About
Antisaccades is a gross estimation of injury or dysfunction of the frontal lobe, by assessing the brain’s ability to inhibit the reflexive saccade (toward a visual stimuli) and “override” that movement leading to a saccade in the opposite (mirrored) direction. [1] Saccadic eye movement is primarily controlled by the frontal cortex.
To perform the antisaccade trial, an individual is asked to fixate on a motionless target (the starting cross “+”) in the center of the screen. A stimulus (“X”) is then presented to one side of the target. The individual is asked to perform a saccadic movement in the direction away from the stimulus and then return back to briefly fixate on the starting cross and await the appearance of the next stimulus. For example, if a stimulus is presented to the left of the starting cross, the patient should rapidly move their eyes toward the right. Failure to inhibit a reflexive saccade is considered an error.[1]
REFERENCES :
[1] (Levy, D.; Mendell, N.; Holzman, P. (2004). "The antisaccade task and neuropsychological tests of prefrontal cortical integrity in schizophrenia: empirical findings and interpretative considerations". World Psychiatry. 3 (1): 32–40. PMC 1414662. PMID 16633452).
Purpose of the Test
The antisaccade test is an important tool for investigating the complex nature of voluntary behavior. In this task, participants are instructed to suppress the natural response to look at a peripheral visual stimulus and look in the opposite direction instead. Analysis of saccadic reaction times, SRT (the time from stimulus appearance to the first saccade) and the frequency of direction errors (looking toward the stimulus) provide insight into saccade suppression mechanisms in the brain. Patients diagnosed with a variety of neurological and/or psychiatric disorders affecting the frontal lobes and/or basal ganglia produce markedly different SRT distributions and types of direction errors, which highlight specific deficits in saccade suppression and inhibitory control. The anti-saccade task therefore provides valuable insight into the neural mechanisms of saccade suppression and is a valuable tool in a clinical setting.(1)
(1) Mechanisms of saccade suppression revealed in the anti-saccade task. Brian C. Coe and Douglas P. Munoz. Published:27 February 2017
The “Testing Blocks” and “Trials”
The RightEye Antisaccade Test consists of a battery of four (4) Testing Blocks, each containing fourteen (14) Antisaccade Trials. The entire Antisaccade Test should take 2-3 minutes to complete. After an initial calibration exercise (9-point motor function), a new screen will appear before each testing block is initiated. This screen includes the instructions for the upcoming testing block. The user presses <Enter> when they are ready to proceed. The testing blocks will appear in random order and each antisaccade trial within the testing block will also run in a random order.
- Distractor 1 (Contralateral proximal distractor; CPD):
Location: opposite direction to the target at an eccentricity of 2-degrees from the starting cross at a 56cm distance - Distractor 2 (Ipsilateral proximal distractor; IPD):
Location: same direction to the target at an eccentricity of 2-degree from the starting cross - Distractor 3 (On-target; OT):
Location: Distractor appears at the same location as the starting cross - No-Distractor (Target Only; TO):
No distractor present, show only the target cross
Note:
1. There are no stimuli located superior midline, superior right, superior left, inferior right, inferior midline, inferior left lines of gaze. If these need to be added additional time will need to be allowed.
2. Distractor stimuli are only presented at 0 and 2-degrees. This decision is made due to the research (Walker et al., 1997) suggesting the greater “disruption” latencies at these distances.
Metrics
Antisaccade count (#): The frequency (count) of antisaccades. Antisaccades defined as either:
- A movement with a certain amplitude, in any direction that is not toward the target. Not toward the target is defined as defined as anything outside of the prosaccade boundary (see CGP as a precedent). The movement occurs after the removal of the Starting Cross. It is the first movement of the eye only.
- A movement a certain distance, in any direction that is not toward the target. Not toward the target is defined as anything outside of the prosaccade boundary (see CGP as a precedent). The movement that occurs after the removal of the Starting Cross. It is the first movement of the eye only.
Prosaccade count (#): The frequency (count) of prosaccades. Prosaccades defined as either:
- A movement with a certain amplitude, in any direction that is toward the target. Toward the target is defined as within a XX visual angle (see CGP as a precedent). The movement occurs after the removal of the Starting Cross. It is the first movement of the eye only.
- A movement a certain distance, in any direction that is toward the target. Toward the target is defined as within a XX visual angle (see CGP as a precedent). The movement that occurs after the removal of the Starting Cross. It is the first movement of the eye only.
Saccadic amplitude (degrees): Amplitude in the horizontal direction, measured in degrees. Reports on both eyes.
Saccadic latency (ms): Delta between when the starting cross disappears, and the users eyes leave the starting cross AOI. Measured in milliseconds. Reports on both eyes. Calculates the mean value and the standard deviation.
Target accuracy (millimeters): The distance, on the X-axis, between the location of gaze coordinates at the time the target cross disappears. Reports on both eyes.
Saccadic onset (ms): the time when eye velocity increased above peak velocity measured by when the starting cross disappears, and the eye reaches an amplitude of >=2 degrees.
NOTES:
There are no stimuli located superior midline, superior right, superior left, inferior right, inferior midline, inferior left lines of gaze.
Distractor stimuli are only presented at 0 and 2-degrees. This decision is made due to the research (Walker et al., 1997) suggesting the greater “disruption” latencies at these distances.
Research
The following research papers are the premise and foundation for the test.
- Walker R, Deubel H, Schneider WX, Findlay JM. Effect of remote distractors on saccade programming: Evidence for an extended fixation zone. J Neurophysiol. 1997; 78: 1108–1119. PMID: 9307138
- DeSimone JC, Everling S, Heath M (2015) The Antisaccade Task: Visual Distractors Elicit a Location-Independent Planning ‘Cost’. PLoS ONE 10 (4): e0122345. doi:10.1371/journal.pone.0122345