Prosaccades Test

About

Prosaccades is a well-known test that is used to examine saccadic eye movements. In a typical prosaccade task, participants are instructed to fix on a central dot. Then, they have to direct their gaze toward a target stimulus appearing at the periphery as quickly and as accurately as possible. Research has shown that saccadic eye movements are associated with multiple cognitive processes including processing speed, attention, and inhibitory control (Hutton, 2008; Noiret et al., 2017).

To perform the prosaccade 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 toward 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 left. Failure to inhibit a reflexive saccade is considered an error.

  

Prosaccades typically have a faster reaction time than antisaccades.

Purpose of the Test

Prosaccade test is designed to assess the reflexive guided eye movement towards a suddenly appearing target with or without the presence of a distractor.  

The “Testing Blocks” and “Trials”

The RightEye Prosaccade Test consists of a battery of four (4) Testing Blocks, each containing fourteen (14) prosaccade Trials. The entire Prosaccade 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 prosaccade trial within the testing block will also run in a random order.

1. 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
2. Distractor 2 (Ipsilateral proximal distractor; IPD): Location: same direction to the target at an eccentricity of 2-degree from the starting cross
3. Distractor 3 (On-target; OT): Location: Distractor appears at the same location as the starting cross
4. No-Distractor (Target Only; TO): No distractor present, show only the target cross

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