The different |papilla| on the |tongue| show some area-specific patterns of |taste| selectivity. There are four basic |tastes|: sweet, sour, salt, and bitter. The flavors that we |taste| are actually combinations of the four |tastes|. The sides of the |tongue| tend to be sensitive to sour and salt closer to the apex (tip). The tip tends to be sensitive to sweet, while the back of the |tongue| is most sensitive to bitter. The common experience that some sweet substances, such as saccharin, have a bitter aftertaste is partly a result of the area-specific patterns of |taste|. The sweet |taste| is experienced first, at the tip of the |tongue|, but is mixed with bitterness as the substance moves toward the back of the |tongue|.
