God Soul Mind Brain

including the contents of your own awareness.

    Spatial neglect is often described as a problem of paying attention to the left side of space. Yet I have described it here as a loss of awareness of the left side of space. What is the relationship between awareness and attention? A great deal is now known about visual attention, about the neuronal machinery that underlies it. A beautifully simple framework called “biased competition” was worked out by a group of scientists led by the neuroscientist Desimone. (Desimone is my big brother, scientifically speaking—he grew up in the same Princeton lab that I did, but ten years earlier.) In this framework, visual signals are in constant competition in the visual system. Suppose I am scanning a crowd for a friend. Should I concentrate first on the face in front of me or the one to my right? The visual stimuli compete within my visual cortex, each one struggling to gain the upper hand and quash the processing of other stimuli. This competition is biased by a range of incoming signals. If I choose to look to my right, that motor plan may provide a bias, causing the visual stimuli on my right to win the competition. If an object suddenly lunges at me, the salience of the stimulus will bias the competition in its favor and cause that signal to win. If I choose to look for a face with a red cap, that choice will bias the competition toward some visual stimuli and against others. Essentially, when I attend to a particular visual stimulus, one visual signal has won the competition and is processed to the partial exclusion of other signals that have lost the competition.

    In this framework for understanding visual attention, there really is no “attention area” of the brain, no area that when damaged would cause a loss of attentional control. It is therefore not really correct to think of spatial neglect as a loss of the attention center for the left side of space. However, if cortical areas for social perception compute the property of awareness and attach that property to specific items, computing in effect “I am aware of X, I am aware of Y,” then this awareness signal presumably serves as a powerful biasing signal in the attentional competition. Damage the machinery for assigning awareness to anything on the left side of space, and you tilt the attentional competition hugely against the left side of space. Stimuli on the left side of space lose the competition and are minimally processed. In this view, the primary deficit in spatial neglect is a loss of awareness, a property computed by the social machinery; a consequence is a loss of attention.

Language

    Any circuitry in the brain that gives rise to consciousness must be closely related to the circuitry for language. Many computations in the brain are opaque to consciousness, but language is relatively available to consciousness. Moreover, whatever in the brain is conscious, it can understand when spoken to, and it can report on itself through language. Therefore we might look for a brain area that combines expertise at social perception with a close connection to language structures.

    The answer again is STP and TPJ. In humans, these areas in the left hemisphere of the brain lie directly beside the large cortical area involved in language comprehension. Language is an outgrowth of social interaction, a refinement of sending and receiving hints about mental states. The close proximity between the circuitry for social perception and for language therefore makes some engineering sense. Structures that need to interact are placed next to each other. In one speculation, through millions of years of human evolution, the social perceptual region on the left side of the brain expanded and part of it turned into the language comprehension area.

The automaton

    What would happen if all areas that underlie social perception were completely destroyed on both sides of the brain? Presuming the patient still retained the ability to speak and understand language, what functions would remain? (No such patients have been reported, and I sincerely hope none ever are.)

    Doctor: “What is your name?”

    Patient: “Bill.”

    Doctor: “Are you conscious?”

    Patient: “I’m sitting in a chair.”

    Doctor: “Being conscious means that you are aware. Are you aware of sitting in the chair?”

    Patient: “I’m sitting in it.”

    Doctor: “Am I aware of you?”

    Patient: “You’re sitting in another chair.”

    Doctor: