Primates have forward facing eyes rather than one on each side of their head. This provides binocular vision because each eye's field of vision overlaps creating a three dimensional image. Binocular vision enables primates to accurately assess distances and depth which is extremely useful for maneuvering within their complex environment.
Primates extensively rely on their keen eyesight and color vision. Color vision helps primates detect ripe fruits and vegetation.
Primates have a skeletal structure, called a postorbital closure, which forms a bony cup around each eye. The closure helps protect primates' foremost sense—vision.
The sense of smell is not as keen as other senses, such as vision, for diurnal (active during the day) primates. However, it still plays a role in reproduction, communication, and food evaluation in most primate species.
In general, smaller primate species hear higher frequencies than larger species. Great apes and humans have reduced high—pitch detection, but better discrimination of sounds in the middle of the hearing range. It was once thought reduced high—pitch detection of primates was an adaptation for speech. It is now thought to have diminished due to the absence of selective pressure to hear high frequencies.