This line shows the test PCC scores (y-axis) of SIF encoder on the news corpus when the number of training corpora increases (xaxis).
the left-most blue dot indicates the test result of SIF encoder on news corpus when trained on news corpus itself (that is, the first training corpus is used); the second point indicates the test results of SIF encoder on news corpus when trained on news and captions corpora (i.e., the first two training corpora are used); the third point indicates the test results of SIF encoder on news corpus when trained on news, captions, and wordnet corpora (that is, the first three training corpora are used), so on and so forth.