This is probably one of my most controversial opinions, but I think that the mood of a person can affect the outcome of an experiment. To be clear, this is entirely based on speculation on my part and I have no evidence supporting my opinion. In addition, while I think experimenter mood could potentially affect all types of experiments, I think this is especially true of any experiments that need a consistent or gentle touch.
Let me give you a hypothetical example of how this might play out. Say you are having an exceptionally bad day: you slept through your alarm and didn’t get coffee, then when you were waiting for the bus a car drove by and soaked your clothes, because it was also pouring rain. You finally get to the lab and realize you forgot your keys at home and you are the only one there that day so you need to call security to let you in and end up waiting for 15 minutes outside the lab door while you do this. By the time you are ready to sit down and start your experiment, you are probably more than a little bit grumpy. This could result in tapping vials more aggressively, moving the flies around faster than normal, exerting a bit too much force when mouth pipetting, not being patient when waiting for your flies to settle and starting the experiment prematurely, not paying attention to which buttons you click and forgetting to start the video on time, etc. The same is true if you are excessively happy. This also comes with an inability to focus, more enthusiastic taps, less gentle aspiration, etc.
Emotions like anxiety and nervousness can also result in inconsistency in your data, but perhaps in the opposite direction. Imagine you are too hesitant when tapping your flies, or your aspirations are very light and you have to try several times to get the flies into the behavior arena. Or perhaps you end up taking longer than usual for each experiment, resulting in the experiments being run at a different time of day than typical. There are a hundred different scenarios that could potentially contribute to variability in your data collection. One hopes that the behavior is robust enough that it isn’t impacted by these mood fluctuations, but I suspect that experimenter mood, like temperature and humidity, contribute to the typical day-to-day variability in behavior.
It’s probably superstitious of me but I think it’s best to be optimistic when doing behavior assays. However, this also comes with the caveat that you want to make sure your experiments are done blind so you don’t accidentally influence your results. No matter what, if you think your mood could be affecting the outcome of your behavior experiments, take notes on it in your lab notebook.
Patience and consistency is key when performing any type of behavior experiments. Having stable emotions can help with reducing day-to-day variability in behavior experiments. So how do you get your emotions steady enough on a day-to-day basis to ensure you are getting consistency with your experiments? My recommendation is on behavior days, have a short routine that helps settle you. When you get to the lab, do a few minutes of fly pushing, answer a few emails, get everything ready for your experiments, then listen to a couple of your favorite songs or 15 minutes of a podcast or audiobook. Then take a few deep breaths, center yourself, and start your experiment.