scientific american special edition - 2002 vol 12 no1 - the hidden mind

[...]... from the July 1998 issue COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC 27 Holtzman’s work was especially intriguing because it raised the possibility that there were finite attentional “resources.” He posited that working on one kind of task uses certain brain resources; the harder the task, the more of these resources are needed—and the more one half of the brain must call on the subcortex or the other hemisphere... front of the split-brain subject The left and the right hemispheres easily picked the correct card The left hand pointed to the right hemisphere’s choice and the right hand to the left hemisphere’s choice [see illustration at right] We then asked the left hemisphere, the only one that can talk, why the left hand was pointing to the object It did not know, because the decision to point was made in the right... University and I studied in many split-brain patients the perception of what are called illusory con- SCIENTIFIC AMERICAN THE HIDDEN MIND COPYRIGHT 2002 SCIENTIFIC AMERICAN, INC LAURIE GRACE Testing for Synthesis Looking for Illusions ILLUSORY CONTOURS REVEAL that the human right brain can process some things that the left cannot Both hemispheres can “see” whether the illusory rectangles of this experiment... becomes more specialized the farther the information moves along the visual pathway [see illustration on page 22] At the start of the pathway, images from the retina at the back of each eye are 20 channeled first to a pair of small structures deep in the brain called the lateral geniculate nuclei (LGN) Individual neurons in the LGN can be activated by visual stimulation from either one eye or the other but... to choose the most appropriate small picture As seen below, the right hemisphere— that is, the left hand— correctly picked the shovel for the snowstorm; the right hand, controlled by the left hemisphere, correctly picked the chicken to go with the bird’s foot Then we asked the patient why the left hand— or right hemisphere— was pointing to the shovel Because only the left hemisphere retains the ability... They are transient, lasting usually for only a fraction of a second Because coalitions in the visual system are the basis of what we see, evolution has seen to it that they form as fast as possible; otherwise, no animal could survive The brain is handi- the same part of the visual field The early visual system on the left side of the brain receives an input from both eyes but sees only the part of the. .. received exclusively by the right side This shows that none of the information required for visual awareness can reach the other side of the brain by traveling down to the brain stem and, from there, back up In a normal person, such information can get to the other side only by using the axons in the corpus callosum A different part of the brain— the hippocampal system— is involved in oneshot, or episodic,... visual field to the right of the fixation point The converse is true for the right side If these two conflicting inputs are rivalrous, one sees not the two inputs superimposed but first one input, then the other, and so on in alternation In the exhibit, called The Cheshire Cat,” viewers put their heads in a fixed place and are told to keep the gaze fixed By means of a suitably placed mirror, one of the eyes can... when the monkey’s percept is sometimes up and sometimes down? (The researchers studied only the monkey’s first response.) The simplified answer— the actual data are rather more messy— is that whereas the firing of some of the neurons correlates with the changes in the percept, for others the average firing rate is relatively unchanged and independent of which direc- When we clearly see something, there... field occupied by the face, the face is wiped out The movement of the hand, being visually very salient, has captured the brain’s attention Without attention the face cannot be seen If the viewer moves the eyes, the face reappears In some cases, only part of the face disappears Sometimes, for example, one eye, or both eyes, will remain If the viewer looks at the smile on the person’s face, the face may . attempting unwittingly to solve the movie-in -the- brain part of the conscious -mind problem for most of the history of the field. The en- deavor of mapping the brain regions in- volved in constructing the movie began almost. for the movie-in- the- brain. The idea of spectator is con- structed within the movie, and no ghost- ly homunculus haunts the theater. Objec- tive brain processes knit the subjectivity of the. we automati- cally generate a sense of ownership for the movie-in -the- brain. The two parts of the problem are related, with the latter nest- ed in the former. Separating them is a use- ful research