The pleasure machine argument is flawed for a number of reasons:
1) It assumes that, despite having never been inside the pleasure machine, but having lots of experience of the world outside of it, you could make an unbiased decision about whether to enter the pleasure machine or not. It's like asking someone if he would move all his money from a bank he knows a lot about to a bank he knows basically nothing about and that is merely claimed to make him richer than his current bank. I'm sure that if someone would build a machine that, after I stepped into it, actually made me continually very, very much happier than I've ever been, it would have the same effect on me as very heavy paradise drugs have on people: I would absolutely want to stay inside the machine for as long as I could. For eternity, if possible. I'm not saying it would be a wise decision to step into the pleasure machine, (see point 2, 3 and 4 below), but after having stepped into it, I would probably want to stay there for as long as I could. Just as this choice might be considered biased because my experience of the pleasure machine can be said to have made me "unhealthily addicted" to the machine, you are just as biased in the other direction if you have never been inside of it. It seems most people have only a very vague idea about how wonderful it would actually feel to be continually super happy, and this makes them draw unfair conclusions when faced with the pleasure machine argument.
2) We know that "pleasure machines" either don't yet exist at all, or, if they exist, have so far always seemed to come with too high a prize in the long run (for example, we are told that drugs tend to create more pain than pleasure in the long run). This makes us spontaneously tend to feel sceptical about the whole idea that the pleasure machine suggested in the thought experiment would actually give its user a net pleasure increase in the long run. This skepticism may never reach our conscious mind, it may stay in our subconscious, but nevertheless it affects our attitude toward the concept of a "pleasure machine". The concept of a pleasure machine that actually increases pleasure in the long run is a concept that never gets a fair chance to convince us on its own merits before we subconsciously dismiss it because we know that if someone claimed to have built such a machine in the real world, it would most likely be a false claim.
3) Extreme happiness tends to make us lose control of our actions. Giving up control of our actions usually decreases our chances to maximize our pleasure in the long run, so this further contributes to make the pleasure machine argument unfair.
4) If all human beings stepped into pleasure machines and never got out of them, there would be no more development (by humans): If instead some or all humans continue to further the tech development and further expand in universe, it will be possible to build even better pleasure machines later on, than the pleasure machine in the thought experiment. There will always be a trade-off between "cashing in" (by using some time and other resources to build and stay in "pleasure machines") and postponing pleasure for the sake of tech development and expansion in order to make possible even greater future pleasure. The most pleasure-maximizing such trade-off may very well be one that doesn't include any long stays in pleasure machines for the nearest 100 years or so. (At some point, we should "cash in" and enjoy huge amounts of pleasure at the expense of further tech development and expansion in universum, but that point may be in a very distant future.)
Related: Not for the Sake of Happiness (Alone), Value is Fragile, Fake Fake Utility Functions, You cannot be mistaken about (not) wanting to wirehead, Utilons vs. Hedons, Are wireheads happy?
When someone tells me that all human action is motivated by the desire for pleasure, or that we can solve the Friendly AI problem by programming a machine superintelligence to maximize pleasure, I use a two-step argument to persuade them that things are more complicated than that.
First, I present them with a variation on Nozick's experience machine,1 something like this:
Most people say they wouldn't choose the pleasure machine. They begin to realize that even though they usually experience pleasure when they get what they desired, they want more than just pleasure. They also want to visit Costa Rica and have good sex and help their loved ones succeed.
But we can be mistaken when inferring our desires from such intuitions, so I follow this up with some neuroscience.
Wanting and liking
It turns out that the neural pathways for 'wanting' and 'liking' are separate, but overlap quite a bit. This explains why we usually experience pleasure when we get what we want, and thus are tempted to think that all we desire is pleasure. It also explains why we sometimes don't experience pleasure when we get what we want, and why we wouldn't plug in to the pleasure machine.
How do we know this? We now have objective measures of wanting and liking (desire and pleasure), and these processes do not always occur together.
Moreover, these animal liking expressions change in ways analogous to changes in human subjective pleasure. Food is more pleasurable to us when we are hungry, and sweet tastes elicit more liking expressions in rats when they are hungry than when they are full.4 Similarly, both rats and humans respond to intense doses of salt (more concentrated than in seawater) with mouth gapes and other aversive reactions, and humans report subjective displeasure. But if humans or rats are depleted of salt, both humans and rats react instead with liking expressions (lip-licking), and humans report subjective pleasure.5
Luckily, these liking and disliking expressions share a common evolutionary history, and use the same brain structures in rats, primates, and humans. Thus, fMRI scans have uncovered to some degree the neural correlates of pleasure, giving us another objective measure of pleasure.6
As for wanting, research has revealed that dopamine is necessary for wanting but not for liking, and that dopamine largely causes wanting.7
Now we are ready to explain how we know that we do not desire pleasure alone.
First, one can experience pleasure even if dopamine-generating structures have been destroyed or depleted.8 Chocolate milk still tastes just as pleasurable despite the severe reduction of dopamine neurons in patients suffering from Parkinson's disease,9 and the pleasure of amphetamine and cocaine persists throughout the use of dopamine-blocking drugs or dietary-induced dopamine depletion — even while these same treatments do suppress the wanting of amphetamine and cocaine.10
Second, elevation of dopamine causes an increase in wanting, but does not cause an increase in liking (when the goal is obtained). For example, mice with raised dopamine levels work harder and resist distractions more (compared to mice with normal dopamine levels) to obtain sweet food rewards, but they don't exhibit stronger liking reactions when they obtain the rewards.11 In humans, drug-induced dopamine increases correlate well with subjective ratings of 'wanting' to take more of the drug, but not with ratings of 'liking' that drug.12 In these cases, it becomes clear that we want some things besides the pleasure that usually results when we get what we want.
Indeed, it appears that mammals can come to want something that they have never before experienced pleasure when getting. In one study,13 researchers observed the neural correlates of wanting while feeding rats intense doses of salt during their very first time in a state of salt-depletion. That is, the rats had never before experienced intense doses of salt as pleasurable (because they had never been salt-depleted before), and yet they wanted salt the very first time they encountered it in a salt-depleted state.
Commingled signals
But why are liking and wanting so commingled that we might confuse the two, or think that the only thing we desire is pleasure? It may be because the two different signals are literally commingled on the same neurons. Resarchers explain:
Conclusion
In the last decade, neuroscience has confirmed what intuition could only suggest: that we desire more than pleasure. We act not for the sake of pleasure alone. We cannot solve the Friendly AI problem just by programming an AI to maximize pleasure.
Notes
1 Nozick (1974), pp. 44-45.
2 Steiner (1973); Steiner et al (2001).
3 Grill & Berridge (1985); Grill & Norgren (1978).
4 Berridge (2000).
5 Berridge et al. (1984); Schulkin (1991); Tindell et al. (2006).
6 Berridge (2009).
7 Berridge (2007); Robinson & Berridge (2003).
8 Berridge & Robinson (1998); Berridge et al. (1989); Pecina et al. (1997).
9 Sienkiewicz-Jarosz et al. (2005).
10 Brauer et al. (2001); Brauer & de Wit (1997); Leyton (2009); Leyton et al. (2005).
11 Cagniard et al. (2006); Pecina et al. (2003); Tindell et al. (2005); Wyvell & Berridge (2000).
12 Evans et al. (2006); Leyton et al. (2002).
13 Tindell et al. (2009).
13 Aldridge & Berridge (2009). See Smith et al. (2011) for more recent details on commingling.
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