The [I] as in “bit” and [i] as in “beat” are two vowel sounds that cause non-native speakers a lot of problems, especially if your first language is Spanish or if your first language does not have long vowel sounds. Unfortunately, mispronouncing these two sounds will definitely affect your intelligibility during the speaking section of the TOEFL iBT.
Articulation tip for the [I] vowel sound
Produce this sound with a soft tongue and lips and with the mouth more vertically open.
Like the [i] sounds, the [I] sound is a high front unrounded vowel.
This is a short vowel sound.
Articulation tip for the [i] vowel sound
Produce this sound with a soft tongue and lips with a vertically smaller opening of the mouth. However, the mouth is opened wider horizontally than the [I] sound.
Like the [I] sound, the [i] sound is a high front unrounded vowel.
This is a long vowel sound.
In the following video, you will be able to practice these two vowel sounds extensively. In fact, I recommend that you go through all the practice exercises, even making voice recording of the exercises and comparing your pronunciation to the native speaker’s in the video. If you feel you need more practice, I invite you to join my TOEFL Speaking Boot Camp course so you can work on these and all the other vowel and consonant sounds of American English: http://onlinetoeflcourse.com/wp-content/uploads/2013/01/30-Day-7-Step-Study-Guide-for-Speaking-1.pdf