Invitation to Psychology

140 Chapter 4 Neurons, Hormones, and the Brain

reasonable explanation for the laughter (Gazzaniga,

1967). Indeed, Michael Gazzaniga (1989), the lead-

ing psychological scientist who did this and a lot of

other split-brain research, has called the left hemi-

sphere an “interpreter” that is continually provid-

ing a reasonable (though not always accurate) story

to explain our thoughts, feelings, and behaviors. As

another neuroscientist put it, the left hemisphere is

the brain’s spin doctor (Broks, 2004).

The Two Hemispheres:

allies or opposites?

The split-brain operation is still being performed,

although more rarely, now that better medica-

tions are available to treat severe epilepsy. Studies

on left–right differences have also been done

with people whose brains are intact (Hugdahl

& Westerhausen, 2010). Using the technologies

only seen the right side of the image, that was the

face it saw and reported. When patients pointed

with the left hand, which is controlled by the right

side of the brain, the right hemisphere was giving

its version of what it had seen.

In another study, the researchers presented

slides of ordinary objects and then suddenly flashed

a slide of a nude woman. Both sides of the brain

were amused, but because only the left side had

speech, the two sides responded differently. When

the picture was flashed to one woman’s left hemi-

sphere, she laughed and identified it as a nude.

When it was flashed to her right hemisphere, she

said nothing but began to chuckle. Asked what she

was laughing at, she said, “I don’t know ... noth-

ing ... oh—that funny machine.” The right hemi-

sphere could not describe what it had seen, but it

reacted emotionally just the same, and the talking

left hemisphere was compelled to come up with a

“Look at the center

The Rhythms of Sleep

(a)

(b) “Point to the person you saw.” Left hemisphere (c) Right hemisphere

Figure 4.11 Divided View

Split-brain patients were shown composite photographs (a) and were then asked to pick out the face they had seen

from a series of intact photographs (b). They said they had seen the face on the right side of the composite, yet they

pointed with their left hands to the face that had been on the left. Because the two cerebral hemispheres could not

communicate, the verbal left hemisphere was aware of only the right half of the picture, and the relatively mute right

hemisphere was aware of only the left half (c).

Get Involved! TaP, TaP, TaP

Have a right-handed friend tap on a paper with a pencil held in the right hand for one minute. Then have

the person do the same with the left hand, using a fresh sheet of paper. Finally, repeat the procedure,

having the person talk at the same time as tapping. For most people, talking will decrease the rate of

tapping—but more for the right hand than for the left, probably because both activities involve the same

hemisphere (the left one), and there is competition between them. (Left-handed people vary more in terms

of which hemisphere is dominant for language, so the results for them will be less predictable.)