IN 1965, Prime Minister Lee Kuan Yew broke down and cried on television when he spoke of how Singapore would be separated from Malaysia.

That moving image is one of the most enduring moments of Singapore's modern history in the minds of Singaporeans, according to a recent survey.

Almost nine out of 10 citizens are aware of it.

But it was the opening of the two casinos in 2010 that most respondents remember.

Similarly, the two 2011 MRT breakdowns on the last weekend before Christmas, that affected nearly 100,000 commuters each time, left a lasting impression.

The survey by the Institute of Policy Studies, which will be presented at a seminar on Monday, aims to give a glimpse into which historical events had the biggest impact on Singaporeans.

In conducting the study, researchers sought to explore these questions: Which events in our history do Singaporeans remember best? Do they believe these events are important to them and to future generations of Singaporeans? How do they recall, retell and perceive these Singapore stories?

IPS interviewed 1,500 citizens face-to-face between August and October last year (2014).

They were shown a list of 50 historical events selected by researchers - from the founding of modern Singapore in 1819 to the General Election in 2011 - and asked if they were aware of each.

The three least-remembered events were the security crackdowns Operation Coldstore in 1963 and Operation Spectrum in 1987 when leftist politicians and activists were detained, and when terrorists took hostages aboard the Laju ferry in 1974.

Fewer than one-fifth said they had heard of the events.

IPS senior research fellow Leong Chan-Hoong, who led the study, said it was the first of its kind in Singapore.