Random Dot Kinematogram Task (RDK)

Background

Random Dot Motion (RDM) Displays, also known as Random Dot Kinematograms (RDK), are animated visual stimuli used in neuroscience and psychology to study how the brain processes motion and makes perceptual decisions. They consist of a cloud of dots on a screen in which a specific percentage move together in a unified direction (the "signal"), while the rest move in random directions (the "noise"). The defining feature of an RDM display is its motion coherence. For example, at a 10% coherence level, 10% of the dots will travel in a target direction (e.g., right), while the remaining 90% jump randomly. By manipulating the coherence levels up and down, individuals' motion processing thresholds can be measured.

Praveen K. Pilly and Aaron R. Seitz (2009) argue that despite the convenient use, RDM results heavily depend on the implemented algorithm which makes it difficult to make cross-study comparisons. Online applications of RDM further complicate the issue. In 2022, Kim Yaghoubi and colleagues used 'a constant stimuli' experimental design to compare motion thresholds collected with Millisecond's implemented RDM displays to a traditional laboratory assessment in MATLAB with Psychtoolbox. Yaghoubi and colleagues found that the data of both assessments were largely consistent with each other showing that these findings can serve as reference points for expected thresholds assessed remotely on different platforms.

It is important to note that the Millisecond implementation used by Yaghoubi and colleagues depends on the Inquisit 6 implementation of the task. The Inquisit 7 implementation of the study leverages Javascript code introduced by Sivananda Rajananda and colleagues in 2018 for online RDM research. All Inquisit 7 RDM displays are presented via an animated html-element that uses the jsPsych framework (Josh de Leeuw, 2008) and the "jspsych-rdk.js" plugin by Rajananda and colleagues. The implemented Javascript code increases control over the RDM display (e.g. it allows researchers to easily change the aperture).

Task Procedure

The aperture type used by Yaghoubi and colleagues (2022) is a circle with 100 dots. The selected RDM algorithm is consistent with the Brownian Motion (BM) algorithm: Signal and noise dots are recruited afresh in each frame and move at the same speed. The number of signal dots recruited in each frame depends on the tested coherence level and their motion direction on the selected angle. A total of ten coherence values (0.02 - 0.5) x 4 direction angles (45,135,225,315) with two display durations (200ms vs. 800ms) are tested in a within-participant design. Each of the 80 trials are repeated twice. The order of the trials within each block of 80 trials is determined randomly.

During each trial, participants see the RDM display for the specified time. After 500ms a cross is displayed. One of the axes points in the direction of the coherent movement and participants are asked to click on the direction of the coherent dots with their mouse of finger. If participants select the correct directional axis within 22.5 degrees, the response is scored as correct. Response feedback is provided for 500ms.

What it Measures

Random Dot Motion (RDM) displays measure visual motion processing

Psychological domains

• Visual Motion Perception: Ability to infer the speed, direction, and spatial path of moving objects based on visual sensory inputs
• Visual Motion Processing: The visual system's ability to analyze spatiotemporal changes in light on the retina as movement

Main Performance Metrics

• Accuracy: Proportion Correct responses for each coherence level tested (by duration)
• Threshold: Coherence value estimated to produce 50% correct responses

Psychiatric Conditions

The following patient groups show impaired motion processing based on RDM research

• Schizophrenia
• Bipolar Disorders
• Alzheimer’s Disease (AD)
• Parkinson’s Disease (PD)
• Autism Spectrum Disorder (ASD)
• Traumatic Brain Injury (TBI)

Test Variations

References

Search Google Scholar for peer-reviewed, published research using the Inquisit Random Dot Kinematogram Task (RDK).

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Braddick, O. J. (1974) A short-range process in apparent motion. Vision Research, 14, 519-527.

Pilly, P.K. & Aaron R. Seitz, A.R (2009) What a difference a parameter makes: A psychophysical comparison of random dot motion algorithms, Vision Research, 49, 1599-1612, https://doi.org/10.1016/j.visres.2009.03.019.

Yaghoubi, K. C., Kabbara, S., Arian, S., Kobaissi, H., Peters, M.A.K., Seitz, A.R. (under review). Comparing random dot motion in MATLAB vs. Inquisit Millisecond.