There is a subjective way you experience the world. This is way it is like for you to listen to Jazz, to look around curiously, or to taste dark chocolate. It is hard to know about what it is like for you to experience these things simply by observing your behavior. This phenomenal consciousness is what makes the mind-body problem hard.
Today and tomorrow, I will write about attention and phenomenal consciousness. Today’s post is about how attention is reflected in the structure of conscious experience. Tomorrow I will write about what this may tell us about the nature of consciousness.
Attention has often been discussed as related to the easier aspects of consciousness that concern mental functioning and not subjective experience. But attention also affects phenomenal consciousness. What it is like for you when you are listening to a Jazz piece depends on whether your attention is focused on the sound of the saxophone, on that of the trumpet, on the rhythm or on the subtleties of the melody. You will have one kind of conscious experience when you pay attention to the words you are reading, and a different kind of conscious experience when you begin to focus on the scenery outside. And your experience of the chocolate differs depending on whether you concentrate on tasting it or whether you quickly throw it in your mouth while all your attention is on getting some work done. How are we to explain the ways in which differences in attention are reflected in differences in consciousness?
One approach is to look at the way attention affects appearances: how it affects the way the music sounds, the way your environment looks, and the way the chocolate tastes. This approach has led to a rich, widely and controversially discussed, body of experimental evidence. Marisa Carrasco and her lab, for example, have studied how attention affects appearances along a number of dimensions. For example, they have studied the effect of attention on the apparent contrast of a Gabor patch. They find (or claim to find, as some controversy remains) that a 22 percent contrast Gabor patch at the focus of attention looks like a 28 percent contrast patch outside the focus of attention. Attention thus seems to boost apparent contrast by about six percent. This is not the only such effect: similar results are obtained with regard to apparent color saturation, apparent size, apparent speed, and apparent time of occurrence; the attended parts of ambiguous figures tend to look closer, edges get assigned to what is attended to, and attention enhances the spatial resolution of conscious vision, while it degrades its temporal resolution. And sometimes – but not always, as Carrasco’s experiments demonstrate! – you may not be able to see the gorilla at all, if your attention is focused on something else.
But is the way attention shapes consciousness exhausted by those effects on appearances? I don’t believe that it is, and indeed by focusing on those effects, we miss the most important contribution of attention to phenomenal consciousness. I offer two arguments for this conclusion.
First, the effects of attention on appearances are small (look again at this six percent difference), diverse (as I have suggested in the last paragraph), and sometimes surprising: who would, for example, have expected that attention decreases temporal resolution? But there seems to be a kind of unity to what it is like to focus attention on something, and an effect that is easy to detect from the first-person point of view. There is a kind of phenomenal prominence or experiential highlighting that is common between different cases of attention. This creates a phenomenal mismatch between the phenomenal unity and vividness of attention, and the diversity and rather obscure character of its effects on appearances.
Second, the effects of attention on appearances can always be replicated without attention. Instead of making the saxophone sound louder by turning attention to it (supposing that attention has that effect), simply turn up the volume of the saxophone mic! Instead of increasing apparent contrast with attention, just increase the contrast of the actual figure on the screen. And instead of increasing the spatial resolution of a figure through a covert shift of attention, just put that figure at the high-resolution center of your eye (the fovea) even while your attention is elsewhere. Generally, this replicability follows from what I call the worldly character of appearances: appearances concern how the world looks (or sounds) to the subject, and therefore no distinctive aspect of a subject’s mental life, like attention, is ever necessary for whether an experience instantiates such an appearance. From this it follows that it is possible to create an experience that replicates all the effects of attention on appearances, but does so with a different distribution of attention (maybe attention is fully diffused). But, I believe, many such appearance replicas feel different from the experience with the original distribution of attention. What it is like to focus attention on the saxophone isn’t at all what it is like to hear a loud saxophone while attentively listening to something else. There is a kind of internal stance we take with our focus of attention that cannot be outsourced to the world. For this reason, we can easily discriminate an attention episode from its replica from the first-person point of view.
But how else does attention affect phenomenal consciousness? Attention structures consciousness into center and periphery. William James puts this nicely:
… how false a notion of experience that is which would make it tantamount to the mere presence to the senses of an outward order… Without selective interest, experience is utter chaos. Interest alone gives accent and emphasis, light and shade, background and foreground – intelligible perspective, in a word.
Priority structures, as I argue, manifest in consciousness as phenomenal structure. Appearances concern phenomenal qualities that characterize the individual parts of your experience. But there is also a phenomenal manifestation of how those parts are put together: which part is central in experience, and which is in the periphery. The parts of experience are compared and connected by relations of relative peripherality and centrality.
Indeed, this manifestation in consciousness is part of what gives us a grip on the priority relations that I wrote about in my last posts. One way to connect phenomenal structure and priority structure is to think of our acquaintance with the former as what fixes (or at least constrains) reference to the latter: a priority relation is in part that relation, which we know of in consciousness.
Phenomenal structure, in my view, characterizes not only perceptual experience but also conscious thought. Like perception, conscious thought has parts. Different parts may be central in your experience of thinking that thought. Think of the difference between thinking that you will walk to the café (instead of taking your bicycle, as usual), and thinking that you will walk to the café (instead of walking to the bank, which you had originally planned). Conscious thought further, as William James again noted, tends to be accompanied by a “halo or penumbra” of mental images, feelings, and associations that “surround and escort” that thought. What it is like for you to think that thought indeed may be colored by those associations and feelings, and it may remain in a central position only because of this penumbra around it. Conscious thought, like perception, often has the form of theme and thematic field.
Phenomenal structure implies that experience is not, as David Hume thought, “a heap or collection of different perceptions”, which “may be consider’d as separately existent”. Peripherality relations cannot exist separately from what they relate, and what it is like to have an experience that is structured in these ways will not be exhausted by the combination of what it is like to experience all of its parts. The parts of the field of consciousness are enmeshed in attentional nets.
 See p. 161 of Structuring Mind for references.n
 This is compatible with the view that attention can occur unconsciously, just like a visual experience of the property of being oval might fix reference to that shape, even though there are some ovals we cannot see.
Repeating a word: as the brain receives (yellow), interpretes (red), and responds (blue) within a second, the prefrontal cortex (red) coordinates all areas of the brain involved. (video credit: Avgusta Shestyuk/UC Berkeley).
Recording the electrical activity of neurons directly from the surface of the brain, using electrocorticograhy (ECoG)*, neuroscientists were able to track the flow of thought across the brain in real time for the first time. They showed clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response to a perception.
Here’s what they found.
For a simple task, such as repeating a word seen or heard:
The visual and auditory cortices react first to perceive the word. The prefrontal cortex then kicks in to interpret the meaning, followed by activation of the motor cortex (preparing for a response). During the half-second between stimulus and response, the prefrontal cortex remains active to coordinate all the other brain areas.
For a particularly hard task, like determining the antonym of a word:
During the time the brain takes several seconds to respond, the prefrontal cortex recruits other areas of the brain — probably including memory networks (not tracked). The prefrontal cortex then hands off to the motor cortex to generate a spoken response.
In both cases, the brain begins to prepare the motor areas to respond very early (during initial stimulus presentation) — suggesting that we get ready to respond even before we know what the response will be.
“This might explain why people sometimes say things before they think,” said Avgusta Shestyuk, a senior researcher in UC Berkeley’s Helen Wills Neuroscience Institute and lead author of a paper reporting the results in the current issue of Nature Human Behavior.
For a more difficult task, like saying a word that is the opposite of another word, people’s brains required 2–3 seconds to detect (yellow), interpret and search for an answer (red), and respond (blue) — with sustained prefrontal lobe activity (red) coordinating all areas of the brain involved. (video credit: Avgusta Shestyuk/UC Berkeley).
The research backs up what neuroscientists have pieced together over the past decades from studies in monkeys and humans.
“These very selective studies have found that the frontal cortex is the orchestrator, linking things together for a final output,” said co-author Robert Knight, a UC Berkeley professor of psychology and neuroscience and a professor of neurology and neurosurgery at UCSF. “Here we have eight different experiments, some where the patients have to talk and others where they have to push a button, where some are visual and others auditory, and all found a universal signature of activity centered in the prefrontal lobe that links perception and action. It’s the glue of cognition.”
Researchers at Johns Hopkins University, California Pacific Medical Center, and Stanford University were also involved. The work was supported by the National Science Foundation, National Institute of Mental Health, and National Institute of Neurological Disorders and Stroke.
* Other neuroscientists have used functional magnetic resonance imaging (fMRI) and electroencephelography (EEG) to record activity in the thinking brain. The UC Berkeley scientists instead employed a much more precise technique, electrocorticograhy (ECoG), which records from several hundred electrodes placed on the brain surface and detects activity in the thin outer region, the cortex, where thinking occurs. ECoG provides better time resolution than fMRI and better spatial resolution than EEG, but requires access to epilepsy patients undergoing highly invasive surgery involving opening the skull to pinpoint the location of seizures. The new study employed 16 epilepsy patients who agreed to participate in experiments while undergoing epilepsy surgery at UC San Francisco and California Pacific Medical Center in San Francisco, Stanford University in Palo Alto and Johns Hopkins University in Baltimore. Once the electrodes were placed on the brains of each patient, the researchers conducted a series of eight tasks that included visual and auditory stimuli. The tasks ranged from simple, such as repeating a word or identifying the gender of a face or a voice, to complex, such as determining a facial emotion, uttering the antonym of a word, or assessing whether an adjective describes the patient’s personality.
Abstract of Persistent neuronal activity in human prefrontal cortex links perception and action
How do humans flexibly respond to changing environmental demands on a subsecond temporal scale? Extensive research has highlighted the key role of the prefrontal cortex in flexible decision-making and adaptive behaviour, yet the core mechanisms that translate sensory information into behaviour remain undefined. Using direct human cortical recordings, we investigated the temporal and spatial evolution of neuronal activity (indexed by the broadband gamma signal) in 16 participants while they performed a broad range of self-paced cognitive tasks. Here we describe a robust domain- and modality-independent pattern of persistent stimulus-to-response neural activation that encodes stimulus features and predicts motor output on a trial-by-trial basis with near-perfect accuracy. Observed across a distributed network of brain areas, this persistent neural activation is centred in the prefrontal cortex and is required for successful response implementation, providing a functional substrate for domain-general transformation of perception into action, critical for flexible behaviour.
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