People think - using a number of techniques, they may have an internal voice that they use as a "guide" however that not the only way one "thinks".
Many people - hearing, HOh or Deaf when thinking about doing various things sort of internally visualize doing/completing the task. For example - when you think about cleaning a room in your house you might visualize (for a fraction of a second) what the room will look like clean and then proceed to work towards that final visualization.
If one is making a list of things to do - like a shopping list, they may see pictures of the item itself or the words, or they may internally hear, feel, taste etc something directly connected to that item.
For those who have some residual hearing - or where born hearing or HOh and went deaf later in life (post-lingually) we often (but not always) retain some amount of "internal auditory memory" - sort of like having an internal recording of what words sound like ... using this memory we MAY continue to "hear" words for various things internally, even though we are no longer able to physically hear the sounds/words anymore.
Many Hoh and Deaf people who use sign language (ASL, BSL etc) have a sort of internal muscle memory regarding how signs "feel" when formed - so as we go through a list etc we may have a "phantom feeling" of the signs being formed with our hands ... or we may visualize the sign for a flash of a second.
It's important to remember that infants don't have language - yet they are able to think (experience is the limiting factor, not language). Infants now what they want, dream, have preferences etc ... yet have (at least initially) no "formal language" to express themselves.
Language allows one to COMMUNICATE one's thoughts (to others), however thought is not limited to or constricted by formal linguistic barriers.
Hope that helps a bit ?
