In the experiment, subjects received, in each trial, a pair of sounds played from headphones. The subject self-initiated each trial by clicking mouse on the monitor screen. The first sound was then presented together with a green square on the left side of a computer monitor in front of the subject. This was followed by a delay period, indicated by ‘WAIT!’ on the screen, then the second sound was presented together with a red square on the right side of the screen. At the end of the second stimulus, by presenting the two squares, subjects were required to compare the two sounds and decide which one was louder, then indicate their choice by clicking the green square if the first sound was louder or the red square if the second sound was louder. Then a question asked from the subject about the sureness of correctness of the response and the subject has to indicate a percentage between zero to one hundred. After settlement of the sureness, the Written feedback about the correctness of their response was provided on the screen, for individual trials. There are 150 trials in each session. Each subject participated only in one session.