Just to clarify, I looked this question up, and the original sentence is:
Cognitive psychology is yet another branch of psychology. Researchers in cognitive psychology look at how people learn, how people solve problems, and how brains store information.
Answer:
The best option is:
No change
Step-by-step explanation:
The original sentence does not contain a comma splice or a fused sentence.
A comma splice is the use of a comma to join sentences that were originally independent. That happens in the first option given - "Cognitive psychology is yet another branch of psychology, researchers in cognitive psychology look at how people learn;"
A fused sentence happens when we put together two independent clauses with no punctuation or conjunction to connect them. That happens in the second option given: "Cognitive psychology is yet another branch of psychology researchers in cognitive psychology look at how people learn..."
Therefore, the best option in NO CHANGE, since the original sentence is correctly punctuated.