This series begins with The Machine in the Ghost
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The previous overview of motivation omitted discussion of the two most important factors that shape behavior in the more advanced animals, pain and pleasure. They are each a huge and open topic that deserves focused consideration. Both are extremely complex physiological phenomena that are entangled with the conscious experience of humans and other animals whose brains are sufficiently complex. The wooliness of these phenomena and the heavy philosophical and psychological baggage that comes with them make us want to avoid bringing pain and pleasure into the development of our artificial mind until we really find it necessary or at least important to do so. Nevertheless, that time is likely to arrive sooner or later, if our goal is an advanced artificial mind. Here, we will go no further than to briefly consider the field of answers to two large questions about pain and pleasure: "How do they work in motivating natural organisms?" and "Might they work similarly for artificial organisms?"
Natural Organisms
What Is Pain and What is Pleasure?
Pain and pleasure are important parts in the foundation of mind. Painful and pleasurable experiences are very immediate to our conscious selves, and their influence over our conscious and subconscious behavior can range from barely noticed aversions and urges to nearly absolute control. Crude attempts to manipulate the behavior of animals or other people through discomfort or enticement, the carrot and the stick, are surely as old as society itself. Nevertheless, the things we so easily call pain or pleasure remain very difficult to define operationally beyond simply saying that they are internal states that encourage or discourage actions. Indeed, pain and pleasure are such fundamental and complex subjective experiences that they may ultimately defy any attempt at sharp definition.
One dictionary tells us that pain is "physical suffering or discomfort caused by illness or injury; a feeling of marked discomfort in a particular part of the body." The International Association for the Study of Pain (IASP) defines pain with disappointing looseness as "An unpleasant sensory and emotional (conscious) experience associated with actual and potential tissue damage or described in terms of such damage." (here) If we consider even our own personal experiences of pain, it should be clear that any definition must be sufficiently broad to include several varieties of pain and their various ranges of degree. As a motivator, pain encourages behavior that lets us escape or cope with physical harm.
Pleasure is defined, with the same looseness, as 'a feeling of happy satisfaction and enjoyment' or a 'sensual gratification' by the dictionary. Pleasure seems to differ from pain in very basic ways. Whereas pain stimuli are transmitted from special sensing nerves to the spinal cord and brain, there seem to be no such specialized pathways for pleasure. Pleasure appears to be a more complex phenomenon than pain, originating higher in the neural hierarchy and associated with more complex behaviors driven by higher cognitive functions.
As a motivator, pleasure serves to encourage behavior that produces gain or satisfies basic homeostatic needs that are not necessarily associated with a present threat. Pleasures are associated with insufficiencies. We begin to feel mild hunger well before suffering the effects of malnutrition. Hunger intensifies over time until it is satisfied, but then ceases before becoming a disabling problem in itself. The satisfaction of hunger is a pleasure, yet while the degree of pleasure from eating is proportional to the hunger, we can be pleased by eating even when not particularly hungry. We can also be pleased by situations that are highly abstracted from particular needs, as when listening to music we like or when an interesting idea surfaces. The realm of pleasure seems to extend well beyond immediate necessity and even deeper into the complex web of the mind's psychological and social relations than does pain.
Pain, Pleasure and Consciousness
Our first understanding of pain and pleasure is experiential; we know them directly as conscious perceptions. Indeed, we may wonder whether pain and pleasure have any meaning or value outside of consciousness. Direct experience is also how we know other base motivational perceptions such as hunger, thirst and lust, which seem to connect to both pleasant and displeasant states that are at least analogs of pain and pleasure.
To fully understand and perhaps use these kinds of motivators that have conscious aspects, we must first pierce down through our conscious experience of them into the subconscious and define them first on a physiological level and then build on that base to extend into a psychology that is illuminated by the underpinning physiology.
Let's begin by thinking about the well–known knee–jerk reflex. This reflex works to the same effect that we attribute to pain; it is a detection and feedback mechanism that recognizes imminent damage to a body part and induces action to prevent the damage. However, there is no pain sensation associated with the knee–jerk. In fact the brain is not even involved in the process at all. What we are consciously aware of is only the aftermath of the reaction, which usually surprises us. We did not intend that leg to jerk. We didn't will it or even expect it to happen the first time.
Now consider a simpler animal, the leech. Do you think a leech experiences pain or pleasure? The nervous system of the leech has been studied quite thoroughly and the relations between nervous system function and the animals several aversion and seeking behaviors is well understood. If something touches a leech, it will begin a swimming behavior that may result in escape from attack. If something touches it near the head, it will contract and be still. If a leech finds a warm surface, it will explore for a feeding site. If its mouth–parts detect certain chemicals, it will begin a feeding behavior. Contradictory stimuli such as being touched while feeding result in more complex behavior that depends on factors such as state of hunger.
Are all of these behaviors simple mindless reflexes like our own knee–jerk, or can we attribute some very rudimentary conscious feelings of pain and pleasure to them? This question may remain arguable, but the simplicity of the leech nervous system supports the negative side of the argument. While nerves that operate with the same cell signaling chemistry as nociceptors, the pain neurons, have been found in the leech and other simple animals, there simply are no neural structures present in the animal that could support any sort of consciousness at all. At the very least, it is safe to say that any possible leech feeling of pain or pleasure must be insignificantly minor compared to the rich experiences provided by the mammalian brain. If we accept that the behavior of simple animals is fully unconscious reflex, then we can be encouraged in assuming that artificial organisms can at the very least be capable of similar complex animal–like behavior. So far, attempts to reproduce animal behavior in automatons have been limited to simple locomotion that does not try to emulate more complex aversion and seeking behaviors. (See lamprey robots and this video for examples.)
The most striking and clear evidence of the deep complexity of the human pain response comes from the results of a brain surgery performed to ease intractable pain. Before the procedure, the patient suffered nearly constant and severe facial pain. As related by Antonio Damasio in his book, Descartes' Error,
"I vividly recall the particular patient, sitting in bed waiting for the operation. He was crouched in profound suffering, almost immobile, afraid of triggering further pain. Two days after the operation, ... he was a different person. He looked relaxed, like anyone else, and was happily absorbed in a game of cards.... "
When asked about the pain, the patient said the pain was still there, just as before, but now it didn't bother him anymore. Same pain, but the suffering was gone. The important fact revealed by the patient's post–operative response to pain is that the conscious experience of pain is a composite thing rather than a pure, elemental thing. Pain is built up of layers, much like a Photoshop image. Even more importantly, each layer seems to be contributed by a different neural structure in the brain, spinal cord and peripheral nervous system. There is no simple correspondence between the triggering of nociceptors and the final conscious experience of pain. The pain signals that arrive at the brain stem are distributed to many places in the brain and the brain can send signals back down as far as the spinal cord to modulate the original signals. As a result, many other brain states affect the final conscious experience that we call pain.
Where do pain and pleasure enter in the evolution of organism complexity?
If we assume that consciousness requires some minimum level of complexity to support it, then we must look at the tree of life and wonder were on the branching lines of increasing complexity does conscious experience of pain and pleasure enter. Is there evidence that can help us decide? If the conscious feeling of pain and pleasure and other conscious perceptions have particular value in shaping behavior, then we should expect to see evidence of that in the behavior of animals and their success in nature, either as quantum steps or as a smoother progression of abilities that have no better explanation.
Pain and pleasure clearly do not extend in kind or degree in any linear and continuous way across the wide range of life from the simplest to the most complex of organisms. An amoeba does not feel pain. A leech very probably does not feel pain. Does a fish feel pain? A dog? It's easy to believe dogs feel pain much as we do for two reasons. First, a dog's reaction to evidently painful stimuli is similar to our own; second, a dog's brain and body structures are very similar to our own. The same similarities suggest that we share some aspects of the pleasure experience.
Can an artificial mind experience pain and pleasure? I believe most of us are strongly inclined to say 'no' to that idea. Our attitude toward this question, as well as the question's answer, is tied to the possibility of consciousness in an artificial organism. I hold this to be an open question.
The Process of Pain
Current neuroscience and psychology do not consider pain to occur locally at the neurons that detect injury; it is regarded as a subjective experience that arises in the higher brain. Pain begins with the stimulation of special types of nerve cells called nociceptors. Those nerves carry their signals to the spinal cord, which may immediately return a motor signal to the relevant muscles or other effectors (reflex), or first process the signal a bit and then send it to the brain, or simply send it directly on up to the brain. The pain signals that ascend the spinal cord enter the brain at the thalamus, which is the gateway and switchboard for almost all sensory input from the body.
The brain is not passive to pain; it modulates the sensory inputs it receives by sending signals back down the spinal cord to modify or even block the upward signals. Two areas of the brain that are involved in reducing pain are the periaqueductal gray body (PAG) and the nucleus raphe magnus. Neurosurgeons have implanted electrical stimulating electrodes near the PAG of some patients with severe pain – a small electrical shock through these electrodes can relieve pain in some patients" (See this). When pain signals arrive at the thalamus, many parts of the brain are notified and a lot of integrating and balancing of brain states takes place before the final conscious experience is constructed and the mind-body generates its active response.
The Process of Pleasure
Pleasure happens in a way very different from pain. While pain has very clear and specific sensory origins, pleasure can arise from many kinds of sensory stimulation. It can even arise from thoughts and memories, without any significant sensory stimulation at all. A slight running tickle on the side of your neck can be intensely pleasant if you believe it to be the gentle touch of a potential mate or it can be so unpleasant as to make you flail wildly to remove the bug you believe to be crawling there. Any of the senses can generate pleasure, but the pleasure seems to depend on a person's mental context. A sudden break-through solution to a difficult problem can produce a very pleasant state of excitement and eagerness, and even a memory can bring about a warm feeling of comfort and satisfaction. Pleasure seems to be about a release of tensions and expectations for future reward as well as immediate satiation.
The parts of the brain involved in the pleasure state are mostly located in the central, evolutionarily older structures deep in the brain and the brain stem. They include the 'dopamine reward system', a structure that extends from the raphe nucleus in the brain stem via the ventral tegmental area into the nucleus accumbens. The latter two organs send signals into the prefrontal cortex and have receptors for most of the drugs of abuse, including opioids, ethanol, barbituates, amphetamines, nicotine and cannabinoids. This brain system can be stimulated directly to produce insatiable states of pleasure that motivate animals to continually induce the stimulations. Normal functioning of the pleasure system typically involves satiation, in which the desire for a pleasure is reduced by the result of the behavior it encourages. It is thus self-limiting. Pleasure from food or sex, for example, decreases when the organism acts on the desire to achieve a goal. All other brain areas that can generate pleasure connect to this system.here Pleasure seems to be a greatly more complex process than is pain, and thinking of our own pleasure experiences surely confirms that.
What are the advantages?
What do the conscious phenomena of pain and pleasure bring to an organism that simpler, unconscious discouragement and encouragement mechanisms cannot? A summary of those advantages might divide them into present and future effects.
The present effect of pain to change our behavior when a condition harms us or is immediately about to harm us. It alerts us and discourages us from behavior that continues or worsens the pain (harm) in the immediate present, and thus allows us to minimize injury or avert it. For all but the slightest injuries, a different kind of pain, less intense but enduring, will continue beyond the initial hurt; such pain serves to keep our attention on the injury and reminds us take measures to prevent secondary injury or complications until healing is finished. Those are the present effects of pain. In creatures that have higher cognitive functions for learning, pain also serves to alter the future behavior of the organism with respect to the circumstance in which the injury occurred. A human child, and most likely any mammal, will learn to not touch a hot stove, usually from a single experience. Compare that to the many experiences needed to learn things that don't involve pain. Pain may be the basis for all of our negative emotions and the discouraging elements of our thinking. We chose to not do things because our feeling is that the result will produce a situation that we associate, perhaps very tenuously and subconsciously, with memories of pain.
Pleasure, on the other hand, has the immediate effect of encouraging behavior that satisfies some need, like eating, drinking and sex. Basically, it makes us do things that we really must do to survive as individuals and species, things that without pleasure we might not be bothered to do. What we call pleasure is very probably a rather complex bundle of feelings and body reactions. Nobody has really analyzed pleasure to anyone's satisfaction, although the huge amount of work being done on addiction is revealing many clues.
Pleasure is deeply involved in altering learning and future behavior in the same way as is pain. It seems to play a particular role in planning and the execution of plans. Plans are designed to achieve specific future goals whose achievement depends on our associating them with a complex mix of future pleasures of different and many kinds, which are often manifest as emotions. Working for future reward is quite different from immediate rewards such as performing sex. In sex, we have strong and increasing reward at almost every moment until the 'goal' is reached, upon which our body stops rewarding our actions. There is no moment-to-moment satisfaction from working toward a distant planned goal in many cases. You can take some degree of daily satisfaction from watching your house being built, for example, but something like a planned retirement involves very little present reward until it actually comes to be.
The future effects of pain and pleasure can be powerful and complex, and they may be fundamental to full-blown intelligence. In society, we very early learned that the association of pain and pleasure with behavior can be used to alter the behavior of individuals and groups of people. It begins with parents and children, but certainly doesn't end there. The carrot and the stick are used in any situation where there is more than one person.
The conscious experience of pain and pleasure and the emotions they engender may be necessary for organisms whose behavior is controlled to any extent by a consciousness that can override autonomous behavior. It is likely involved in prioritizing the many goals that stand simultaneously and lets the conscious self know what most needs action by focusing attention and limiting the subjects to which thought is applied.
Artificial Systems
In natural organisms, pain and pleasure provide survival benefits for highly complex systems, but they also provide a grounding for the development of emotions for high-level social behavior. We can easily see reflections of our own intimate experiences of pain and pleasure in others of our kind. That creates a deep sense of sameness that founds empathy and sympathy. Recognition that others like us feel pain and pleasure much as we do gives us a way to understand each other and a means of influencing the behavior of others in social situations.
We can hypothesize that pain and pleasure might serve artificial organisms in the same two ways. Pain and pleasure analogs should be considered when designing the architecture of the artificial mind for efficient goal–oriented behavior and self protection. For machine minds that will interact with humans and animals, experiential pain and pleasure are essential for understanding the natural organisms and their behavior. Such experience–grounded understanding is important for cooperation and essential for sophisticated interaction based on natural language.
The hypothesis that pain and pleasure found the emotions is an important idea to consider when we aim for a social artificial intelligence. It opens a door to practical realization of machine emotions and consciousness by suggesting that we can begin by implementing in an artificial system the lowest and most simple mechanisms that are the foundation of primitive pain and pleasure, and building incrementally upon that base as needs arise.
But do robots need pain? Does pleasure provide benefits that 'pure' rational intelligence cannot? Is it even possible for an intelligent machine to understand the conscious human experience well enough to communicate and function at high cognitive levels in a human environment without knowledge of pain and pleasure grounded in its own personal experience? It may turn out that rational intelligence alone can solve the problems that pain and pleasure have evolved to solve for natural organisms. I don't think so, but we shall see.
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