OPI (version 3.0.4)

opiPresent_for_SimHensonRT: opiPresent_for_SimHensonRT

Description

Determine the response to a stimuli by sampling from a cumulative Gaussian Frequency-of-Seeing (FoS) curve (also known as the psychometric function).

For internal use only, use opiPresent().

Value

A list with elements:

• err NULL if no error, a string message otherwise.

• seen TRUE or FALSE.

• time The response time.

Arguments

stim

A list that contains at least:

• level which is the stim value in cd/\(\mbox{m}^2\).

fpr

false positive rate for the FoS curve (range 0..1).

fnr

false negative rate for the FoS curve (range 0..1).

tt

mean of the assumed FoS curve in dB.

dist

The distance of the stimulus level from tt in appropriate units (same as rtData$Dist).

...

Any other parameters you like, they are ignored.

Details

As the response time returned for a false positive is determined separately from a positive response, we first check for a false response. If there is no false response, we use the FoS formula $$1-\mbox{pnorm}(x, \mbox{tt}, \mbox{pxVar})$$ where x is the stimulus value in dB, and pxVar is $$\min(\mbox{cap}, e^{A\times\mbox{tt}+B}).$$ The ceiling cap is set with the call to opiInitialize, and A and B are from Table 1 in Henson et al (2000), also set in the call to opiInitialise using the type parameter.

Thus, this function is the same as for SimHenson, but reaction times are determined by sampling from rtData as passed to opiInitialize. The dist parameter is the distance of the stimulus level from the true threshold, and should be in the same units as the Dist column of rtData. The default is just the straight difference between the stimulus level and the true threshold, but you might want it scaled somehow to match rtData.

Examples

    # Stimulus is Size III white-on-white as in the HFA
chooseOpi("SimHensonRT")
data(RtSigmaUnits)
res <- opiInitialize(type = "C", cap = 6, rtData = RtSigmaUnits)
if (!is.null(res$err))
  stop(paste("opiInitialize() failed:", res$err))

dist <- (10 - 30) / min(exp(-0.098 * 30 + 3.62), 6)
result <- opiPresent(stim = list(level = dbTocd(20)), tt = 30, fpr = 0.15, fnr = 0.01, dist=dist)
print(result, quote = FALSE)

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