(For previous posts in this series, see here.)

In post #6 in this series, I discussed the 1963 Grey Walter experiment in which patients who had electrodes implanted in their brain’s motor cortex that could send a signal to advance a slide were surprised that the projector seemed to anticipate their decision to advance the slide. Does this mean that their unconscious neural activity had decided to advance the slide before telling the conscious brain that it had decided to do so? If so, it seriously undermines the idea of free will. In his book Consciousness Explained (1991, p. 167) which discusses the experiment, Daniel Dennett warns that it is premature to accept this conclusion because it is based on the articulated sense of surprise reported by the patients, and the brain is not the most reliable of historians.

In the ‘multiple drafts’ model that Dennett suggests of how our brain works, the brain is not a recording and playback device that faithfully captures all that is going on around us. Instead, it is constantly creating different narratives to make sense of our experiences. These narratives are rapidly thrown into our consciousness and then disappear, to be replaced by new ones. The version that ‘sticks’ in our consciousness and become retained as the ‘true’ memory of what happened may not necessarily be the one that is the most faithful to the events as they actually happened.

The freedom to construct stories is not absolute, however, since our brain imposes some rules that restrict which narrative is selected as the ‘final’ one. For example, major sensory events have to be retained. If you definitely saw your friend Joan entered the room before your friend George, then the narratives will retain that order. But if you did not carefully note Joan’s facial expression as she entered, your narratives might vary with her looking happy or sad or angry depending on the need of the narrative.

The narratives that our brain constructs will also conform to our strong expectations (based on our prior experiences and learning) of how the world works and will not produce narratives in which, for example, people fly around because that would be going against what we strongly believe. If you stubbed your toe and felt pain, the narrative will not replace the pain with pleasure. However when we sleep, the brain enforcer also relaxes and so our dreams can be much wilder, though even there our senses impose some constraints. We have all experienced times when we were asleep and some sound that happened in our surroundings (a siren or telephone or door bell) seemed to be seamlessly woven into the narrative of our dreams. This is because of our brain’s ability to rapidly produce a narrative that incorporates any external reality.

We can think of the brain not as a scrupulous historian but as more like a highly imaginative, quick, and prolific writer of historical fiction. As with such authors, certain rules apply. There are certain anchoring events that cannot be changed (World War II must come after World War I, for example) but there are many things that are open for speculation because they are not firmly anchored by our senses or records or our memories or our understanding of how the world works, and the writer has great freedom to invent narratives that are plausible that connect the events that we are sure about. The version that is finally chosen to be published could well be based on idiosyncratic factors that have nothing to do with how accurate the story is about all these unanchored details.

This model of the brain also explains why our memories are so unreliable about some things and why we have the phenomenon of ‘false memory’. Witnesses to a crime turn out to be extraordinarily unreliable when reporting from memory on things that happened right before their eyes, which is why it is desirable to jot down notes at once for any thing that we want an accurate record of later.

I think all of us have experienced instances when something that we were sure happened in the past is challenged by someone who was also there (a relative or an old friend) who has a different recollection. What likely happened in such cases is that when we recounted that event, our brain picked out from all the narratives one that filled in all kinds of details that may not have happened but which made the story make sense or more interesting, and the repeated verbal recounting of these false events then became anchored so that all future narrative constructions treated these as incontrovertible facts, cementing them even further. Robert and Tamar Krulwich tell Ira Glass of This American Life an amusing story that perfectly illustrates how false memories can arise.

In the Grey Walter experiment, the brain expects to receive visual feedback (the slide advancing) on the successful execution of an act (pushing the button). The patients experience surprise when the feedback arrives earlier than expected. But does the feeling of surprise necessarily arise from the fact that (as the patients reported) the conscious thought to advance the slide came after the slide actually advanced?

The multiple drafts model gives us an alternative possibility. Because of our prior experiences, our unconscious brain is conditioned to know that effects do not occur instantaneously after causes. There is always a small time lapse involved in signals being sent and received though this may be so small that our conscious brain may see things as instantaneous. Because of this the unconscious brain expects feedback to occur after a certain minimal short time interval (say 300 ms) has elapsed after the decision to act. Any feedback that arrives before that time interval has elapsed may cause the unconscious brain to react in surprise, even though the cause may still precede the effect.

So it is quite possible that even if the slide advanced after the patient pushed the button and there was no seeming denial of free will or violation of causality, the unconscious brain still reacted with surprise because the time interval between the push and the slide advancing was less than expected. It is possible that the brain, always constructing narratives to make sense of things, might be ‘explaining’ its own sense of surprise by creating a fictional storyline in which the patient is made to think that the slide advanced before the decision was made, when in actual fact it is possible that the conscious thought did precede the act (thus maintaining the idea of free will) but by a time interval less than the expected one (thus causing the sense of surprise).

Grey Walter did not carry out follow up studies to investigate this question and it had to await the 1983 studies of Benjamin Libet.

Next: The famous and controversial Libet studies.