after completion of the experiment , students should have a fundamental understanding of weber s law and its applications to tactile stimuli . they should be able to describe the relationship between the physical intensity of a stimulus and perceived intensity . . they should be familiar with the operation procedures of the cortical metrics stimulator as well as fundamentals of sensory data collection and analysis . the cortical metrics cm-4 four - point vibrotactile stimulator ( figure 1 ) was used to conduct the exercise . it interfaced with a personal computer ( laptop ) through an internal data acquisition box ( daq ) made by national instruments ( ni daq usb-6259 ) . all computers were networked together to allow centralized data storage in the cortical metrics neurosensory diagnostics database . this allowed for instant on - line data analysis at the end of the exercise . one of the subject s hands was placed on the ergonomic armrest , while the other hand was used to press one of two buttons , located on a response device ( mouse ) connected directly to the pc . one trial consisted of the delivery of two simultaneous vibrotactile stimuli , each through independent probe tips , for the duration of one half of a second . these stimuli consisted of 25 hz sinusoidal vibrations of the probe tips at protocol - specified amplitudes . one of the two stimuli , the standard , was delivered at a constant amplitude throughout a run . the other stimulus , the test , was delivered at amplitudes that were always greater than the amplitude of the standard , but were otherwise varied according to the tracking method used . the digit locations of both the test and standard stimuli were assigned randomly by the computer . the subject responded as to which stimulus felt more intense by clicking the left or right button on the response device , assigned respectively to the left or right digit . a modified bksy method , also known as the staircase or up and down method , was used to track subject performance ( cornsweet , 1962 ) . the bksy method is an adaptive tracking method in which each test stimulus amplitude depends on both the preceding test stimulus amplitude and the subject s response . in this particular experiment , two variations on the bksy method were used . at the beginning of a run , tracking was conducted with a bias of one : a correct identification of the greater amplitude stimulus lead to a decrease in the test amplitude by a specified step size and an incorrect answer lead to an increase in test amplitude by the same step size . later in the run ( after 10 trials ) a bias of two was added to the tracking method ; a subject had to deliver two consecutive correct answers for the test amplitude to decrease by one step size , while one incorrect answer lead to an increase in test amplitude by one step size . the bias of one for the first ten trials allowed for the subject to track down quickly , while later increasing the bias to two , increases the accuracy of the results of the run by decreasing the effects of good guessing ( tannan et al , 2006 ) . the method stopped after 20 completed trials . during a run a subject was able to track down to the smallest test amplitude which he / she could consistently differentiate from the standard , that subject s discrimination threshold ( jnd ) . for each run , the test amplitude started at twice the standard amplitude . the step size at which the test amplitude was increased or decreased was 10% of the standard stimulus ( e.g. , 0.02 mm for a 0.20 mm standard ) . these settings allowed the test stimulus strength to start out well above the discrimination threshold , but low enough for the subject to track down to his / her jnd within the twenty trials that were administered during the run : experience has shown that most subjects can reach their discrimination threshold within ten to fifteen trials . the standard amplitudes for each run were as follows : 0.2 , 0.4 , 0.6 , 0.8 mm . maximum and minimum amplitudes were user specified in the protocol so that the stimulator only delivered amplitudes within its proper operating range ( 02 mm ) . the maximum amplitude was set to 3x the standard , while the minimum amplitude was set to the standard amplitude plus 5um . for example , for the first test ( 0.2 mm standard and 0.40 mm test ) the minimum amplitude was 0.205 mm . after each run was completed , the program generated a graph of the test amplitude versus trial number ( figure 2 ) . it was determined that most subjects reach their discrimination threshold by the last five trials of a test ; therefore the average of the last five test amplitudes is used as the discrimination threshold . the subject s discrimination threshold was determined for each test , and data was subsequently collected from all students in the class ( n=11 ) . the difference limen ( dl ) for each subject was determined by subtracting the standard amplitude from its corresponding final test amplitude for each run . the averages of the dl at each standard amplitude were determined for a sub - group of five students as well as for the entire class . the students then compared their own dl ( n=1 ) with the average dls for the group of selected sub - group five people ( n=5 ) , as well as the entire class ( n=11 ) . students compared the three different graphs in order to evaluate the effects of increasing the sample size on experimental results . students also considered the general form of these graphs and verified that it was in accordance with the linear relationship predicted by weber s law . the cortical metrics cm-4 four - point vibrotactile stimulator ( figure 1 ) was used to conduct the exercise . it interfaced with a personal computer ( laptop ) through an internal data acquisition box ( daq ) made by national instruments ( ni daq usb-6259 ) . all computers were networked together to allow centralized data storage in the cortical metrics neurosensory diagnostics database . this allowed for instant on - line data analysis at the end of the exercise . one of the subject s hands was placed on the ergonomic armrest , while the other hand was used to press one of two buttons , located on a response device ( mouse ) connected directly to the pc . one trial consisted of the delivery of two simultaneous vibrotactile stimuli , each through independent probe tips , for the duration of one half of a second . these stimuli consisted of 25 hz sinusoidal vibrations of the probe tips at protocol - specified amplitudes . one of the two stimuli , the standard , was delivered at a constant amplitude throughout a run . the other stimulus , the test , was delivered at amplitudes that were always greater than the amplitude of the standard , but were otherwise varied according to the tracking method used . the digit locations of both the test and standard stimuli were assigned randomly by the computer . the subject responded as to which stimulus felt more intense by clicking the left or right button on the response device , assigned respectively to the left or right digit . a modified bksy method , also known as the staircase or up and down method , was used to track subject performance ( cornsweet , 1962 ) . the bksy method is an adaptive tracking method in which each test stimulus amplitude depends on both the preceding test stimulus amplitude and the subject s response . in this particular experiment , two variations on the bksy method were used . at the beginning of a run , tracking was conducted with a bias of one : a correct identification of the greater amplitude stimulus lead to a decrease in the test amplitude by a specified step size and an incorrect answer lead to an increase in test amplitude by the same step size . later in the run ( after 10 trials ) a bias of two was added to the tracking method ; a subject had to deliver two consecutive correct answers for the test amplitude to decrease by one step size , while one incorrect answer lead to an increase in test amplitude by one step size . the bias of one for the first ten trials allowed for the subject to track down quickly , while later increasing the bias to two , increases the accuracy of the results of the run by decreasing the effects of good guessing ( tannan et al , 2006 ) . the method stopped after 20 completed trials . during a run a subject was able to track down to the smallest test amplitude which he / she could consistently differentiate from the standard , that subject s discrimination threshold ( jnd ) . for each run , the test amplitude started at twice the standard amplitude . the step size at which the test amplitude was increased or decreased was 10% of the standard stimulus ( e.g. , 0.02 mm for a 0.20 mm standard ) . these settings allowed the test stimulus strength to start out well above the discrimination threshold , but low enough for the subject to track down to his / her jnd within the twenty trials that were administered during the run : experience has shown that most subjects can reach their discrimination threshold within ten to fifteen trials . the standard amplitudes for each run were as follows : 0.2 , 0.4 , 0.6 , 0.8 mm . maximum and minimum amplitudes were user specified in the protocol so that the stimulator only delivered amplitudes within its proper operating range ( 02 mm ) . the maximum amplitude was set to 3x the standard , while the minimum amplitude was set to the standard amplitude plus 5um . for example , for the first test ( 0.2 mm standard and 0.40 mm test ) the minimum amplitude was 0.205 mm . after each run was completed , the program generated a graph of the test amplitude versus trial number ( figure 2 ) . it was determined that most subjects reach their discrimination threshold by the last five trials of a test ; therefore the average of the last five test amplitudes is used as the discrimination threshold . the subject s discrimination threshold was determined for each test , and data was subsequently collected from all students in the class ( n=11 ) . the difference limen ( dl ) for each subject was determined by subtracting the standard amplitude from its corresponding final test amplitude for each run . the averages of the dl at each standard amplitude were determined for a sub - group of five students as well as for the entire class . the students then compared their own dl ( n=1 ) with the average dls for the group of selected sub - group five people ( n=5 ) , as well as the entire class ( n=11 ) . students compared the three different graphs in order to evaluate the effects of increasing the sample size on experimental results . students also considered the general form of these graphs and verified that it was in accordance with the linear relationship predicted by weber s law . a sample plot for the group of 11 students is shown below ( figure 3 ) . the data we collected from this group of 11 students supported the linear relationship between the difference limen ( s ) and the standard amplitude ( s ) predicted by weber s law , and plotting this data resulted in a nearly linear graph , with a linear correlation coefficient of 0.994 . the data from the group of five students along with the data from a single individual were still roughly linear , but much less so , with linear correlation coefficients of 0.935 and 0.794 , respectively . clearly , larger sample sizes gave a better approximation of weber s law than smaller sample sizes . the exercise was designed to introduce students to weber s law using the cm-4 stimulator as a tool in quantitative testing and measuring of sensory perception . weber s law was selected as the subject of this lab because it provides an easily understandable concept as well as a simple protocol for students to test . the cm-4 stimulator was the instrument of choice due to its particular suitability to the task at hand , as well as its versatility , making it a particular valuable research tool to understand . the cm-4 stimulator has a wide range of applications in the area of tactile sensory testing . simple protocols and portability not only make it ideal for an undergraduate lab setting but for clinical testing and research as well . the integrated software makes it possible to execute protocols that can be adjusted and applied without constant human intervention . the automatic skin detection and programmable test parameters that enable precise control of the amplitude and frequency of stimuli allow for reproducible protocols and reduction of sources of error . by the end of the exercise paper , students gained a conceptual understanding of weber s law and its application to sensory testing . students saw the value of larger experimental sample sizes as well as becoming familiar with the fundamentals of tactile sensory data collection and analysis . the linearity of the collected data is easy to understand , and since linearity in any biological study is rare , we view this result as significant and robust , especially given that it can be collected in a classroom / laboratory setting . to verify that students accomplished the learning objectives laid out in the introduction of this paper , the instructor may elect to distribute a short quiz . the assessment should be short , and could consist of short - answer questions / problems such as the four below : 
 define weber s law.provide an example of how weber s law relates to tactile perception.design an experiment to test weber s law.when empirically evaluating a scientific hypothesis , is a large or small sample size preferred ? why ? when empirically evaluating a scientific hypothesis , is a large or small sample size preferred ? the exercise was designed to introduce students to weber s law using the cm-4 stimulator as a tool in quantitative testing and measuring of sensory perception . weber s law was selected as the subject of this lab because it provides an easily understandable concept as well as a simple protocol for students to test . the cm-4 stimulator was the instrument of choice due to its particular suitability to the task at hand , as well as its versatility , making it a particular valuable research tool to understand . the cm-4 stimulator has a wide range of applications in the area of tactile sensory testing . simple protocols and portability not only make it ideal for an undergraduate lab setting but for clinical testing and research as well . the integrated software makes it possible to execute protocols that can be adjusted and applied without constant human intervention . the automatic skin detection and programmable test parameters that enable precise control of the amplitude and frequency of stimuli allow for reproducible protocols and reduction of sources of error . by the end of the exercise paper , students gained a conceptual understanding of weber s law and its application to sensory testing . students saw the value of larger experimental sample sizes as well as becoming familiar with the fundamentals of tactile sensory data collection and analysis . the linearity of the collected data is easy to understand , and since linearity in any biological study is rare , we view this result as significant and robust , especially given that it can be collected in a classroom / laboratory setting . to verify that students accomplished the learning objectives laid out in the introduction of this paper , the instructor may elect to distribute a short quiz . the assessment should be short , and could consist of short - answer questions / problems such as the four below : 
 define weber s law.provide an example of how weber s law relates to tactile perception.design an experiment to test weber s law.when empirically evaluating a scientific hypothesis , is a large or small sample size preferred ? why ? when empirically evaluating a scientific hypothesis , is a large or small sample size preferred ?