When someone points at a distant object, an observer understands that the pointer is looking at something and calling the attention of other to it. Pointing is often termed an "indicative gesture" and functions as a way of referring to an object or event (called "referential pointing"). In this sense, referential pointing functions similarly to a word. In the wild, chimpanzees have not been observed using pointing gestures to direct another's attention. In laboratory conditions featuring extensive contact with
humans, chimps can learn to use pointing to direct a human's attention to something desired, such as a piece of food or a place to go. Paradoxically, however, they fail to understand the human's intention when the human points at something. Thus, in one study the experimenter sat between two boxes, one of which contained food. The experimenter pointed at that box. The chimp chose that box reliably only when the experimenter's outstretched arm and hand almost touched the box. But when the experimenter moved away from the boxes by 3 meters or so, the chimp no longer reliably approached the indicated box. The chimp thus failed to understand referential pointing. We tested the dolphin's understanding of referential pointing by placing three objects, left, right, and behind the dolphin, each at approximately 3 meters distance. We could then refer to these objects by pointing at them or by using the gestural language symbols familiar to the dolphin. In each case, the dolphin was required to choose the referenced object and take the action to it indicated by a gestural symbol (e.g., leaping over it, swimming under it, touching it with the tail, etc.). For example, we can either sign Hoop Under using symbolic gestures, or we can point at the hoop and then give the gestural symbol Under. In either case, the dolphin understood to swim under the hoop. Surprisingly, the dolphin not only understood a direct point to an object with arm and finger extended, but also understood a cross-body point, in which the left arm is extended across the body to indicate an object to the right, or the right arm is extended across the body to indicate an object to the left. Moreover, sequences of points can be used to instruct the dolphin to take the object pointed to second to the object pointed to first, using the same inverse grammar as is used in the wholly symbolic language described earlier. The dolphin was equally adept at carrying out the instruction whether the two objects were referred to symbolically, or by pointing, or by some combination. Given the armless anatomy of the dolphin, it seems surprising that a dolphin would so easily understand the human pointing gesture, while chimps do not. Possibly, the dolphin understands because it uses an acoustic analog of pointing, its highly focused echolocation beam. One dolphin may in fact detect what another is inspecting through echolocation by listening to the echoes returning from the emitter's beam.
| The chimpanzee is able to choose reliably when the experimenter's hand is close to the object. || |
| The chimpanzee cannot choose reliably when the experimenter is further away. |
Herman, L.M., Abinchandani, S.L., Elhajj, A.E., Herman, E.Y.K., Sanchez, J.L., & Pack, A.A. (2000). Dolphins (Tursiops truncatus) comprehend the referential character of the human pointing journal. Journal of Comparative Psychology, 113(4), 347-364.
Herman, L. M. & Uyeyama, R. K. (1999). The dolphin's grammatical competency: Comments on Kako (1998). Animal Learning & Behavior, 27-18-23.
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