Key

A predefined key name which should be inserted to mark the artificial response. Be sure to select a key which is not used by the subject to differentiate between the artificial time stamp and the subject’s responses.

This command must be inserted after the RK trial command and before the trial event which represents the stimulus onset. The artificial response will be generated in sync with this onset. The time difference between the subject’s response and the internally generated response will then represent the delta between stimulus onset and the subject’s response.

For example, if you ask a subject to synchronize the key press with the onset of a second stimulus (estimate time interval), you want to record potential responses before and after the second stimulus in order to get early and late responses. To achieve this, you must start response registration already with the first stimulus but you are actually interested in the response latency relative to the onset of the second stimulus. Using the GR-command you can generate an artificial response at the time of the second stimulus. This allows you compute the delta between onset and response by subtracting the latency of the subject’s response from the artificial response.

Please note that you must increase the number of the to be recorded key presses in the RK-command by one in order to include the GR-generated response.

 Example for generating a response to sync with stimulus onset

PICTURE Start N
PICTURE Press N
POSITION Center P 0,0          ; Center position
KEY Response
SHL SHR SPACE

TRIAL T1
CS 1500          ; Blank Screen
RK Response 0 2          ; Record Two Keys Presses
SP Start Center 1 ?          ; Show Start in center of screen
GR SPACE          ; Generate Response at next trial command
SP Press Center 1 1500          ; Show Stimulus in center of screen