What type of stimulus did Ebbinghaus use in his memory studies?

Ebbinghaus utilized nonsense syllables in his memory studies to examine the processes of learning and forgetting. By employing these meaningless combinations of letters (such as "DAX" or "TIK"), he minimized the influence of prior knowledge or associations that could bias the results. This choice allowed Ebbinghaus to focus specifically on the mechanisms involved in memory retention and recall.

Using nonsense syllables helped create a controlled experimental environment where he could systematically assess how various factors, such as the amount of practice or the retention interval, affected memory performance. This methodology was groundbreaking at the time and laid the foundation for future research on memory by emphasizing the importance of systematic and empirical approaches to psychological phenomena.