Chapter 4 Sensation and Perception sensation stimulation of sense organs perception selection organization and interpretation of sensory input the subjective experience of physical reality its not always the same as the info thats being transmitted to us psychophysics study of how physical stimuli are translated into psychological experience sensation is both more than or less than perception visual illustrates the difference between perception and sensation is different sensation sensory organs absorb energy from physical stimuli in the environment we hear the sound due to neural impulses sent to brain perception the brain organizes this input and translate it into something meaningful what we hear isnt always what is being sent exactly to our brain our brain interprets input and add things to or takes things out this is PERCEPTION things are ADDED OR TAKEN AWAY its not exactly what our senses detect Psychophysics Basic Concepts begins with detectable stimulus absolute threshold detected 50 of the time the weakest stimulus that is still detected at least 50 of the time just noticeable difference JND smallest difference detectable 50 of the time weber s law size of JND proportional to the size of initial stimulus if you can tell the difference between a just noticeable difference of pounds like 50 lbs to 55 lbs you can notice it in 100lbs and 105 lbs the thalamus is the first stop for all sensory input THEN it goes to the corresponding lobe occipital temporal etc retina pathway through the brain the visual cortex where visual input goes the retina shows a picture that is upside full of holes and blocked by blood vessels this isn t what we actually end up seeing though obviously what we see is a product of the occipital lobe not what we see in the retina perception is MORE than sensation sensation occurs in the sensory cells in the retina but thats not our conscious experience of what vision is its not what we end up seeing distal stimulus the true nature of the actual object proximal stimulus image formed on the retina the brain must eliminate confusing signals fill in the blanks turn the image right side up get rid of the holes and this is perception quarterbacks perceive where the runner is going getting accurate info about the world around us is the goal of the visual system when people walk towards us we know that they are not getting larger perceptual constancy perceived as remaining relatively constant even if the image on the retina says otherwise we see things with our mind and our eyes our previous experience and expectations constantly give rise to perceptions prior experience gives you very different ways of looking at the same distal stimulus analytic way of seeing seeing things in its parts the stimulus intensity at which it can be detected at least 50 of the time absolute threshold subliminal perception we know that things that people are not consciously aware of having been exposed to can affect them a stimulus flashed under 1 20th of a second they did not consciously see it but it did affect them even stimuli were not consciously aware of having experienced can influence us sensory adaptation decline in sensitivity to an unchanging stimulus if its shown at a constant intensity than were not as susceptible to respond to it we won t respond to stimuli that are remaining constant when a sound is in the background and eventually fades away its because our ear stops reacting to the waves in the air because they re unchanging light electromagnetic radiation amplitude perception of brightness wavelength perception of color most of electromagnetic spectrum we can t see pupil regulates amount of light when its dark our pupil expands so it lets in more light so we can see the brain tells the pupil if it needs to dilate or constrict or not just because were not aware that its happening doesn t mean the brain is not part of it happening we don t think about doing it but the brain controls the entire process the actual receptor cells lie in the retina image on retina is 2D and upside down but we see a 3d world even though it captures a 2d image we have a blind spot that would leave a big black circle in our sight if our brain did not fill in the blanks that the retina image leaves we don t see with our eyes they just pick up visual info and the brain interprets it retina photosensitive sensory cells lie optic disk optic nerve connection and blind spot Receptors rods black and white low light vision find edges cones color and daylight vision and color adaptation both change their sensitivity depending on light conditions becoming more or less sensitive to light as needed the neural impulse is the way in which the brain and entire body process info rods and cones have a number of special neurons that attach to like horizontal cells and bipolar cells theres a lot going on the photoreceptive cells sensory neurons lie behind all these kinds of cells which explain the holes in the image on the retina the optic nerve is the means by which action potentials are sent to the thalamus and then the occipital lobe remember contralaterality principle the focal point in the retina is the fovea where there are the most cones but there are the least amount of rods here at the fovea rods allow peripheral vision the farthest from our center cones are for what were visually focused on that s where we need detail and color peripheral vision we have to detect movement and objects but we don t necessarily need color and detail there the blind spot where the optic nerve leaves the retina there are no rods or cones as threshold decreases sensitivity increases cones aren t good in darkness but rods are light strikes the back of retina rods and cones neural signals bipolar cells ganglion cells optic nerve optic chiasm opposite half brain sensory neurons take physical energy from environ and transform into neural impulses main pathway lateral geniculate nucleus in thalamus all sensory neural impulses go there first except smell then the thalamus sends it to the appro part of brain left visual field right hemisphere and vice versa after info is processed in primary visual cortex info has to be transmitted to other areas that are responsible for different kinds of perception such as identifying what a word is you go to the lexicon in the temporal lobe seeing something as a 3d object is in the parietal lobe Hubel and Wiesel Feature Detectors planted electrodes in different axons in the primary visual
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