rtdists (version 0.11-5)

rr98: Ratcliff and Rouder (1998, Exp. 1) Luminance Discrimination Data

Description

Responses and response times from an experiment in which three participants were asked to decide whether the overall brightness of pixel arrays displayed on a computer monitor was "high" or "low". In addition, instruction manipulated speed and accuracy between blocks.

Usage

rr98

Format

A data.frame with 24,358 obs. and 12 variables:

id

participant id, factor with three levels

session

session number, integer

block

block number, integer

trial

trial number within a block, integer

instruction

factor with two levels: "accuracy" for blocks with accuracy instructions; "speed" for blocks with speed instruction

source

factor with two levels: distribution strength was drawn from, "dark" and "light"

strength

proportion of white to black pixels were varied by 33 equally spaced proportions from zero (all 1,024 pixels were black) to 1 (all 1,024 pixels were white). with 0 darkest and 32 lightest. Integer.

response

factor with two levels: "dark" and "light"

response_num

numeric response variable such that 1="dark" and 2="light"

correct

boolean indicating whether or not source==response. (Does not seem to be used in the original analysis.)

rt

response time in seconds

outlier

boolean indicating whether or not the response was considered an outlier by Ratcliff and Rouder (1998), i.e., RTs outside of (200ms, 2500ms)

Details

The Experiment is described in the following by Ratcliff and Rouder (1998, pp. 349):

In Experiment 1, subjects were asked to decide whether the overall brightness of pixel arrays displayed on a computer monitor was "high" or "low". The brightness of a display was controlled by the proportion of the pixels that were white. For each trial, the proportion of white pixels was chosen from one of two distributions, a high distribution [i.e., light] or a low [i.e., dark] distribution, each with fixed mean and standard deviation. Feedback was given after each trial to tell the subject whether his or her decision had correctly indicated the distribution from which the stimulus had been chosen. Other than this feedback, a subject had no information about the distributions. Because the distributions overlapped substantially, a subject could not be highly accurate. A display with 50 from the high distribution on one trial and the low distribution on another.

Stimuli

The stimulus display for Experiment 1 was a square that was 64 pixels on each side and subtended 3.8 degree of visual angle on a PC-VGA monitor. [...] In each square, 3,072 randomly chosen pixels were neutral gray, like the background, and the remaining 1,024 pixels were either black or white; the proportion of white to black pixels provided the brightness manipulation. There were 33 equally spaced proportions from zero (all 1,024 pixels were black) to 1 (all 1,024 pixels were white). The two distributions from which the bright and dark stimuli were chosen were centered at .375 (low brightness) and .625 (high brightness), and they each had a standard deviation of .1875.

Procedure

A subject's task was to decide, on each trial, from which distribution, high or low brightness in Experiment 1, the observed stimulus (stimuli) had been sampled. Subjects made their decision by pressing one of two response keys. On each trial, a 500-ms foreperiod, during which the display consisted solely of neutral gray, was followed by presentation of the stimulus; presentation was terminated by the subject's response. In Experiment 1, speed-versus-accuracy instructions were manipulated. For some blocks of trials, subjects were instructed to respond as quickly as possible, and a "too slow" message followed every response longer than 550 ms. For other blocks of trials, subjects were instructed to be as accurate as possible, and a "bad error" message followed incorrect responses to stimuli from the extreme ends of the distributions. Experiment 1 had ten 35-min sessions, and Experiments 2 and 3 had four sessions. In Experiment 1, subjects switched from emphasis on speed to emphasis on accuracy every 204 trials. Each session consisted of eight blocks of 102 trials per block, for a total of 8,160 trials per subject. Each session consisted of eight blocks of 102 trials, for a total of 3,264 trials per subject in each experiment. For all trials in each experiment, subjects were instructed to maintain a high level of accuracy while responding quickly, and an "error" message indicated incorrect responses. Responses were followed by a 300-ms blank interval, and the error message was displayed for 300 ms after the blank interval.

Examples

# NOT RUN {
data(rr98)
rr98 <- rr98[!rr98$outlier,]  #remove outliers
head(rr98)
#   id session block trial instruction source strength response response_num correct    rt outlier
# 1 jf       2     1    21    accuracy   dark        8     dark            1    TRUE 0.801   FALSE
# 2 jf       2     1    22    accuracy   dark        7     dark            1    TRUE 0.680   FALSE
# 3 jf       2     1    23    accuracy  light       19    light            2    TRUE 0.694   FALSE
# 4 jf       2     1    24    accuracy   dark       21    light            2   FALSE 0.582   FALSE
# 5 jf       2     1    25    accuracy  light       19     dark            1   FALSE 0.925   FALSE
# 6 jf       2     1    26    accuracy   dark       10     dark            1    TRUE 0.605   FALSE

## See vignette for more examples.
# }