OPI (version 2.1)

fourTwo: 4-2 Staircase

Description

fourTwo is a 4-2 dB staircase beginning at level est terminating after two reversals. The final estimate is the average of the last two presentations. It also terminates if the minStimulus is not seen twice, or the maxStimulus is seen twice.

Usage

fourTwo.start(est=25, instRange=c(0,40), verbose=FALSE, makeStim, ...)
fourTwo.step(state, nextStim=NULL)
fourTwo.stop(state) 
fourTwo.final(state)

Arguments

est

Starting estimate in dB

instRange

Dynamic range of the instrument c(min,max) in dB

verbose

True if you want each presentation printed

makeStim

A function that takes a dB value and numPresentations and returns an OPI datatype ready for passing to opiPresent

...

Extra parameters to pass to the opiPresent function

state

Current state of the fourTwo returned by fourTwo.start and fourTwo.step.

nextStim

A valid object for opiPresent to use as its nextStim.

Value

• Multilple locations{ fourTwo.start returns a list that can be passed to fourTwo.step, fourTwo.stop and fourTwo.final. It represents the state of a fourTwo at a single location at a point in time and contains the following.
  • name:
  { fourTwo}
• A copy of all of the parameters supplied to fourTwo.start: startingEstimate=est, minStimulus=instRange[1], maxStimulus=instRange[2], makeStim, and opiParams=list(...).
• currentLevel:
  The next stimulus to present.
• lastSeen:
  The last seen stimulus.
• lastResponse:
  The last response given.
• stairResult:
  The final result if finished (initially NA).
• finished:
  "Not" if staircae has not finished, or one of "Rev" (finished due to 2 reversas), "Max" (finished due to 2 maxStimulus seen), "Min" (finished due to 2 minStimulus not seen).
• numberOfReversals:
  Number of reversals so far.
• currSeenLimit:
  Number of times maxStimulus has been seen.
• currNotSeenLimit:
  Number of times minStimulus not seen.
• numPresentations:
  Number of presentations so far.
• stimuli:
  Vector of stimuli shown at each call to fourTwo.step.
• responses:
  Vector of responses received (1 seen, 0 not) receieved at each call to fourTwo.step.
• responseTimes:
  Vector of response times receieved at each call to fourTwo.step.
• }

  fourTwo.step returns a list containing

  • state:
  { The new state after presenting a stimuli and getting a response.}

• resp:
  The return from the opiPresent call that was made.

code

fourTwo.final

Details

This is an implementation of a 4-2 1-up 1-down staircase. The initial staircase starts at est and proceeds in steps of 4dB until the first reversal, and 2dB until the next reversal. The mean of the last two presentations is taken as the threshold value.

Note this function will repeatedly call opiPresent for a stimulus until opiPresent returns NULL (ie no error occured).

If more than one fourTwo is to be interleaved (for example, testing multiple locations), then the fourTwo.start, fourTwo.step, fourTwo.stop and fourTwo.final calls can maintain the state of the fourTwo after each presentation, and should be used. See examples below.

References

Please cite: A. Turpin, P.H. Artes and A.M. McKendrick "The Open Perimetry Interface: An enabling tool for clinical visual psychophysics", Journal of Vision 12(11) 2012.

http://perimetry.org/OPI

See Also

dbTocd, opiPresent

Examples

# Stimulus is Size III white-on-white as in the HFA
makeStim <- function(db, n) { 
    s <- list(x=9, y=9, level=dbTocd(db), size=0.43, color="white",
             duration=200, responseWindow=1500)
    class(s) <- "opiStaticStimulus"

    return(s)
}
chooseOpi("SimHenson")
if (!is.null(opiInitialize(type="C", cap=6)))
    stop("opiInitialize failed")

    ##############################################
    # This section is for multiple fourTwos
    ##############################################
makeStimHelper <- function(db,n, x, y) {  # returns a function of (db,n)
    ff <- function(db, n) db+n

    body(ff) <- substitute(
        {s <- list(x=x, y=y, level=dbTocd(db), size=0.43, color="white",
                  duration=200, responseWindow=1500)
         class(s) <- "opiStaticStimulus"
         return(s)
        }
        , list(x=x,y=y))
    return(ff)
}

    # List of (x, y, true threshold) triples
locations <- list(c(9,9,30), c(-9,-9,32), c(9,-9,31), c(-9,9,33))

    # Setup starting states for each location
states <- lapply(locations, function(loc) {
    fourTwo.start( makeStim=makeStimHelper(db,n,loc[1],loc[2]),
              tt=loc[3], fpr=0.03, fnr=0.01)
})

    # Loop through until all states are "stop"
while(!all(st <- unlist(lapply(states, fourTwo.stop)))) {
    i <- which(!st)                         # choose a random, 
    i <- i[runif(1, min=1, max=length(i))]  # unstopped state
    r <- fourTwo.step(states[[i]])               # step it
    states[[i]] <- r$state                  # update the states
}

finals <- lapply(states, fourTwo.final)    # get final estimates of threshold
for(i in 1:length(locations)) {
    cat(sprintf("Location (%+2d,%+2d) ",locations[[i]][1], locations[[i]][2]))
    cat(sprintf("has threshold %4.2f
", finals[[i]]))
}

if (!is.null(opiClose()))
    warning("opiClose() failed")