A cognitive psychologist investigates whether the duration of exposure to blue-wavelength light before sleep affects cognitive performance the next morning. Group 1 is exposed to 30 minutes of blue light before bed, while Group 2 is exposed to 2 hours. The next morning, all participants complete a 10-minute standardised reaction-time task, and their mean response latency (in milliseconds) is recorded.
Which of the following describes the operationalised dependent variable in this study?
The duration of exposure to blue-wavelength light (30 minutes vs 2 hours)
The general cognitive performance of the participants the next morning
The mean response latency in milliseconds on the 10-minute reaction-time task
The sleep quality or sleep duration of the participants during the night
