By Darryl Ayo
Two different kinds of thinking, in my opinion:
1) caption box is a narration. Sometimes a recollection, other times, a present-tense thought-track of the events at hand.
In other cases, the caption box is used to indicate a person speaking aloud when the art is showing something else. For example if Detective Jones is interrogating Joe the Poolshark who recalls the evening of the murder, the art may illustrate the scene while the spoken dialogue would be overlaid in caption boxes because it isn’t being spoken IN the scene.
2) thought balloons are very good at showing us incidental thoughts. The “wow, she’s hot” thoughts or the part where you shake a guy’s hand and say “pleased to meet you” but inwardly think “jerk.” From my childhood, the Chris Claremont Uncanny X-Men thought balloons, which amounted to paragraphs of personal reflection and exposition did not look good on the page. But short, emotional bursts of unspoken thought are perfect for the thought balloon.