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Psychology 2115A/B
Stephen Lupker

Lecture: 2 September-14-11 2:30 PM Psychophysics  Gustavo Fechner  Worked in the Monism theory  When you provide a stimulus it will create sensors that are activated  The question is how strong does that stimulus have to be to activate enough sensory for people to hear it or sense it (absolute threshold)  Plot a graph with the y axis saying yes "they sensed something", then have the intensity on the x axis, if the intensity is below the threshold then it will be zero as people can not hear it, but if you go past the threshold then the y axis will be 100%  Realizing that there is a threshold that people must pass to sense things  This is called a Psychometric function (function that relates a physical intensity that is measured to something)  Question: how do we know what the absolute threshold is?  Fechner gave us ideas to calculate the Threshold Methods of Limits : you take a stimulus somewhere around the threshold, if it is below the threshold you present it to the person and they will say no and then you increase the intensity until they cross over the threshold line, eventually the persons response will change from no to yes ( basically taking things to the limits) Method of Constant Stimuli : you pick about ten different stimuli and present them to person randomly and they answer yes or no and do each one about ten times, there should be some low intensities that every ten times the person heard the same stimuli should be no and the same with some high intensities heard all ten times they should say yes all of the times  Fechner came up with some rules and tricks  Do the multiple trials each time  Multiple trials going up and down intensities (people tend to do two things: Error of anticipate (so they jump and say no earlier so that it stops and moves on to solve this take the average to even out all the errors)Error of Perseveration (people keep giving you the same answer to solve this you need to change from high intensities to low ones (alternate) or you can take the average  If Fechner was right we would get a graph that looks like a flat like then a straight increase up to 100% and then a flat line from there  Instead we get a increasing wavy line (like one side of a bell curve)  Not caused by and anticipation or preservation error needs another explanation  When you listen to a sea shell you do not actually hear the ocean but the brain functions within your ears (spontaneous activity)  The idea is that the activity in your auditory or visual system is the background for any tone that happens, the error might be a spontaneous activity occur making one feel as though they heard something  What is happening is that there is some kind of stimuli happening, you might also get a blast of the activity that is presented to you, together it combines and you hear something  The Question now is: what is the threshold then?  Fechner`s answer is find 50% and that`s the intensity of the absolute threshold  The Question: how big of a difference must there be to make a distinction between intensities?  Need to start off with a standard stimulus and then you must apply another stimulus and ask the person if they are the same or not  The standard stimulus must not change  Some will be the same and some will be different  Called ``comparing stimulus ``  So you set yourself a standard weight and then you get a second weight ask if they are different, you feel the standard then feel the comparison, then you will pick which one is heavier, and continue to compare them and eventually you will get something that is the same, and then continue and eventually you will get a comparison that
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