Vernier {MPDiR}

Psychometric Functions for Vernier Judgement of Phase Difference between Drifting Gratings

Description

A pair of adjacent, horizontal luminance gratings (sine- or square-wave spatial profiles, 0.8 cycles/degree and equal contrast = 0.30) drifting at 2 or 8 Hz. The gratings were separated by a 30-arcmin lateral gap. On each trial, the grating pair was drifting either upward or downward and the phase shift between the gratings was chosen at one of 8 values between -50 and 50 degrees. The observer was instructed to report which grating appeared shifted upward. The method of constant stimuli was used.

Usage

data(Vernier)

Format

A data frame with 64 observations on the following 8 variables.

Phaseshift

a numeric vector giving the Phaseshift between the pair of gratings

WaveForm

a factor with levels Sine Square giving the spatial luminance profile of the gratings

TempFreq

a factor with levels 2 8 indicating the temporal frequency in Hertz of the moving gratings

Pc

a numeric vector, indicating the proportion of trials on which a particular grating appeared to be shifted upward

Direction

a factor with levels Downward Upward indicating the direction of motion of the grating pair.

N

a numeric vector indicating the number of trials on which a condition was presented

NumUpward

a numeric vector indicating the number of trials on which the observer responded that a particular grating was shifted upward

NumDownward

a numeric vector indicating the number of trials on which the observer reported a particular grating as shifted downward

Source

Data kindly provided by H. Sun.

References

H. Sun, B. B. Lee and R. C. Baraas Systematic misestimation in a vernier task arising from contrast mismatch, Visual Neuroscience, 2008, 25, 365–370.

Examples

data(Vernier)