Report On Light Box Psychology Experiment

Today in our Intro to Psychology Lab we are looking to prove Weber’s Law. As our lab manual describes, “an increment in stimulus intensity is a JND when the stimulus intensity is changed by some fixed percentage.” In this definition JND stands for ‘Just noticeable difference’, meaning “the smallest change in magnitude of some standard stimulus that is reliably distinguishable from that standard.” Our class trusts old man Ernst Heinrich Weber and we expect that as the original light intensity increases, it will take a larger increase in comparison light to notice a difference, and change will occur at a fixed percentage

Participants In total we had eight Drake University students that were enrolled in Introduction to Psychology Lab. Zero of these students were psychology majors/minors and were all freshman. Ages of the students ranged from eighteen to nineteen.

Materials

To conduct this experiment, we used a PC with SPSS software, a light box, and two 6W 120V light bulbs for the light box. This experiment was performed in a room that had the capability to be pitch-black.

Procedure

Eight students and one professor entered the windowless room to begin the experiment. Sitting at a square table, four students sat in chairs in a line on the north and west sides of the table. The light box was propped up, in an attempt to be at eye height, on the south east corner of the table directed towards the North West corner. Once all lights in the room had been turned off the professor began the experiment by starting the light box with both bulbs at thirty. With the student’s eyes on the lights the professor would increase the intensity on the right side of the light box (the students left), until three people announced they had noticed the change. The new comparison intensity is recorded, and the lights reset. We repeated the same process for initial intensities of forty, fifty, sixty, and seventy.

Results

A correlation coefficient was examined to determine whether there was a relationship between the original light intensity. The correlation coefficient, r = 0.951, indicated a strong, positive relationship between the original light intensity and comparison light intensity in which the original light intensity increased, and the comparison light intensity increased; however, the results were statistically significant, with a p = 0.007.

Discussion

From our point of view, it looks like Weber knew what he was talking about. In that as the original light intensity increases, it generally took a larger increase in comparison light to notice a difference. That doesn’t mean this experiment in particular isn’t without its problems. For starters, a sample size of eight college freshman is abysmally small. If I were to do this experiment again, I would try to get as large of a sample size as possible with as much diversity in age as possible.

Another glaring issue that is easily visible in our data, our first point is a little bit of an outlier. While this isn’t a limitation of the study, I believe it’s important to mention. If I were to remedy this, I would start the experiment with a couple of test trials to get the participants warmed up. Next up on the chopping block I’d offer the positioning of the light box. If we want consistent data I think it would be much more intuitive if we had the participant looking directly at the light box. In our case, sitting on the two sides of a square table, we had all sorts of angles that may have influence participants vision. In summary, there are many ways this experiment could be improved but I believe there is nothing wrong with the concept itself.