Real Rubber Arms
Overview | Article Summary
| For Instructors | For
Students
Botvinick, M., and Cohen, J. (1998). Rubber hands that 'feel' touch
that eyes see. Nature, 391, 756.
Overview:
Coordinating Perception
Sensation and perception in individual modalities are quite well understood.
For example, researchers have traced visual pathways from the retina through
the brain to the visual cortex. Other researchers have categorized many
tactile receptors, described differences between them in terms of structure
and function. Still other researchers have examined the vestibular system
in order to better understand kinesthetic sensation and perception.
For all we know about individual modalities, however, we know very little
about how these different modalities are combined to give us a unified
understanding of the environment and our place in it. Botvinick and Cohen
(1998) used an innovative approach in their investigation of the coordination
of vision, touch, and proprioception.
Overview | Article Summary | For
Instructors | For Students
Article Summary
Have you ever tried writing while looking at a mirror image of your writing?
This is a difficult task because vision seems to override seemingly automatic
processes of writing. Even sequencing writing from left to right is difficult
because in the mirror, a left-to-right sequence moves the opposite direction.
Illusions such as mirror writing, provide interesting insights into the
organization and coordination of perceptual systems. Botvinick and Cohen
(1998) created an illusion in which tactile stimulation is referred to
an artificial limb. They used this illusion to discover an interesting
relationship between vision, touch, and proprioception.
In the first experiment, participants placed their left arm on a table.
A screen was placed over the arm and a rubber arm was placed on the table
immediately in front of the person. The participant watched the rubber
arm while two small brushes were used to simultaneously and synchronously
stroke the back of the rubber hand and the back of the participant's own
hand. After 10 min, the participants completed a questionnaire on the experience.
Botvinick and Cohen found that the participants experienced an illusion
that the hand they watched being stroked was their own hand! In other words,
when the strokes on the real hand and the rubber hand were synchronized,
people ignored the fact that their arm was located to their left side behind
a screen. Botvinick and Cohen hypothesized that this illusion occurred
because vision, touch, and proprioception are correlated to the extent
that proprioception can be distorted when visual and tactile information
is coordinated.
To test their hypothesis that proprioception can be distorted, Botvinick
and Cohen performed a second experiment. Participants were stoked in the
same way as in the first experiment. After a protracted period of stroking,
the participant reached under the table with his or her right hand to indicate
where the real hand was located. Participant's indications were displaced
to the right toward the rubber hand - the stronger the illusion for a participant,
the closer to the rubber hand the participant pointed! To rule out simple
errors of judgment, Botvinick stroked control participants hands asynchronously
(the strokes on the rubber hand followed a slightly different time pattern
than the strokes on the real hand); these participants indicated the location
of their left hand much more correctly.
This illusion demonstrates how one perceptual system, in this case vision,
can overrule another system, in this case proprioception. It also provides
clues as to how we recognize and define ourselves in relation to the world.
Overview | Article Summary
| For Instructors | For Students
For Instructors
Links to the Lecture
Students enjoy, understand and remember illusions. They provide a great
way to demonstrate perception and the interaction of perceptual systems.
The following activities demonstrated different ways in which perceptual
systems and cognition interact:
-
Visually guided motor behavior crosses the central plane with difficulty.
This makes it difficult to learn any motor behavior by watching it face-to-face,
because actions are perceived in the left visual field but must be produced
by the right side of the body. This phenomenon is easily demonstrated by
having a volunteer (a) hold his or her arms straight out with backs of
the hands facing each other, (b) cross the right hand over the left, (c)
clasp the hands together, and (d) bring the clasped hands toward the body
and up until the fingers are facing up. This has the effect of placing
the fingers on the right hand on the left side of the body and vice versa.
Point to a finger and have the volunteer raise that finger while keeping
the hands clasped and in the same position. The person invariably raises
the opposite finger (ie., if you point to the left finger which is in the
right visual field, but the person raises his or her right finger which
is in the left visual field).
-
Automatic processes can override other perceptual processes.
The Stoop interference effect works well to demonstrate how an automatic
process can override other perceptual processes.
-
Speech perception is cross-modal in nature. The McGurk effect,
an illusion demonstrating how speech perception is guided by both visual
and auditory perception, is demonstrated in this on-line psychology lab
site
and works well even in a large lecture class.
Overview | Article Summary
| For Instructors | For Students
For Students
About the Authors
Matthew Botvinick is a graduate student in the Department of Psychology,
Carnegie Mellon University. His supervisor is Jonathan
Cohen.
About the Journal
Nature, the "world's most prestigious
weekly journal of science," publishes research that has the potential to
have an impact far beyond the narrow audience that reads most scientific
journals. They also have an extensive on-line presence. This site is well
worth exploring frequently.
Links to Life
Here is a news
report summarizing Botvinick and Cohen's work.
This research has implications for understanding phenomena such as phantom
limb pain. Here is a report
of a study (also reported in Nature) in which mirrors were used to "reconstruct"
amputated limbs.
Here is an interesting article
on the phantom limb phenomenon written by Ronald Melzack, the premier researcher
in the psychology and neuropsychology of pain.
Just like introductory psychology textbooks tend to separate perception
from the different modalities, educators consider learning from different
modalities. Here is a Learning
Styles Checklist you can complete to determine whether you are a visual,
auditory, or tactile/kinesthetic learner. Here is a comparable but slightly
longer inventory.
Do you like illusions? There are many, many visual illusions posted
and explained at Illusionworks. |
