function prev(value,time) {
                  var nrSlides  = slides.choice.length;
                  var currSlide = slides.whichChoice;
                  var slide     = slides.choice[currSlide];
                  var currLevel = slide.showLevel;
                  var toon = show;
  
                  direction = 'backward';
  
                  if(currLevel-1 <= -1) {
                      if(currSlide-1 <= -1) {
                          nextSlide = nrSlides - 1;
                      } else {
                          nextSlide = currSlide - 1;
                      }
                      number = nextSlide;
                      slides.choice[nextSlide].showLevel = 
                          slides.choice[nextSlide].nrLevels - 1;
                      id = slides.choice[nextSlide].id;
                      toon = show || slides.choice[nextSlide].show;
                      if (toon) {
                      hideTimeSensor.startTime = time;
                      hideTimeSensor.stopTime  = time + 3;
                      } else {
                      slides.whichChoice = nextSlide;
                      }
                      update = 3;
                  } else {
                      slide.showLevel    = currLevel-1;
                      level = slide.showLevel;
                      update = 4;
                  }
              }