What does the SDR Assess?
The Spatial Delayed Response Task (SDR), also known as the oculo-motor
delayed response (OMDR), has been used extensively for assessing spatial
working memory. Spatial memory refers to the memory of where objects
are located, and working memory, sometimes called short-term memory,
refers to the temporary retention of information that is being actively
manipulated.
Description of the Task
Subjects focus on a central fixation cross on a computer screen.
While fixated (staring at the cross), a dot-shaped cue flashes in one of
32 possible locations towards the outer edge of the screen. Then a
delay period occurs. During the delay, a series of geometric shapes
appear in place of the fixation cross. Subjects must press the
spacebar whenever the diamond shape appears. This ensures the
subjects will continue to look at the center of the screen and not stare
at the location the dot cue appeared. After the delay, the fixation
cross returns, and the subjects must point on the computer screen where
they remember seeing the dot cue. The examiner directs a dot-shaped
computer cursor underneath the spot to which the subjects point, and
selects that location.
The length of the delay can be changed to assess shorter vs. longer
memory (e.g. 5 seconds vs. 60 seconds). The number of cues can also
be manipulated (e.g. one dot vs. two). Responses are measured in X
and Y coordinates and compared to the actual location the dot cue
appeared. Trials are repeated to obtain a mean error in millimeters
for each type of trial.
Randomly, a trial will occur in which the dot re-appears after the
delay and the subject must simply point at the dot as it is present on the
screen (this is called a "Cue Present" or "Freebie" trial). These
trials account for any error the examiner may have while selecting where
the subject points, or any difficulty the subject may have in pointing
accurately at the screen.
Who has taken the SDR?
The SDR has been utilized in human children as young as 4 years, adults, and geriatric
populations, in healthy persons as well as those affected by
Parkinson's, Tourette's, and diabetes. Monkeys with training have
also performed the task.
For more information about the task, please contact
Dr. Hershey.
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