which contains three tiny bones (hammer, anvil, stirrup). These three amplify that sound wave by 30 times o The first bone hammer is attached to the eardrum o Stirrup is attached to the oval window which forms the boundary between inner and middle ear  The inner ear contains the cochlea (tube containing fluid)  The cochlea also contains the basilar membrane (running around the tube)  The organ of corti is on the basilar membrane and it has around 16000 tiny hair cells  These hair cells are connected to a tectorial membrane - These hair cells receive the amplified waves o They then synapse with the auditory nerve cells o Then they send the impulse to the auditory cortex in the temporal lobe via the thalamus - When sound waves hit the eardrum, pressure is created at the oval window by the three tiny bones o This pressure makes the fluid in the cochlea go into motion o The fluid waves vibrate the basilar membrane which then bends the organ of corti o This bending results in the release of neurotransmitters between the hair of the corti and the auditory nerves outside o Thu
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