Most of us use our eyes and ears to negotiate our environment, but what about other senses such as touch? Do we use mechanical contact and touch to perceive the lay of the land over the long range? Steven Harrison and Michael Turvey from the University of Connecticut are fascinated by the information our bodies derive through touch. ‘Traditionally touch – the sense concerned with stimulation of the body's mechanoreceptors that occurs throughout the day – was thought to be the basis for passively knowing what you are coming in contact with only,’ says Harrison. However, he and Turvey were curious to find out if we might use the sense to localise our position in an environment. In other words, can we use the sense of touch to actively extract information about the environment that will allow us to orient ourselves? Harrison and Turvey decided to find out by walking blindfolded students through a relatively simple landscape guided only by a long cane (p. 1436).
Recruiting 46 undergraduate volunteers from the university's Psychology department, Harrison constructed a 0.8 m channel that was crossed by three low removable steps and bounded by 2 cm high PVC tubing for the human guinea pigs to explore. Covering the eyes of each subject with a pair of blacked out goggles and providing them with a long cane, Harrison guided each individual to the channel and gave them time to adjust to navigating the channel and steps, guided by the canes alone.
Next Harrison trained the volunteers to move around and familiarise themselves with the simple landscape (a channel crossed by three steps) by telling them when to begin and stop walking. After directing the volunteers along the channel, Harrison asked them to return to an unmarked location that he designated as ‘home’.
After an hour of familiarisation with the environment and the location of ‘home’, Harrison began testing the students' abilities to navigate their way around the channel. Telling the volunteers to walk back and forth along the channel as they encountered and negotiated steps that he positioned at various locations, Harrison eventually directed each student to a location and then asked the student to return to their starting point, guided only by the sensory information that they had gathered using the cane.
The students were surprisingly good at finding their way back to their starting point even when there was only one step and when Harrison added a second and third step to the channel, their accuracy improved even more. Harrison also secretly shifted one of the steps in each environment by a few metres for one group of students and found that these individuals shifted their ‘home’ position by the same amount. And when Harrison tested the students' responses to an environment with two steps after secretly moving the second step, he found that the students shifted their perception of ‘home’ to a location that preserved the relative positions of the two steps. The students were able to find their way home guided only by sensory information gathered about the environment through their sense of touch.
‘We've got evidence that mechanosensation is not a proximal sense [restricted to direct contact], and in the same way that the visual system allows us to encode our location in the environment with respect to its structure, this same capacity seems to be something that mechanosensing has as well,’ says Harrison.
