op <- options(digits.secs = 6)

t=Sys.time()

time = function(t) {
	txt=substr(t,12,30)
	le=nchar(txt)
	h=as.numeric(substr(txt,1,2))
	m=as.numeric(substr(txt,4,5))
    s=as.numeric(trimws(substr(txt,7,le)))
    return(c(h,m,s,h*3600+m*60+s))
}
		
min.delay =  2
max.delay = 10
n.trials  = 5


measure.my.reaction.times =
  function(n.trials=  5,
           min.delay= 2,  # seconds
           max.delay=10,  # seconds
           show.as.you.go=FALSE) {   # show indidivual times
           	
  	reaction.times = rep(NA,n.trials)
  		print(noquote(""))
  	  print(noquote("As soon as GO sign appears, press RETURN key"))
  		print(noquote(""))
	for(trial in 1:n.trials) {
	  t.0 = time(Sys.time())
    t.start = t.0[4] + runif(1,min.delay,max.delay)
    #print(noquote("wait"))
    while( time(Sys.time())[4] < t.start ) {
	  }
	  t.message = time(Sys.time())[4]
	  #print(Sys.time())
    input <- readline(prompt=noquote("GO"))
    t.response = time(Sys.time())[4]
    #print(Sys.time())
    reaction.times[trial] = round(1000*(t.response  - t.message))
    if(show.as.you.go) print(c(trial,reaction.times[trial]))
  }
return(reaction.times)
}

# examples

measure5times = measure.my.reaction.times()

measure25times = measure.my.reaction.times(25)

# note: JH hasn't figures out how to keep responses
# that occur befire the GO notice from messing up the
# remining timings. suggestions welcome
# JH 2017.08.25