Audio sight for blind archers: Sasayama 2013 study

The paper presents an audio sight for blind archers. A small three-axis magnetic sensor mounted on the bow reads the Earth's magnetic field and works out azimuth and elevation; a receiver placed near the archer turns the offset from the target into sounds, sent to wireless headphones. If the target is to the left only the left earpiece sounds, if it is to the right only the right one, with pulses whose rate changes over 64 levels (from 0.29802 to 19.9737 Hz) depending on how many degrees off the aim is; the pitch of the tone says whether the target is above (2,450 Hz) or below (1,634 Hz), and when the aim is centred the pulses become a continuous tone. The sensor weighs 34 grams with batteries and runs for about two hours on two SR44 button cells.

To test it, six well-trained sighted archers from the university club shot blindfolded and with their eyes open. Blindfolded, the mean score was 58% of the eyes-open score on the standard face, 64% on a face that scores only left-right error and 77% on one that scores only up-down error. The authors put the better vertical result down to the good postural stability of a trained archer, and conclude that the system makes archery possible for blind people.

The test took place indoors at 10 metres, with a 16-pound bow (Samick Polaris) and aluminium arrows, on an 80 cm World Archery face. Before shooting, the archer presses a switch that zeroes the difference between magnetic north and the direction of the target. Each archer shot 12 practice arrows, then 6 arrows blindfolded and 6 with eyes open, on three types of face: the standard one, one with zones scoring only horizontal error and one scoring only vertical error. The comparison is between mean scores in the two conditions.

The sensor is an Aichi Steel AMI306; data reach the receiver by radio through an NEC TY24FM-E2024 module, and a microprocessor works out the angles with the CORDIC algorithm. The receiver weighs 130 grams without its battery box and sends the sound to the headphones over Bluetooth.

This is a four-page conference paper with six archers and six arrows per condition: too little to estimate how well the system performs. The participants were sighted archers wearing a blindfold, people who learned to shoot by looking; no blind archer was tested, and for someone who has never seen the outcome could be different. The percentages are ratios of mean scores: the appendix table with each archer's means and standard deviations, cited in the text, is not in the PDF, and there is neither a statistical comparison nor a blindfolded test without the system, which would be the most useful baseline for judging how much the sound helps. Nor is the order in which the blindfolded and eyes-open series were shot given.

The paper does not say how the sensor behaves near metal objects or steel structures, which can disturb a magnetic reading, and the test was at 10 metres with a light bow, far from competition distances and draw weights.

For a sighted archer the study changes nothing about how to shoot. It is of interest to those who coach or support visually impaired archers: it shows that a light sensor on the bow can turn the aiming direction into sounds clear enough for a blindfolded archer, at 10 metres, to score more than half of the eyes-open total. Compared with the same group's earlier system, the stated advantage is a practical one, as there is no longer a cable running from the bow to a battery on the belt.

The paper mentions that tactile aiming aids also exist, which the authors consider awkward for a blind archer; this work offers an audio alternative but does not compare it with them. That up-down held up better than left-right (77% against 64%) is a useful pointer for anyone designing such aids, but with six archers and six arrows it remains only an indication.