Killer whales have a well-developed, acute sense for hearing underwater. A killer whale's brain and nervous system appear physiologically able to process sounds at much higher speeds than humans, most likely because of their echolocation abilities.
Soft tissue and bone conduct sound to a toothed whale's middle and inner ears. In particular, fat lobes in the whale's lower jaw appear to be an adaptation for conveying sound to the ears.
Killer whale vision is well developed.
The strongly convex (spherical) lens of a marine mammal differs from that of a land mammal.
In the eye of a land mammal, the cornea focuses light rays toward the lens, which further focuses the light rays onto the retina. Underwater, the cornea isn't able to adequately focus waves into the lens because the refractive index of water is similar to that of the interior of the eye.
The eye of a marine mammal compensates for this lack of refraction at the cornea interface by having a more strongly spherical lens. It is more similar to the lens of a fish's eye than the lens of a land mammal's eye.
In air, a marine mammal's eye compensates for the added refraction at the air-cornea interface. At least in bright light, constricting the pupil helps, but it doesn't fully explain how a whale achieves visual acuity in air. Research is ongoing.
DNA analysis of several other species of toothed whales indicated that the eyes of these whales do not develop pigment cells called short-wave-sensitive (S-) cones, which are sensitive to blue light. Researchers theorize that all modern cetaceans, including killer whales, lack these visual pigments and therefore aren't able to discriminate color in the blue wavelengths.
Behavioral evidence suggests that bottlenose dolphins, a closely related species, can detect three if not all four primary tastes. The way they use their ability to "taste" is unclear.
Scientists are undecided whether dolphins have taste buds like other mammals. Three studies indicated that taste buds may be found within 5 to 8 pits at the back of the tongue. One of those studies found them in young dolphins and not adults. Another study could not trace a nerve supply to the taste buds. Regardless, behavioral studies indicate bottlenose dolphins have some type of chemosensory capacity within the mouth.
Olfactory lobes of the brain and olfactory nerves are absent in all toothed whales, indicating that they have no sense of smell. Being air-breathing mammals that spend a majority of time under water, a sense of smell would go largely unused in killer whales.