Once you have the sound file containing all of your stimuli, you'll need to segment it into smaller, individual files for each stimulus. You can do this using the free acoustic analysis software Praat, available at praat.org.
Once you open Praat, you'll see that both a "Praat Objects" window and a "Praat Picture" window appear at start up. You won't be using the Praat picture window, so you can close that.
Before we begin cutting a sound file, let's just see what sounds look like in Praat. In the top menu, go to "Open" --> "Read from file" and choose your sound file. It should now appear highlighted in the Objects window. Click on "View & Edit" on the right-hand menu to see your sound file:
The recording list:
Once you've chosen a perception task, it's time to make stimuli for it.
How many stimuli do I need?
The answer to this question isn't simple. You'll need to strike a balance between getting a sufficient amount of data and how long you can reasonably expect people to sit and do your experiment. In our lab, we generally have to recruit participants with extra credit, the promise of snacks, and desperate pleas, so any experiment over an hour or an hour and 15 minutes is unlikely to have many people sign up. If you can pay people they'll be more willing to do a longer experiment, but that means more money you'll have to shell out for each person. Since your experiment is likely to be made up of two or more tasks, such as both discrimination and lexical decision plus a background questionnaire, each task in itself shouldn't be longer than about 25 minutes, if possible. Shorter tasks will also prevent participants' attention from wandering too much, which means more reliable data. A 20-minute AXB or oddity task is already very boring even with a break, and with difficult contrasts it can also be mentally taxing and demoralizing. I know some psychology experiments have participants doing one repetitive task for an hour (how?!), but if you don't want participants to constantly time out on trials because they are falling asleep or trying to surreptitiously check their phones, keep it shorter.
Welcome to my blog! I've decided to use this space as a how-to for creating and running perception experiments, both as a way to organize my thoughts and as a way to help you, random person on the internet. I'm writing this for an audience (assuming you exist) that has some knowledge of L2 phonology, but no practical experience running experiments.
So let's get started! First of all, if you're excited to start a perception experiment, as we all should be, you have a research question in mind that you want answered. This research question will determine what kind of task you should use, as different types of tasks examine different levels of processing. In this post I'll outline common types of research questions along with their corresponding appropriate task(s).