![]() (Rod cells respond to lower light levels than cone cells.) Researchers theorize that all modern cetaceans, including all toothed whales, lack S-cone cells and therefore aren't able to discriminate color in the blue wavelengths.īehavioral studies have suggested they might have some color vision. Without this adaptation, a dolphin would be nearsighted in air.Ī dolphin's retinas contain both rod cells and cone cells, indicating that they may have the ability to see in both dim and bright light. In air, certain features of the lens and cornea correct for the refraction of light caused by the transition from aquatic to aerial vision.There is currently no reference that measures distance of visual capability. Studies show that the visual acuity of dolphins is similar or below the range of many terrestrial animals. Their eyes are adapted to mitigate varying light intensities. Bottlenose dolphins have a double slit pupil allowing for similar visual acuity in air and water.A dolphin's eye is particularly adapted for seeing under water. Humans and most land mammals cannot effectively localize sounds under water.Įars, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps).ĭolphins have acute vision both in and out of the water. This separation of the ears allows a dolphin to localize sound, which is important for echolocation. Ligaments hold each ear in a foam-filled cavity outside the skull. In dolphins, ears aren't attached to the skull.In particular, fat lobes in a toothed whale's lower jaw appear to be an adaptation for conveying sound to the ears. Soft tissue and bone conduct sound to a dolphin's middle and inner ears.They lead to reduced ear canals that are not connected to the middle ears. A dolphin's small external ear openings don't seem to be important in conducting sound.This is well within a dolphin’s range of hearing. Human speech falls within the frequency band of 100 to 10,000 Hz (0.1 to 10 kHz), with the main, useful voice frequencies within 300 to 3,400 Hz (0.3 to 3.4 kHz). The range of hearing of a young, healthy human is 15 to 20,000 Hz (0.015 to 20 kHz).The average hearing range for humans is about 0.02 to 20 kHz. In other studies, the hearing range for the bottlenose dolphin has been measured in 75 to 150,000 Hz (0.075 to 150 kHz). Bottlenose dolphins hear tones with a frequency up to 160 kHz with the greatest sensitivity ranging from 40 to 100 kHz.In addition, a dolphin's auditory nerve supply is about three times that of humans - possibly providing more ultrasonic information to a dolphin's central nervous system for echolocation. The dolphin's auditory nerve is about twice the diameter of the human eighth nerve (connecting the inner ear to the brainstem) leading to more rapid sound processing for dolphins.The auditory cortex of the brain is highly developed.It would be improper to attempt to quantify or qualify the intelligence of animals using only human guidelines.ĭolphins have a well-developed, acute sense of hearing. In fact, a reliable and consistent intelligence test for humans has yet to be developed. Rating the intelligence of different animals is misleading and extremely subjective. The ability of an animal to process information is based upon its brain anatomy as well as the specific experiences the animal has. Hypotheses that large brain size in dolphins indicates high intelligence are untested and disputed. One likely theory is that a larger brain size in dolphins may be at least partially due to an increased size of the auditory region to facilitate sound processing. Scientists are still determining what aquatic adaptations require the large brain size. Bottlenose dolphin brains are larger than many other mammals of the same body size. Comparisons of mammal brains are described as the ratio of brain size relative to body size.
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