Psychological  e  Experiment -  t  The  i  Invisible  g  Gorilla

Two cognitive scientists undertook an experiment in which they asked volunteeres to watch a short video. On the video there were a few people throwing  2  two  balls. There were two teams: one in white t-shirts, the other  one  in black t-shirts. The volunteers were supposed [1] to count how many times the ball was passed between people in white t-shirts.
In the middle of the 60-second video something passed through the middle of the playing team. It was a woman dressed as a gorilla. She stopped for a few seconds, beat her chest and  then  walked away.
After watching, the volunteers were asked how many times the ball was thrown and  ...  whether they had  seen  seen  [2] the gorilla. It turned out that about half of the people  didn't see   hadn't seen  it. The video was played again and those who  didn't see  hadn't seen  the  dressed  disguised  woman were  wery  very  suprised. Some of them accused the staff of switching tapes when they weren't looking.
This led to a [3] conclusion that we  often  don't  often  [4] see what's in front of our own eyes. We  belive  believe  that our perception is better that is actually is.

This and other social experiments are described in a book called [5] "The  i  Invisible  g  Gorilla and  o  Other  w  Ways  o  Our  i  Intuition  d  Deceives  u  Us",  written by Christopher Chabris and Daniel Simons. It is a good read, eye-opening and witty. The authors try to help us to see things as they really are, supporting their claims with a lot of evidence and real-world examples.

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[1] It may be better to say that the volunteers were "instructed" to count...

[2] If this is a real report that you are preparing, it would be better to say that half the volunteers had not "noticed" the gorilla.  They had seen the gorilla, but had not noticed it--this is, after all, a cognitive experiment.

[3] If this was the only conclusion, you should write that it was "the" conclusion.

[4] Be careful here.  To say "we don't often see X" means we rarely see X.  To say "we often don't see X" means we usually see X, but sometimes do not.

[5] If this is a real report, you should say that the book is "entitled" XYZ.  To say that a book is "called" or "named" XYZ is okay in casual writing, but not appropriate for a report.