 Although he attempted to regulate his daily routine to maintain more control over his results, his decision to avoid the use of participants sacrificed the external validity of the study despite sound internal validity.In addition, although he tried to account for his personal influences, there is an inherent bias when someone serves as researcher as well as participant.Also, Ebbinghaus's memory research halted research in other, more complex matters of memory such as semantic and procedural memory and mnemonics.