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.
data(Vernier)A data frame with 64 observations on the following 8 variables.
Phaseshifta numeric vector giving the Phaseshift between the pair of gratings
WaveForma factor with levels Sine Square giving the spatial luminance profile of the gratings
TempFreqa factor with levels 2 8 indicating the temporal frequency in Hertz of the moving gratings
Pca numeric vector, indicating the proportion of trials on which a particular grating appeared to be shifted upward
Directiona factor with levels Downward Upward indicating the direction of motion of the grating pair.
Na numeric vector indicating the number of trials on which a condition was presented
NumUpwarda numeric vector indicating the number of trials on which the observer responded that a particular grating was shifted upward
NumDownwarda numeric vector indicating the number of trials on which the observer reported a particular grating as shifted downward
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.