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Chapter I: Uniqueness of the Human Mind >> Definition of the human mind

Definition of the Human Mind

“Abstract thinking” does not provide a good definition of human uniqueness

What is the definition of the human mind? Scientists are remarkably clever in describing human consciousness. In a recent article on human consciousness published in Scientific American I counted over 20 definitions of human consciousness, including: “we know it when we see it” and the “presence of abstract thinking”. The “presence of abstract thinking” is most commonly used to identify uniqueness of the human mind. However, there is no clear definition of abstract thinking. Abstract thinking is often defined as a quality that is uniquely human. This is circular reasoning.

When abstract thinking is defined in more rigorous terms as “the process of generalization by reducing the information content of a concept or an observable phenomenon”, it stops being a unique quality of the human mind. It can be argued that Vervet monkeys of East Africa have concepts of a leopard, snake, eagle, and baboon. The warning calls sounded by monkeys do not describe any one specific animal. These calls describe a class of animals. Therefore these calls are abstracted from a specific object and may hypothetically qualify for abstract thinking. (See Griffin, 2001 for in depth discussion of this and many other animal mind issues.)

Further, the experiments designed to test abstract thinking, in the same/different and matching-to-stimulus paradigm, found abstract thinking to be present in chimpanzees, orangutans, baboons, rhesus monkeys, dolphins, sea lions, parrots, pigeons, and other animals (e.g. Premack and Premack, 1983; Katz, 2002). In these experiments animals are trained to categorize objects into several categories (e.g. trees, flowers, faces, etc.). When animals are comfortable sorting objects in the training set, they are presented with novel stimuli (novel pictures of trees, flowers, and faces). Accurate categorization of novel stimuli means that the animal has learned an abstract rule that transcends the training set. For example, pigeons were trained to select objects that belong to a particular category by pecking with their beaks. Pigeons were able to discriminate among paintings by different artists. They were also able to group pictures into categories such as “trees” and “faces”. We are forced to conclude that either these experiments do not test abstract thinking or that abstract thinking is not unique to humans.

So what makes the human mind unique? To start the discussion, let us broadly classify properties of the human mind into four categories and then compare humans and animals within each category:

1. Speech and communication: humans can speak and understand spoken language.
2. Emotions: humans can be angry, hungry, scared, compassionate, etc.
3. Memory: humans can remember things they have seen (smelled, heard, touched) in the past. They can recreate in their mind images of things that they have seen (smelled, heard, touched) in the past.
4. Humans have the ability to imagine things that they have never seen before. Close your eyes and imagine an apple somewhere you have never seen it, for example on top of a whale. You have never seen an apple on top of a whale, however your mind was able to synthesize this new image. There is no name for the ability of the mind to synthesize new, never-before-seen images. I’d like to call this ability of the human mind “mental synthesis”.

Let us see how animals measure up to these four qualities of the human mind.

Human mind versus animal mind

1. Speech and communication

Ask a child: “what can humans do that animals cannot?” and you are likely get the following answer: “animals cannot talk”. In fact, this is incorrect. Many animals use sounds to exchange information over distances – primates, whales, dolphins, and birds are the most famous examples. Birds sing, whales whistle, dolphins use clicks and whistles, and chimpanzees combine grunts, gestures, postures and facial expressions to “talk” to other chimps in the wild.

Further, chimpanzees can be taught sign language and perform no worse than a three-year-old child. Do chimpanzees have a language? Well, maybe chimps do not have as much language as we humans do, but chimps can definitely exchange information between themselves. An interesting exercise is to study what kind of information can be exchanged. It turns out that chimps’ “words” in the wild primarily describe emotions. As noted, chimps have signs that indicate that they are excited, hungry, bored, or scared. When a chimp sees a leopard, the chimp vocalizes a loud alarm call meaning "danger, predator." When a food source is located, the chimps will often vocalize with loud calls to inform other chimps that food has been found.

As we discussed above, Vervet monkeys of East Africa sound different warning for a leopard, an eagle, a snake, and a baboon. Each of the warning calls results in a different reaction. It is true that monkeys cannot communicate the exact location of a predator, and whether or not it is headed in the direction of the group. However, that fact shall not bar us from concluding that animals can exchange meaningful information.

Finally, it can be argued that the calls used by Vervet monkeys to warn of a leopard, a snake, an eagle, and a baboon are in fact symbols for these predators. After all, these calls do not describe any specific animal. Monkeys do not have names for each particular leopard. They describe a class of animals just like humans use the word leopard to describe a class of animals. It is a symbolic representation of leopard just like a cup is a symbolic representation of class of vessels used for storing fluids. Thus, in a way, animals can use a symbolic language to exchange information.

We will compare animal language to human language in more detail below, but for now I hope I have convinced you that the mere existence of speech and communication, even existence of a symbolic language, cannot distinguish humans from animals.

2. Emotions

Ask any dog owner if his or her dog has emotions. You will hear an unambiguous answer: “Yes!“ Their dogs can be sad when the owner is leaving the house and visibly happy when the owner comes back. Animal emotions are well documented. As we discussed above, not only do chimpanzees have emotions, but they also have over 30 signs and vocalizations capable of describing those emotions to other chimps.

3. Memory

As we have already discussed above, chimps can outperform humans on particular short-term memory tests, and the long term-memory of humans is no match for many food-storing animals such as squirrels and Clark's nutcrackers. It is well known that animals can remember places, faces, as well as smell, touch, direction, and time. For example, mice perform well in spatial memory tests such as the Morris water maze. In the typical paradigm, a mouse is placed into a small pool of water which contains an escape platform hidden a few millimeters below the water surface. Visual cues, such as colored shapes, are placed around the pool in plain sight of the animal. The mouse swims around the pool in search of a platform (mice are not fond of swimming). The mouse's escape from the water reinforces its desire to quickly find the platform, and on subsequent trials the mouse is able to locate the platform more rapidly. This improvement in performance occurs because the mouse has learned and can remember where the hidden platform is located relative to the visual cues. After some practice, a mouse can swim directly to the platform from any point in the water maze.

A mouse swimming in a Morris Water Maze.

4. Mental synthesis

A classical experiment involves a dog holding a stick in its teeth. The dog is standing in front of a picket fence in which one vertical board has been removed. In order to receive food the dog needs to cross through the fence without dropping the stick. If an adult human was tested in this experiment, he or she would have no problem planning the passage through the fence: the human would solve the problem by imagining himself walking through the fence by turning his or her head until the stick is held vertically and fits through the opening. However, the naïve dog will keep hitting the fence with the stick, rotating its head back and forth until it accidentally finds a solution. This experiment suggests that the dog lacks the ability to visually plan the action in its mind. Once the dog figures out the correct position of a stick necessary to pass through the fence, it will remember the trick for life (Video 1.15).

Another classical experiment involves a chimpanzee. A small opening in a watermelon is used to remove all the soft filling, and nuts are placed inside. The opening is so small that the chimp can fit its hand into the watermelon but not its fist. The chimp has no problem reaching the nuts, but cannot get its fist full of nuts back out of the watermelon. While an adult human would quickly be able to imagine a way to get the nuts out of the watermelon (for example by flipping the watermelon), the chimp will continue trying in vain to pull its fist full of nuts through the hole.

These two experiments demonstrate that animals are not capable of visually planning their actions in their mind. Since humans use mental synthesis to visually plan their actions, these experiments are an indication that animals may not be able to use mental synthesis. If so, mental synthesis could be a unique quality of the human mind. However before we discuss this question in more detail, we need a better definition and more examples of mental synthesis.