Echolocation: a 'sixth sense' for blind people

Could echolocation - a skill commonly linked with bats - be used as a "sixth sense" for blind people? Researchers have found that blind people using echolocation are just as susceptible to visual illusions as sighted people.

Echolocation is most commonly associated with bats, who use the technique to navigate and find food.

Echolocation is a process whereby sound waves are used to determine the location and size of objects within a particular area. 

Returning sound waves rebounding from objects provide positional information to those that are unable to see them.

In the new study, published in Psychological Science, researchers from the Brain and Mind Institute at Western University, Canada, demonstrate that echolocation works in partnership with other senses to provide information to people with visual impairment.

Some blind people use echolocation to assess their environment and find their way around. They will either snap their fingers or click their tongue to bounce sound waves off objects, a skill often associated with bats, which use echolocation when flying.

Researchers found that blind participants in the study were susceptible to the size-weight illusion - also known as the Charpentier illusion - when using echolocating techniques such as snapping their fingers or clicking their tongues while making a judgement about the weights of different sized cubes.

The size-weight illusion is most frequently explained with the example of two boxes - a small one containing 1 kg of feathers and a large one containing 1 kg of iron. The size-weight illusion causes people to perceive the smaller box as heavier, despite them both having the same mass.

Ironically, the proof for the vision-like qualities of echolocation came from blind echolocators wrongly judging how heavy objects of different sizes felt.

Succumbing to the size-weight illusion

For the study, participants were asked to judge the weight of three cubes. The cubes all shared the same weight but were differently sized and could only be lifted by the participants pulling a string attached to the top of each box.

Participants were split into three different groups: blind people using echolocation, blind people not using echolocation, and a group of participants without any visual impairment.

People from the blind group that did not use echolocation were successful at judging that the boxes were of equal weight. However, their success was not matched by either of the other two groups of participants.

The sighted group, where each member was able to see how big each box was, overwhelmingly succumbed to the 'size-weight illusion' and experienced the smaller box as feeling a lot heavier than the largest one.

Blind participants using echolocation also succumbed to a robust size-weight illusion following the use of finger snaps and tongue clicks prior to lifting the boxes.

Could echolocation be used to completely replace vision?

This showed that echolocation was able to influence their sense of how heavy something felt. This resembles how visual assessment influenced how heavy the boxes felt in the sighted group.

The team's findings were consistent with earlier work from the team in which they had observed blind echolocating participants using "visual" areas of their brains when processing echoes that they had made.

This new study shows that echolocation is not just a functional tool to help visually impaired individuals navigate their environment, but actually has the potential to be a complete sensory replacement for vision.

According to the authors, the study is the first to show a sensory substitution technique actively influencing conscious perception through an intact sense.

References:

1. The size-weight illusion induced through human echolocation, Gavin Buckinham, et al., Psychological Science, doi: 10.1177/0956797614561267, published online 19 December 2014, abstract.
2. Heriot-Watt University news release, accessed 23 December 2014.
3. Western University news release, accessed 23 December 2014.