Your observation is correct. Each function has its own workspace in Matlab. The contents of the files are loaded into the callback's workspace, but they are deleted as soon as this function is left afterwards. Try this:
function airflow_input_Callback(hObject, eventdata, handles)
airflow_input = importdata('airflow_test_data.txt');
area_data = load('norm_airflow_area');
dev_data = load('norm_airflow_dev');
disp(area_data)
disp(dev_data)
end
You see, that the variables are imported, but not forwarded magically to the base workspace of the command window. If you really want to do this, use:
assignin('base', 'area_data', area_data);
