November 6, 2012
Researchers Train Humans To Sense The World Like Rats
April Flowers for redOrbit.com - Your Universe Online
By moving their facial whiskers back and forth about eight times a second to locate objects in their environment, rats use a sense that humans don´t: whisking. Researchers from the Weizmann Institute of Science in Rehovot, Israel, however, have set out to learn whether humans could acquire this sense with practice, and if so, what could understanding the process of adaptation tell us about our normal senses?
The team of scientists attached a "whisker" — a 30 cm-long elastic hair with position and force sensors at its base — to the index finger of each participant. Two poles were placed slightly to the front at arm's distance on either side of the seated subject. One pole was slightly further back than the other.
The blindfolded participants were then challenged to figure out which pole — left or right — was farther back using only their whiskers. The displacement between the front and back poles was reduced to the point when the subject could no longer distinguish front from back as the experiment continued.
On day one, subjects picked up the new sense so quickly that they could correctly identify a pole set back by only eight cm. An analysis of the data showed that the subjects did this by figuring the spatial information from the sensory timing. In other words, the subjects moved both hands at the same time, and could tell which pole was farther back because that hand made contact first.
On day two, when they repeated the testing, the research team discovered that the subjects had further improved their whisking skills. On average, the sensory threshold decreased to just three cm, while some subjects were able to sense a displacement of less than half an inch. Their ability to sense time differences did not change over the two day testing period. Instead they improved the motor aspect of their whisking strategies. By slowing down their hand motions, they were able to sense a smaller spatial difference, in effect lengthening the delay time.
“We know that our senses are linked to muscles, for example ocular and hand muscles. In order to sense the texture of cloth, for example, we move our fingers across it, and to seeing stationary object, our eyes must be in constant motion. In this research, we see that changing our physical movements alone — without any corresponding change in the sensitivity of our senses — can be sufficient to sharpen our perception,” explained Dr. Avraham Saig, one of the study´s author.
Using the data from the experiments, the team created a statistical model to describe how the subjects updated their world view as they acquired the new sensory information, from the beginning to the point where they were able to rely on their newly acquired ℠whisking´ sense. Based on the principles of information processing, the model could explain the number of whisking movements needed to arrive at the correct answer. It was also able to explain the pattern of scanning that the subjects employed — a gradual change from long to short movements — which allowed the flow of information to remain constant.
“The experiment was conducted in a controlled manner, which allowed us direct access to all the relevant variables: hand motion, hand-pole contact and the reports of the subjects themselves,” says Dr. Goren Gordon, another researcher involved in the study. “Not only was there a good fit between the theory and the experimental data, we obtained some useful quantitative information on the process of active sensing.”
“Both sight and touch are based on arrays of receptors that scan the outside world in an active manner,” says Professor Ehud Ahissar, the study´s lead investigator.
“Our findings reveal some new principles of active sensing, and show us that activating a new artificial sense in a ℠natural´ way can be very efficient.”
Dr. Amos Arieli adds: “Our vision for the future is to help blind people ℠see´ with their fingers. Small devices that translate video to mechanical stimulation, based on principles of active sensing that are common to vision and touch, could provide an intuitive, easily used sensory aid.”