Demonstration 2.2 Method of Constant Stimuli
Your participant should be blindfolded, so that he or she cannot see the numbers on the cups. For each trial, ask the participant to report if the water tastes sweet (Yes) or not (No) and record the response (Y or N) in the table below. [If you want to insert an occasional catch trial, fill up one cup with only water (e.g., Cup 0). You’ll need to modify the response sheet appropriately.]
Trial / Cup / Response (Y/N) / Trial / Cup / Response (Y/N)1 / C3 / 26 / C5
2 / C6 / 27 / C10
3 / C5 / 28 / C1
4 / C10 / 29 / C6
5 / C8 / 30 / C2
6 / C2 / 31 / C9
7 / C1 / 32 / C8
8 / C3 / 33 / C3
9 / C9 / 34 / C8
10 / C4 / 35 / C4
11 / C5 / 36 / C10
12 / C7 / 37 / C5
13 / C1 / 38 / C7
14 / C6 / 39 / C9
15 / C2 / 40 / C4
16 / C7 / 41 / C7
17 / C10 / 42 / C1
18 / C3 / 43 / C7
19 / C1 / 44 / C4
20 / C6 / 45 / C8
21 / C9 / 46 / C6
22 / C5 / 47 / C3
23 / C8 / 48 / C10
24 / C4 / 49 / C2
25 / C2 / 50 / C9
Calculate the percentage of “yes” responses for each of the ten cups, then record those percentages on the graph below.
Once you’ve graphed all ten points, connect each point. Use the line at 50% to determine the threshold. Drop a line down from the point at which your response line crosses the 50% line. Where that line falls on the x-axis determines the threshold.