A lot many captions coming up, isnt ??? Well that is one of the things we were taught in our communication class. At first glance,it doesnt seem very different from each other, but to an observative eye, it reveals a lot more. The daily application of these are evident in the newspaper's where each article essence is captured in the subject title. For instance,the title "Economic Survey 2008-2009" would be an Topic Caption since it just tells the reader that the article is about the Economic survey 2008-2009, but stops at that. It doesnt go on to tell in more detail about the Economic Survey etc.
Compare it with a title "Air India’s bailout: is there light at the end of the tunnel?". From the caption itself, one could infer that Air India had got into financial trouble and that it had approached a regulatory body for bailing it out of trouble. And the article maybe describes if there is any end to the problem faced by the Air India.. One single topic gives us so much information that its almost like its talking to us. I know thats an exaggeration yet in the second case, the article topic is similar to someone talking and telling about itself. more like self-explanatory. in contrast, the other topic was more static and just introduced the topic.
Now that you have spent much time in reading this,what significance does this hold to you. here comes the most important part. The knowledge of what we write and its ability to express itself, can help us be more self aware while writing. This is most useful while writing resumes, wherein instead of Topic sentences if one could use Talking sentences it would reveal a lot more about oneself. And believe me, this is a major factor in resume writing. Now that you have become conscious of this fact like me,you could be more resourceful with your words usage while making your resumes or writing articles.