Gerneral Psychophysics Thesholds JND s Psychophysical scaling The visual system The retina Info processing Perception of color Trichromatic theory Opponent process theory Sensation the passive process of bringing information from the outside world into the body and to the brain Stimulation of sensory organs Perception has to do with selection organization and interpretation of sensory input it is making sense of the world around us Psychophysics studies how sensation is turned into perception Thresholds limits in which the human sensory system works o Ex Loudest and softest sound you can hear softest touch you can feel JND just noticeable difference o Ex how loud does the sound have to get before you can tell it increased o Our perception of the world around us is not precisely calibrated if it were we would be aware of the extra weight on our shoulders from dead skin o JND is about how much of a difference must there be until we can tell there has been an increase or decrease JND s are a constant proportion of the intensity of the initial stimulus Proportion for weight is 1 30 meaning it must increase by 1 30 of the initial weight for us to tell it has gotten heavier for a 30lb weight u must increase by 1lb to notice Another ex You cant see stars in day but you can at night because intensity of light being given off by stars can not compare to the suns however at night the intensity is noticeable although it has not changed Sensory modalities 1 60 for brightness for tones it has to increase by 1 10 weight 1 30 moderate loudness range 1 10 pressure on the skin has to increase by about 1 7 these fractions are called weber fractions The more intense a stimulus is the more it has to increase for us to be able to tell the increase Ex loud music has to increase more than quiet music for us to recognize The Visual system Psychophysical scaling mapping of the proportion that a particular stimulus modality needs to increase in order for you to notice the increase o You don t need an increase of the JND when at limits Maximum and Minimum Ex If lifting weight and benching max 300lbs you can notice the difference when someone places a finger on the bar o Whats being measured is subjective experience Psychological experience mental event Cornea protects eye and lets light through Lens focuses light on the retina Pupil controls the amount of light that reaches retina Iris muscle which dialates and restricts pupil so that in low light conditions a certain amount of light may get in Electromagnetic raditation the amplitude of height of the wave corresponds and reflects the lightness o Wave length roughly affects color Transduction transferring energy from one form to another its what occurs with electromagnetic energy Retina very thin neural tissue its absorbs light processes visual information and sends info on to the brain In center of retina there is hole called optic disc o Light that falls on this spot isn t being processed there are no rods and cones here hence why it is commonly refered to as the blind spot o Blind spot typically not a problem Only circumstance where it could be is when driving Neurons in retina take information from retina further into the brain where it is processed Axons are bundled together and leave the retina through the optic disc The retina is covered with sensory apparatus they respond to light and transduce electromagnetic radiation Retina absorbs light through rods and cones o Cones made for bright light and for color have very high visual accumulity which means very sharp about 7 000 000 of them Are concentrated right in the center of the retina Fovea area in center of retina where there is all cones and no rods This is why when you want to see something you direct your eyes right at what you want to see This is because when directed at the object light reflects off of the object and strikes the fovea where the highest volume of cones is o Rods specialized for low light conditions not a very sharp picture don t process color very well about 120 000 000 If you want to find something in the dark look of to the side of where you think it is When you do this the light reflecting off of the object will hit the perimeter of your eye where the rods are allowing you to see the object o We have about 127 000 000 light receptors but only about 1 000 000 optic nerves Each optic nerve is taking in a bunch of information and combining the info into a fire or don t fire decision remember that neurons fire Each optic nerve has a receptive field which means it responds to one area of the retina Light that strikes one part of the receptive field has the opposite effect of light striking the other part of the receptive field If light falls more strongly on the center the optic neuron is going to be more likely to fire Information is always coming from 2 sources its coming from the external world and from our memory which helps us perceive the world around us
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