This function extracts (x_pos, y_pos) of first word in each text line from the region file
get_start_pts(region_file, trial_num)A "*.csv" character list recording the name of the region file
An integer indicating the trial number of the current start_pts
A data.frame recording the left position of the first word in each line of the text in each trial. It has three columns:
x_pos: x position of the first word in each line of the text.
y_pos: y position of the first word in each line of the text.
trial_num: Integer indicating the trial number of the current start_pts.
This function reads region_file and gets (x_pos, y_pos) of first word in each text line. Then, it bounds (x_pos, y_pos) with trail_num into a data frame, and return the data frame.