A participant in one experiment needs to decide whether a flash and a sound are simultaneous or not for many possible asynchronies between the flash and the sound (x in seconds). For each asynchrony, the flash and sound are presented 100 times. In the below graph the proportion of 'simultaneous' responses (y) areis plotted as a function of the asynchrony 
I want to fit a 3-parameter gaussianGaussian distribution to these data. I used least squares (below). My question is whether least squares is the most standard/orthodox form to proceed for this kind of fitting. It makes sense to use maximum likelihood estimation here? How can be done?
x<-seq(-.3,.3,.1) yes<-c(10,45,90,100,60,10,5) #simultaneous responses y<-yes/100 leastSquares<-function(p) sum((y-p[1]*dnorm(x,p[2],p[3]))^2) p<-optim(c(.001,0.1,.210),leastSquares)$par xseq<-seq(-.3,.3,.01) yseq<-p[1]*dnorm(xseq,p[2],p[3]) plot(x,y) lines(xseq,yseq)