Is Our Experience a Construction of the Apparatus of our Brain?

1. “Color phi.” If two closely spaced dots are alternately and briefly lighted in rapid succession, a single spot is seen to move between the two. If the two spots are different colors, a moving spot is seen that suddenly changes its color at the halfway point. (The two spots are lit for 150 msec each, with a 50 msec gap between them.)

How do we know suddenly to change the color before the second flash occurs?

2. The “cutaneous rabbit". A person’s arm is mechanically tapped in different places (e.g. 5 taps on the wrist, then 2 near the elbow, then 3 more on the upper arm). The person reports that the taps seem to travel in a regular sequence over equally spaced points up the arm, as if a little animal were hopping along the arm.  (Nasa diagram)

How do we know that after the 5 taps on the wrist, there were going to be some taps near the elbow?  (If only the wrist is tapped then all of the taps are felt at the wrist.)


3. A person’s left cortex is stimulated before his left hand is stimulated. We expect that he will feel two tingles: first his right hand (cortically induced), and then his left hand (due to the additional distance, close to a meter, the nerve impulses must travel from the hand to the brain.) In fact, however, the person reports exactly the opposite: "first left, then right."

4. Subjective delay of consciousness of intention. A person is asked to make a "spontaneous" decision to flex one hand at the wrist while noting the position of a clock. The reported time of the conscious decisions lagged up to 350 - 400 msec behind the onset of a "readiness potential" recorded from scalp electrodes.

Diagram adapted from Carver, Rita,
Exploring Consciousness

5. “Precognitive carousel.” A person looks at slides and presses a button when she wants to see the next. The button is a fake - what moved the slides was electrical activity in the brain’s cortex. Subjects reported that they were surprised when the slides moved just as they were "about to" push the button.
6. A person is instructed to push a button upon feeling a touch upon his arm. 200 msec after being touched, the person pushes the button, then apologizes for accidentally pushing the button. Due to normal reaction time, he pushed the button 200 msec after being touched. But 300 msec later, his brain’s sensory cortex was electrically stimulated to mask the conscious perception of the touch. He responded properly to a stimulus he did not perceive.

Does decision-making occurs prior to consciousness with conscious intent at most having an "executive veto" role in decision making? (Note: the “veto” has its own readiness potential!)

How does the brain’s apparatus construct our conscious experience? See Dennett and Kinsbourne for their two models:

The Cartesian Theater (CT). All sensory information converges to one point in the brain from which our stream of consciousness is generated.

The Multiple Drafts Model (MDM). There is no central point. Localized discriminations in different areas of the brain are not represented for a more central discriminator (thus avoiding a homunculus). Our stream of consciousness is a number of parallel streams of conflicting and continuously revised contents (drafts) where no single one is the true version. Also the objective temporal properties of particular states do not necessarily determine the temporal properties of subjective experience.

What does this have to do with free will?

In Mapping the Mind, Rita Carver states, “When we look inside the brain we see that our actions follow from our perceptions and our perceptions are constructed by brain activity. In turn, that activity is dictated by a neuronal structure that is formed by the interplay of our genes and the environment.”


Carver, Rita, Mapping the Mind, University of California Press, 1998.

Carver, Rita, Exploring Consciousness, University of California Press, 2002.

Dennett, Daniel and Kinsbourne, Marcel, “Time and the Observer: The Where and When of Consciousness in the Brain,” in Behavioral and Brain Sciences (1996) [available at ]

Dennett, Daniel, Consciousness Explained, Little Brown & Company, 1991.

Gazzaniga, Michael S., The Mind’s Past, University of California Press, 1998.

Gazzaniga, Michael S., "The Split Brain Revisited," Scientific American, July 1998.

Kornhuber, H. H., "Cerebral Cortex, Cerebellum, and Basal Ganglia: An Introduction to Their Motor Functions," in The Neurosciences, Third Study Program, eds. F. O. Schmitt and F. G. Worden (Cambridge, Mass.: Massachusetts Institute of Technology, 1973), pp. 267-80.

Pickover, Clifford A., Time: A Traveler’s Guide, Oxford University Press, 1998.

Return to Honors PS1500 home page

Last modified:  Wednesday, February 07, 2007 06:24 PM