When apes experience human-rearing and are exposed to a human language they begin to display the human patterns of self-awareness and self-reflection by 6 months of age. An obvious index of self-awareness is the use of a mirror to view the self as the self is being intentionally altered (or immediately after it has been altered). Many apes explore their image by seeking out a mirror to look at their teeth, their tongue, their ears, their eyes and other portions of their body that could be observed only in a reflected image. Linguistically competent apes expand this awareness by beginning earlier and by elaborating. They paint their faces, put on wigs, shawls and monster masks, and rush to the mirror to see how the look. They try to blow bubbles with bubble gum while using mirrors to watch their cheeks. They practice displays by adding fur capes as they swagger in front the mirror. They seek out live video images to see things that even a mirror would not reveal. Only a live camera image can reveal their epiglottis and allow them to learn to vibrate it in real time (Menzel, Savage-Rumbaugh, and Lawson, 1985; Savage-Rumbaugh, 1986).
Their concern with understanding the appearance of the self from the perspective of another arises from the bifurcated, or dualistic, view of the self, whose roots lie in the I/Me distinctions embedded in the structure of the human language which they are acquiring. The doer/viewer duality of consciousness enables the youngster to think about what it is doing, the appearance of its action, and/or how the action will be perceived by others — all at the same time. When this dualistic process begins to operate, there emerges, within a single brain and body, the capacity to consciously separate the imaged self into that of the doer of one’s actions and the viewer of those same actions (Bates, 1990). The viewer begins to sometimes hold an action by the doer in abeyance, or sometimes even to reflect upon the past actions of the self as doer with a certain amount of chagrin and dismay. This is the formative basis of mental time travel and the mental construction of alternative world views (Suddendorf and Corballis, 2009).
h/t @ Lapidarium notes