Science News - February 25, 2012

all, the two often go together: Focusing on a tart, crunchy bite of a Granny Smith makes the experience more tangible, enhancing your awareness of it. And when attention is diverted, obvious things escape detection — a slip called inattentional blindness. The most famous example comes from a study in which observers are asked to count the number of times a basketball is passed between people. Engrossed in the ball-watching, many viewers are oblivious to a man in a gorilla suit who ambles into the middle of the scene, beats his chest and ambles out.

Pay attention

But just because consciousness and attention are often linked doesn’t mean that they are the same thing. A gripping demonstration comes from a recent experiment’s subliminal spiders. Participants who were terrified of spiders watched a screen as pictures of a spider or an outdoor scene flashed for 20 milliseconds — a split second that many scientists think is too fast to detect. None of the subjects could report what was flashed, indicating that the people who saw the spiders were not conscious of them.

Later, the participants were asked
to walk into a room and touch a real
tarantula. People who were exposed to
the spider pictures got closer to the real
spider than those who saw the natural
scenes. The subliminal spiders desen-
sitized people and reduced their fear,
even though the participants were
oblivious, psychologist Joel Weinberger
of Adelphi University in Garden City,
N.Y., and colleagues reported last year
in Consciousness and Cognition. Though
the pictures flashed too quickly to break
into consciousness, the mind took note.

Now you see it Carefully designed experiments (one outlined below) allow scientists to separate the confounding effects of attention from awareness. Such studies have revealed that visual inputs don’t reach consciousness as soon as they hit the primary visual cortex, as many researchers had thought. SOURCE: M. WATANABE E T AL/SCIENCE 2011

Aware

Left eye Right eye

Unaware
Left eye Right eye

1. By showing study participants a grating in either the same eye as a circle or a different eye, researchers can manipulate awareness of the grating.

2. By adding a demanding task, in this case the command to focus on a letter, researchers can draw attention away from the grating in some cases.

This setup offers a way to study
people who have awareness
without attention, attention with-
out awareness, both or neither. c
c
c

Attention
Attention

c

No attention
No attention

their attention distracted by a counting job. At the same time, the team manipulated the participants’ awareness of the afterimage-inducing circle by showing it to only one eye while flashing a checkerboard pattern to the other eye. When the mind toggles to this dazzling pattern, the circle remains outside of consciousness.

In this way, participants could attend to something they didn’t see (attention without consciousness) and see something they didn’t attend to ( consciousness without attention).

At the end of the experiment, once all the signals on the screen were turned off, the volunteers indicated how long the aftereffect lasted. Surprisingly, attention and awareness had different effects, the team reported in 2010 in the Proceedings of the National Academy of Sciences: The more attention a person deployed, the shorter the afterimage lasted. The more conscious a person was of the stimulus, the longer the afterimage lasted.

Though some scientists are still skeptical, these results and others like them appear to separate attention and consciousness, meaning each may have its own role in the brain. “The attentional spotlight picks out aspects of the environment and highlights them,” says van Boxtel. In contrast, consciousness may be a synthesizer that merges bits of information into a broader picture.

Recent studies designed specifically to clarify V1’s job show that when attention is removed from the equation, V1 behavior is no longer tied to consciousness.

In an fMRI study reported in the Nov. 11 Science, participants were either made aware of a striped pattern on a screen or not. Then, they either focused attention to the pattern or away from it. Like the study on aftereffects, this setup allowed scientists to separate awareness from attention. The fMRI signal in V1 didn’t change as the stripes became visible or invisible if attention held steady. But when attention shifted, so did V1 activity, Watanabe’s team reported.