Simplify the following text for a Grade 11 native English-speaking person.
Original: Littman tentatively attributed the popular imagery to Pavlovâ s contemporaries Vladimir Mikhailovich Bekhterev and John B. Watson , until Thomas found several references that unambiguously stated Pavlov did , indeed , use a bell .
Simplified: Littman tentatively attributed the popular imagery to Pavlovâ s contemporaries Vladimir Bekhterev and John B. Watson , until Thomas found several references that clearly said Pavlov did , indeed , use a bell .