Locked in Syndrome

These paired activities, from Paul Curzon of the CS4FN team, offer an interesting slant on search algorithms and their relative efficiency.

Students are asked to consider sufferers of ‘locked-in syndrome’, a condition that leaves a healthy mind inside body that is, often, completely paralysed. If the sufferer can move one part of the body, for instance by blinking, then a way to give them a ‘voice’ can be found. This involves the use of search algorithms to choose from the alphabet one letter at a time; Professor Stephen Hawking uses a similar approach.

By linking this effort to a game of ’20 Questions’, the lesson shows that there are more efficient ways of selecting letters than by simply going through the whole alphabet. The author Jean-Dominique Bauby wrote his autobiography, ‘The Diving Bell and the Butterfly’, using such a system. It becomes clear that small improvements in the algorithm for selecting letters can mean big savings in time when they are repeatedly ‘run’, i.e. while writing a book. The result shows how ‘divide and conquer’ approaches to search are more efficient that binary search methods. It then extends the topic to look at indexes, and offers suggested ‘unplugged’ extension activities.

Detailed background information is contained within the ‘searching to speak’ accompanying document.

The activity would be useful from lower secondary through to A-Level computing and computer science.