Arduino to Matlab Interfacing problem

So I kinda figured out how to interface my arduino to matlab when using two computers and connecting them with transceivers. However, my next problem is, I want my matlab to readily listen to arduino whenever it sends, or in regular intervals (say, every 3 seconds).

Could anybody help me with the code?

This is my code when I'm sending something to arduino.

delete(instrfindall) 
clear all 
global a;
a = serial('COM10'); % define serial port 
a.TimerPeriod=1; 
a.Terminator='LF'; 
fopen(a); 
a.BaudRate=9600; % define baud rate