My decade old hypothesis came true — consciousness in blindsight

 In attention, brain injury, consciousness, Neurology, neuroscience, Our latest work, subliminal, the brain, unconscious, unconscious processes

It is rare for a scientist to have one’s speculative ideas and hypotheses supported by others, and even more rare in one’s own lifetime. And when such a prediction is about the fundamental nature of our mind, then it is extra gratifying!

Often, many scientists — perhaps particularly in neuroscience — focus on hypotheses that can be tested during the next experiment. Since we know so little about the brain and the mind still, we have not yet had the chance to formulate larger, more coherent ideas about how the brain works — and let alone how it can produce a mind, and consciousness. Here, I want to share the joy of such a discovery, but also allow myself to indulge in a bit more about the background of the discovery, and why it is important.

A scale for consciousness

More than a decade ago I published one of my first papers. Entitled “Introspcection and subliminal perception”, it was co-authored with Prof. Morten Overgaard, and the paper was based on my MA thesis work on methods for studying consciousness. During this work, I discovered that most ways researchers tried to understand consciousness involved merely asking people bluntly whether they had experienced a stimulus or not. As in “Did you see it? Please answer yes or no.” Consciousness, it seemed, was already treated as an either-or phenomenon, and it was as if scientists had already made up their minds about the nature of consciousness.

Contrary to this, even everyday experiences suggested otherwise: instead of always being either fully conscious about something or being completely unconscious of something, we know that we have gut feelings, vague sensations and fleeting thoughts that can barely be called “conscious.” Indeed, I think you’ll agree that if pressed to answer whether these experiences are conscious or not, many times you would possibly call them unconscious.

But this is a problem of the measuring stick we were using, and not your experiences as such. Indeed, since many studies used this method, it was even likely that we were missing the goal of understanding consciousness by a mile or two. So instead, I suggested that we should change the measuring stick.

The first phase was to rethink the way we asked the questions. Some people suggested asking participants how certain they were about their report — but certainty and consciousness are merely the same thing. In many such typical experiments, participants were asked to watch something being presented for a brief time on a screen, and report whether they saw it or not, and then guess what had been shown. Indeed, when reporting using an either-or score, we would make some strange observations: when people stated that they did not see anything, they were still better than chance levels at guessing what had been presented. It was as if the mind could still perceive the stimulus, although it didn’t reach conscious thought. This led to the birth of the concept subliminal perception.

Different types of measures were used, including yes/no, certainty, and even wagering on one’s choice — that is, betting on one’s guess. But they all retained the same view that consciousness was an either-or phenomenon. Here, I begged to differ. We allowed people to use a more graded scale — sometimes even invent their own scale — to describe their experiences. The scale was named the Perception Awareness Scale (or PAS). What we found showed that decades of research on subliminal perception could be wrong! That is, we saw that:

  • when people said that they had no experience of a briefly shown stimulus, they were NOT better than chance at guessing what was shown
  • only when they had a vague glimpse of something being shown, they were better than chance at guessing. It still felt like just guessing, but they still had a vague feeling of something being shown

This finding, which has been replicated many times, shows us that in part subliminal perception is not as straightforward as one would normally think. Instead of being completely unconscious about a stimulus, it rather seems that better than chance guessing requires us to have some kind of experience of the stimulus.

Vague feelings and residual consciousness

Indeed, prominent early thinkers and practitioners in psychology had already thought otherwise. For example, one of the founders of modern psychology, William James, introduced the concept of “fringe” experiences. That is, experiences that were neither fully conscious or unconscious, but fleeting images, thoughts or impressions. Decades later, researchers like Bruce Mangan deepened our understanding of this by dividing between sensory fringes (those feelings that were caused by our senses, such as a barely noticeable wind on your arm), and non-sensory fringes (like the eerie feeling of knowing someone or something, but without having access to the full memory).

In neuroscientific research, studies by Zeki and Ffytche made some substantial observations. These researchers studied blindsight — patients that are blind due to a lesion to their primary visual cortex, but still demonstrate preserved functions in the blind field in blindsight patients. Indeed, When subjected to damage to the primary visual cortex, people will not be able to see stimuli presented to certain areas of the visual field. At the same time, evidence has been accumulating that such “hemianopic” patients (and monkeys) possess wide-ranging residual visual capacities or ‘blindsight’ in the blind part of their visual field.

The black region marks the blind region of the visual field. One has the patient do a series of forced-choice trials. One presents a light on half the trials, and forces the subject to guess on each trial whether or not the light has been presented. Numbered insets indicate percent correct. There is near-chance (43% correct) performance when the light was flashed in the blind spot (labeled "Disc"). However, performance was well above chance for all other positions within the blind region. As far as the subject is concerned, none of the lights were seen, although for some positions he had a non-visual feeling that something happened (hatched area). This non-visual awareness of a visual stimulus has been described by subject GY as "The nearest I ever get, and it is not a fair comparison, is waving your hand in front of your eyes when they are closed. You are kind of aware that something happened but you don't quite see it."

The black region marks the blind region of the visual field. One has the patient do a series of forced-choice trials. One presents a light on half the trials, and forces the subject to guess on each trial whether or not the light has been presented. Numbered insets indicate percent correct. There is near-chance (43% correct) performance when the light was flashed in the blind spot (labeled “Disc”). However, performance was well above chance for all other positions within the blind region. As far as the subject is concerned, none of the lights were seen, although for some positions he had a non-visual feeling that something happened (hatched area). This non-visual awareness of a visual stimulus has been described by subject GY as “The nearest I ever get, and it is not a fair comparison, is waving your hand in front of your eyes when they are closed. You are kind of aware that something happened but you don’t quite see it.” From http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/attention/attention.html

During their research, Zeki and Ffytche made some very interesting observations: patients who had “blindsight” did not always report being completely blind. Instead, such patients can sometimes report that they still had vague experiences of something being present. They could name it “like a mouse under a blanket” and “it’s not a something, but not a nothing either.” Zeki and Ffytche named the phenomenon the Riddoch syndrome, after a military doctor who in 1917 claimed that soldiers suffering from damage to the primary visual cortex still had vague feelings of
stimuli presented to their blind visual field.

Riddoch himself was ridiculed for these suggestions by leading neurologists at his time., but his work was supported by work decades later by Zeki and Ffytche. In their paper, they describe the study of a patient, G.Y., who was hemianopic after a lesion to the primary visual cortex (area V1). Typically, G.Y claimed to have vague feelings of stimuli presented to his blind visual field, comparing this to moving his hand in front of his eyes while they are closed.

The claim and the support

However, Zeki and Ffytche did not use a systematic way of studying consciousness, and used a rating scale that conflated subjective experience and confidence. As above, these two measures do not go naturally hand in hand. So, in my 2004 paper, Overgaard and I invented the PAS — an approach to allow participants to rate and rank their experiences, rather than their confidence about their guesses. The original paper has now (by today’s count) been cited by 139 scientific papers, and it has been used to study the nature of consciousness, in psychiatry and neurology, in studying the brain bases of the mind, and even how brands are perceived.

In that original paper, we made the relatively bold prediction that blindsight actually is NOT blindsight. In fact, we contended that it was a measurement error, because researchers were using the either-or measure of consciousness. So, we suggested, if “blindsight” patients were allowed to use the PAS, then we would possibly find that they were not in fact completely blind. Instead, we would possibly see that to be better than chance at guessing that something was shown in their “blind” field, it would only happen when they had a vague fringy feeling that something was present, and NOT when they reported being completely unconscious about the stimulus.

And indeed, this is exactly what a team of researchers have now found! In their paper in Frontiers in Psychology, researchers Mazzi, Bagattini and Savazzi show that better than chance guessing depended on a minimum level of consciousness. Here is an excerpt from the abstract:

A hemianopic patient (SL) with a complete lesion to the left primary visual cortex was tested. SL was asked to discriminate several stimulus features (orientation, color, contrast, and motion) presented in her impaired visual field in a two-alternative forced-choice task. SL had to report her subjective experience: in the first experiment as “seen” or “guessed,” whereas in the second experiment as the degree of clarity of her experience according to the perceptual awareness scale. In the first experiment, SL demonstrated a performance above-chance in the discrimination task for “guessed” trials, thus showing type 1 blindsight. In the second experiment, however, SL showed above-chance performance only when she reported a certain degree of awareness, thus showing that SL’s preserved discrimination ability relies on conscious vision. These data show that graded measures to assess awareness, which can better tap on the complexity of conscious experience, need to be used in order to differentiate genuine forms of blindsight from degraded conscious vision.

The crazy implication of this support for my original claim is wonderfully summarised by the authors at the very end of the paper:

(…) the present paper reports additional evidence of a patient with a complete lesion to V1 who, nonetheless, retains some kind of awareness of the stimuli presented to her impaired visual field, thus implying that V1 is not necessary for visual awareness, despite its importance for normal vision (…)

In other words: although the primary visual cortex is necessary for a rich visual experience, it is NOT necessary for visual awareness/consciousness. What this tells us is an important part of the mind and the brain: primary sensory areas are not the crucial part for being conscious. Instead, these regions are important for the richness in content of our experiences. When these regions are gone, we are left with a dimnished, poorer experience of the world, but nevertheless an experience as such.

Being able to nail down some of the crucial aspects of how our minds work, and how the brain creates the mind, is extremely gratifying, even a decade after the original claim was made 😉

 

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