问个读了很长时间一直不懂的句子

As far as we could determine ,they (a group of people )went to sleep just as quickly and slept just as long as the previous subjects (another group of people ) did . ----这样就清楚多了.
就我们所覌察而决定, 这一组人与先前那组人一样地迅速入睡并睡眠一样长时间.

感觉subjects后面应该是逗号,因为一个句子还没说完呢.或者之前那句与其意义连贯.
as far as这里是 只要...(就)..的意思
只要我们能断定他们像先前那些志愿者睡的又快又香的话, ...

只能意会，不能言传
as far as=直到……

尽所能,就
As far as I know: 就我所知
as far as I understand: 就我所理解

直到我们可以确定他们入睡的速度和前面提到的那些人一样快,睡眠时间和那些人一样长.