Research Interests

We perceive motion in three dimensions, even though each eye only receives a two dimensional image. How does our brain combine the two images into a 3D percept?

I am a post-doctoral researcher in the lab of Alex Huk, funded by a two year Netherlands Organisation for Scientific Research (NWO) fellowship. We use neuro-imaging (fMRI), psychophysical experiments, and computational modeling. Our lab closely collaborates with the labs of David Ress and Larry Cormack.

Neural circuits underlying the perception of 3D motion

The macaque middle temporal area (MT) and the human MT complex (MT+) have well-established sensitivity to both 2D motion and position in depth. Yet evidence for sensitivity to 3D motion has remained elusive.

We showed that human MT+ encodes two binocular cues to 3D motion, one based on estimating changing disparities over time, and the other based on interocular comparisons of retinal velocities.

By varying orientation, spatiotemporal characteristics, and binocular properties of moving displays, we distinguished these 3D motion signals from their constituents, instantaneous binocular disparity and monocular retinal motion. Furthermore, an adaptation protocol confirmed MT+ selectivity to the direction of 3D motion.

These results demonstrate that critical binocular signals for 3D motion processing are present in MT+, revealing an important and previously overlooked role for this well-studied brain area.

A paper on our findings has been published in Nature Neuroscience. You can also download the supplementary materials (.pdf) and view animations of the stimuli.

Percepts of motion through depth without percepts of position in depth

It is a fundamental challenge for the visual system of primates to accurately encode 3D motion.

Prior work on the perception of static depth has employed binocularly 'anti-correlated' random dot displays, in which corresponding dots have opposite contrast polarity in the two eyes: a black dot in one eye is paired with a white dot in the other eye. Such displays have been shown to yield weak, distorted, or nonexistent percepts of position in depth.

We showed that the perception of motion through depth is not impaired by binocular anticorrelation. Although subjects were not able to accurately judge the depths of these displays, they were surprisingly able to perceive the direction of motion through depth.

A paper on our findings has been published in the Journal of Vision. A demonstration accompanies the paper.

The stereokinetic effect

An ellipse rotating in the image plane can produce the 3D percept of a rotating rigid circular disk. In theory, the motion of the 3D percept cannot be reliably inferred based on the 2D stimulus.

However, when we quantitatively estimated the perceived 3D motion, we found that it was nearly identical across observers, suggesting that all observers had the same 3D percept.

We assumed that given the 2D stimulus the visual system generates a rigid 3D percept that is as slow and smooth as possible. The percepts predicted by these assumptions closely matched the experimental data, suggesting that the visual system resolves perceptual ambiguity in such stimuli using slow and smooth motion assumptions.

A paper on our findings has been published in Vision Research. A demonstration accompanies the paper.