![]() ![]() Know how to make it more difficult, and vice versa. Participant's performance is too high, the task is too easy, so PEST must Making the task easier and making it harder. ![]() Note that the process requires that PEST `knows' the difference between Thus, itĪccelerates the rate of change between steps in order to reach the Well above, or well below, their actual performance threshold. Performance hasn't changed after many steps, the participant is performing The fourth rule is based on the assumption that if the participant's That the third level after a reversal is the same as the last-but-two levelīefore the reversal. The last-but-one level before the reversal. The second rule ensures that the second level after a reversal is the same as Were tested recently (which was found to give the wrong performance level). The first rule avoids retesting the participant at the same level as they For step four and beyond, double the previous step-change.For the third step, if the step-change before the previous reversal wasĪ doubling, do not double the previous step-change.On the second step in a given direction, use the same step-change.On the first step-change in a given direction (i.e.`home-in' on the desired level, and that track any changes that might occur These rules are designed to generate a sequence of levels that quickly Deviation limit The maximal difference (in number of trials) between the desiredĪccuracy and the actual accuracy, beyond which the level should be changed. Target accuracy The performance accuracy level to be achieved by the participant.Įxpressed as a floating point number between zero (0%, or all wrong), and (The algorithm, if uncorrected,Ĭan choose negative or values that are otherwise unsuitable for the Minimal value The smallest absolute value of step. Maximal change The largest absolute difference between consecutive steps. Positive value causes an increase in level when performance is too high,Īnd vice versa. ![]() First change The direction (positive or negative) and amount by which to change the Input Parameters Starting level The level of the IV for the first step. Trial A single stimulus-presentation to which the participant should Step-change The change in level between steps. Step A contiguous sequence of trials at a given level. DV The response from the participant (the Dependent Variable). Terminology Level The task stimulus-property being adjusted (the Independent Variable or The rules that govern the level chosen at each change. The participant with the minimal number of trials. PEST is especially efficient in obtaining a given performance level from A series of consecutive trials at the same Whenever the IV is changed, the accuracy is Participant's accuracy is too high, the IV's level is changed to make the Thus, PEST presents trials at a certain level of the IV, and if the Stimuli are presented until the participant responds correctly (simpleĭetection, or the correct selection from a number of options) to a given For instance, Taylor and Creelman tested participants'Ībility to detect a sound by varying its loudness until participants detectedįor a test of mental-processing speed, one might adjust the rate at which Moreįormally, a property of some signal (the independent variable) is adjusted toįind the magnitude that results in a performance of specified accuracy (theĭependent variable). It is a set of rules for adjusting the difficulty of a task to quicklyįind the point at which performance reaches a predefined level. (Journal of the Acoustical Society of America, Volume 41, Number 4, Douglas Creelman, in "PEST: Efficient Estimates on Probability Functions" The PEST algorithm is based on the procedure described by M. PEST: Parameter Estimation by Sequential Testing PEST: Parameter Estimation by Sequential Testing Introduction ![]()
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