Do pupil-based binocular video eye trackers reliably measure vergence?

Hooge, Ignace T. C.; Hessels, Roy S.; Nyström, Maria

doi:10.1016/j.visres.2019.01.004

Cited by 57 publications

(68 citation statements)

References 71 publications

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“…The Pupil signal, more accurately, the centre of the pupil image in the eye camera, has been blamed for several amplitude and gaze position artefacts in eye-movement data resulting from dynamics in the human pupil itself (Hooge et al 2019;Hooge et al 2016;Holmqvist 2015;McCamy et al 2015;Drewes 2014;Drewes, Masson, & Montagnini 2012). However, in our measurements with a pair of artificial eyes, the pupils are static, physical features that will neither oscillate, constrict nor dilate, and therefore none of those pupil-induced artefacts can happen in our data.…”

Section: Calibration Mathematics?mentioning

confidence: 83%

Small eye movements cannot be reliably measured by video-based P-CR eye-trackers

Holmqvist

Blignaut

2020

Behav Res

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For evaluating whether an eye-tracker is suitable for measuring microsaccades, Poletti & Rucci (2016) propose that a measure called 'resolution' could be better than the more established root-mean-square of the sample-to-sample distances (RMS-S2S). Many open questions exist around the resolution measure, however. Resolution needs to be calculated using data from an artificial eye that can be turned in very small steps. Furthermore, resolution has an unclear and uninvestigated relationship to the RMS-S2S and STD (standard deviation) measures of precision (Holmqvist & Andersson, 2017, p. 159-190), and there is another metric by the same name (Clarke, Ditterich, Drüen, Schönfeld, and Steineke 2002), which instead quantifies the errors of amplitude measurements. In this paper, we present a mechanism, the Stepperbox, for rotating artificial eyes in arbitrary angles from 1 ′ (arcmin) and upward. We then use the Stepperbox to find the minimum reliably detectable rotations in 11 video-based eye-trackers (VOGs) and the Dual Purkinje Imaging (DPI) tracker. We find that resolution correlates significantly with RMS-S2S and, to a lesser extent, with STD. In addition, we find that although most eye-trackers can detect some small rotations of an artificial eye, the rotations of amplitudes up to 2 ∘ are frequently erroneously measured by video-based eye-trackers. We show evidence that the corneal reflection (CR) feature of these eye-trackers is a major cause of erroneous measurements of small rotations of artificial eyes. Our data strengthen the existing body of evidence that video-based eye-trackers produce errors that may require that we reconsider some results from research on reading, microsaccades, and vergence, where the amplitude of small eye movements have been measured with past or current video-based eye-trackers. In contrast, the DPI reports correct rotation amplitudes down to 1 ′ .

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Section: Calibration Mathematics?mentioning

confidence: 83%

Small eye movements cannot be reliably measured by video-based P-CR eye-trackers

Holmqvist

Blignaut

2020

Behav Res

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“…In addition, any drift that we observed was much slower (100s of milliseconds) than the return of the pupil overshoot within the iris (10s of milliseconds). A second concern is that the pupil generally does not dilate/constrict symmetrically, which could lead to changes in measured vergence angle if the pupil changes in size (Drewes et al, 2014;Hooge et al, 2019). In humans, this asymmetry is predominantly in the direction that dilation results in measurements of divergence (Drewes et al, 2014;Hooge et al, 2019).…”

Section: Methodsmentioning

confidence: 99%

“…A second concern is that the pupil generally does not dilate/constrict symmetrically, which could lead to changes in measured vergence angle if the pupil changes in size (Drewes et al, 2014;Hooge et al, 2019). In humans, this asymmetry is predominantly in the direction that dilation results in measurements of divergence (Drewes et al, 2014;Hooge et al, 2019). We examined this in a subset of mice outside of our experiments and when we introduced large changes in luminance that more than doubled or halved the pupil size, we found extreme examples of changes in vergence as large as those observed in humans.…”

Section: Methodsmentioning

confidence: 99%

Mice Discriminate Stereoscopic Surfaces Without Fixating in Depth

2019

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Stereopsis is a ubiquitous feature of primate mammalian vision, but little is known about if and how rodents such as mice use stereoscopic vision. We used random dot stereograms to test for stereopsis in male and female mice, and they were able to discriminate near from far surfaces over a range of disparities, with diminishing performance for small and large binocular disparities. Based on two-photon measurements of disparity tuning, the range of disparities represented in the visual cortex aligns with the behavior and covers a broad range of disparities. When we examined their binocular eye movements, we found that, unlike primates, mice did not systematically vary relative eye positions or use vergence eye movements when presented with different disparities. Nonetheless, the representation of disparity tuning was wide enough to capture stereoscopic information over a range of potential vergence angles. Although mice share fundamental characteristics of stereoscopic vision with primates and carnivores, their lack of disparity-dependent vergence eye movements and wide neuronal representation suggests that they may use a distinct strategy for stereopsis.

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“…We share Quinlan & Culham (2007)'s concern that light from eye-trackers strays into the visible spectrum, introducing disparity cues. Other concerns included the fact that research eye-trackers "are not accurate enough to be used to determine vergence" (Hooge et al, 2019), that eye-tracking would be impractical given our use of parallax barriers, that calibration targets would be on the wrong focal plane, and that calibration would compromise the naivety of the subjects.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Does Vergence Affect Perceived Size?

Linton

2020

Preprint

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Vergence (the angular rotation of the eyes) is thought to provide essential distance information for size constancy (perceiving an object as having a constant physical size). Evidence for this comes from the fact that a target with a constant retinal size appears to shrink as the rotation of the eyes increases (indicating that the target has reduced in distance). This reduction in perceived size is supposed to maintain a constant perception of physical size in natural viewing conditions by cancelling out the increasing size of the retinal image as an object moves closer. Whilst this hypothesis has been extensively tested over the last 200 years, it has always been tested in the presence of confounding cues such as a changing retinal image or cognitive cues to distance.Testing members of the public with normal vision, we control for these confounding cues and find no evidence of vergence size constancy. Statement of RelevanceThis work has important implications for the neural basis of size constancy and for multisensory integration. First, leading work on the neural basis of size constancy cannot differentiate between recurrent processes in V1 (based on triangulation cues, such as vergence) and top-down processing (based on pictorial cues). Since our work challenges the existence of vergence size constancy, and therefore much of the basis of the recurrent processing account, our work indicates that top-down processing is likely to have a much more important role in size constancy than previously thought.Second, vergence size constancy is thought to be largely responsible for the apparent integration of the retinal image with proprioceptive distance information from the hand in the Taylor illusion (an afterimage of the hand viewed in darkness appears to shrink as the observer's hand is moved closer). This explanation for the Taylor illusion is challenged, and a cognitive account proposed instead.

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Do pupil-based binocular video eye trackers reliably measure vergence?

Cited by 57 publications

References 71 publications

Small eye movements cannot be reliably measured by video-based P-CR eye-trackers

Small eye movements cannot be reliably measured by video-based P-CR eye-trackers

Mice Discriminate Stereoscopic Surfaces Without Fixating in Depth

Does Vergence Affect Perceived Size?

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