stimulusframes attribute

The stimulusframes attribute specifies the stimulus presentation sequence for a trial in terms of vertical retrace frames of the monitor.

Member of

Syntax

/ stimulusframes = [framenumber = stimulusname, stimulusname, ...; framenumber = stimulusname, ...]

/ stimulusframes = [framenumber = list.name]

/ stimulusframes = [framenumber = selectionmode(stimulusname, stimulusname, stimulusname, ...)]

Parameters

framenumber

A non-negative integer specifying a vertical retrace frame.

stimulusname

The name of a stimulus defined elsewhere in the script to be presented on the specified frame.

list.name

The name of a list that selects the stimulus to be presented on the specified frame.

selectionmode

One of the following values:

Value	Description
noreplace	Randomly selects without replacement which stimulus in the group to run.
noreplacenorepeat	Randomly selects which stimulus in the group to present without replacement and without selecting any single stimulus consecutively.
replace	Randomly selects with replacement which stimulus in the group to run.
replacenorepeat	Randomly selects which stimulus in the group to present with replacement and without selecting any single stimulus consecutively.
sequence	Runs each stimulus in the group.

Remarks

The stimulusframes attribute schedules stimuli to be presented on particular vertical retrace frames in the <trial>’s frame sequence. The framenumber represents the ordinal position of the frame within the sequence. If a stimulus is assigned to a frame, it will be displayed at the onset of that frame. If no stimulus is assigned to a frame, the display is not changed during that frame and previously displayed stimuli will remain visible. Multiple stimuli can be assigned to a single frame, in which case all of those stimuli are displayed simultaneously at the onset of the frame.

Alternatively, stimulus presentation can be defined in terms of milliseconds using stimulustimes.

A vertical retrace frame is the interval during which a the screen is painted from top to bottom. Video presentation on a digital monitor is not continuous over time but instead consists of discreet frames during which the screen is painted (think of the frames in an animated cartoon or a motion picture). On a digital monitor, stimuli must therefore be presented for durations that are multiples of a duration of a single frame, and the shortest time interval a stimulus can be presented is the duration of 1 frame.

On most standard monitors, the screen is repainted every 16.7 ms (60 hz) or 13.9 ms (72 hz) — these frequencies are known as the vertical frame rate or simply the frame rate. Some video systems permit the frame rate to be adjusted in the Windows control panel. Consult your hardware dealer to determine how to adjust the frame rate for your monitor.

Examples

The following trial presents a forward and backward masked prime for exactly 1 vertical retrace frame, and then presents a target stimulus that remains on the screen until the subject responds:

<trial mytrial>
/ stimulusframes=[1=forwardmask; 2=prime; 3=backwardmask; 4=target]
/ validresponse=("a", "b")
/ correctresponse=("a")
</trial>

The following trial presents a forward and backward masked prime for exactly 1 vertical retrace frame, and then presents a target stimulus that remains on the screen until the subject responds. The particular forward and backward mask used on each trial are selected from list elements called forwardmaskselector and backwardmaskselector respectively:

<trial mytrial>
/ stimulusframes=[1=list.forwardmaskselector; 2=prime; 3=list.backwardmaskselector; 4=target]
/ validresponse=("a", "b")
/ correctresponse=("a")
</trial>

The following trial presents a focusstimulus for 10 vertical retrace frames, then presents a two stimuli simultaneously on the left and right of the screen:

<trial mytrial>
/ stimulusframes=[1=focusstimulus; 10=lefttarget,righttarget]
/ validresponse=("a", "b")
/ correctresponse=("a")
</trial>