psyphy (version 0.3)

ecc2: 4-afc Detection and Identification of Letters

Description

Letter detection and identification at 2 degrees eccentricity in the visual field. On each trial, one of four letters (b, d, p, q) were presented in one of four positions (superior, inferior, left, right) in the visual field. In a given session, the letter height was fixed. Six contrast levels were tested in each session. The data indicate the proportion of correctly identified positions, referred to here as detection, and the proportion of correctly identified letters, conditional on correct identification.

Usage

data(ecc2)

Format

A data frame with 48 observations on the following 5 variables.

Contr

numeric. The contrast of the stimulus, defined as Weberian contrast.

task

a factor with levels DET ID indicating the two tasks, detection and identification.

Size

a numeric vector indicating the letter height

Correct

an integer vector indicating the number of correct responses (DET or ID).

Incorrect

an integer vector, indicating the number of incorrect responses.

References

Yssaad-Fesselier, R. and Knoblauch, K. (2006) Modeling psychometric functions in R. Behav Res Methods., 38(1), 28--41.

Examples

data(ecc2)
library(lattice)
xyplot(Correct/(Correct + Incorrect) ~ Contr | Size * task, ecc2, 
		type = "b", scale = list(x = list(log = TRUE), 
		y = list(limits = c(0, 1.05))),
		xlab = "Contrast", ylab = "Proportion Correct Response",
		panel = function(x, y, ...) {
			panel.xyplot(x, y, ...)
			panel.abline(h = 0.25, lty = 2)
			})